Radiation probes indicate NO melt through at Fukushima Unit 1

Tepco has recently released measurements that provide convincing evidence that virtually all of the corium in Fukushima Daiichi unit #1 remains safely stored inside an intact reactor pressure vessel. Despite all claims to the contrary, no substantial quantities of that material have melted through the pressure vessel to fall onto the concrete floor of the surrounding containment structure.

It has always seemed far fetched to me to think that material from a nuclear reactor that melted several hours after fission has stopped contains the power density necessary to melt through carbon steel pressure vessels that are 6-12 inches thick. My basis for making that statement comes from having spent several sleepless nights in a drydock watching people with specially designed torches cutting into submarine hulls to provide maintenance access. I also had the opportunity during at least one repair period to be the guy responsible for signing the requisition chits for the pallets full of gases used to power those torches.

Melting thick steel is not a job for a mass of metal that is only being heated by radioactive decay whose heat production is falling rapidly.

A couple of days ago, Tepco drilled a hole into the thick concrete foundation that supports the reactor pressure vessel. The hole was approximately 8.7 meters above the containment floor. The workers then inserted a radiation probe. Based on the readings from the probe, it is not possible to truthfully assert that the corium left the reactor pressure vessel and made it to the floor of the containment under the vessel.

The probe registered its highest reading (11 Sv/hr) at the level where it was inserted – 8.7 meters above the containment floor. I do not know the details of the apparatus, but it is reasonable to assume that the workers were using gravity to lower the probe and had no mechanism that would enable the probe to be raised above the entry point.

The measured radiation dose rate was lower at all points below the entry point until it reached a minimum at the surface of a pool of water at the bottom of the space. The other sensors inserted with the radiation measuring probe determined that the water was fresh – with a chloride concentration of about 19 parts per million – and that it was about 2.8 meters deep. The radiation reading at the surface of the pool of water was only 0.5 Sv/hr.

Those radiation readings indicate that the radiation source is at the top of the space, not the bottom. It is a little difficult to paint a complete picture with words, so I captured an image from a document posted on the US NRC web site titled Reactor Concepts Manual, Boiling Water Reactors.

The image is a BWR/6, which is not the same model as the Fukushima units, but it has roughly the same configuration of a reactor pressure vessel with control rods that are inserted from the bottom and is mounted in a concrete foundation with several meters of empty space between the bottom of the vessel and the floor of the containment.

The space under the reactor pressure vessel that I am describing is near the number 24 in the image below. As other points of reference, the normal location of the fuel in a BWR is at number 15, and the control rod drive mechanisms are at number 22.

Tepco’s recently measured information needs to be widely disseminated and discussed by nuclear professionals. Some of those professionals have spent decades attempting to model and predict the interaction of corium and concrete under the “worst case” assumption that reactors that melt due to insufficient cooling will also melt through their pressure vessels to fall onto the concrete.

Perhaps we can use real world experience from the unintended “theory to practice” events at Fukushima to show the modelers and the regulators that “worst case” analysis does not provide any realistic prediction of what will actually happen in the real world of carbon steel pressure vessels, latent heat of fusion, water, and measurably limited heat from radioactive decay.

Hat tip to Leslie Corrice who has been providing Fukushima Updates about three times per week for more than 18 months. The specific issue that provided this information is October 12, 2012.

If you want facts and data about Fukushima events and post accident efforts, Les’s Hiroshima Syndrome is a terrific place to start.

About Rod Adams

147 Responses to “Radiation probes indicate NO melt through at Fukushima Unit 1”

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  1. DV82XL says:

    Somehow I don’t think this will get the press that a finding that the core had been breached would….

  2. Daniel says:

    Someone recently wrote that the term ‘Cold Shutdown’ was never used before in the context of nuclear power stations before Fukushima.

    Is this true and is the term ‘cold shutdown’ erroneous in this context?

    • pete51 says:

      ‘Cold shutdown’ has been used in the US nuclear power industry for a long time.

    • Nuclear Guy says:

      Cold Shutdown is in every plant’s technical specifications and depending on the country and interpretation of the definition it refers to the conditions where the reactor is no longer physically capable of boiling water (<200F), and in some countries it also refers to the reactor being depressurized.

      The context of cold shutdown is hard to determine with Fukushima. If the fuel is scattered throughout the containment, then you have to look for evidence that boiling has stopped occurring, so the 200F criteria does not directly apply.

  3. James Greenidge says:

    Rod, why are you making Jane Fonda and Jack Lemon mad like this??

    James Greenidge
    Queens NY

  4. Leslie Corrice says:

    Rod,

    Your kind words about my on-going efforts has caused me to rhetorically blush. Thank you. Reading such accolade from someone whom I have respected for years, is amazing. Uh…did I say “thank you”?

    Leslie Corrice

  5. Bill Rodgers says:

    Rod,

    My concern is that the individuals whose models that have been the backbone of the core melt through analysis will either hold their turf with an iron fist or will try to nuance the situation. And if it isn’t the modelers it will be the regulators. The naysayers will hold onto their beliefs which is that a core meltdown will automatically go through the concrete. There will still be people who come up with a hundred and one “what-ifs”.

    There are more data points to determine including the status of the other two reactor cores. If either of these have worse damage then #1, expect to see push back against changing any of the models. Which means real life will lose to the computer modeling and regulators again.

  6. Daniel says:

    Patrick Moore in India today in response to Greenpeace’s anti nuclear position :

    Speaking to The Hindu, Mr. Moore said he would not hold Greenpeace alone responsible for the “myths,” but it was part of a larger movement. “Greenpeace is the tip of the spear — they set a lot of trends. I saw the writing on the wall long ago when they decided to call for banning chlorine and termed PVC ‘poison plastic’.

    They are against half the elements on the Periodic Table.”

  7. Pete51 says:

    Is it really such good news that most or all of the core is still in the reactor? The RPVs do not hold water. The cooling water pumped in leaks out into the containment. If the fuel is still in the RPV, this makes recovery of the fuel that much harder. All spent fuel handling operations are normally done under many feet of water shielding. At least the bottom of the containment does have a water level of ~2.8 feet. It might actually be easier if the fuel was at the bottom of the containment drywell.

    What is the overall plan? Try to seal the leaks out of the containment, and then flood everything up? Remove the fuel with robots? Even if it is still in the RPV, it could well be a solidified mass of corium at the bottom of the vessel. There is a great deal of difficult engineering ahead.

    • Pete51 says:

      Should be…2.8 meters (9 feet)…

    • Daniel says:

      @ Pete51,

      Your comment:

      There is a great deal of difficult engineering ahead.

      My point of view:

      Are you suggesting that the ‘clean up’ be done as fast as possible ? I for one like the other approach which I think is less costly. Let time do the work for you and attack the task slowly as more decays would make the job easier.

      • Cal Abel says:

        Well, there is an old adage of cleaning up spills. Stop the spill, contain the spill and start from the outside and work in. This approach is more than likely what they are taking. It will do exactly what you are recommending Daniel. TEPCO needs to figure out how to contain the water inside the RPV and dry wells. The next step will likely be video. I don’t know how electronics will perform in an 11 Sv/hr radiation field. That is a very big number but not likely insurmountable. They are also probably going to repeat this exercise for the other two units. As I recall from the INPO report Unit 1 was worse off – having the least cooling early on.

        If the bottom of the RPV is sealed and not melted through they may even start sooner. Who knows. Also incase if anybody missed it Nuclear Technology November issue had an article “Study of Fukushima Daiichi Unit 4 Spent-Fuel Pool. Looks like the helicopter radiation readings were from the streaming term from lower water level in the pools ~2m above top of the fuel, and that the pool never got above 90 C and the latent heat of vaporization of water kept the used fuel nice and cool. The pool level did get low, ~ 0.5 m more than likely due to failure of the pool level indicator. Once they identified the low level they had the capability to immediately add water and did so.

        If I could take this report and cram it down Jazcko’s throat, I would. The prick earned such humiliation. My question to the NRC is in light of this information how important are those new measures you are requiring. Are they going to provide value or arre they going to be more gold plating making reactors more expensive? Anybody from the NRC like to comment on that, I’d love to hear your opinion.

        ANS members can access the article here: http://www.new.ans.org/pubs/journals/nt/v_180:2

        • Pete51 says:

          The following pdf link from TEPCO offers some insight to the overall plan. They are planning plenty of R&D just to understand the scope of the whole project. This recent camera inspection is obviously a small part of that R&D investigation.
          http://www.tepco.co.jp/en/nu/fukushima-np/roadmap/images/t120730_02-e.pdf

          These sentences address their plan to perform the fuel removal operations underwater:
          “Basic policy is defined as removing fuel debris while it is completely underwater from the viewpoint of dose reduction.”

          and:
          “Because fuel debris will be removed underwater, develop and validate methods and equipment for identifying and repairing PCV damage locations, investigating location/conditions of fuel debris, and debris removal in high radiation and narrow spaces.”

        • jmdesp says:

          I don’t think 11 Sv/hr is really impressive. We have all sorts of nuclear medicine equipments that outputs a *lot* more radiation than that, and I’d be surprised if some of the electronic doesn’t receive at least part of the time.

          • Cal Abel says:

            The problem comes in with the spacing of the transistors on solid state materials. Most small cameras rely upon these types of transistors. What occurs is that as the spacing of the transistors becomes so small that an electron produced through the photo electric effect, Compton scattering, or pair production will induce a small current across the transistors. This introduces “noise” into the circuit and can cause the circuit to shut down if the field becomes too large, by overwhelming the signal of the base process.

            The more radiation resistant the camera the larger it will be. I don’t know how sensitive they are or what size they can use and how much shielding they can put on it. All I’m noting is that there is an effect and adds an additional level of complexity, and one that can be resolved, but may prove to be very challenging.

      • Stephen Anderle says:

        And safer. You get in a rush in construction ,you make mistkes and have to strt over.

    • Stephen Anderle says:

      A meltdown happened once before, at Three Mile Island. The engineering is already there. Here it is just going to take getting to the vessels, in another two years like they did at T.M.I.. Wait till the radiation is down then go in and remove the fuel.

      • Pete51 says:

        The TMI reactor vessel did not leak water. The likely leakage points for the Fukushima reactors are the control rod penetrations in the bottom of the RPV. If they can find a way to seal the water leakage from the containment, then they can fill up the drywell with water, which will also back-fill the reactor. I think that was their original plan when pumping in the seawater, but it didn’t work out that way.

        • nuclear guy says:

          accident management procedures have you flood the containment when you lose assurance that you can maintain core or vessel integrity. It is a strategy to cool the reactor through the walls of the RPV, and also to promote and strengthen containment integrity, as it becomes the principle barrier against radioactive release.

          the seawater injection would be in line with SAMG procedures throughout the industry when you no longer have assurance that you are capable of safeguarding the reactor.

    • Engineer-Poet says:

      What is the overall plan? Try to seal the leaks out of the containment, and then flood everything up? Remove the fuel with robots? Even if it is still in the RPV, it could well be a solidified mass of corium at the bottom of the vessel. There is a great deal of difficult engineering ahead.

      I have no idea what the plans are, but my Oil Drum co-contributor Dave Summers has great expertise in water-jet cutting.  These jets can cut rock; slicing up a poorly-consolidated mass of ceramic and metal so that it can be vacuumed up by a venturi pump and removed to settling and particle filters wouldn’t be a technological stretch, and fiber optics and whatnot can keep electronics out of the radiation field.

  8. Robert Steinhaus says:

    @Rod – You know a lot more than I know about the Navy and the practical capabilities of great nuclear ships. Could the USS Ronald Reagan and the Navy nukes onboard have sailed to the rescue of the people of Northern Japan following the earthquake and saved the day?

    The USS Ronald Regan was 100 miles away from the Fukushima Daiichi reactors at the time of the earthquake [1]. If the order had been given by President Obama, the sailors of the USS Ronald Reagan could have anchored in the bay in front of the Fukushima Daiichi reactors and attempted to deploy cabling to supply emergency power to sustain the emergency core cooling of the stricken reactors.

    I want to be fair to the Navy guys and not blame them for not going to the rescue of the stricken Fukushima reactors in the first hours of the disaster. The failure was not with the Navy but was with the advisors to the President that did not make the suggestion that we use the USS Ronald Regan to avert catastrophe. I personally believe that if the President had been presented with information in the early hours of the disaster he would have given the order to send the USS Ronald Regan to attempt a heroic intervention and rescue.

    It would have made a significant difference to American prestige and to confidence in the application of US nuclear technology to have attempted to use the fine skills of the Navy nukes (sailors) and the power of a great mighty nuclear ship to avert a nuclear disaster. My opinion is just that we missed an opportunity in not sending the ship to at least make an attempt.
    The Navy just followed orders, and the order from the President never came.
    [1] – http://news.discovery.com/human/us-carrier-navy-crew-radiation-exopsure-japan-110315.html

    • Daniel says:

      @ Robert,

      I remember an interview done with a commander of such a Navy ship during the Fukushima crisis. It is vague and I do not recall all the details but the commander did not look worried to give a helping hand.

