Advances in high temperature nuclear reactor fuel – TRISO integrity at 1800 C!

The Idaho National Laboratory released the following exciting news on September 25, 2013.

IDAHO FALLS — A safer and more efficient nuclear fuel is on the horizon. A team of researchers at the U.S. Department of Energy’s Idaho National Laboratory (INL) and Oak Ridge National Laboratory (ORNL) have reached a new milestone with tristructural-isotropic (TRISO) fuel, showing that this fourth-generation reactor fuel might be even more robust than previously thought.

Cross section of TRISO fuel particle

TRISO particle – 1 mm diameter

In the past three years, David Petti, director of the Very High Temperature Reactor Technology Development Office, and his team have studied the safety of TRISO fuel. New insights come courtesy of post-irradiation examination of the fuel, which has been a team effort between INL and ORNL.

Their findings reveal that after subjecting the fuel to extreme temperatures — far greater temperatures than it would experience during normal operation or postulated accident conditions — TRISO fuel is even more robust than expected. Specifically, the team found that even at 1,800 degrees Celsius (more than 200 degrees Celsius greater than postulated accident conditions) most fission products remained inside the fuel particles, which each boast their own primary containment system.

“The release of fission products is very low,” says Petti.

TRISO fuel particles are the size of poppy seeds. Break one open, and it looks like the inside of a tiny jaw-breaker. An outer shell of carbon coats a layer of silicon carbide, which coats another layer of carbon and the uranium center — where the energy-releasing fission happens. Byproducts of the fission process have the potential to escape the fuel, especially at very high temperatures.

To study the fuel under accident conditions, Petti and his team placed six capsules inside INL’s Advanced Test Reactor core, where they were subjected to neutron irradiation. Then, controlled, high-temperature testing of the irradiated fuel in furnaces at INL and ORNL demonstrated that fission product release remains relatively low at high temperatures postulated to occur in accidents and beyond.

“This first series of TRISO test fuel has performed above the team’s expectations, both during its three years in the ATR, and throughout the subsequent high-temperature testing,” says John Hunn, ORNL project lead for TRISO fuel development and post-irradiation examination.

TRISO particles in matrix

TRISO particles in matrix

“The ability of the fuel to retain fission products at such high temperatures translates directly to enhanced safety of the reactor,” said Paul Demkowicz, the technical lead for post-irradiation examination of TRISO fuel for the Very High Temperature Reactor program. “This sort of test data is important input for reactor design and reactor licensing.”

He and his team were able to identify the few individual particles that did secrete cesium and isolate them for further analysis. They did this by dissolving the matrix that contained the particles — thousands in each chalk-sized fuel pellet.

“We’ve developed a tool that uses computer-controlled automation to sort through thousands of irradiated particles and identify the rare defects,” said Hunn. “Careful study of these few defective particles, along with the numerous particles that perform well, allows us to complete the TRISO fuel development circle by connecting the fabrication process and material properties to performance in the reactor.”

The insights gained will also “improve our ability to fabricate even better particles in the future,” said Demkowicz.

Petti wants to further explore the fuel particles’ limits. “If the fuel performs well at 1,800 [degrees Celsius], what about higher temperatures?” he said.

This revelation comes 11 years into INL and ORNL’s joint study of TRISO fuel, which began in 2002. TRISO fuel was developed and used in Germany in the 1980s. U.S. researchers have shown that their own version of the fuel can achieve more than twice the burn-up levels — that is, the amount of the fuel that is used to release energy — clocking in at nearly 20 percent burn-up.

—INL-13-022—

(Emphasis added.)

I hope this means that the fuel needed to make Adams Engines a reality will be commercially available in the not too distant future.

About Rod Adams

84 Responses to “Advances in high temperature nuclear reactor fuel – TRISO integrity at 1800 C!”

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  1. Daniel says:

    @ Rod,

    Who must approve the fuel ? DOE or NRC ?

    • Brian Mays says:

      The NRC … but only in the US.

    • Maddy says:

      The NRC will have to approve the TRISO fuel using its standard process of reviewing technical evaluation reports, SARs etc, submitted by the fuel vendor for the applicant utility. The DOE is engaged in the Advanced Gas Reactor TRISO fuel development program in order to demonstrate the performance of the UCO TRISO in normal and extreme accident conditions, provide parameters for TRISO fuel manufacture, irradiate candidate fuel, perform proof-tests for the fuel etc. The DOE AGR TRISO fuel program is doing the “long-term” research needed to qualify the fuel under NQA-1 2000, and 2008 quality assurance regime, and not just the simple NRC 830 Rule for general research. The fuel vendor will still have to do the Appendix B 10 CRF 50 fuel testing to demonstrate the first-core TRISO fuel performs just as well as the DOE research program’s TRISO. DOE and NRC are working together on the TRISO fuel, Gas reactor, NGNP licensing under the EPACT 2005 mandate.

      Sorry this is a long answer, but I wanted to clarify that NRC always licenses fuel for commercial reactors, and DOE does the long term research to provide data to the NRC, industry, etc.

      These great results to date for the accident conditions heat-up safety tests (up to 1800 C) are just the beginning. DOE has more TRISO fuel under irradiation, and hopefully will be given the funding to complete the entire set of planned irradiation campaigns and post-irradiation examinations and safety tests…….

  2. Daniel says:

    Could this fuel run into existing reactors And What would the bénéfits be ?

    Could the AP 1000 swallow this ?

    • Engineer-Poet says:

      TRISO fuel is not being pitched for water coolants.  It incorporates its own moderator, so I suspect that it would show a strongly positive void coefficient.

