Explosion at nuclear plant occurred in the secondary containment structure
Corrected with New Headline (Updated information and graphics on Sunday, March 13, 2011 at 0440 EDT)
I am going to leave my original text below, so it does not look like I am using updated information to avoid responsibility. During a day of confusion, there were conflicting reports about the source of an explosion and cloud of white smoke at Daiichi Unit 1. I theorized that the explosion happened in the turbine building and came about as a result of earthquake induced leaks in the hydrogen cooling system that I suspect is used for the electrical generator.
As time progressed and the fog of coverage lifted, it became more clear that the building that was damaged was, indeed the reactor building and that the specific section of the building damaged was the secondary containment steel framed structure. The type of construction in that section is sheet metal attached to steel frame, those sheets can be blown off by a very small pressure differential between the inside and outside.
Here is a link to a New York Times photo that helps to illustrate the current state of the area identified by the red brackets in the included graphic. http://www.nytimes.com/imagepages/2011/03/13/world/13nuclear2.html You can find a detailed explanation of the damage to Daiichi Unit 1 at Events at the Fukushima Daiichi Nuclear Power Plant in Japan
Bottom line – my guess was wrong, but the important part of the containment remains intact and continues to protect the public from any negative health effects as a result of any core damage that is occurring due to a lack of circulating cooling water.
Original text follows:
I initially posted the following as an update to the post titled Nuclear plant issues in Japan are the least of their worries but have now decided to post this as an independent observation and expand a little bit on it. Here is what I posted at 11:20 am EST on March 12, 2011.
There have been reports of a hydrogen explosion and walls crumbling to expose a steel frame at what is described as an outbuilding at the Fukushima Daiichi power station. Those reports triggered my memory of a hydrogen explosion that occurred at the Tampa Electric Company Gannon coal fired power plant on April 8, 1999.
In the Gannon Station case, the hydrogen for the explosion came from the cooling system for the very large electrical generator. Maintenance workers apparently did not ensure that the system was properly purged before opening it for maintenance.
My guess is that a similar generator cooling system was in use at Fukushima Daiichi. Considering the devastation that has occurred as a result of the earthquake and the tsunami, it would not be terribly surprising if the electrical generator cooling system developed some hydrogen leaks. From what I have read about the actions taken to cool down the nuclear fuel inside the reactor, which is inside a robust containment building, not a steel frame building, I am guessing that the explosion had nothing to do with the heat source that normally supplies the the steam to turn the turbines that turn that electrical generator.
I am quite willing to eat crow if it turns out I am wrong.
Since posting the above, I have watched the video of the explosion several times. It appears to confirm my guess; the explosion takes place in the background of the reactor buildings that are visible and there does not appear to be any damage to any of those reactor buildings.
When the video moves to a closeup, however, there is the potential for confusion because the reactor building to the far right is cut out of the picture leaving one to believe that the explosion might have occurred in the third of three visible reactor buildings.
Update: It looks like I might have been guessing wrong. About thirty seconds after I posted this blog, a friend passed a link to a photo clearly showing that the top of the reactor building had been damaged and exposed a steel frame.
The reports still indicate that the actual containment and reactor vessel are not damaged; the area at the top this kind of BWR is not part of the containment structure.
Anyone know a restaurant that serves edible crow? End Update.
Most BWRs of that vintage have metal siding for walls at the top elevation, since there’s nothing essential on the top elevation that needs protection. Looks like the siding was blown off but the concrete structure below it containing the essential things is intact.
There’s typically no way to accumulate hydrogen up at that level, so a explosion from the turbine generator hydrogen cooling system sounds plausible.
Generator hydrogen is kept inside by a seal made of pumped oil at each end of the generator shaft. The oil pumps have a battery backup (to prevent this sort of explosion), but those batteries can’t last forever. When the pumps stop, the hydrogen escapes. This design is used in nearly all fossil and nuclear plants.
Looks to me like the Rx building went. Explain to me how generator hydrogen gets into the reactor building. Is the turbine in the same building?
Turbine is in a separate building. Either the turbine explosion blew the siding off the adjacent building, or some strange process got the hydrogen into a building where it normally doesn’t exist.
Top of the reactor building blew off – crane area. See this picture.
Appears that they lost the Reactor Building. Picture is not that clear but based on other pictures they have a lot siding, unlike VY. I can’t tell from the picture what the integrity of the Spent Fuel Pool is, but that would be a concern considering the severity of the explosion that occurred
Correction, later pictures indicate that the RB is standard design. They lost the siding at the top 3rd which would be expected based on the type of explosion they had.