      The commander, as I recall him, was confident, fully equipped and had no fear of the situation. But like you said, he never got the order from Obama and he seemed to be fully aware of the minimal risks and dangers he and his crew would face in the case of a civil nuclear incident.

      I am sure this interview can be accessed. I am confident it was aired on CNN.

    • George Carlin says:

      Robert,

      If the navy could have assisted, and the President was briefed on the situation (hindsight is 20/20 but) and failed to act, this is just another instance in which the current President has failed to act and/or show leadership. I am not a big fan of the challenger (Romney) but I just cannot put my faith in our current President again. Fukushima was a perfect time for him to push for the government to inform people of radiation and the true facts of the situation in Japan. What we got was FUD from most all media outlets and the NRC chairman (appointed by our current President) spreading unwarranted fear about the spent fuel ponds.

      • Daniel says:

        @ George

        I remember early in the crisis. The Japanese were running out of dosimeters. And there was this US Navy ship fully equipped next door.

      • James Greenidge says:

        No Obama guy here, but maybe in ironic hindsight it was far better that the U.S. Navy didn’t gallop to the rescue and cheat pro-nuclear power advocacy by blowing the one mega nightmare the antis had over us like a Damocles sword; that ANY meltdown was DOOMSDAY and mega-deaths galore assured. Instead we get THREE meltdowns in a row by a hammer of God and yet zit casualties and property damage other than fear! This was an incidental major proof of concept that exploded lots of myths in one shot and gives anti-nuke nightmares and fear-mongers one whale less credibility and ammo to deny nuclear energy as a safe power source, even in the most catastrophic incidents whose casualties rates other energy providers hold with envy. It’s up for the nuclear industry and organizations on both sides of the Pacific not to drop this major PR ball for public nuclear acceptance.

        James Greenidge
        Queens New York

        • George Carlin says:

          Interesting point. Nuclear PR really needs to start promoting this fact because I think the general public still thinks it was a catastrophic incident.

          • justin lane says:

            It was and still is a catastrophic incident. My wife miscarried and now has to take thyroid medicine for the rest of her life. All your money grubbing lies do not deceive us, we know exactly what did this to a perfectly healthy young woman who was pregnant during the fukushima fallout. Now you geniuses cant stop the leaks into the pacific. Personally, i hope you truly believe this idiocy so that you will not inherit the especially hot corner of nuclear powered hell reserved for those who promote this crap.

    • Engineer-Poet says:

      If the order had been given by President Obama, the sailors of the USS Ronald Reagan could have anchored in the bay in front of the Fukushima Daiichi reactors and attempted to deploy cabling to supply emergency power to sustain the emergency core cooling of the stricken reactors.

      I could be wrong, but I believe there was a technical obstacle to doing this:  both the backup diesel generators and their connection panels were in the building basements, which were flooded.  Even if the Ronald Reagan had steamed to the rescue and cables brought in, it may not have been possible to connect them.

    • Paul Lindsey says:

      I don’t think REAGAN or any other USN ship could have provided power to the existing equipment at Fukushima, because USN uses 60 Hz and Fukushima uses 50 Hz power. Also, REAGAN’s shore power connections are 4160v.

      • Vince says:

        Thats why they make frequency converters. Every obstacle has a solution.

      • nuclear guy says:

        Most of the US nuclear plants I’ve worked at, visited, or learned about, use 4160 power for their ECCS systems.

        Even if a power source was available though, the issue would then be having functioning breakers, MCCs, and switchgear.

    • John Randall says:

      Robert,

      The US Navy did give assistance. I learnt of this reading the exchange between Naoko Suzuki and Bruce Thompson in the comments of this article.
      http://online.wsj.com/article/SB10001424052970203961204577271152728725214.html?mod=WSJ_article_comments#articleTabs%3Dcomments
      The exchange is on page 1, starting with Bruce Thompson’s “Here is the explanation as to why ..”
      and ending with his link to this item.
      http://www.c7f.navy.mil/news/2011/03-march/040.htm
      The exchange between Naoko and Bruce is a fascinating meeting of cultures.

    • Margaret Harding says:

      In fact, a portable diesel generator was flown in on the 12th. There was so much damage that they had no place to hook it up to bring power back to the site. Thus the navy might have provided additional support, but likely would not have been able to avert the core melt and subsequent explosions.

  9. Stephen Anderle says:

    Could be he just wasn”t informed well enough on what Japan needed and what we had available. Or maybe Japan thought they could do it without our help. Or maybe no one thought.

  10. atomicliesnuclearwinds says:

    So you think because there are 2.8 meters of water this proves no melt how? We already know there was melt through. This has already been admitted by Tepco… I guess you might have missed that huh? Grasping at straws is what this sounds like- desperate grasping no less…

    • Rod Adams says:

      @atomicliesnuclearwinds

      So you think because there are 2.8 meters of water this proves no melt how? We already know there was melt through.

      No. I think that the fact that the radiation level is highest near the bottom of the Reactor Pressure Vessel (RPV) and gets steadily lower as the detector is moved away from the RPV toward the containment floor proves that the source of the radiation is in the RPV and not on the containment floor.

      I understand the way that radiation spreads and its intensity falls with distance from the source. That is a fundamental law that cannot be changed. As my friend Ted Rockwell often states “Everyone may be entitled to their own opinions, but not to their own facts.”

      With regard to what Tepco has already admitted – on what basis did they make that admission? Was it based on measured reality or modeled guesswork? Forgive me, but I will stick with measured reality every time when the alternative is a guess based on “worst case” analysis.

      • atomicliesnuclearwinds says:

        Water masks the radiation levels… and less than 9 feet of water when they are putting in quite a few tons of water per hour does not sound like good news to me…The containment “floor” is where the little bit of water that is measured is… of course it is lower in the water… water is a shield for radiation… we all know that Rod… it is leaking like a collander… they are pouring in tons of water per hour and there is only 9 feet in the bottom part of the vessel because the basement is full and it takes it a bit to drain into the basement and then into the ground… I do not think your guesswork is any better than Tepco’s in this case…

        • Rod Adams says:

          @atomicliesnuclearwinds

          l’m fairly certain that you have no earthly idea what you are talking about. Do I hear a second to that opinion?

          • atomicliesnuclearwinds says:

            It stands to reason if there was a nuclear explosion inside of that containment, which, although we have been lead to believe could not happen, certainly IS a possibility that some of the fuel fragments have lodged in the upper containment vessel… I am fairly certain that you have an agenda, and protecting the people is not included in it… Since the fuel was likely blown into a trillion tiny pieces, I do believe this is entirely plausible, regardless of the nuclear industry mainline that would have us ignorantly believe such a thing is not possible when in fact it is not only possible, but in this case? Highly probable. Also, let us not forget that tedious little factor of the defect in this type of reactor that can allow the upper “lid” to lift during such an explosion, even if it were not nuclear but rather hydrogen, when the lid was lifted it would have allowed fuel particles to become lodges in the seals and when it resumed its former position, the fuel particles would be trapped there… Prove that I am wrong?

          • Rayne Nichols says:

            It stands to reason if there was a nuclear explosion inside of that containment,

            No earthly idea what talking about: confirmed

          • Leslie Corrice says:

            While water is a very good shield (1 ft. lowers radiation level by ~10X), the increasing rad level with increasing elevation shows the source is not in or under the water. I’d like to see what the rad levels are above the endoscopic entry point, but it seems that isn’t possible. For this ex-nuclear water chemist, the bottom line is that the chemistry of the water is all wrong if the solidified corium is under the water. Direct contact to the source will always result in the highest concentrations. However, the cesium concentration of the water inside the PCV is more than 10X LOWER than the waters in the basement of the reactor building outside the PCV. If there’s corium under the inner PCV water (as postulated by essentially the entire Japanese nuclear community), the chemistry should be the other way around.

        • ddpalmer says:

          I second Ron’s opinion that atomicliesnuclearwinds has no earthly idea what he is talking about.

          Yes, water will act as a shield. But if the source of radiation is under the water, the radiation level will still increase as you approach the water’s surface. In this case the radiation level decreases as you approach the water, thus the source of radiation is not under the water but somewhere above the water.

          • atomicliesnuclearwinds says:

            There was a huge explosion in this vessel, as I have explained above… and when that happened, and the lid lifted, as was proven to be a flaw in this design long ago? Nuclear fuel particles lodged in the upper vessel and remain there, without benefit of water to shield it… thus the higher readings higher in the vessel.

          • EM1(SS) says:

            Ummm, a “nuclear” explosion cannot happen. There is a very defined level of radioactive material needed to support an explosion, and this is level is not easily attained, it required quite a bit of enrichment. This enrichment is quite expensive, and cost prohibitive when making fuel for a nuclear power plant. Universally, fuel is enriched to about 10%, where as it takes about as much as 90% to make it “weapons grade”, ie explosive. The explosion that took place at the Fukushima plant was a hydrogen explosion, the most likely and probable type of explosion given the circumstances the reactor was in. If the fuel is hot enough, Zirconium-water reactions begin to happen, leading to a release of hydrogen, which in turn explodes extremely easily. Case in point, the Hindenburg. At any rate, hydrogen rises and collects at altitude, therefore the explosion to happen above the fuel. Yes, the upper lid can come off, but the explosion that would cause that to happen would have occurred at the top of the pressure vessel, not in the fuel, and thus would not likely have “blown the fuel into a trillion tiny pieces” and even if the fuel was obliterated, it would not have traveled towards the explosion to become lodged in the upper pressure vessel area when the lid “resumes its former position”. That being said, if the reactor somehow evaded laws of physics, and underwent a nuclear explosion, the containment vessel would not have held, and we would not be having this discussion…

            As for the radiation/shielding concept, we are not analyzing the data in that fashion. We are analyzing the gradients, not the actual values. Of course if there is fuel underwater, the readings above the water would be less due to the shielding effects, but the gradient would not change, hence our focus on analyzing that aspect of the surveys TEPCO performed. Our interpretation of this data is in fact quite the opposite of us grasping for straws, we are analyzing the most recent set of raw data to be published. I dont care what TEPCO says or thinks, they have their own agenda as well, but the data speaks for itself, for anyone who is capable of analyzing it and listening to it…

          • EM1(SS) says:

            Correction to my October 21, 2012 at 6:48 PM comment: fuel is enriched to *no more than* 10%… Mostly fuel is enriched to 5% or less…

  11. EL says:

    This article contradicts the official summary and interpretation of the result provided by TEPCO.

    http://english.kyodonews.jp/news/2012/10/187744.html

    “Considering the water’s radiation level and other data, Tokyo Electric Power Co. said the fuel, which is believed to have melted through the pressure vessel and accumulated in the outer primary container, does not appear to be releasing large amounts of radioactive substances because it is kept cool.”

    Any discussion of the discrepancy?

    • Brian Mays says:

      “… which is believed …”

      Which is believed by whom? By TEPCO? By the journalist writing the article? By Greenpeace? The article never says.

      I see a convenient use the passive voice to cover up that the journalist doesn’t have any information but wants to play up the scariest angles that he or she can come up with.

      There is no discrepancy. This is just a case of crappy reporting.

      • EL says:

        So you have nothing besides a writing critique … and no specific analysis to contradict the claim from TEPCO that the corium has melted through, and is “cooler” outside the PCV than inside?

        • Brian Mays says:

          EL – That is more than you have. Where is this “claim from TEPCO that the corium has melted through”?

          “Which is believed” is an entirely different statement than “TEPCO believes.”

          Your trollish behavior of putting up a vague statement from a sparse news report and then demanding “specific analysis” to counter it is not appreciated. Go play these stupid games somewhere else. Thank you.

          • EL says:

            Wow … do you always see only what you want to see in a press article? The statement attributed to TEPCO discusses the temperature of the fuel outside PCV … which article suggests is “cooler” (although it has not been measured directly). If you would like to misunderstand this differently, we’re speaking a different language and are not looking at the same article. All I can say … I’m thankful you’re not a journalist reporting on this story.

          • Brian Mays says:

            What does the temperature of the fuel have anything to do with what Rod has written in this article?

            You’re not trying to compare Rod’s figures on rate of dose to vague estimates of temperature in the Kyodo article, are you?! If so, then you’re even more foolish than I had originally thought.

            I don’t know about a different language, but it appears that your confusion has lead you to speaking in entirely different units on entirely different physical quantities. In journalism and in random blog comments by the scientifically illiterate, these things don’t matter much, but to make sense out of any real scientific or technical issue, such details are extremely important.

          • EL says:

            No analysis … again. You seem particularly skilled at finding certainty where there is none. Care to tell us how (and provide some credible analysis)? TEPCO officials don’t agree with you, and can’t seem to keep their mouths shut.

            http://ajw.asahi.com/article/0311disaster/fukushima/AJ201210110078

            “TEPCO said radioactive materials may be flowing differently in the two reactors.”

            “TEPCO’s Ono said it is difficult to identify where the source of radiation is from the available data.”