      • Paul Wick says:

        But silicon carbide clad fuel rods are under development, along with changing the fuel to uranium oxide pellets laced with beryllium oxide for much better heat dissipation. I would love to hear of the heat capacity of these things relative to the TRISO pellets. If meltdowns become impossible or just very highly improbable, this would understandably reduce the costs of construction of LWRs immensely. Especially in countries lacking a hostile regulator that is ultimately the slave of fossil fuel interests via Congress. (i.e. the NRC)

        • Maddy says:

          Just so you know, ORNL is working on a new fuel with silicon carbide (SiC) cladding that uses standard TRISO fuel embedded in a SiC matrix to make the compacts (cylinders like pellets) vs. using the graphite matrix used in the gas-cooled reactor fuel. This is being funded under the DOE “Accident Tolerant Fuel” program that is looking for replacement fuel for LWRs that will not produce hydrogen during severe accidents. Current LWR fuel uses zirconium alloy cladding that reacts violently with water, creates hydrogen, etc. as we have seen in the Fukushima Daiichi events. Replacing the Zircalloy tubes and other fuel structures in LWR fuel (channel boxes in boiling water reactors, spacer grids, etc) with SiC/SiC composite materials is part of the DOE research strategy.

          The NRC is not hostile–just doing their jobs well. The DOE AGR TRISO research team has to be thinking at least 5 years ahead of the NRC research and licensing staff to be able to get the right experiments and results to answer NRC’s concerns.

          • jmdesp says:

            They are however suspicions for Fukushima that gamma-rays induced radiolysis of water also had a part in the volume of hydrogen generated, so it’s not guaranteed that this new cladding would fully solve the problem.

          • Cyril R. says:

            The root cause issue with Fukushima wasn’t hydrogen, but lack of cooling. If you have passive cooling, then you don’t have Fukushima, even with zirconium alloy cladding. On the other hand, if you have no cooling, but SiC cladding, you will still get fuel melting because the temperature will exceed the melting point of SiC (!).

            The main reason why these claddings are really interesting is power uprating.

          • JimHopf says:

            Given that no new nuclear projects are going forward (starting) today and some already-built plants are even closing due to high regulation-driven costs, I can’t agree that NRC are “doing their jobs well”. The safest nuclear plant is one that’s shutdown or not built, eh? The exact opposite is true. Public health and safety is actually harmed by making nuclear regulations ever stricter, resulting in reduced nuclear use its replacement with fossil fuels that are orders of magnitude more harmful and dangerous.

            I don’t believe that individuals at NRC are actually (intentionally) hostile to the industry. What we have is an institution, and industry overall, that has lost its way over several decades. We all think we’re just “doing our jobs”, with ingrained mindsets of unrealistically conservative analyses and the requirement of absolute proof of everything. The underlying basis is the notion that (unlike all other forms of pollution) any significant release of radioactivity is absolutely unaccceptable, and must be prevented almost regardless of cost. If one does happen (e.g., Fukushima), even more requirements are layered on to eliminate the possibility of something like that ever happening again, never mind the fact that Fukushima showed that the consequences of a worst-case accident are orders of magnitude less than the assumed “horrific” consequences that existing hyper-strict regulations were based on.

            The result of all this is rather spectacular. NRC is not required to subject any of its regulations to cost/benefit analysis (something that EPA always has to do). If one did evaluate nuclear regulations, many/most of them would pencil out to many billions of dollars per life saved. Meanwhile, the fossil industry successfully blocks EPA regulations that only would have cost ~$10,000 per life saved. Coal kills ~13,000 every year in the US alone, and we do nothing. Fukushima, the only significant release in non-Soviet nuclear’s entire history kills ~0 people, and costly new regulations are added on, w/o any serious political debate or opposition. If we didn’t have long-term institutional insanity, NRC would have responded to Fukushima by significantly *relaxing* nuclear regulations, overall.

            Not only are regulatory requirements overly burdensome (especially for small reactors, given the lack of potential impact), NRC’s review process is far too costly and takes far too long. The costs of the review process alone (hundreds of millions) has become a significant political issue in many states. How can it be that a SCOL application (i.e., a carbon copy of a previous, RCOL application for the exact same reactor design), for a site that already has reactors (and detailed environmental analyses) still takes many years and costs hundreds of millions. It should be one, maybe two years tops, at a cost of no more than ~$50 million. And the review times for any new reactor design, be it an LWR SMR, let alone anything like an HTGR, are simply ridiculous.

            Its no surprise that most new reactor technologies will be persued and developed in countries like China.

          • Paul Wick says:

            From the NRC’s own site (8 freaking years’ to certify a frickin’ boiler and they still have not done so. I don’t doubt that individual employees are fabulous. But something is rotten in Denmark.)
            “Economic Simplified Boiling-Water Reactor (ESBWR)
            A 4,500-MWt nuclear reactor design, which has passive safety features and uses natural circulation (with no recirculation pumps or associated piping) for normal operation. GE-Hitachi Nuclear Energy (GEH) submitted an application for final design approval and standard design certification for the ESBWR on August 24, 2005.”

        • John ONeill says:

          Are there operational advantages to using silicon carbide cladding apart from resilience in an overheating situation? I’ve heard reactor zirconium is expensive because you have to separate out any hafnium – could silicon carbide be cheaper, or allow higher burnup?

          • Rod Adams says:

            @John O’Neill

            The fact that naturally occurring zirconium contains hafnium is one of the almost poetic reasons why I think humans are supposed to be using fission energy. Zirconium is an almost perfect cladding material for a water cooled reactor as long as you keep the temperature under control. The separated hafnium, with its large neutron absorption cross section, resistance to neutron induced swelling and resistance to corrosion in high temperature water makes it a rather valuable material for controlling neutron population.

            We get two valuable materials from essentially the same mining operation.

      • Maddy says:

        No, the TRISO fuel is designed to be used in a helium cooled gas reactor (either pebble bed or prismatic block design). The MODERATOR is the graphite blocks/pebbles. The coolant is the helium. The graphite-moderated helium gas-cooled reactor designs have ZERO moderator void coefficient because the helium gas is essentially transparent to neutrons! The graphite moderator provides a large negative temperature coefficient, and the fuel Doppler temperature coefficient is also negative. This provides superior safety characteristics for the HTGR so that accidents/transients take long periods of time (compared to light water reactors) and much slower dynamics. The highest temperatures in the HTGR are reached for the depressurized cool-down, helium escapes, pumps turned off case where the fuel heats up to 1600 C over 3 days. The extra 200 C margin shown in the INL tests so far exceed any accidents that can be postulated.
        The Chinese have even done transients without scrams (control rod insertion) to demonstrate the robust behavior of TRISO-fueled gas cooled reactors.