Jim,
You are correct. Only BWR 6, ABWR, and ESBWR, (with the exception of hope creek BWR-4) have steel reinforced reactor buildings over the refuel floor elevation. The part of the reactor building (better to call it secondary containment for BWR) at the refuel floor elevation and above is really nothing more than industial siding. It will blow out with an overpressure of less than 1 psi. what is disconcerting from the single enlarge picture of the explosion from the earlier comment is that the reactor building overhead crane collapsed and fell onto the refuel floor of Fuku-1. I would be very concerned for the spent fuel pool.
No way that hydrogren came from the main generator. My opinion is that Fuku-1 did a manual vent of the primary containment to the secondary containment to relieve primary containment overpressure condition (reported to be well over the primary containment design pressure). Unknown to me if they realized that they had significant H2 generation from the core. It is possible that they vented to the secondary containment planning to then filter the release throught the standby gas treatment system once they got some AC power back. (this is all speculation on my part). Also it appears that they never installed a hardened primary containment vent backfit in US BWR Mk I containments per NRC GL 89-16.
Those pictures at 0:33 – 0:45 on the video are burning LNG holders. That is extraordinarily dangerous, but it’s nothing to do with a nuclear plant – those are pictures of the fire at the refinery.
They are conflating an oil/gas refinery or storage complex with a nuclear reactor.
And why not – it makes great video and keeps the suckers coming back for more “information”. Increases ratings and pays the bills.
Yes, this is the gas refinery (see pictures 15,16,17):
http://www.theatlantic.com/infocus/2011/03/earthquake-in-japan/100022/
NBC just trotted out Joseph Cirincione as their designated
Yes, I heard this guy speaking a few minutes after the explosion on Fox News. The one time I wish they’d have a little bias, they invite a Liberal tool to be the expert. No offense to pro nuke liberals…
He quickly went into the China Syndrome as the worst case.
He is no nuclear weapons expert. The people who are the real experts don’t get on TV and talk about it.
Graphic at NEI says explosion was from hydrogen in secondary containment (which is the reactor building), NOT from hydrogen venting off the MTG in the turbine building.
http://www.nei.org/howitworks/boiling-water-reactor-design
Rod Adams has never worked at a BWR, and is NOT a BWR expert.
BTW, note the elevated spent fuel pool in the upper right. That’s exposed to the environment now. And what is cooling that with no diesels for the spent fuel pool pump motors?
If spent fuel pool is intact this is the least of their worries. All they will need to do is provide makeup to the pool. Preferably freshwater rather than seawater.
If it’s exposed, they could just fly water in, somewhat like they do for forest fires. I honestly don’t know; I’m no BWR expert either. It was just a random thought…
Prediction: If Japan shuts down its entire nuclear power industry, and replaces only 50% of the electricity lost with coal-fired power, the extra radiation emitted DAILY will exceed the entire radioactive release as a result of the Fukushima accident.
That having been said, this incident, and the Japan nuclear industries substandard safety practices and preparations, point up the need for replacing older reactors with newer designs, preferably LFTRs, which operate at atmospheric pressure and can be passively cooled without the need for an independent power supply.
As others have pointed out, those tanks are the storage tanks at the LNG facility.
Not surprised they are using video of the LNG plant burning to the ground since reporters always assume a hyperbolic cooling tower must mean a nuclear plant. When telling a story why let strict adherence to the facts stop someone.
Reporters? Even calculus and trig teachers think only about nukes when we are talking about hyperbolic functions. It pisses me off.
My guess is that water reacted with the fuel cladding at high temperature to release large quantities of hydrogen in the reactor cooling system. The resulting pressure lifted the reactor vessel relief valves venting the H2 into the reactor building. The mixture was ignited by some source inside the building.
In my opinion it was a big mistake to allow a large volume of explosive mixture to accumulate in the building. There is a range of fuel air concentrations that is flammable. The velocity of flame propagation depends on concentration, and is very slow at the minimum flammable concentration. The intensity of the blast indicates a large volume of fuel air mixture near the optimum fuel air ratio for high velocity propagation.
The explosion could have been prevented by;
1
Undoubtedly you are correct and the actions mentioned would have been desirable. But if you have no power and pressure in the drywell has exceeded 100 psig what would you do? Easy to suggest actions that are not achievable.
What would I do? Jim, if each plant had a containment vent filter designed for accident conditions I would vent the containment through the filter. No active systems required.
For this situation I would install ignition devices near the containment vents of any other reactors in danger of fuel damage due to lost cooling water. If radiation levels or hydrogen concentration is too high already I would vent the reactor building through the turbine hall, using the turbine hall vent fans to draw air out of the reactor building. It may be necessary to create a hole in the opposite side of the reactor building to let fresh air enter the building.