            Handouts released by TEPCO during their Press Conference.

            http://www.tepco.co.jp/en/nu/fukushima-np/handouts/index-e.html

            WNN appears to be attending the same Press Conferences and reading the same TEPCO Handouts as Kyodo News, Asahi Shimbun, and others speaking directly with officials closest to this data. Or a more simple approach, just look at what others have said in this thread that points to gaps and uncertain results.

          • Rod Adams says:

            @EL

            You wrote:

            No analysis…again

            Did you even read my initial post and the link that I provided to Hiroshima Syndrome’s Fukushima Accident Updates? http://www.hiroshimasyndrome.com/fukushima-accident-updates.html

            Just in case it is too much trouble for you to click, here is a quote:

            Today, Tepco has posted the results of the first water sample taken inside the unit #1 Primary Containment Vessel (PCV). We find results that come as more than a bit of a surprise. The interior water’s results have been compared to analyses of the water’s outside the PCV, in the basement of the unit #1 reactor building, taken in late September. First, the Cesium contamination level inside the PCV is half of the concentration found outside (35,000 Bq/cc vs. 74,000 Bq/cc). Thus, the interior water is significantly less contaminated than that in the outer reactor building. Second, the chloride level inside is ten times less than outside (19 part per million vs. 200ppm). This means that the salt concentration inside the PCV from the seawater used to cool unit #1 beginning at 8pm on March 12, 2011, is tremendously lower than outside. (Tepco; Kyodo News) This strongly suggests several things. First – the water inside the PCV is being recirculated more efficiently than that outside the robust containment walls. In other words, the recycled fresh water being injected into unit #1 is diluting the interior waters better than the exterior. Second – there can be no mixing of interior and exterior waters or the two sets of analyses would be essentially the same. While the concentration differences give us a better picture of the PCV’s interior environment, it raises a whole new set of questions as to what the actual water flow-path(s) through the building might be. Third – the interior water being lower in Cesium content than the exterior implies that the melted-then-re-solidified corium mostly remains inside the RPV itself. If the corium was mostly outside the RPV and heaped on the base-mat of the PCV – melted completely through the Reactor Pressure Vessel (RPV), as surmised by just about everyone in Japan – the interior waters should be massively higher in Cesium contamination than the exterior.

            (Emphasis added/)

            Les Corrice has been following this story closely for 18 months. He has a solid background in nuclear plant operations. I suspect he has a better understanding of what actually happened than any reporter who is attempting to translate the words of a company spokesperson (which are already translated from accurate technical language in an attempt to make it understandable to someone not versed in the jargon).

          • Brian Mays says:

            And now we see the typical troll tactic of flooding the comments with mindless hyperlinks hoping that nobody actually reads them. At least you’re consistent.

            Unfortunately for you, however, your links only confirm and reinforce what Rod has written above.

            For example, consider this excerpt from your first link (emphasis mine):

            The maximum radiation level of 11.1 sieverts per hour was detected at a height of 8.6 meters from the bottom of the containment vessel.

            Radiation levels generally fell toward the lower parts of the containment vessel. The reading was 4.7 sieverts per hour near the water surface and 0.5 sievert in the contaminated water. … The company believed that almost all melted fuel fell through the bottom of the pressure vessel and accumulated in the outer containment vessel. Under that scenario, radiation levels would rise toward the bottom of the containment vessel.

            Since radiation levels decrease toward the bottom of the structure, what are we to conclude about where all the melted fuel is?

            Now that your own links demonstrate that you’re a fool, will you please go away and play your stupid games elsewhere?

          • EL says:

            And now we see the typical troll tactic of flooding the comments with mindless hyperlinks hoping that nobody actually reads them … your links only confirm and reinforce what Rod has written above.

            Typical rebuttal is more like it. Do you always mis-read articles, and disregard statements that don’t support to your view? TEPCO model for “melt through” is described in two documents:

            MAAP Analysis and Core Concrete Reaction

            http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_08-e.pdf

            The Evaluation Status of Reactor Core Damage at Fukushima Daiichi Nuclear Power Station Units 1 to 3

            http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_04-e.pdf

            The newest data from water samples, absorbed radiation doses, and camera views inside Unit 1 PCV do not disprove these results (and the conservative assessment that “most of the fuels have melted and trickled down into the lower region of the RPV,” or along control drives as indicated in their graphic, p. 3). TEPCO officials have stated as much … and from multiple lines of evidence (gas concentrations in PCV, water levels, heat balance and injection record, radiation readings from top to bottom, thermometer values, etc.). They have proposed several possible interpretations, and have yet to suggest there was no melt-through. Throwing away evidence, or misreading current or past statements and data, doesn’t reinforce anything. It actually suggests the opposite, that you haven’t made your point and your claim that TEPCO got it wrong requires further testing and analysis.

            Did you even read my initial post and the link that I provided to Hiroshima Syndrome’s Fukushima Accident Updates?

            Yes I did. She did nothing to explain the low dose readings in Unit 1 (11 Sv/h compared to 72.9 Sv/h measured in Unit #2), the charred or burnt appearance of containment, and the very high readings near the east side of the torus (where readings are still impossible due to high radiation in the area). Some have suggested “Corium may have traveled out pipe penetrations, or out one side of the bottom head then out the downcomer paths into the torus room.” It’s interesting to note some readers have suggested something similar in the comments below.

          • Rod Adams says:

            @EL

            First of all Leslie Corrice is a he, not a she.

            Secondly, I appreciate the links you provided to Tepco’s analysis. I hope you go back and read them carefully to see how many uncertain words are used and how many times there was a statement made that the analysis based on conservative assumptions did not match the measurements.

            I was particularly struck by the statement that the expected gases formed by interaction between curium and concrete were not detected, leading to a presumption that the absence of the predicted gases meant that the reaction must have stopped. Of course, the absence of the gases could also indicate that the reaction had never started.

            The radiation measurements that Tepco released sometime around Oct 12 for unit 1 simply do not match an assumption that the cerium is located under the water instead of being located inside the reactor pressure vessel. Radiation level always increases as a detector gets closer to a source, even if the source is under some shielding.

            With regard to your statement about the readings in Unit 2, please provide a link. A number that does not provide the location or even the date is not terribly useful. I confess that I have not been following all announced data.

          • EL says:

            With regard to your statement about the readings in Unit 2, please provide a link.

            http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120327_02-e.pdf

          • Brian Mays says:

            Do you always mis-read articles, and disregard statements that don’t support to your view?

            EL – I think that it is you that should answer this question. It is not my fault that your links do not support your silly claims (as I have pointed out above). All of the whining in the world on your part will not change that.

            But trolls march on. Now you’ve trotted out results from a computer model that are about a year old, as if that adds something new to this discussion. Sheesh!

            Whatever. I’m tired of this stupid game and I’m done with this troll.

          • EL says:

            Brian Mays wrote: Where is this “claim from TEPCO that the corium has melted through”?

            I seem to recall you asked for this information. Or is correctly quoting you no longer up to your standards of misdirection?

            Any other analytically useless comments to add?

          • Rod Adams says:

            @EL and Brian

            Please stop attacking each other directly. It is not terribly interesting reading.

    • an observer says:

      EL, That well is still leaking in the Gulf of mexico.
      Go somewhere and blog about that.
      Or, would that be bitting the hand that feeds you?

      • EL says:

        Do you have any analysis to provide, or do you just wish to muddle up these threads (like Brian Mays above) with inconsequential personal attacks?

  12. Sean Houlihane says:

    Yes, it is interesting that the breach (and there was loss of pressure?) is less severe than was reported – still I am not sure that this means that the worst-case is overly stringent. We thought that these reactors had been properly shut down some time (90 min?) before loss of cooling so I don’t feel this is a good example of real worst-case containment. I agree it is very disappointing that this positive news is unlikely to be reported since the media thrives on disaster scenarios and little else.

  13. Mike Greaves says:

    Not so fast.

    I would be thrilled if the unit 1 RPV bottom held up.
    And the coverage at Hiroshima Syndrome is awesome.
    But without flow-rate data we can draw no conclusions from those ppm numbers.
    If the fresh water flow rate has been sustained at high enough levels through the PCV bottom over the last 19 months, it will have stripped away all surface-exposed water-soluble Cs from the corium. Remember, the corium is fused, not just sintered, and will have much lower porosity than fuel pellets. Thorough washing of the corium surface is very possible and the Cs concentration in the PCV water could be very low now, even though it’s sitting on top on tonnes of corium.

    I think we need more data. Pictures will be awesome and I am incredibly anxious to see them.

  14. Navy Nuke EM1(SS) says:

    Hello all,
    Before I start this, I would like to say that I am not a reporter or a scientist, and I am not making any scientific claims to the veracity of any report or article presented to this point. I am a nuclear trained submariner, that is all… That being said, what I believe Mr. Adams was attempting to show was how radiation field gradients can be used to determine location and amount of activity. Radiation theory is something all nuclear trained sailors are heavily indoctrinated in, we spend countless hours in training learning how to calculate dose rates, how they change with distance, and the effects of shielding. The great part of analyzing field gradients is that it can be done purely qualitatively. So, looking at the original article, Mr. Adams stated that the probe was inserted some height above the containment structure’s floor, and subsequently lowered to the surface of the water at the bottom of the pool. During this procedure, radiation levels lowered to a minimum directly above the waters surface. Making an assertion that the source of the radiation was high in the structure is not something that states directly that fuel did not leak out of the pressure vessel, it just says that the concentration of activity is not where it would be expected had a large portion of the fuel melted through the containment. Secondly, referring to a contributor’s comment stating more research needs to be done considering the possibility that the fuel is in a melted puddle covered by some amount of water: The beauty of using radiation gradients is that they point in the direction of activity, regardless of any other factor. When using the equations to calculate dose rate relationships and how they change with distance and shielding, you see that shielding only offers a coefficient to the equation, it doesnt change the characteristics of the gradient itself, (ie radiation levels would still be highest closest to the source, and diminish as distance was increased). Actual values would be much less, but the gradient itself would remain unchanged. Also, and this is particular topic is something that I am not by any means an expert in so by all means, shoot me down if this is not applicable, is not the purpose of keeping the fuel cool to keep it from melting? Maybe I am confused by the comments, but I would be inclined to say that if the core did melt, and melted through the pressure vessel to land on the containment floor, then subsequent cooling would only serve to minimize future damage to the structure, but if the core melts and lands in a puddle, hasnt most of the damage already been done? At least from a radiological control perspective anyway. I understand covering it with water is imperative to keep it cool to keep it from causing more damage, and I understand it provides shielding, but wouldnt that chunk of fuel be just as radioactive regardless of its temperature? And thirdly, just an assumption from my end, but support equipment is required for naval vessels to port in most other countries, due to them using 50Hz distribution systems. When they supply us power, they have equipment that converts 50Hz to 60Hz for us to use, and this equipment is usually located on the pier or nearby. Knowing that a tsunami caused all of this, I would guess that none of that equipment was functional, and even if it was functional, I am not sure they would be designed to be reversible, ie I doubt they would be able to take 60Hz and make it into 50Hz. I know we had personnel and resources to offer, but as far as supplying power to the core cooling systems to keep them operating, I am not sure how much ee could have helped… At any rate, as a closing statement, I would like to apologize for any grammatical or typographical errors, I am typing this from my phone :) Have a fine Navy day! Fast Attack Tough!
    EM1(SS)

    • Brian Mays says:

      The beauty of using radiation gradients is that they point in the direction of activity, regardless of any other factor.

      This is an important point that deserves additional emphasis.

      wouldnt that chunk of fuel be just as radioactive regardless of its temperature

      Well, there might be a slight effect in that higher temperatures could make it easier for trapped radioactive gasses to escape, but that is very minor. Yes, you’re right; the temperature shouldn’t make any significant difference.

      • EM1(SS) says:

        @ Brian

        I quite often write and say things that are logical in my head but not to anyone else because out of whatever train of though I have, I tend to skip key steps… Horrible affliction, trust me… Anyways, what I meant to use as the emphasis was the radiation measurements taken, and the applied use of a few standard point source dose rate equations:

        DRa x da^2 = DRb x db^2 ; where DR is Dose Rate, d is distance from the source, and the subscripts a and b serve to identify to points of measurement.

        DRsh = DRunsh x 10^-n ; where DR is still Dose Rate, the subscripts sh and unsh simply define whether the DR is measured with or without shielding respectively, and the 10^-n is a coefficient used to determine how much DR is affected by the shielding.