        • Cyril R. says:

          No, the highest temperatures are reached with control rod failure in a large commercial design. The Chinese reactor that you mention is a tiny prototype that can efficiently conduct heat away to the vessel. Not so with a larger reactor.

          Analysis of ATWS events with GT-MHR and PBMR show that temperatures can easily exceed 1800C in this class of transient. The reactor will shut itself down on passive feedback, but not until very serious fuel damage has occurred (>>1800C). The PBMR runs especially hot as its pebble bed has poor contact area for conduction.

          • Brian Mays says:

            Nah … That’s not right. The control rods make very little difference in the temperatures that occur during the accident. The time scales of the reactor physics and the thermal physics are so different that, when it comes to the temperatures that are reached, the shutdown of the reactor can be considered almost instantaneous.

            The real concern in an ATWS is whether the reactor would restart itself (i.e., return to critical) after the core cools down. Without active cooling, this wouldn’t happen for a couple of days, so there’s plenty of time to do something to prevent it (that’s why you have a reserve shutdown system), but it would affect a decision on whether to actively cool the core, should the cooling systems become available.

          • Cyril R. says:

            Brian, if only it were that rosy. It’s not. There’s all sorts of reactivity insertions such as xenon decay, that effectively produce reactor fission power. Not much compared to the normal fission power, but a lot compared to the decay power that the passive decay heat removal system is designed for…

            We discussed this before, for example the sensitivity study by Syd Ball:

            http://web.ornl.gov/~webworks/cppr/y2005/jrnl/124263.pdf

            This is for the GT-MHR. The P-LOFC gets to below 1300C peak fuel temp. The P-LOFC with ATWS gets to over 1700C peak fuel temp. The difference between significant fuel failure and no fuel failure… control rods are important for gas cooled reactors!

            They are not very important for fluoride salt or lead cooled reactors. Check the PB-AHTR reference that only gets to around 850C (and all at low pressure) for the similar transient (ATWS+LOFC).

          • SB says:

            Who says you need rods to shut down the reactor? No current commercial gas cooled reactor relies on rods alone, and I highly doubt any future reactors could get licensed with only one shutdown system either.

          • Rod Adams says:

            @SB

            True. The German AVR could be shut down with the simple act of turning off the circulating blowers. The core heated up and the negative temperature coefficient of reactivity shut it down. Decay heat kept it hot and below critical for at least a weekend; when the operators came back on Monday they could execute a controlled, but quick startup by simply turning the blowers back on and starting to withdraw steam from the steam generators.

          • Cyril R. says:

            Rod, yes but as I’ve noted elsewhere, these reactors are small. The AVR was only a 46 MWth reactor. Such small reactors can more efficiently conduct heat away from the hottest part of the core. Not so with a larger reactor like GT-MHR, which achieves a peak fuel temperature of over 1700 degrees Celsius even with an intact primary loop (P-LOFC) ATWS event.

            It’s true a reserve shutdown system comes in handy, but it’ll be even more convincing if we can sell a reactor design as safe even with total power failure plus control rod failure. Preferably also with some sort of damage to the vessel, maybe a small leak or pipe break. This will satisfy the critics. As it stands, ATWS with a small pipe break causes large amounts of fuel damage to the GT-MHR, and even more to the PBMR (though the latter seems to have died a death from lack of funding). I think the PB-AHTR safety case is extremely convincing, compared to the gas cooled versions.

          • Brian Mays says:

            There’s all sorts of reactivity insertions such as xenon decay, that effectively produce reactor fission power.

            Cyril – Do you really think that we didn’t include iodine and xenon into our models?! You are trying to lecture to a professional who has done these calculations himself.

            We discussed this before, for example the sensitivity study by Syd Ball …

            Yes, we did discuss this before, and apparently you didn’t learn anything the first time. Let’s hope that you do better this time around.

            Seriously, Cyril, you’re starting to sound like Bas. You’ve read one study, and then you think that you’re some sort of expert on the subject. So you end up saying things that are patently not true, such as, “the reactor will shut itself down on passive feedback, but not until very serious fuel damage has occurred (>>1800C).”

            No … sorry, but the reactor shuts itself down, and the real concern (as all of your references point out) is recriticality, just as I tried to explain above. Pay attention this time and learn something!

            This is for the GT-MHR. The P-LOFC gets to below 1300C peak fuel temp. The P-LOFC with ATWS gets to over 1700C peak fuel temp. The difference between significant fuel failure and no fuel failure … control rods are important for gas cooled reactors!

            Well (with all due respect to Dr. Ball), as I stated before, I believe that he gamed the parameters to produce an “interesting” result. His report claims that the results are highly dependent on the parameters chosen and that the results were not intended to be representative (so don’t take them as gospel, as Bas would do), but merely a basis for future parametric studies.

            They are not very important for fluoride salt or lead cooled reactors. Check the PB-AHTR reference that only gets to around 850C (and all at low pressure) for the similar transient (ATWS+LOFC).

            No … it’s not at all a similar transient! In the Oak Ridge calculations, recriticality doesn’t occur until 28 hours and the fuel temperature doesn’t exceed the 1600 °C “limit” until about 36 hours of simulated time. (For the GT-MHR, the times are 36 hours until recriticality and 48 hours until the temperature “limit” is reached.)

            Meanwhile, the Berkeley (PB-AHTR) document that you use for comparison presents results for only the first 5000 or 6000 seconds (that’s less than two hours, by the way). That’s not enough time for even the buildup of Xenon, much less time for it to increase reactivity by decaying away.

            Most damning to your argument, however, is that even your PB-AHTR reference states that, “for liquid cooled reactors, the anticipated transient without scram (ATWS) has the potential to be a more severe transient than it is in modular helium reactors, as negativity reactivity feedback may not be sufficient to minimize the total power output before substantial increases in coolant temperatures occur.” This, of course, completely undermines the point that you were trying to make. Maybe you should pick a different reference the next time you try to bring up this topic?