I would run the fire protection sprinklers in the turbine hall. This would wash out most harmful nuclides and avert an explosion. Sprinklers and fans do not require a great deal of power. Portable industrial generators could do the job. Not a great solution, but much better than another explosion.
Bill, you are conflating the building with the containment. At a PWR they are the same entity. At a BWR, they are separate/discrete entities. The BWR containment doesn’t have a relief valve, someone has to intentionally open a valve to depressurize it. BWR containment is already inerted (the building is not, since people have to work there). Leakage from containment s retained inside the building, and scrubbed thru HEPA/charcoal filters prior to release (assuming power is available to run the fans).
Cpragman, I did not conflate the building with the containment. Read the last paragraph again.
BWR containment should have a relief valve. A slow controlled leak rate is far preferable to containment rupture.
Operators should maintain the pressure below design limits. If the core melts through the reactor vessel they should probably vent it down to atmospheric pressure to avoid a violent ejection if the containment melts through.
When this is done there will probably be some changes recommended. Fortunately, next generation designs have largely addressed these issues.
They did not lose containment, so it is not a shame. It is entirely possible that a relief valve lifted, and the hydrogen ventilated was a flammable mix, which ignited when vented, since it was then outside the inerted containment. So your suggestions #2 and the relief path could well have been followed, and the explosion resulted anyway – but in non-nuclear-safety portions of the plant; the secondary portion of the reactor building, exposing the underlying containment structure, still intact.
Thanks for your post. It is good analysis, and mirrors some of the features that were undoubtedly incorporated into the original design and construction, even way back in 1970.
The combination of the explosion, which NEI has indicated occurred in the secondary containment, and the decision to cool with seawater suggests that things are bad enough that they’ve decided to sacrifice the unit to prevent a worse outcome. Once the chlorides in the seawater get a hold of the materials in the reactor at those temperatures, I think they’ll never be able to explain away the potential for future stress corrosion cracking.
Hey Rod, just a suggestion, but perhaps, since it appears that the verdict is in that this was the containment building, maybe you should change the subject line of the posting? Or, perhaps a followup post with a corrected headline? I realize you posted an update at the end of the article with the correction, but seems like the incorrect headline should not continue to proclaim an incorrect statement of the situation?
Iit was the secondary containment at the top of the primary containment of this GE Mark I BWR. Here is a cross section:
http://uvdiv.blogspot.com/2011/03/some-links-on-fukushima-daiichi-1.html
Incredibly irresponsible of CBS, who is working in there newsroom. The pictures they are showing at the beginning of the broadcast are of a burning LNG plant! These people are incompetent. We really need competent reporting on issues like this.
Rod – This is a time for pro-nukes to stick together.
In the interest of pro-nuclear brotherhood (and out of no small amount of respect for the nation’s finest nuclear Blogger) I would like to pass along the following tidbit.
Crows are currently a protected species under the 1936 the Migratory Bird and Game Mammal Treaty with Mexico which was additionally amended in 1972.
Much as I am certain that you are fully willing, as a gentleman and man of your word, to go through with your promise to “eat crow” I advise caution. You should check with The U.S. Fish and Wildlife Service (USFWS) before predating and consuming crow to avoid breaking the law.
There are just a few small out of the way restaurants that may be willing to serve crow (under the table) if your tip is large enough. If you cannot be swayed in your announced intension I might suggest a discrete inquiry at:
The Crows Nest Restaurant Santa Cruz, California
Rod
The images in the CBS News video at the 36 second mark look like petrochemical tanks. I wouldn’t be surprised if the footage was from refinery or chemical plant fire.
Thank-you for keeping up with the story. I will be checking your blog tomorrow.
Thanks
Roy
Interesting BraveNewClimate does good job of educating people of current situation
http://bravenewclimate.com/2011/03/12/japan-nuclear-earthquake/#more-3897
Also
http://www.scientificamerican.com/article.cfm?id=fukushima-core
Would be interesting to see how much you techies agree
It would be nice to know greater detail about how the Zr cladding would interact with water to produce hydrogen as described in the NEI site. They put a few qualifiers in their statements so the bottom line right now is we still don’t know the whole story behind the explosion.
@:36sec, this looks like a picture I saw Friday of a fire at a petrochemical plant (at least that’s what was reported when I saw it).
That is a PetroChemical Plant and it is somewhat irresponsible that they are showing that video at that time when they are talking about a Nuclear plant. You are correct about Hydrogen being used for cooling of the Generator Set.
It seems an oil refinery fire. Nothing to do with the nuclear plant.