        Note that calculating the effect of shielding has no input for distance, and calculating a DR at some distance has no input for shielding. They are two separate equations, and they are used completely independently of each other. The real point of that section was to say that even if the pool of water provided shielding to a chunk of fuel at the bottom, as the probe was measuring radiation levels above the water, the only effect on the measurements taken would be that they would be much weaker than if there was no water. Any radiation measurements, regardless of whether shielding is present or not, will lower as distance from the source is increased. Couple that qualitative analysis with the actual findings TEPCO published from their report, and we see that because the readings were higher at the insertion point, and lower at the floor, then the insertion point must be closer to the source of the radiation than the floor. I am aware TEPCO said all of that, I was just trying to present the math behind the readings so there would be little room for using journalistic interpretation against the findings themselves. TEPCO has said a lot of things, some probably less accurate or realistic than others, but if they are posting raw empirical data I feel quite confident in using that data to derive my own scientific conclusions. Moreover, I believe TEPCO’s initial assertions that fuel had leaked out of the pressure vessel are simply a result of occupational conditioning. We are all trained for worst case scenarios, we expect them and plan for them, so when we find evidence that “discounts” our original assumptions, that is a cause for rejoice, not picking apart the scientists who present the information or the journalists who disseminate it. But I digress… I suppose I picked the wrong community for employment if misconceptions and tilted biases unnerve me as they do…

        Also, thank you for confirming my assumptions on fuel temperature. I had thought about the possibility of fission product gasses escaping but discounted their effects on the overall radiation fields under the assumption that the majority of the gasses would have been released at the time of melting, and most of that would have decayed away by now. Anyways, thanks again!

        • Brian Mays says:

          EM1(SS) – I understood completely what you said, and in particular, I thought that the sentence of yours that I highlighted above expressed the heart of the matter rather powerfully and succinctly.

          Certainly, almost all of the core’s inventory of radioactive gasses (primarily noble gases) were released at the time of the accident. The rest have decayed away to nothing by now. I agree with you 100%. Nevertheless, I have found it wise to always keep radioactive gasses in the back of one’s mind, because they can sometimes pop up and result in unexpected consequences.

          For example, you might recall that sometime in the past year there was concern about a recriticality in one or more of the Fukushima reactors, because TEPCO had found trace amounts of radioactive Xenon in air samples taken from inside the containment structure. Further (more sober) analysis of these readings demonstrated that this Xenon was due to spontaneous fission — a naturally occurring phenomenon — but that didn’t stop the usual scaremongers from blowing up this minor reading into a major catastrophe.

    • Rod Adams says:

      @EM1 (SS)

      Thank you so much for stopping by and demonstrating how practical and effective the Navy’s radiation training program is.

      As you stated, we have solid reasons for developing an ingrained understanding of radiation, radioactive material, and the way that our sensors can help us safely use that understanding.

      Also thank you for mentioning the 50 hz / 60 hz issue. As I recall, our Secretary of State made an announcement early in the casualty that we were sending “coolant”. It was later determined that she meant that we were sending generators, but they were not useful since they produced the wrong frequency power.

      • Rob Brixey says:

        50 Hz power can be created by 60 hz generators by governor adjustment.
        You’d derate the generator because of reduced air flow through the windings.
        Maybe defeat UF / UV relays if any exist.
        That may be an excuse, but would be among the lamest of excuses.

        The “coolant enroute” , in my opinion was Boric Acid, knowing they would attempt Containment Flood, the boron inventory required to assure a continued shutdown condition is huge. In BWR speak, its called Cold Shutdown Boron Weight, pretty reasonable for RPV inventory, orders of magintude larger for a Containment inventory.
        Sodium Pentaborate rocks up at low temperatures, Boric Acid is more easily pumped in as a solution.

        The lack of official detail is pitiful.

        • David Walters says:

          Rob…no…this is jerry rigging at it’s worse. The relays alone would be really impossible to ‘defeat’ as it would leave the generator on board as subject to major winding temperature flux that could destroy them. There is a reason for these relays.

          Secondly, it’s not the governor alone that protects the generator from under (or over) frequency but the entire generator is tuned and build around one frequency AND one voltage where the power output is regulated by the system itself (the load), the RPMs or speed of the generator which itself is paralleled to the load, that is the speed of the generator is exact same as that of the system it’s paralleled too, and potential/power transmitters/relays.

          If these ship were designed with *built in frequency converters*, or generating DC it would be easy to convert it to whatever frequency and voltage you wanted to plug into. But jerry-rigging a nuclear powered turbine/generator set? I don’t think so.

          • Rob Brixey says:

            Without divulging too much, some generators are designed to operate substantially below 60 Hz for variable speed loads.
            Besides that, I agree, neither of us want to destroy equipment.

          • Rod Adams says:

            @Rob Brixey

            I’ll also not divulge too much by asking if you have any idea how one would route power from the variable speed generators you are implying exist to a load several hundred yards away? How much cabling would you need and how much would it weigh? Where was the nearest source of such material in the aftermath of the earthquake and tsunami?

          • Bill Rodgers says:

            Without taking this discussion too much off topic, just wanted to add some additional discussion to the subject of using Naval ships to power a shore based power grid.

            There are several issues that must be dealt with which EM1(SS) and David Walters discuss.

            Other questions that would need to be asked are:

            Are the shore based grid connections available or were they too severely damaged during the tsunami?

            If not then where will the 100 of yards of cabling come from as Rod asks? On our ship we only had enough to get from midships to the pier with allowances for tidal action which was probably about 100-150ft of cable (and that is probably an overly generous estimate). Not the 1/2 mile of cabling that would be necessary at Fukushima. Look at how many days it took to lay the cable that was eventually laid down from one part of the site to another. And how will those cables connect to the shore system? Different grids mean different connection designs.

            How much power is available from the ship? The ship can not go into shut down mode or compromise its operational committments unless the Pentagon changes its orders. So how much power can be committed to power a shore based grid system without impairing safe operation of the ship and the crew?

            And will that power be sufficient to handle emergency loads required of a reactor’s emergency cooling systems? I am working on a job that requires up to 2MW for a single aux feed pump starting current to prevent motor burnout. How many emergency feed pumps can be started with a ship based system and then, once started, safely operated?

            The discussion above is even before the losses that will occur when taking a 60 Hz/4160V system and transforming the frequency/voltage signal into the local grid requirements. Variable frequency generators are available but not common and involve losses. So reduce the power available from the ship by the losses to heat during transformer operations.

            There have been only a few instances where Navy or Army ships have been used to power shore based facilities. Those situations have been when no emergency existed.

            The USS Lexington powered Tacoma WA during 1929-1930 time period and, as Rod’s own article discusses, the Army used their mobile reactor to assist in providing power to the Panama Canal.

            http://atomicinsights.com/1996/08/first-nuclear-power-barge-pioneer-barge-built-america.html

            (Note: This discussion is neither comprehensive nor verified as 100% correct. The purpose was to quickly provide a design-based approach about some of the challenges that would need to be overcome if the USS Ronald Reagan or the USS George Washington attempted to provide electrical power to the Fukushima emergency efforts.)

          • David Walters says:

            Just on this to answer Rod’s question…I’ve had direct experience with this after the famous Loma-Prieta Earth quake that blacked out norther Cali with a 7.1 quake.

            We had a Fast Frigate (FF “Knox class”, circa 1965) come over to offer us power. We asked for steam instead to keep our hotwell hot and the temps slightly elevated on the turbine. I was plant liaison with the ship given my experience in working on US navy ships specifically on a dozen FFs of this kind (and personally not wanting to be in all the chaos at the plant itself!).

            The frigate crew, as many surface ships have trained for, wanted badly to demonstrate their ability to provide us with station power. The Pier they were docked at (look up Pier 70, SF, on goggle maps) is about 300 yards away. they had high voltage cable for 3 times that stowed away and with which they laid it out on the pier itself just in case. I do not remember what they had to do in terms voltage/HZ configuration but apparently, Rod, your USN is WELL prepared for this sort of thing and trains for it. I never knew this until that day of the quake.

            Our plant runs, when online, at only about 4 MWs of station power, easily supplied by this relatively small steamer powered frigate. It seems the USN has the ability to provide small amounts of AC power to any US system it can access via several hundreds yards of cable.

        • EM1(SS) says:

          I agree that 50 Hz generation is possible, and I also agree all the things you mentioned would be required. I cannot be too specific regarding our operating procedures; however, I can say that as far as Naval Nuclear Power is concerned, we do not do anything without an approved operating procedure to follow. Those ratings you refer to are redline specifications, we are not permitted to operate our equipment in those conditions. Also the UF/UV relays that would need to be overridden often serve multiple purposes, and the parameter information they provide is not usually only an indication of bus frequency or voltage. Overriding them may remove their input into a more complicated system or systems, one that I cannot specify. I can say that such bypassing of installed safety features would not be approved in any situation, but most especially in the case of using a nuclear powered warship to respond to a nuclear accident. Again, I agree completely that it would be possible, and I as an Electrical Operator would be more than able to facilitate such action, but I am also aware that everything that would need to be done to accomplish that would never get approved due simply to the increased risk of damage we would subject ourselves to. Another facet of operating generators out of their rated limits is not directly related to the generator itself, but more on the regulating and governing equipment. The governors we use are less able to provide stable control of frequency, less able to effectively sustain a linear speed droop with load, and perhaps most importantly provide significantly less transient load response stability. Loading, speed governing and voltage regulation operate together in a balanced relationship. When one is in a weaker capacity, the others are affected, and often experience detrimental effects due to the abnormal operating conditions the weaker system is causing. For example, speed oscillations caused by a governor’s inability to control speed at low load and low RPM conditions can cause excessive transients in the voltage regulator’s excitation circuits, as well as increasing the likelihood of reverse powering the generator you are attempting to use. Cascading effects lead to an electrician’s nightmare very quickly. At any rate, I am not defending the decisions of my superiors per se, I am simply analyzing and assessing the risk to benefit ratio, and for me as an electrician, I would be hard pressed to impose that high of a chance for equipment failure on my equipment…

    • EZ says:

      If I understand you correctly it’s like a light bulb. Every time I double my distance from the light bulb the amount of light that reaches me decreases to 1/4 of what it was before (I’m talking about the Inverse Square Law). If I put a sheet of cloudy glass between me and the bulb the total amount of light that reaches me becomes less, but the relationship between me doubling my distance and the decrease in light reaching me remains the same. If I understand things correctly this is high school level physics. I hope everyone commenting here has at least that level of understanding.

      • EZ says:

        That last sentence was kind of rude of me. Sorry about that.

      • Rod Adams says:

        @EZ

        Radiation spreading follows exactly the same laws of physics as light or heat. From a point source, the relationship is as you have stated – the Inverse Square Law – because the energy coming from that point source spreads around the surface area of a sphere.

      • Bill Hannahan says:

        EZ, your math is correct for a point source. What is the math if you move from five feet to 10 feet from a source that is 20 feet in diameter?

        • Engineer-Poet says:

          Hah, I see I’m not the only one who noticed that!

        • Brian Mays says:

          The intensity of the field decreases by a factor of 1.78.

          When dealing with an inverse-square field, any spherically symmetric source is going to look like a point source as long as you are outside of its outer boundary.

          This is basic mathematical physics.

          • Bill Hannahan says:

            Hello Brian, thanks for your answer. I see that you have assumed that the source is uniformly distributed in a sphere 20 feet in diameter with no self shielding. I understand this concept for fields, electric, gravitational etc. Consider some other configurations.

            1… Uniformly distributed in a sphere 20 feet in diameter with self shielding.

            2… Uniformly distributed over a flat plate 20 feet in diameter.

            3… Uniformly distributed over a curved plate 20 feet in diameter.

            4… Non-uniformly distributed in a sphere 20 feet in diameter.
            a… Concentrated on the front side of the sphere with no self shielding.
            b… Concentrated on the back side of the sphere with no self shielding.

            4… Concentrated on the edge of a disk 20 feet in diameter.

            In each case assume the activity is adjusted to provide the same field strength at five feet. Will the attenuation at 10 feet be the same in all cases?

          • Brian Mays says:

            I see that you have assumed that the source is uniformly distributed in a sphere 20 feet in diameter with no self shielding.

            Bill – I answered the question that you posed.

            I did not assume that the source is uniformly distributed; my answer is more general than that. My only assumption about the distribution was that the source is spherically symmetric, and how could I assume otherwise when you didn’t give any more information than a diameter?

            How could I assume any shielding when you said nothing about the material and its attenuation? I also assumed that the effects of scattering are negligible for the same reason.

            From far enough away, any configuration is going to look like a point source to a reasonable approximation.

            Close up, things will appear different, but one thing doesn’t change: the gradient of the field still points to the strongest source after distance and shielding have been factored in.

        • EZ says:

          Bill Hannahan, I guess it’s more complicated then I thought it was. Larger objects could probably be though of it term of multiple points, but unlike a single point I don’t think it would be possible to be sure of their exact locations because there would be multiple possible locations that fit with the same readings. If the majority of the radioactive material is relatively close together, and if the sensor has enough distance from those materials, it should be possible to determine those material general location with some degree of accuracy even if even if precise details (exactly where all the point are) remains unknown. I think that is what Brian Mays is talking about below, though I’m not completely sure of that.