            Please, please stop acting like Bas. Actually read your sources; understand what they are talking about; realize that the details are important; look for the limitations of various calculations and results; and don’t compare apples to oranges. Sorry to be so harsh, but you have been very stubborn on this point, so a wrist-slap is appropriate.

      • Cyril R. says:

        Graphite is incompatible with hot water and steam. However, TRISO type of fuel without the graphite is being pitched for use in supercritical water reactors. It is called micro fuel element, MFE. I will refer you to an excellent paper on the subject from Talbert et al.

        http://faculty.olin.edu/~jtownsend/Renewable%20Fall%202006/docs/Hans'%20article.pdf

        The direct cooling of the particles has quite a few advantages, as you can see… also nice to be able to use a supercritical water turbine that is fairly off the shelf.

  3. John T Tucker says:

    Thats above the melting point of Iron and steel and the liquefaction of concrete. As the fuel stays better contained at high temps I wonder if a similarly based technology could be suited to higher temp reactors that could also be used for industrial processes / space propulsion systems.

    • Brian Mays says:

      The entire core of the reactor is ceramic — primarily graphite.

      Particle fuel (TRISO is an example of particle fuel) has been proposed as the basis for space propulsion systems. Some interesting research into this concept was done once upon a time.

    • Engineer-Poet says:

      Better yet, it’s above the boiling point of lead.  If the reactor vessel(s) of a LEADIR could stand up to such temperatures, it would provide a very neat system for emergency cooling:  lead gas bubbles up to a condenser, liquid lead flows down, condenser glows madly but otherwise does nothing.

      This assumes that the melting of the LEADIR’s frozen-lead jacket wouldn’t already have increased the thermal dissipation enough to dump all the excess heat.

      • Cyril R. says:

        You won’t see such high temperatures in liquid cooled high temperature reactors such as AHTR and LEADIR. The coolant is too good and the reactor can be designed to not lose coolant (cavity, pool type design). This option is unavailable in gaseous coolants, where pressure (amount of coolant in core) can be lost leaving only conduction. Convection plus conduction is way better than conduction alone in removing heat.

        A good reference is the M.Sc. thesis of Alain Griveau.

        http://pb-ahtr.nuc.berkeley.edu/papers/07-001_PB-AHTR_LOFC_Griveau.pdf

        The max ATWS temperature in PB-AHTR (pebble fuel fluoride coolant) rises to only about 850 Celsius, versus over 2000 degrees Celsius in PBMR (pebble fuel helium coolant).

  4. Jim Holm says:

    Skyscrubber.com is about TRISO applications. Please check it out.

    Also check out General Atomics’ EM2 reactor.

    • Joel Riddle says:

      Is the EM2 proposed to use TRISO fuel?

      Rod,
      I want to retire to an Adams Engine-powered yacht someday around mid-2044.

  5. Smilin Joe Fission says:

    This is very interesting! This is part of why I entered into the nuclear field!

    I only wish that these breakthrough’s (findings) could translate into real reactors quicker.

  6. Dan says:

    This stuff could be the future. China has a small prototype of this type of reactor using helium coolant and they have demonstrated that it is completely impossible to meltdown or have an out of control reaction. Complete inherent safety, no pumps, diesel generators or batteries needed. Add in fuel that seals in the radioactive materials even in a worst case accident and you have a reactor with near perfect safety.

    You can run the things on thorium, uranium and on the so called “nuclear waste” from light water reactors depending on design. Basically infinite, cheap, reliable energy. I saw one proposal where you could theoretically eliminate over 70% of light water reactor “waste” by using it as fuel with high burn up. Once you are done everything is indefinitely sealed in the pebbles, easy to store in Yucca or the Waste Institute Pilot Project assuming the govt ever gets its act together.

    The high temperatures can replace process heat from gas in every industry and do it cheaper than fossil fuels. Efficient high temp hydrogen production is possible Also by being able to operate at high temperatures you can get great efficiencies, the only thing I disagree with many of the proposed designs is the helium coolant. We will have a shortage of that, ideally a reactor should be as sustainable as possible. There is only so much helium stored in gas fields in Texas. It is also essentially unrecoverable once used and lost in the atmosphere.

    Nitrogen from an Adams Engine would be better and avoid the lengthy and costly development of a special helium turbine that has never been built. Air turbines have been around since the 50′s Molten salt coolant would be even better because you would have the high temps and efficiency but be able to operate at atmospheric pressure, so no leaks in an accident and no huge pressure vessels. A gas would likely have to be pressurized and run at a high velocity introducing possible problems from flow induced vibrations. The high heat capacity of molten salt would make it compact with all the advantages of liquid metal cooled reactors but with none of the drawbacks.

    Molten salt is nonreactive with the graphite in the pebbles and you can use the hastelloy-n materials developed by ORNL for the rest of the reactor components as necessary. The only theoretical way a reactor of this design could have a public harming accident is if the graphite pebbles caught on fire. I have heard conflicting stories over whether this is even possible. Current plan is to purge vessel of oxygen and coat pebbles in substance that makes them not catch on fire. By using molten salt instead of a gas that can leak out and be replaced with oxygen you eliminate the possibility of this even happening under any circumstance, even a Fukushima style act of God.

    Someone at Berkeley is supposed to be working on a concept like this. I saw they planned to have a molten salt pebble bed reactor connected to a helium turbine. They should use nitrogen so they wouldn’t have to reinvent the wheel. Air is mostly nitrogen so you could take something off the shelf from the aerospace industry. Gas turbines would be smaller, cheaper and easier to maintain than steam turbines.

    This will likely have better economics than light water reactors, which are already cheaper than coal if you have mercury and sulfur scrubber. No active systems, no massive containment or pressure vessels, atmospheric pressure so less wear and tear and hence less maintenance. Molten salt corrosion doesn’t effect the hastelloy-n alloys, water is corrosive at high temps and pressures in current designs. With enough experience of how they work a molten salt pebble bed could last over a century.

    Massively greater efficiency and much less construction cost. Not just cheap ultra reliable electricity, cheap process heat and synfuels. Mix in some electric cars and the world is golden. This is the solution to resource depletion and global warming. Not the ridiculous solar panel nonsense and bird chopping windmills. America is lucky to have a gas boom now, something that actually has to have a chance of working will have to replace it. Denmark with its windmills has quadruple our energy prices with just over 20% wind. Germany’s electricity is now triple US prices and from some projections is supposed to go up by 20% in cost just THE NEXT YEAR. Some people are actually claiming this is a success?

    The only remaining possible issue is quality control of the TRISO pellets.

  7. GaryN says:

    I was reading the page on using HEU
    http://atomicinsights.com/does-highly-enriched-uranium-make-it-easier-to-build-more-compact-reactors/
    and now am wondering if this could be used in conjunction with HEU, as it seems (I’m no nuclear engineer) that the combination could reduce the size of a reactor even more?
    I was also surprised to find how many research reactors are running fuel at 90% enrichment levels, as in our (Canada) Slowpoke units, and there does not seem to be a lot of security around these units.
    I do see though that there is a program to reduce use of civilian HEU, but is stricter control, and limiting enrichment levels just another way for regulators to ‘knee-cap’ nuclear power generation?
    http://www.nti.org/analysis/reports/civilian-heu-reduction-and-elimination/

    • Brian Mays says:

      The Fort St. Vrain reactor in Colorado used TRISO fuel with high enriched uranium (HEU) combined with a thorium fuel cycle. Nevertheless, this didn’t make the reactor “small.” It was so large that it used prestressed concrete for the reactor vessel.

      HEU is a headache. General Atomic’s fuel manufacturing plant for Fort St. Vrain was locked down with high security, and in a post 9-11 world, the security would be even higher today. The fuel plant where Rod’s company manufactures HEU fuel for the US Navy is an example of what it would take. The extra security costs money.

    • Cyril R. says:

      TRISO fuel is mostly graphite and coating, so that takes up space. However, higher enrichment can make very compact metallic alloy fuels, as used by the military (navy) and also by fast sodium cooled reactors. Several times higher power density than civilian PWRs is possible.

  8. Maddy says:

    The US policy is not build any new reactors that would use HEU fuel. The DOE NNSA has been tasked with removing all HEU fuel from research reactors (including DOE reactors, which have not been converted), so using HEU fuel is out of the question for a new reactor.

    BUT HEU TRISO fuel, as well as Pu-bearing TRISO fuel has been used before in the GA HTGRs (Peach Bottom). Pu burning TRISO is planned for the Russian MHGTR to get rid of the Russian Pu stockpile.

    The pebble bed design would use 8-10% enriched TRISO and the NGNP prismatic fuel would use TRISO at 14-19% enriched uranium fuel. The NGNP AREVA design could also use spent nuclear fuel from LWRs for the fuel kernels for TRISO fuel.

    Rather than burn the HEU, and thereby contaminating it with fission products, and only reducing the effective enrichment by 20% or so by burning it, it is much easier to reduce the HEU unirradiated stockpile material by blending it down. The USEC/Russia megatons-to-megawatts program, now finished, has blended down Russian HEU, and the resultant product has been the source of over 1/3 of the US power reactor fuel!! The new USEC/TENEX agreement will carry on the down-blending effort. Remember we have lots of depleted uranium “tails” so it easy to down-blend it, rather than burn HEU down to ~80% and then have to recycle it to get the remaining uranium out!!

    So your comment that the HEU restrictions on civilian power plants is hurting nuclear power is not correct. The HEU restrictions enable fuel vendors to get down-blended feedstock for fuel fabrication, without having to go through the SWU process. Mixing it down is easier than putting virgin uranium into diffusion chambers, or centrifuges……

    • GaryN says:

      Thanks Maddy for that informative post. The one use I did read about for HEU in the Slowpokes was for space heating in areas where alternative fuel supplies are expensive or unavailable, such as northern Canada, and a study of the proposal (by the Makivik Corporation) was made in 1983. The Russians were also considering a 500 MW unit, I don’t think that went anywhere either, but it seems like it would have been a reasonable use of HEU. I’d be happy with a simple 5 KW space heating device for my home, the cost of electricity is getting unbearable for use as a heat source.

  9. Jeff S says:

    Is there any preliminary estimates, yet, on how much this fuel will cost to manufacture? I’ve heard one of the problems that TRISO fuel, in general, faces, is that it’s much more expensive than traditional fuel to manufacture. Of course, the cost to manufacture something has a lot of room for variation – based on economies of scale, manufacturing processes that might potentially be developed that reduce the costs, etc, so a cost isn’t written in stone, but, based on currently available manufacturing techniques, would it be relatively favorably priced, or very expensive?

    • Cyril R. says:

      Yes, it’s easily several times the manufacturing cost of PWR fuel.

      However, that’s a pointless thing to say; PWR fuel fabrication costs about 0.1 cent per kWh to manufacture. Enrichment is about 0.2 to 0.3 cents/kWh, as is the cost of the fuel itself.

      The enrichment cost for gas cooled reactors is higher, but they get more power (deeper burn) in return. Pretty much cancels out.

      The fuel cost for gas cooled reactors is lower due to the increased burnup and increased thermal efficiency. Maybe save a 0.1 cent/kWh there.

      So in all we’d probably be talking about an added cost of perhaps half a cent per kWh.

      Hardly breaking the bank.

      The capital cost is not so certain. Gas cooled reactors are potentially simpler, reducing cost. But they are also much bigger so you need a lot more tons equipment/kW. Anything from reactor vessels to foundations. Though some of the more optimized designs like GT-MHR are doing pretty good in this materials inventory department. Still, the higher temperature involves considerable cost too. I don’t expect gas cooled reactors to be cheaper than modern BWRs like Kerena or ESBWR.

      • Rod Adams says:

        @Cyril R.

        You wrote:

        I don’t expect gas cooled reactors to be cheaper than modern BWRs like Kerena or ESBWR.

        Maybe not. However, gas cooled reactors offer the option of using a smaller, simpler, and potentially less expensive heat engine – a direct Brayton cycle compressor-turbine.