          I’ve been thinking about this problem all day, and what I think is that more data points would be helpful. If there are only two data points then there are multiple possible configurations that could account for them, but every time you add another data point the number of possibilities go down. This investigation took 8 reading, 9 if you count the initial entry point, so I don’t think it’s complacently unreasonable to think that something could be learned from it. If someone had a detailed Hypothesis about the state of things inside unit 1 then they could check if there Hypothesis fits with the data. If not they know their hypothesis is wrong and needs to be revised or thrown out which seems like useful information to me. Also, if there hypothesis does fit the date, while that doesn’t tell them anything for sure, it gives it weight. Especially if no one can come up with a viable alternative.

          I think that I should probably mention that as interesting as I find this kind of stuff nothing particularly qualifies me to talk about it so if I’ve made some errors sorry about that. Also, sorry for any spelling and grammar errors, I’m to tired right now to do my usual amount of proof reading.

          • Bill Hannahan says:

            EZ, thanks for your answer.

            Right now they are trying to get an idea of where the fission products are, however the data is so limited, there are multiple possibilities that could produce similar results. They will need a detailed visual and radiological survey to understand the situation accurately enough to form a plan of action.

            EZ, you have had a rough introduction to AI, rougher than you deserve in my opinion. I suspect some of the most assured commenter’s will be proven wrong.

            You have an inquisitive nature and are searching for the truth. Keep studying and you will be fine.

          • Engineer-Poet says:

            Larger objects could probably be though of it term of multiple points, but unlike a single point I don’t think it would be possible to be sure of their exact locations because there would be multiple possible locations that fit with the same readings.

            You could determine the distribution using gamma cameras to perform a type of tomography (moving the cameras around and looking at the luminosity along various rays going both up and down), but it sounds like they’re nowhere close to that level of sophistication.

          • EM1(SS) says:

            Bill,
            To answer the scenarios you proposed requires a good deal of assumptions and math. The first assumption that can be made is that any source, from a great enough distance, appear to be a point source, as stars do in the night sky although we know them to be veritable giants inconceivable to our feeble minds. The second assumption is that at some distance, that “point” source will begin to appear as something else besides a point, be it a line or a plane or even a three dimensional body. The third assumption is that if the source is of sufficient distance to be considered a point, then all activity comprising it – regardless of how distributed – can be condensed into a single central location relative to the actual locations of radioactive sources concerned. A more specific aspect of this assumption implies that for non-uniformly distributed sources, the activity within can still be consolidated to a central point, although that point may be in a physically different location from the spatial center of the same three dimensional body. (Kind of like how the center of gravity of a ‘weeble-wobble’ is much lower than the actual center of the toy by volume alone, due to the weighted bottom of the toy. In the same way, a concentrated source of activity in any location within the body will ‘move’ the source-as-a-whole’s center location towards the concentrated activity.) Fourth assumption is that radiation effects from any given individual particle are not affected by any parameters or specifications of the source as a whole, and as such the measured exposure rate at any one location is the *sum* of all the radiation emitted from all activity whose radiation fields can measurably affect that area. This may seem innocuous, but it is actually a very critical assumption. It is what leads to the assertion that there are many different possibilities that can exist (infinite in fact) for any set of measured radiation readings. This assumption cannot be underestimated, but you can understand why it works that way. The equations we have are much more efficient when we know the activity, and we know it’s exact location and physical parameters. I can with incredible accuracy predict the radiation measurement at any given location, provided I know the source, it’s location, and whether or not it is shielded; however, when the equations are used in reverse, especially to identify a variable with an already large set of possible solutions, that accuracy is all but nonexistent. That being said, this assumption only directly applies to a purist, quantitative analysis, and a good deal of the inaccuracy can be ameliorated by using these equations in terms of proportionality or a strictly qualitative analysis. Fifth assumption – one that I am imposing to avoid the use of higher level math to evaluate radiation field gradients – complex calculus-based field calculations can be simplified by removing a dimension and performing multiple repeated calculations on the resulting (n – 1) body at various intervals and summing their solutions. For example, a 1 cubic foot, cube-shaped source could also be relatively accurately analyzed by performing 1 square foot plane source calculations at a specific interval. In the above example, I might calculate the exposure from a one square foot plane of the cube’s side that was facing me, then calculate another exposure of a one square foot plane one inch deep into the cube, then two inches deep and so on and so forth. I would then sum all the exposures I calculated and that would approximate the same exposure I would have calculated using calculus to integrate the source. (In fact I am integrating, just not continuously as calculus is designed to do) A very important aspect of this assumption is that by doing so, I because I am only ‘looking’ at a small chunk of the activity per calculation, the distances at which that transition between point-source-characteristics and something-else-characteristics will be much closer to the source as mentioned in assumption number two. Combine this fact with assumption number four, and calculating exposures inside the containment (relatively close to the source) becomes much easier. An applied extension of assumption number five allows one to rather easily calculate how self-shielding impacts measured exposure rates. Simply put, just apply a shielding coefficient to each individual calculation prior to summing them, and your resulting exposure at that given point should reasonably accurately account for the effects of self-shielding. Now, that the novel of assumption are out of the way, on to qualitatively (and semi-quantitatively) answering questions:

            First, some specific assumptions: I will use 100 Curies (Ci) as my activity estimate. For self shielding, I will assume that the source is sitting in water and thus I will use the qualities of water for assuming shielding. I will also assume that all scenarios mentioned are representative of how you consider the pressure vessel to be configured. Specifically, I will assume the “flat plate” is representative of just a compressing all activity into a plane large enough to account for the size of the pressure vessel, the “curved plate” I assume is indicative of the wall of the pressure vessel as it appears to an observer, the “non-uniform distribution” I suspect you mentioned to discern how the physical layout of the fuel inside the pressure vessel may alter readings, and the “disk” is a similar compression-type analysis like the flat plate, except the source is compressed into a disk whose plane is in line with the observer. Also, I plan to use the roentgen, as it is a unit I am familiar with…

            1) Uniformly distributed, 20′ diameter sphere with self-shielding:
            First, I divided the sphere into bisecting planes at an interval of 0.5 feet, in such a manner that each plane would be perpendicular to a line between the center of the plane and the measurement point. Then I calculated the activity in each plane based on that plane’s volume compared with total activity. Then I calculated an unshielded exposure rate for the appropriate distance, for each of the bisected planes. I then applied the appropriate shielding coefficient to each of the calculated exposure rates, and then summed them all for the total exposure. Calculated exposure rate at five feet: 240.06 mR/hr

            2) Uniformly distributed, 20′ diameter flat plate:
            Fairly simple plane source, the measurement point is beyond the transition at which the source acts as a point source, so Calculated exposure rate at five feet: 22.676 R/hr

            3) Uniformly distributed, 20′ diameter curved plate:
            First, I divided the curved plate into lines that were in line axially to the curvature of the plate. These lines were equally spaced around the curvature of the disk by a factor of 22.5 degrees. I then calculated the length of each line, and distributed the activity evenly and proportionately among them. Next I calculated the distance of each line to the measurement point and calculated the exposure rate from each line. The closest lines were within their transition points, which lead to their gradients responding differently than a point source would with distance. Summing all the individual exposure rates, Calculated exposure rate at five feet: 12.501 R/hr

            4a) Non-uniformly distributed, 20′ diameter sphere, no self-shielding, concentrated in the facing side:
            Using the data accumulated by scenario number one, I doubled the activity in each half of the sphere, and then summed only that half’s exposure rate. Calculated exposure rate at five feet: 10.534 R/hr

            4b) Non-uniformly distributed, 20′ diameter sphere, no self-shielding, concentrated in the back side:
            Calculated exposure rate at five feet: 3.3179 R/hr

            5) Non-uniformly distributed, 20′ disk, concentrated on circumference of disk:
            First, I assigned designated points evenly spaced around the circumference of the disk. Each point was separated by 22.5 degrees from the next point. I then evenly distributed the activity amongst the designated points. I then calculated the distance between each of the points and calculated the exposure rate at the measurement point for each point. Finally, I summed all individual point exposure rates. Calculated exposure rate at five feet: 8.9239 R/hr

            Now for the last part… You mentioned adjusting the activity for the same field strength at five feet, and then recalculating at ten feet and determining the attenuation? I am not sure what it is that you are looking for, but I made some extra calculations that might answer the concept you were looking for. Given that in the majority of calculations I performed the distances between the measurement point at five feet and the sources were already greater than the transition point where they act as point sources. In other words, adjusting the activity would not affect the way the gradient reacted, the only thing that could do that is the physical arrangement and parameters of the source themselves, which we assume is a constant (we are estimating conditions in an actual containment vessel that we must assume is mostly in a static state). So, adjusting the activity itself doesn’t change much, in fact the only variance in the attenuations I am about to provide is due to the fact that in each scenario the distance from the activity’s centralized location and the measurement point varied. But at any rate, more data as requested, the following values are calculated using the same basis as the five foot analysis, but instead using ten feet. 1) 85.508 mR/hr, 2) 11.111 R/hr, 3) 6.7938 R/hr, 4a) 4.5600 R/hr, 4b) 2.0351 R/hr, 5) 3.7388 R/hr. Linear attenuation factors (these are not useful in any way for analyzing the inverse *square* law, but I provide them all the same for those who appreciate a linear scale vice a more accurate logarithmic scale) are as follows from five feet to ten feet: 1) 35.619%, 2) 48.999%, 3) 54.346%, 4a) 43.288%, 4b) 61.337%, 5) 41.896%. And for the infinitely more useful logarithmic attenuation factors: 1) 0.81167, 2) 0.77145, 3) 0.75857, 4a) 0.64441, 4b) 0.59245, 5) 0.60252. Not considering the shielded scenario, all logarithmic attenuation factors fell within 0.17900, with a standard deviation of 0.00586. Including the shielded scenario, all logarithmic attenuation factiors fall within 0.21922, with a standard deviation of 0.00707. Subjectively I assert that the variances witnessed between my calculated values are based almost entirely on discrepancies resulting from rounding and carrying errors forward.

            In conclusion, physical arrangement and configuration of activity can in most cases be disregarded when presented with a set of measurements taken at different points within a space. In the above scenarios, calculated measurements varied substantially depending on those factors, but in all cases, the attenuation factors remained virtually constant given the same conditions for each measurement. All scenarios indicated an exponentially decaying relationship between values taken at two different measurements. Furthermore, in the above scenarios, each one was evaluated at only two different measurement points, so useful data can be obtained by just two data points. Nine points validates that information, but in general a gradient can be determined by just two points, and the source will always be closer to the highest exposure reading. To apply this to the Fukushima reactors would require more readings to specify *exactly* where the source is, sure, but the readings they provided unequivocally states that the activity is *not* under the pressure vessel. At any rate, I am about Math’d out, so I suppose I will wrap this mini-novella up…

      • EM1(SS) says:

        Very much so indeed, EZ… In fact, in might be interesting for you to note that it is not just ‘like’ a light bulb, it is ‘exactly’ a light bulb. Radiation in the nuclear context is still electromagnetic radiation, just the same as the light from the bulb. The only difference is the energy level of the waves and particles they are comprised of. Nuclear radiation tends to have much more energy than visible light, and thus has the potential to cause much more biological damage, but the principles of its theory, and how shielding affects it, etc, it is all 100% the same… :)

  15. Rob Brixey says:

    Best news I’ve heard from Fukushima. In my opinion, Unit 1 is their worst scenario:
    1) U1 is an Isolation Condenser plant – had no injection during the SBO. U2 and 3 had RCIC / HPCI injection for 1 to 3 days post scram.
    2) U1 had the pressure traces of a High Pressure Melt Ejection, Reactor Pressure lowered drastically coincident to a rapid rise in Containment Pressure.
    3) Containment Temperature trended up to 400C, which may indicate Corium contact with Steel liner. Inability to depressurize makes the BWR susceptible to HPME Severe Accident consequence.

    • Rod Adams says:

      @Rob Brixey

      I hope you agree that those measurements are also consistent with a pipe break. A rapid rise in containment pressure at the same time that primary pressure is falling indicates that water / steam is escaping the primary system into the containment. Since the escaping water was even hotter than normal by the time it escaped, it is not surprising that the containment liner temperature approached 400 C.

      Other indications lead me to believe that the pressure vessel itself will hold water, but that there is probably a pipe break in connected piping that is low enough to prevent the water level in the pressure vessel from rising too much. I suspect that finding and fixing that break will be a challenge, but once it is accomplished, the vessel can be flooded to allow the same kind of fuel removal operation as was accomplished at TMI. It won’t be easy or cheap, but it will be possible and safe.

      • Rob Brixey says:

        I agree both Pressure indications do that on a large coolant release.

        My concern is Containment temperature, which I watched rather closely. If steam and water were doing the heating, every vent would have coincided with a decrease in Containment temperature.

        The HPME is suspect in my opinion because of its association with Direct Containment Heating (DCH)

        400C is about 900F. Sounds superheated to me.
        At these temperatures, electrical penetrations burn out of the Mark I. White smoke emanated from all three Reactor Buildings for days. In my opinion, the Containments are breached to the point of not being floodable. That bugs me because it looked like U1 could hold Containment Pressure. The EOPs / SAGs would have flooded the Drywells to above the Top of Active Fuel (TAF) elevation – if it was possible. The RB Basements are still flooded, likely a symptom of a submerged Containment leak.

        Similarly, RPVs are breached and they could not restore water level above TAF.

  16. Bill Hannahan says:

    Rod, I hope you are right, but the TEPCO data is too poor to confirm your conclusion.

    http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_121010_01-e.pdf

    Consider this alternative.

    1.. The bottom of the reactor vessel fails.

    2… Corium flows downward. Some of it sticks to the control rod drives, more flows to the bottom.

    Visualize the corium as a source of bright light (radiation). The light shines brightest at the insertion point near the control rod drives and diminishes as the detector is lowered away from the drives.

    Water is a great shield, visualize it as inky water. As the detector submerges, it is shielded from the light above and below. They need to survey the bottom to be sure there is no fuel there.

    More importantly, if all water moderated reactors were equipped with a core catcher, battery backed hydrogen igniters and an accident rated vent filter, a meltdown accident will release insignificant quantities of fission products.That could result in more simplification and a lower plant cost.

    • Andy Dawson says:

      “Some of it sticks to the control rod drives, more flows to the bottom.”

      Is that really a credible idea – in that enough corium could “stick” to produce anything like the radiation levels observed near the rpv borrom head?

    • Mike Greaves says:

      “Water is a great shield, visualize it as inky water. As the detector submerges, it is shielded from the light above and below. They need to survey the bottom to be sure there is no fuel there.”

      This comment is spot-on. Radiation gradients tell us little across the boundary from air down into a fast-flowing (and thus potentially cleaner) water surface, unless you go right down the 2.8 m of wafter-column shielding to the PCV bottom where corium could be lying.

      A very very very rough guess-timate of the field at the surface of a multi-tonne corium deposit is 2000 Sv/hr after 19 months from Cs alone (I only claim this to within a factor of 10 because I don’t have the time to do the calculation right and must make many assumptions to get an estimate at all… and only bothered to include Cs gammas…).

      11 Sv/hr seems like just contaminated steel surface from adsorption of volatilized Cs, and that hasn’t been washed clean(er).

      They need to plunk the detector down right at the bottom of the PCV, and preferably in several spots. Also get a good shot of the RPV bottom to check for damage.

      • Rod Adams says:

        @Mike Greaves

        Water is a predictable shield for gamma radiation. General thumb rule for gamma at Cs enegy level is that two feet of water will reduce radiation dose rate by a factor of ten. If the dose rate at the surface of your assumed pile of corium is 2000 Sv/hr, the dose rate at the surface of 2.8 meters of water above the pile should be about 0.06 Sv/hr. (2000/10E4.5) Instead, the level just above the surface was 4.7 Sv/hr according to Hiroshima Syndrome’s report.

        There is no “fast flowing” water in the pedestal area under the reactor pressure vessel.

        I agree that it will be useful when we have radiation measurements all the way to the floor of the containment building. I am pretty certain what those readings will reveal.

        • Brian Mays says:

          Rod – I agree with your estimate of the expected dose rate from the shielding by 2.8 meters of water. I did the calculation myself before I read your comment and got the same answer.

          An additional point to keep in mind is that steel is roughly seven times more efficient at shielding gamma rays than water. Thus, shielding from a 6-inch-thick reactor pressure vessel would reduce a 2000 Sv/hr dose rate to about 30 Sv/hr.

          If Mike’s “guess-timate” of the surface field is good to “within a factor of 10,” then we’re talking about a dose rate at the outer surface of the vessel that is somewhere between 300 Sv/hr and 3 Sv/hr.

          The highest reading in the containment vessel (somewhat away from the surface of the reactor pressure vessel) was 11 Sv/hr.

        • Mike Greaves says:

          “There is no “fast flowing” water in the pedestal area under the reactor pressure vessel.”

          Fast relative to other transport/removal mechanisms, like dissolution and decay. I had understood that they’ve put a big volume through there, and I am assuming the wet zone is well scrubbed. It seems the water itself is no longer a strong source.

          “I agree that it will be useful when we have radiation measurements all the way to the floor of the containment building. I am pretty certain what those readings will reveal.”

          Current info remains sketchy, but I am keeping my fingers crossed too.

        • Mike Greaves says:

          Anyone know if the 2.8 m water column is contacting the RPV bottom? Was it always? (i.e. is the RPV bottom less than 2.8 m above PCV floor)
          Are the CRD components mostly stainless (i.e. low thermal cond.?)

          I recall INPO report saying fuel failure 3 hours post-quake, I’m wondering if the RPV bottom fuel debris had an additional quenching heat sink *beyond* the RPV bottom (like lots of water, or lots of steel in lots of water).

          The radiation data is way too sketchy. I’m wondering if someone has a *better* reason to conclude that the RPV bottom held.

          • Brian Mays says:

            Anyone know if the 2.8 m water column is contacting the RPV bottom? Was it always?

            Based on the slides that were linked to by Bill Hannahan above, it appears that the water is only at the very bottom of the drywell. It doesn’t quite cover the pipes to the torus. This level is well below the bottom of the reactor pressure vessel.

        • EL says:

          Several the statements above point to the technical and scientific importance of “radiation gradients” and that “temperature shouldn’t make any difference.” I’m curious why there has been no discussion of the very different radiation dose readings at the same point in Units 2 and 1. This difference is not slight, but major?

          This seems to be the main data point for a contrast between the approaches suggested in this article (for “no melt-through”), and those of TEPCO (“it is difficult to identify where the source of the radiation is from the available data”).

          Dose readings at similar point in two reactors (with sample taken from 800 – 1000 mm inside PCV).

          Unit 1 (Oct 10 at the first floor grating): 8.2 Sv/h (@1000 mm inside PCV)

          Unit 2 (March 27 at the first floor grating): 72.9 Sv/h (@800 mm inside PCV).

          If the corium is located in the same spot in the two reactors (bottom of RCV), then why such different readings? Do these results look consistent to you and others?

          • Brian Mays says:

            Several the statements above point to the technical and scientific importance of “radiation gradients” and that “temperature shouldn’t make any difference.”

            These are important considerations, but I never expected everyone — particularly those with no background in science or mathematics or those with no common sense at all — to understand these finer points.

            If the corium is located in the same spot in the two reactors (bottom of RCV), then why such different readings?

            There is no way to tell from such a sparse set of data.

            First of all, you’re comparing apples to oranges. If you want to compare Unit 1 to Unit 2 then you have to realize that Unit 2 is larger (i.e., it contained more fuel to begin with) and the measurements for Unit 2 were taken over half a year ago. Based on only the difference in size of the two reactors and the additional radiological decay that has occurred over the last half year, I’d estimate that you should reduce the readings from Unit 2 by a factor of about two to be consistent with the latest readings from Unit 1.

            That’s just the beginning of the adjustments that ultimately would be needed, but they are the only ones based on what we absolutely know today.

            Next, it is quite possible that some of the melted core in Unit 1 escaped through the perforations in the bottom of the reactor vessel and now lies at the bottom of the containment where its radiation is being shielded by water. The data that we have can’t rule that out. Nevertheless, the latest radiation readings reported by TEPCO indicate that there is still a very hot (radiologically speaking) source sitting somewhere above the location that the probe was inserted. Although this evidence is far from conclusive, it strongly points to the assumption that most of the fuel remained within the RPV after the accident.

          • EL says:

            First of all, you’re comparing apples to oranges. If you want to compare Unit 1 to Unit 2 then you have to realize that Unit 2 is larger (i.e., it contained more fuel to begin with) and the measurements for Unit 2 were taken over half a year ago.

            Wouldn’t this mean that Unit 2 has a larger containment design, and a probe 800-1000 mm from PCV wall is further away from RCV? Factor of 2 doesn’t explain the data (which is different by a factor of 9).

            That’s just the beginning of the adjustments that ultimately would be needed, but they are the only ones based on what we absolutely know today.

            Which begs the question. If you are going to dispute what authorities closest to this data have said (“it is difficult to identify where the source of the radiation is from the available data”), why do you think these unspecified uncertainties point in a conclusive way to “no melt through” rather than a need for “further testing and analysis” (which I, and others, have suggested is much needed in this case).

          • Rod Adams says:

            @EL

            I have not yet determined exactly what it means, but the measurements associated with unit 2 to which you linked are clearly labeled as “Measurement result of airborne radiation inside the PCV (approx. 1000mm inside of the internal wall)”. (Emphasis added)

            Those measurements are not just general area readings. They are an apple vs orange comparison to the readings reported from unit 1.

          • Bill Rodgers says:

            @EL,

            To cut to the point, I believe I can state unequivocally that no one here who supports Rod’s article are even remotely suggesting the testing and data collection evolutions are complete. Days of data collection are still ahead for TEPCO. Then more days of analysis by everyone including those of us who are very interested observers. The thing is that many of the observers are just as knowledgeable about nuclear power failures as the people on the ground which is why many of us have strong opinions.

            Moving onto your comment from the news article. First TEPCO had anticipated the fuel had melted into the containment vessel. Their orginal proclamations caused world wide angst and screaming headlines from every anti-nuclear person on the planet who believed the fuel would continue to melt through the concrete structure and become an uncontrollable event

            Now the real time data is suggesting a less catastrophic failure mechanism of the pressure vessel system. So what would you expect the acting general manager to say after the model they have been expecting to be proven correct is now incorrect after their initial data collection?

            Of course he is going to conservatively state that TEPCO is not “certain” where the source of radiation is located. I catagorize his comment as a self-defense mechanism since he knows that anything and everything he states will be put under a microscope.

          • EL says:

            Excellent points. Thanks for the additional comments, and insights into this new information and data.

          • EL says:

            I have not yet determined exactly what it means, but the measurements associated with unit 2 to which you linked are clearly labeled as “Measurement result of airborne radiation inside the PCV (approx. 1000mm inside of the internal wall)”

            Just to clarify a point … Unit 1 and 2 are both “airborne” radiation dose measurements inside the PCV (so I am uncertain about the distinction you are making here). A more recent article published by Denki Shimbun points to another data point missed in the analysis from Les Corrice and yourself. Comparative readings of dose measurements in the Torus room of Units 1 and 2.

            – Unit 1 (Torus Room Investigation on June 26, 2012): high of 10.3 Sv/h (via pipe penetration from above).

            – Unit 2 (Torus Room Investigation on April 19, 2012): high of 110 mSv/h, via robot.

            Les Corrice has an update to his blog dated Oct 19. Reporting on a Japan Times Story, he suggests we are awaiting Cosmic Ray Tomography results for Fukushima Units 1 and 2, which should help identify the location and size of the corium deposits. He also adds: “It should also rather conclusively show whether or not there was a melt-through of the Unit #1RPV bottom head.” Detectors were set up in May in Units 1 and 2, and 1-2 months have been given as a timeline for anticipated results.

  17. Rob Brixey says:

    In June, TEPCO pubished a survey of the RB Basement on Unit 1, in the Torus Area.
    maximum radiation reading was at 4000 OP elevation, 200 mm above the water level in the RB Basement. The reading was 10.3 Sv / hr, this above any of the lower elevations in the DW readings.

    This suggests that fuel has passed that stage, went through a Downcomer Vent pipe connection, or left the Drywell entirely via (SOARCA Peach Bottom page 40 path FL904) a breach into the RB Basement.

    My gut says the new numbers are above fuel, water shielded from the major source which may be in the RB Basement or Torus area.

    TEPCO has removed the June 2012 link, I could not find it today .

  18. Astute says:

    Ha-this is a PRO NUKE INDUSTRY BLOG_you cant trust a word these guys tell you!

    Plus they are caught being contradicted by TEPCO; An industry built on LIES

    ROTFL!!!

    • Rod Adams says:

      @Astute

      Correction. This is a pro nuclear TECHNOLOGY blog populated by many people who have spent their professional lives studying the fascinating, complex and valuable subject. I find it highly amusing to have you visit here and accuse me of both supporting and contradicting the industry. Those conflicting accusations appear within just a few words of each other.

      All are welcome to participate in the conversation, but it is quite uncivil for you to start off your comment with untrue allegations.

  19. Bill Hannahan says:

    @ Brian

    “Bill – I answered the question that you posed.”

    Not really Brian. The question was in the context of this discussion involving a very large, very radioactive damaged reactor. The point of my question is that there are no simple answers, yet you came up with a simple answer to three significant places that is wrong in the context of this discussion. The correct answer is that the question cannot be answered without a lot more information and analysis.

    “My only assumption about the distribution was that the source is spherically symmetric, and how could I assume otherwise when you didn’t give any more information than a diameter?”

    You also assumed that the source material is totally transparent to radiation; no such material exists. Corium is not even an approximation.

    “From far enough away, any configuration is going to look like a point source to a reasonable approximation.”

    True, but not applicable when you are 5 feet away from a 20 foot source.

    “Close up, things will appear different, but one thing doesn’t change: the gradient of the field still points to the strongest source after distance and shielding have been factored in.”