        The Adams Engines I designed are not intended to compete against GW scale light water reactors; they are intended for markets where the competition is a large diesel engine or combustion gas turbine.

        By the way, the highest pressure in an Adams Engine would be about 800 kPa (120 psi or 8 atmospheres).

        • Cyril R. says:

          Yes, the business case of smaller higher value markets is clear. Though we still need the big plants as long as large coal combustion and gas fired CCGT plants remain as competitors in that market. The large baseload plant market is where most of the emissions are, though the point is taken that it is a much more competitive market…

          • Rod Adams says:

            @Cyril R.

            I do not disagree about the need for larger facilities. Just remember, however, that you can much more easily build a 1,000 MWe power station out of 50 MWe generators than you can build 50 MWe generators out of a single unit 1,000 MWe nuclear power plant.

            Series production economics are not magic; they are well understood and have been demonstrated over a couple of centuries.

            The strategy that has worked repeatedly is to find early adopters, refine the design, refine the production facilities, and push out repeatable units with interchangeable parts.

          • Cyril R. says:

            Rod, I’ve a bad feeling about the 20×50 MWe = 1x 1000 MWe plant.

            If series production were so important, why are we not seeing 20×50 MWe coal fired plant units in stead of just one 1000 MWe or 2×500 MWe units? Why are combined cycle gas fired powerplants getting larger and larger? Why didn’t the Chines build hundreds of little dams in stead of a giant singular dams like Three Gorges Dam? Why are the south americans building bigger and bigger dams? Economy of scale.

            Nuclear reactors have huge economies of scale. It remains to be seen that this can be offset by series production. Even if you can get this to work I suspect you still want to push up the module size as much as you can eventually.

            I like it that there’s a good market development strategy in these smaller higher value plants, but the transition of these small plants into competitive baseload markets where you have 2000 MWe coal fired power stations to compete with, remains to be seen.

          • Jeff S says:

            Thanks for the replies everyone!

        • John ONeill says:

          What temperature were you aiming for in normal operation Rod?

          • Rod Adams says:

            @John ONeill

            We wanted to achieve a gas temp close to 950 C on the reactor outlet. That capability was proven during the 21 years that the German AVR operated. We would have accepted any temp above 700 C for early models.

          • Cyril R. says:

            So Rod, what kind of efficiency were you planning on achieving with the small 800 kPa nitrogen turbine, at those temperatures?

          • Rod Adams says:

            @Cyril R

            Efficiency in a simple cycle Adams EngineTM is projected to be on the order of 25-30% depending on the turbine inlet (reactor outlet) temperature.

            There is a roadmap for improvements to that thermal efficiency for later models. My personal design philosophy is to build upon simple, rugged, well proven components operating well within their design profiles. After operational experience, designs can be refined and excessive margins tightened to improve performance – slowly enough so that reliability does not suffer.

        • Cyril R. says:

          Rod, about that pressure – don’t commercial combustion gas Braytons operate at a lower pressure than 800 kPa? More like 300-400 kPa for most models, right?

          • Engineer-Poet says:

            The GE LMS100 operates at a pressure ratio of 42:1.  That is roughly 4.2 MPa at the combustor.

          • Cyril R. says:

            Thanks EP, my source was talking about older industrial gas turbines, the newer aeroderivative ones are usually over 2 MPa. 4 MPa sounds exciting! Must be tough to design for these large pressure ratios in such compact compressors and fuel injection equipment.

  10. Joris van Dorp says:

    Rod writes: “I hope this means that the fuel needed to make Adams Engines a reality will be commercially available in the not too distant future.”

    I hope so too. I have customers who are interested in your engines, if they would be available. When they ask me how quickly Adams Engines (similar concepts) could be commercially available for ordering, I tell them: “My guess is between three years and thirty years, mainly dependent on politics.”. Is that correct? Or should/could I narrow that down now?

    Best regards,

    Joris

    • Rod Adams says:

      @Joris

      Actually, I would increase your range to “between three years and never, mainly depending on politics and financing.”

      The economics can be made to work rather easily on a purely technical basis, but they can also be driven to costs that are impossibly high with focused effort by powerful antinuclear forces – if those forces are not effectively resisted.

      • robjoh says:

        I think the most interesting part of the antinuclear groups are that they do not want to know that there is new solutions out there. The leaded for the Swedish environment party just said that she refused new nuclear plants on any basis. As an engineer I cannot understand such a statement. I would state why I do not like an technology and what is necessary for me to support such a technology.

        • Jim L. says:

          I too am an engineer and it makes me both angry and sad that some leaders will not consider rational discussion about nuclear power. I’ve concluded that there are people who are irrational regarding nuclear power, and thus are never going to consider pro-nuclear actions. It is nearly a religious belief amongst the anti-nuclear people that all fission power is inherently evil, which is ironic since many of the same people are also anti-religious, IMHO.

          • SteveFost says:

            I will proffer a psychological theory. I think your observation is a result of human nature and how people process information and arrive at what they consider true or false, right or wrong.

            People WANT to believe certain things to be true for emotional reasons, or sometimes want not to be proven wrong, *regardless of the facts*. Such reasons can include a strong identification with a specific “tribe”, or having invested oneself in a certain position. Either way a negative emotional response would be generated because pride, ego, or self-esteem is challenged, an unpleasant situation that an individual tries to avoid at all costs.

            No one wants their sense of identity, self-worth or sense of place in the social order to be challenged by being shown to be an idiot! So, the mind goes into denial, finding every reason possible to dismiss the evidence rather than admit to being WRONG and face certain cognitive turmoil and emotional upset. It takes disciplined mental habits to avoid this tendency, to which all of us fall victim at some point.

            So once an anti-nuke always an anti-nuke regardless of all facts and evidence. It takes an emotionally secure and mentally disciplined person to make a public conversion away from deeply held beliefs. Either that or the social environment must be receptive to reduce the risk of disapproval.

      • rubicondsrv says:

        This is why gates and others are taking their nuclear efforts offshore, short of an energy crisis, The only economically sound way to break the backs of the NRC and NNSA regarding novel reactors, HEU, and similar is to develop something that works and would be very hard to block due to its impact on economic competitiveness.