    The correct statement is that the gradient of the field may not point to the strongest source due to the effects of distance and shielding.

    Any answers for the other configurations?

    • Rod Adams says:

      @Bill Hannahan

      You wrote:

      The correct statement is that the gradient of the field may not point to the strongest source due to the effects of distance and shielding.

      I think I understand that you mean that there might be some high concentrations of radioactive material located somewhere in the mass if the mass is 20 feet in diameter and the probe is just 5 feet away.

      However, it almost sounds like you trying to say that if a probe is moved by several meters and shows significantly falling radiation levels from the starting measurement to the final measurement, those measurements still do not prove that the probe was closer to the mass when it started than when it finished. It seems pretty certain to me that the gradient reveals something about the location of the radiation source, especially when well understood phenomena like gravity and shielding are also known bits of information.

      • Jeff Walther says:

        What if there are radiation sources both above and below the probe, and the source below the probe is shielded by 2.8 meters of water?

        Couldn’t that result in decreasing readings as one moves closer to the water’s surface, yet, one would still be moving closer to a source in the water?

        In this scenario, while there is an increasing square law gradient towards the water, there is another, larger *decreasing* square law gradient towards the water, or away from reactor pressure vessel.

        Is there some reason why the mass must have stayed in one piece?

        I’m not advocating one position or another here. I honestly want to know if this scenario is possible/makes sense.

        • Brian Mays says:

          … the source below the probe is shielded by 2.8 meters of water …

          And if there is a source in the bottom of the reactor pressure vessel, then it is shielded by at least six inches of steel and a cylindrical concrete structure that girdles the vessel. Both steel and concrete are more effective shielding materials than water.

          Is there some reason why the mass must have stayed in one piece?

          No.

      • Bill Hannahan says:

        @Rod

        I think I understand that you mean that there might be some high concentrations of radioactive material located somewhere in the mass if the mass is 20 feet in diameter and the probe is just 5 feet away.

        Right Rod, that is one of the minor points I was thinking about in considering my examples. Imagine you are 5 feet away from a solid aluminum sphere 20 feet in diameter. Imagine a very intense point source imbedded just below the surface. If it is oriented with the source closest to you, you are getting a very high dose rate. As you back away the rate will drop off rapidly, similar to an inverse square relationship. Probably not exactly like that due to backscatter from the aluminum.

        If you rotate the sphere so the source is farthest away from you, you will get a low dose rate due to the shielding of the sphere and the distance from the source. As you back away, the rate will drop much more slowly than before.

        However, it almost sounds like you trying to say that if a probe is moved by several meters and shows significantly falling radiation levels from the starting measurement to the final measurement, those measurements still do not prove that the probe was closer to the mass when it started than when it finished.

        Generally a decreasing flux indicates that the probe is moving away from the source, but there are exceptions. For example, consider a direct exposure to a source 20 feet away with a large block of steel next to it. Moving the probe behind the block it can be much closer to the source, yet in a lower field.

        More importantly, in the general case you are right. A decreasing field indicates the probe is moving away from the source that is responsible for most of the field.

        There could be a much stronger source that is too far away to influence the results. My main point is that there could be a much stronger source nearby that is too well shielded to influence the results. This second case is the one Jeff describes below, that might turn out to be true.

        It seems pretty certain to me that the gradient reveals something about the location of the radiation source, especially when well understood phenomena like gravity and shielding are also known bits of information.

        True. A detailed 3D map of the field would tell us a great deal, but right now it is like looking at the Mona Lisa covered by a sheet with a small hole in it.

        • Rod Adams says:

          @Bill Hannahan

          You wrote:

          Generally a decreasing flux indicates that the probe is moving away from the source, but there are exceptions. For example, consider a direct exposure to a source 20 feet away with a large block of steel next to it. Moving the probe behind the block it can be much closer to the source, yet in a lower field.

          Of course that is true, but your question did not mention the presence of a shield and the area under the reactor pressure vessel does not seem to be complicated by the presence of a large block of steel anywhere between the bottom of the reactor pressure vessel head and the floor of the containment. As far as I can tell from the sketches, from the description of the radiation measurements and from logic, there is an open space that is perhaps 10 or more meters tall below the Control Rod Drive Mechanisms (CRDMs) above a rather flat and featureless floor. The RPV is supported above this open space by the heavy, thick concrete and steel pedestal that Tepco had to drill through to insert their probe.

          http://atomicinsights.com/wp-content/uploads/GE-Mark-1-Containment.jpg

          The logical design reason for the existence of the open space is to provide access for inservice inspection and maintenance actions on the CRDMs and the long control rods that they move in and out of the core. Currently, the featureless floor is covered with 2.8 meters (9 feet) of nearly pure water containing little activity and a chloride concentration that is lower than drinking water.

          In that simple geometric space, the radiation readings reported from Tepco provide only one logical conclusion. The dose rate is 20 times higher at an elevation of 8.7 meters than it is at an elevation of 2.8 meters, just above the surface of the water. There is no interfering shield at the top of the geometry other than what I am guessing is a nearly intact reactor pressure vessel and the associated group of control rod drives. At the bottom of the geometry is enough water to reduce radiation readings by a factor of 10E4.5 IF, and only if, the postulated pile of corium has no height of its own. If it leaked and is piled up on the containment surface, there would be less water shielding it.

          • Bill Hannahan says:

            @ Rod
            the area under the reactor pressure vessel does not seem to be complicated by the presence of a large block of steel anywhere between the bottom of the reactor pressure vessel head and the floor of the containment.

            Rod, I don’t know why you latched onto the steel block so hard. I think I made it clear that this is simply an example of how counterintuitive results can happen, and I began the next paragraph with two key words.

            “More importantly, in the general case you are right. A decreasing field indicates the probe is moving away from the source that is responsible for most of the field.

            We know that the source responsible for the field in the airspace below the CRDs is above that space. But we do not know what the field is from the surface of the water down to the bottom, and we do not know what the source of that field is.

    • Brian Mays says:

      The question was in the context of this discussion involving a very large, very radioactive damaged reactor.

      Bill – No, it wasn’t. Please go back and reread the comments. The question was in the context of the math involved in something that behaves according to an Inverse Square Law. Nowhere did you or the person you were replying to mention corium or reactors. The only physical objects mentioned were a light bulb and a sheet of glass.

      The point of my question is that there are no simple answers, …

      If that was your purpose, then you should have explained this clearly. If you wanted to point out such complications as complex geometries or shielding, then you should have mentioned them. Instead, you posed a question that just happens to have a simple answer.

      I can see that you’re miffed that I had a little fun at your expense pointing out that you chose one of the very few configurations for which the most useful way to work the problem is to treat the entire source as a point source. Well, that’s too bad, but whining about shielding and whatnot after the fact doesn’t improve your choice. It just makes you look like a bad sport. Next time, choose a better question or actually try explaining what you mean instead of smugly taunting someone who is sincerely trying to understand these concepts with what you think is a trick question.

      The correct statement is that the gradient of the field may not point to the strongest source due to the effects of distance and shielding.

      That’s just a restatement of what I said, expressed now, however, as a significantly weaker statement that doesn’t tell you all that much.

      Any answers for the other configurations?

      Of course not. They’re all as sloppily posed as your original question, and let’s see … what was that again? … oh yes, “the correct answer is that the question cannot be answered without a lot more information and analysis.”

    • EM1(SS) says:

      Bill,
      I responded with a lengthy mathematical answer to your proposition of scenarios above that may explain a little of why at least I have the opinions I do. I also assumed that the source is transparent, with the exception of the first scenario. With that scenario, I used the shielding coefficient of water, partly because the fuel is likely to be surrounded by water, and partly because using any stronger shielding would have pushed my calculations into the realm of the unmeasurable. I also analyzed the results of all scenarios, both including the self-shielding effect and the dismissal of self-shielding effects. Calculated data indeed varied somewhat because of the shielding, but mostly this resulted in absolute variations in the measurements, the relative variations were much less noticeable, as indicated by the range and standard deviation calculations I provided. I also assumed 100 Ci arbitrarily. I am aware that that core most assuredly contains much more than that, but 100 Ci is nothing to shake a stick at either, so I picked it as just an easy round number that allowed my calculations to fall in a range that was easy to visualize. The biggest assumption I am making is that the containment building is relatively uncluttered, and that the technicians who were taking these measurements were smart enough to not take readings directly behind an RPV support or something, but in any event the data I provided was only intended for a visual-conceptual understanding and grasp of radiation field gradient theory. I of course am not asserting that only one source exists, or that there is no shielding, or anything like that. I would also like to state that I believe I am in the majority when I say that we need much more survey evolutions to get enough data to say anything conclusively, but being that we dont have that data yet, I will still analyze and draw the best conclusions I can from the data I have. Trust me, I will be the first to admit I was wrong when the next survey team finds the chunk of corium melting through the containment floor, but you better believe I will be crunching numbers for the foreseeable future to figure out exactly how I came to an incorrect conclusion and what I can look for to prevent doing so in the future. I think we all share a common link in that aspect, we use our experience and raw data to make conclusions and formulate opinions – and often they are wrong – but for engineering minds like myself, that is all we have to go on. At any rate, I am just trying to convey that I am not trying to stir the fire any more, instead I am simply offering the basis for my own opinions. Half of this is because I know I am wrong a bit, as we all are, and criticism is the only way to fix it, and the other half is to hopefully help explain the concepts we are debating to those readers who may be less familiar or have less experience in these matters than the rest of us have. So, I hope my analysis helps, and I apologize in advance if posting such an analysis ruffles anybody’s feathers, definitely not my intent…

  20. Bill Hannahan says:

    @Brian

    The only physical objects mentioned were a light bulb and a sheet of glass.

    That was another person’s question, not mine.

    …you posed a question that just happens to have a simple answer.

    It does not. You assumed that a 20 foot sphere of radioactive material is totally transparent to radiation; no such material exists. I have not read every shielding book in the world, but I am confidant that none of them would recommend handling such a large source in that way, because it would lead to the wrong answer.

    try explaining what you mean instead of smugly taunting someone who is sincerely trying to understand these concepts

    How ironic that you of all people should mention this. Lets review some of your comments to people who suggested all may not be as well as claimed here.

    Since radiation levels decrease toward the bottom of the structure, what are we to conclude about where all the melted fuel is?

    Now that your own links demonstrate that you’re a fool, will you please go away and play your stupid games elsewhere?

    And now we see the typical troll tactic of flooding the comments with mindless hyperlinks

    Just out of curiosity, what would a mindful hyperlink be like?

    I never expected everyone — particularly those with no background in science or mathematics or those with no common sense at all — to understand these finer points.

    Then, after being exposed to some new ideas by various commenters (your welcome) you write this.

    …it is quite possible that some of the melted core in Unit 1 escaped through the perforations in the bottom of the reactor vessel and now lies at the bottom of the containment where its radiation is being shielded by water. The data that we have can’t rule that out.

    You owe some apologies.

    “The correct statement is that the gradient of the field may not point to the strongest source due to the effects of distance and shielding.” That’s just a restatement of what I said, expressed now, however, as a significantly weaker statement that doesn’t tell you all that much.

    You mean as opposed to strongly telling you something that is not true? Your statement was; “the gradient of the field still points to the strongest source after distance and shielding have been factored in.”

    In reality the gradient of the field is simply the actual gradient of the field, it does not change before or after any analysis is performed.

    Now you could put that data into a computer and it could try to calculate what the field might be in a different configuration, for example without shielding, but that would not be a real field, and it may contain significant errors compared to the real thing, if the new configuration is actually constructed, and the new field is actually measured.

    • Brian Mays says:

      Bill – OK. Now that you’ve experienced a complete meltdown, it’s definitely time to move on. Geez, I’m sorry to have pushed you to this point (that’s the only apology you get … you’re welcome), but I have neither the time nor the patience to deal further with your personal attacks, your petty nonsense, or your tautologies.

      Perhaps you have something constructive to add to the comments on this blog, but smug questions and petty attacks aren’t going to get you very far. Good luck!

    • Brian Mays says:

      In case you’re wondering what I mean by petty nonsense, here is an example:

      You assumed that a 20 foot sphere of radioactive material is totally transparent to radiation; no such material exists. I have not read every shielding book in the world, but I am confidant that none of them would recommend handling such a large source in that way, because it would lead to the wrong answer.

      Self-shielding is only a second-order effect. Even in the limit that the radioactive material is considered to be perfectly self-shielding, the answer to your question becomes reduction by a factor of 1.98, a change of only 10%.

      At a distance of two diameters from the source (40 feet), the difference between the answer with no self-shielding and perfect self-shielding is less than 2%. You’re making a lot of noise about a trivial difference.

      • Bill Hannahan says:

        Brian, first of all thanks for the spell check. I should run all my comments by you before posting.

        Even in the limit that the radioactive material is considered to be perfectly self-shielding, the answer to your question becomes reduction by a factor of 1.98, a change of only 10%.

        The distance from the center of the sphere to the detector increases from 15’ to 20’, a change of 33%. Assuming your new number is correct, the ratio is 10% / 33% = 1/3

        That error ratio is not petty nonsense or trivial by any standard.

        At a distance of two diameters from the source (40 feet), the difference between the answer with no self-shielding and perfect self-shielding is less than 2%.

        Why not take it out to infinity, then your answer would be correct. But go the other way and the error increases.

        Wrong methodology is wrong methodology, even if it gives the correct answer at some point.

        If you used your field theory methodology to calculate dose rate you would be off by a huge amount, probably more than a factor of 100.

        • Bill Hannahan says:

          Opps, looks like I need another spell check.

        • Bill Hannahan says:

          Correction; 0.1 / (1/3) = 0.3 = 30%

        • Brian Mays says:

          (1.98 – 1.78) / 1.78 = 0.11

          That’s approximately a 10% change.

          Meanwhile, moving only 5 feet in the scenario that you proposed nearly halves the dose — a reduction by a factor that ranges between 1.78 and 1.98, depending on the amount of self shielding.

          If you used your field theory methodology to calculate dose rate you would be off by a huge amount, probably more than a factor of 100.

          Physics does not change simply because someone has a bug up his ass.

          Based on the sad attempt that you have put forward as a calculation above, it is pretty clear to me that my mathematics have lost you. At this point, I really think that you don’t have any idea what I’m talking about.

          I can provide details, but perhaps it would be in the best interest of everyone if you would just let this issue drop.

          • Bill Hannahan says:

            @Brian

            Clearly EM1(SS) knows more about shielding than either of us. Assuming his numbers for the self shielded sphere are correct, your error is;

            (2.81 -1.98) / 2.81 = 29%

            He assumed the shield media was water. With corium and steel your error would be larger.

  21. Jason Kobos says:

    Was there a link to pictures taken by the camera that I missed?

  22. Bill Hannahan says:

    @ EM1(SS)

    Your comment October 20, 2012 at 7:16 PM is a very impressive piece of work, thank you very much. I apologize for putting you to so much effort.

    I am going to take some time to think about it. If I have any questions or comments I will get back to you. I look forward to your continuing analysis as we get more data.

    • EM1(SS) says:

      @ Bill,
      Not a problem, the data wasnt directed at you per se, I just addressed you because you provided the scenarios for my analysis. At any rate, after reviewing some of the more recent comments, I feel I am missing something. If we are considering water as the shielding coefficient, then we are assuming that the fuel melted out and is at the bottom of the puddle in the containment building, and if we assume corium and steel, we assume that the fuel has remained in the pressure vessel? So if the question is water or steel for the shielding, and we pick steel, doesnt that give us cause for rejoice in that indirectly we are assuming the fuel remained where it should have? Also, reading the comments about the corium sticking to the CRDMs gave me a useful piece of insight. If the fuel indeed melted out of the pressure vessel, it would have slid down the CRDMs before falling off into the water, and as such I would expect there to be some kind of deposits on the CRDMs. Maybe somewhat whimsical, but I imagine radioactive stalactites hanging from them, as the fuel cooled somewhat as it left the pressure vessel. Now we have no reason to believe the CRDMs are covered in water, we believe them to be well above the surface of the water, so if there is indeed corium deposits clinging to the CRDMs due to the fuel melting through, wouldnt that have a much stronger influence on the readings we obtained at the surface of the water? I assume that no matter how much fuel is submerged, it is shielded by the water, but the fuel stuck to the CRDMs should be relatively unshielded, and thus ought to light up their survey equipment. Secondly, did they sample the water? I would guess so, seeing how they presented a Chloride analysis from it. I was curious if they analyzed for deuterium or tritium. That analysis wouldnt be conclusive at all, but it may help give some facts about the status of that water. I understand Cs being a relatively heavy element is not likely to be floating around in it, but if there is a chunk of fuel at the bottom, I would expect the radiation it emits to create a higher concentration of deuterium and tritium than normal water, and those particles are light enough relative to water itself to allow an assumption that they would be distributed more evenly throughout the pool. I understand that it takes a significant amount of energy to make that much deuterium or tritium, but they could use it as a simple go-no go kind of evaluation. IE, if there is a higher concentration, then there is a chunk of something hot down there, or if not then there might be, but if there is it isnt the majority of the fuel and it isnt as radioactive as we might have thought. That kind of analysis I have never done, so I have no idea how useful or not that would be, just throwing ideas out to the wind, trying to think outside the box a little. We are after all, simply trying to find out the status of the fuel, and where it is, so if that kind of analysis would be somewhat useful, I would like to see the results from it… Anyways, have a great day all, this thread is jogging my creative skills and analysis skills more than I expected!

  23. Bill Hannahan says:

    @EM1(SS)

    If we are considering water as the shielding coefficient, then we are assuming that the fuel melted out and is at the bottom of the puddle in the containment building, and if we assume corium and steel, we assume that the fuel has remained in the pressure vessel? So if the question is water or steel for the shielding, and we pick steel, doesnt that give us cause for rejoice in that indirectly we are assuming the fuel remained where it should have?

    True, but I think both are possible, with part of the core in the reactor vessel and part below. I visualize inside the vessel as having the remaining core and some internal structures melted down into the bottom with water raining down on it and leaking out, so no thick slabs of water for shielding in the reactor vessel, just corium and steel. Down below corium could be submerged in water, just my guess.

    Also, reading the comments about the corium sticking to the CRDMs gave me a useful piece of insight. If the fuel indeed melted out of the pressure vessel, it would have slid down the CRDMs before falling off into the water, and as such I would expect there to be some kind of deposits on the CRDMs. Maybe somewhat whimsical, but I imagine radioactive stalactites hanging from them, as the fuel cooled somewhat as it left the pressure vessel.

    It will be interesting to see if there was one big blowout or numerous small penetrations. The paper I linked on lower head failure points out that melting the small tubing penetrations can fail the pressure boundary without melting through the full six inches of steel.

    I assume that no matter how much fuel is submerged, it is shielded by the water, but the fuel stuck to the CRDMs should be relatively unshielded, and thus ought to light up their survey equipment.

    I would think so. It would depend on the location of the blowout relative to the survey points. There is a grating just above the water and the radiation drops significantly in the air just below the grating, another indication that the primary source for the airspace is above.

  24. MP says:

    This conclusion does not match TEPCO or JNES analysis

    http://www.nsr.go.jp/archive/nisa/english/files/P-4.pdf

    • Brian Mays says:

      A slide from over a month ago reads:

      It is difficult to evaluate the amount of molten fuel that fell into the containment at present. It is expected that useful information be obtained through R&D at the Fukushima site for further assessment of MCCI.

      How does this contradict the more recent R&D measurements at the Fukushima site?

    • jmdesp says:

      The JNES analysis shows a lot of interesting details.

      In the drawing on page 5 of the pdf (10 of the presentation), we see that it’s assumed that the core felt inside the circular concrete walls that support the PCV, and that this circular section has an opening that has left the core flow to the outside.

      It’s a bit unclear to me if they are really showing an opening that they know exists, or one that they assume the melted core created through the wall ? If actually there’s no pre-existing opening then it’s possible that only some of the core went down and stayed inside this area instead of going into the outer part of the torus chamber, which would explain that water analysis shows no contact with the core.

      I think that given all the info on the geometry of PCV, and RPV there is to extract from all this documentations, and the various gradient values shown on page 4 of the Tepco handout, it’s should be possible to deduce with a reasonable level of certainty the info of where the core does lye (I would love to have more points, Tepco just has them). There’s nothing unreasonable in modeling a solidified blob of corium as the “gravity center point” of it’s radioactivity. And we know the core doesn’t float in the air. It we do find a “gravity center point” that’s floating in the air, then there’s actually two separate blob, part of it is on the floor, and the other half is in the PCV. If we find the “gravity center point” is above the lower height of the PCV, then the core is still inside the PCV (or at least enough of it that the center point is not moved down by much).
      It clearly won’t be easy however, the D7 value shows there’s some significant non-linearity in the shielding amount between the measurement and the core.

      It’s very interesting to see on D3 that this unimpressive looking grating can lower almost by half the amount of radiation the probe receives.

      BTW this slide links to this other slide http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120312_04-e.pdf which says :
      – “we succeeded (using the MAAP software) in reproducing the behavior of the plant at the time of the accident fairly accurately for the stages before the core melted.”
      – “On the other hand, the RPV damage of Units 2 and 3 did not occur in this analysis”,
      – “which is contrary to the observed facts”
      Or … their interpretation that the event they observed can only be explained by a melt-through is wrong and the MAAP software is correct.

      • jmdesp says:

        Additional remark :
        – at the penetration tip, radiation is 11.1 Sv/h,and some distance from it but still the same height , it’s only 9.8
        – this means the surface of the concrete is activated and contributes some of the radioactivity (maybe from cesium deposits)
        – we see a structure on the left that gets near the path of the probe. Cesium deposit on top of it will contribute to some additional non-linearity in the level exposure.
        – however the D6 and D5 points that are the nearest from that structure don’t receive that much radiation

        Unfortunately, those measurements really aren’t simple to exploit.
        Tepco, **please** insert a directional probe (or could it be their probe is actually quite directional ?), and give us more data points !

  25. jmdesp says:

    I’ve read on Hiroshima Syndrome the story of the team from LALN that wants to use cosmic ray imaging to picture where the core is.

    It seems to me that this is obviously not needed. That corium is spreading gamma rays everywhere, it’s certainly significantly easier to track them to know for sure where it’s located.

    Of course the intensity of the gamma rays is very much attenuated by the concrete, but they are several tons of uranium. Given the sensibility of the instruments, and the ability of the proper ones to isolate the rays that match the isotopes of the core, I’m quite convinced this wouldn’t be actually very hard. Much easier than the cosmic rays in any case.

    It’s actually surprising nobody has thought of trying to do that yet.

  26. Untermenschen says:

    Could somebody please reply whether failures of the containment penetration assemblies were the contributing factors toward the sudden unexpectedly early release of radiation at the top of the containment following the Fukushima Accident?

  27. Untermenschen says:

    Could somebody please reply whether failures of the containment penetration assemblies were the contributing factors toward the sudden unexpectedly early release of radiation at the top of the containment following the Fukushima Accident?

  28. Bart says:

    Your inital intution about the Corium and steel is incorrect. Corium reaches temperatures of 2400-2800 C within hours. The melting points of high carbon and stainless steel are about 1500 C In other words, the corium is about 1000 degrees hotter than the melting point of steel. A steel cutting torch operates at 3200 C. So the corium clearly was hot enough to melt steel. The corium was uncooled for several months.
    We cannot observe the outer containment area and we don’t enough about the accuracy of the probe, to conclude that it is untruthful to say corium leaked through onto the concrete. One possiblity is that corium burned through the steel, then the concrete and after all the time that elapsed before the probe was put in place, the radiation levels were at the levels the probe read.

    • Rod Adams says:

      @Bart

      Without discussing decay heat production rates, specific heat capacity of the materials, mass of the materials, latent heat of fusion, heat transfer coefficients at the system boundaries, and probably a few additional factors I’m forgetting, there is NO WAY to make the assertions you have made.

      Comparing temperatures as you have done is an absurdly simplified way of describing conditions in a real system. I will admit that my “intuition” is partially responsible for my confidence in the location of the corium, but that intuition is informed by substantial experience in matching instrument indications with predictions derived from thermodynamic equations that include the kinds of factors mentioned above.

    • Andy Dawson says:

      ” One possiblity is that corium burned through the steel, then the concrete and after all the time that elapsed before the probe was put in place, the radiation levels were at the levels the probe read.”

      No, that simply doesn’t work as an explanation – even if that were the case, radiation levels would still rise towards the bottom of the containment (ubless somehow there was no mixing of corium and concrete – in fact, the melted fuel mass would have to have somehow burned it’s way through the concrete base of the containment without spreading at all on contact, or leaving any residual trace contamination.

      But, there’s a rather simpler reason why that can’t have happened. The bottom of the containment is flooded (water was sampled at the same time as the radiation survey was undertaken – it’s referred to in Rod’s initial article above).

      Now, were there an exit hole where the fuel mass had burned through the base of the containment, I can’t really see how there’d be a pool of water in the bottom, can you?

  29. Henry says:

    Well gee whiz, if TEPCO says the cores are safely in the intact reactor pressure vessel, then how can we doubt that! TEPCO has done such a fine job cleaning up and everything is under control!

    Never mind that the ocean is daily poisoned with massive radiation and that the super hot cores are gone, gone, gone! The radiation travels the globe and there is no way to stop it. Of course if TEPCO hadn’t built over old garbage dump on an old river that might have helped. If they hadn’t chopped off the hill and lowered the sea wall, and if they avoided a highly active fault line, – well I digress.

    Clearly the remedy is to pretend that all is well and keep eating lots of Fukushima produce, cattle and seafood! Hey anybody want to go on a Fukushima camping trip? We can camp out for a month right next to those nice, safe, intact reactor vessels!