        I find it amazing that there still is not a NRC equivalent of the FAA experimental certificate that would allow operation of experimental reactors with vastly relaxed regulations in remote areas or underground facilities.

        the fact that one cannot buy a huge chunk of desert and build (and sometimes destructively test) experimental reactors without NRC interference beyond ensuring that any mess is limited to the property limits tells me the entire function of NRC and other federal nuke rules is to prevent widespread commercial use of nuclear technologies.

        • Rod Adams says:

          @rubicondsrv

          I find it amazing that there still is not a NRC equivalent of the FAA experimental certificate that would allow operation of experimental reactors with vastly relaxed regulations in remote areas or underground facilities.

          Ahh, but there is a reasonably equivalent process for class 104 licenses already laid out in law and regulation. Most vendors are reluctant to take advantage of the provisions because they have generally assumed that they could build a fully commercial unit on the first try. Perhaps that is because they aim for units that are too large to build as limited prototypes.

          The key provision allowing experimental demonstration reactors is 10 CFR 50.21 paragraph (c).

          http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0021.html

          • rubicondsrv says:

            Interesting, that would seem to allow for test reactors, yet why are they being built offshore?

            It would seem that this would allow a vendor to demonstrate the viability of the advanced reactor designs that NRC claims to lack sufficient information to certify.

            I suppose there may be some sort of financial incentive to offshore development?

        • Rod Adams says:

          @rubicondsrv

          This is why gates and others are taking their nuclear efforts offshore, short of an energy crisis, The only economically sound way to break the backs of the NRC and NNSA regarding novel reactors, HEU, and similar is to develop something that works and would be very hard to block due to its impact on economic competitiveness.

          I find it a little difficult to respect a man who has $67 billion dollars and cannot figure out how to build his important machines in the USA. Look at all of the excitement that T. Boone Pickens was able to generate for his unrealistic Pickens Plan with the expenditure of less than $100 million.

  11. JimHopf says:

    My understanding is that this reactor simply can’t “meltdown” (i.e., release a significant amount of radioactivity) under any circumstances. Didn’t they test that in Germany? This is even more true if the fuel can take over 1800 C. Due to fundamental material properties, and the reactor’s size and geometry, it can’t have a significant release. Is my understanding correct?

    If it is, I have the following question. Will NRC then allow all reactor components other than the fuel kernels themselves to be classified as “non safety related” or “not important to safety”? Will NQA-1 only apply at the fuel fab facility? Will NRC inspectors only be present at the fuel fab facility (and not at the plant site)? Will NQA-1, and NRC regulations in general, not apply at the plant site? In other words, given that the fuel integrity and be assured, will the plant site be regulated like any other type of power plant (e.g., a natural gas plant), with respect to both operation and all construction and component maintenence activites? Will the plant permitting process be as fast, easy and inexpensive as the permitting/licensing of a gas plant?

    I think I know the answer to this, but my question is, why not? The fact is that most NRC regs, and their general mindset, can not be defended. The results of any cost/benefit analysis on NRC regs would be absurd, especially for a reactor like this. Claims that such strict regs are necessary to “protect public health and safety” do not withstand scrutiny, especially for small and/or advanced reactors. I almost wonder if the industry should challenge the overall body of NRC regs in court. Then again, the “nuclear industry” doesn’t even exist, really, let alone have a spine.

    • John ONeill says:

      That depends on your definition of a ‘significant ‘ amount of radioactivity. The German Thorium High Temperature Reactor had a problem with radioactive dust eroding off the fuel pebbles, some of which escaped to the atmosphere when they were trying to free a pebble jammed in a chute. Then the plant management tried to blame the radiation on Chernobyl ( happening at the same time ) and got caught out lying.I think when the plant was dismantled, at considerable cost, they found more pebbles stuck in a cracked casing. Rod reckons having a design that dropped the control rods straight into the pebbles was a big part of the problem, which would be pretty easy to rectify.
      The Fort St Vrain HTR didn’t use pebble type fuel, and had no issues with radiation release, though plenty of problems with water in the core- also easily cured with better design.
      So though catastrophic melt-down is very unlikely, you’re still not going to get an easy ride from the regulators or the anti nukes.

      • Rod Adams says:

        @John ONeill

        Anyone who expects an “easy ride” for ANY effective technology that does not burn prodigious quantities of hydrocarbons does not understand how our economy and political infrastructure are set up.

        However, that does not mean that people expecting a hard slog and well armed with information, resources, and stamina cannot succeed in disrupting the powers that be.

  12. Rick Maltese says:

    Hi Rod

    Ontario is closing down North America’s largest coal plant in 2014.
    The Nanticoke Generating Station
    http://en.wikipedia.org/wiki/Nanticoke_Generating_Station

    I wish nuclear reactors were a serious consideration to replace the coal.

    It has an 1880 MW power capacity.

    From the sounds of it your designs might be a good match for converting coal plants like these into nuclear plants. Can the existing turbine and boilers be adapted effectively in such a situation?

    • Atomikrabbit says:

      On Great Britain’s second-generation Gas-Cooled Reactors, the AGRs (11 still running today):

      “The design of the AGR was such that the final steam conditions at the boiler stop valve were identical to that of conventional coal-fired power stations, thus the same design of turbo-generator plant could be used.”
      http://en.wikipedia.org/wiki/Advanced_gas-cooled_reactor#AGR_design

      Unless the design uses Brayton cycle, or the secondary side is obsolete or degraded, I don’t see why there couldn’t be a backfit.

      Fort St. Vrain was backfit. Unfortunately it was in the wrong direction – nuclear to methane.

  13. Cyril R. says:

    Brian, don’t be an arrogant and intransigent person. Your worst side is showing again, please try to get that dark side of yours under control. You’re not that knowledgeable about this subject as you would like to tell yourself, you can criticise Ball’s assumptions but the analysis does not show a good safety case in ATWS events. Even with different assumptions you still get way too high temperatures to be comfortable. Quoting from Ball:

    4.4 P-LOFC with ATWS: In this PBMR design, recriticality occurs at about 28 hours, and T(fuel)-
    max reaches 2127°C at 103 hr. Maximum vessel temperatures are also higher, 711°C at 145 hr.
    Fuel failure after 7 days was 57%. Variations in this accident are sensitive to fuel and moderator
    temperature-reactivity feedback coefficients. As with the GT-MHR, if after recriticality the SCS
    is started (with still no scram), peak fuel temperatures would exceed limits even more due to the
    selective undercooling.
    4.5 D-LOFC with ATWS: Recriticality occurs at 31 hr. In this case, T(fuel)-max is 2166°C at 137
    hr, and the maximum vessel temperature (496°C at time = 168 hr) was still rising slowly after a
    week. Fuel failure at the end of the week was 59%.

    —————————-

    These are very large fuel failures. The basic problem is heat transfer that is poor as natural circulation sucks in gas coolant environments, especially when depressurized.

    You have a good point (about your only good point in that otherwise ad hominem post) that the Berkeley results are for shorter term, but please consider the results with the shorter term results from ORNL: about 1100-1300C short term temp for P-LOFC + ATWS for the gas cooled version, 850C for the liquid cooled version… a major improvement even if you get a couple hundred degrees more later on from decay reactivity insertions.

    • Brian Mays says:

      Cyril – Look … I’ve found over the years that these types of discussions are best held face-to-face, over a few beers or cocktails — with the cocktail napkins serving as impromptu blackboards when something important needs to be sketched out for visual comprehension. In that type of setting, you would have had your say, I would have told you that you were full of sh–t and explained why, and you would have accepted my criticism without complaint, because before you could launch your complaint, I would have offered to buy the next round. ;-)

      Sadly, comment sections of blogs such as this are not a very good medium for discussion of such ideas, and we all have our pet peeves. My personal pet peeve is when people blab about the “good” and “bad” of reactor designs and then get things wrong. As someone who occasionally has the opportunity to work on these “paper reactors” — when I am lucky — such misinformation has the potential for real consequences on what I get to work on. But more importantly, if something is wrong, then it is simply wrong. If it is “arrogant” for me to point this out, then fine — I’m arrogant. I’d rather be arrogant and correct than congenial and wrong, but perhaps that’s just my nature.

      Of course, we can all be both arrogant and congenial over a couple of beers, and everything always seems to turn out alright in the end. So I’m recommending beers for everyone.

      • Cyril R. says:

        Agree Brian, you’re right. I’d love to discuss these matters over a beer with you, or multiple beers.

        Lacking beers and face to face contact, we’ll just have to make do with this format. I hope you’ll agree with me that as long as we stick to facts and rebuttal of these facts, playing the ball so to speak, rather than the man, the blog format works reasonably well.

        A couple of things I’d be interested in discussing with you.

        The first is the effect of thermalhydraulics on the ATWS transient. The xenon reactivity insertion worth is around 2400 pcm typically, right (can’t find any other figure than this one)? So if you have a reactor with an alpha of -6 pcm/K then this should only result in an average heatup of 2400/6 = 400C. This isn’t so much as long as the temperature rise is evenly divided, for example an average fuel temperature of 1200C would turn into 1600C with very good heat transfer within the core. It seems that with a pebble bed in a gaseous environment, the dominant heat transfer is radiative within the bed (natural circulation with helium is inefficient). Hence the high temperatures seen by the analysis of Syd Ball, and the temperatures for pressurized or depressurized state were almost similar. Whereas the GT-MHR ATWS that Syd Ball also analysed, got much better heat transfer, as evidenced by the much lower peak fuel temperature during ATWS.

        There are other Berkeley references that considered a GT-MHR type reactor but with FLiBe coolant, and they got to around 1300 Celsius heatup in the ATWS event (time considered up to 70 hours, so much longer than the PB-AHTR work, yet no recriticality up to that time). This seems to indicate the importance of heat transfer in the ATWS type events, which was my main point. The vessel is likely to fail but at least the fuel stays intact, unlike the helium cooled GT-MHR where both the vessel and fuel fail extensively.

  14. Cyril R. says:

    Rod, a couple questions.

    1. What was the burnup level at which this 1800C fuel integrity test was run at?
    2. Is this high temperature fuel the same as previous fuels, namely fuel kernel, buffer carbon, inner pyrocarbon, silicon carbide, outer pyrocarbon? Or does it use the newer layers like zirconium carbide?

    • Rod Adams says:

      @Cyril

      Maddy may be able to correct me, but my understanding is that the fuel had been burned to a level of 20% and is essentially the same design as the German TRISO. The key improvements are in process design and quality control. Demmings would be proud of the continuous process improvement.

      • Cyril R. says:

        If you are correct then that is an even more remarkable achievement; most previous fuel developed has significant fuel failures even at 1600C, at a 20% burnup. 20% is much higher than most commercial designs are going for; if memory serves, PBMR was going for 5-10% burnup.

        • maddy says:

          Our “Triso Triumph” announcement sure has generated lots of buzz-blogs and questions!!
          To answer the question. The average burnup for the AGR-1 TRISO fuel test was 16% FIMA (fissions initial heavy metal atoms) and the peak was 19.5%!! We had no fuel failures during the 600 effective full power days in the INL Advanced Test Reactor. We announced this world record breaking even November 2009.
          The fuel we tested in the heat up furnaces included some 16%, 18% FIMA fuel for 1600, 1700 and 1800 C for 300 hours. The ORNL and INL AGR PIE group has completed a dozen tests this fiscal year. We will heat up the 19.5% FIMA fuel within the next six months and hopefully we will continue to be as successful.

          AGR-2 fuel tests will be completed by December 2013, and it has US UCO and UO2 TRISO fuel compacts, French CERCA UO2 compacts, and South African TRISO particles, compacted at ORNL. The AGR-2 test train will be shipped to the hot cells in spring 2014, and PIEs and safety heat up tests will be done over 2 years—-stay tuned!!!

  15. John Englert says:

    Another nice feature of the TRISO fuel, is that it can be filled with plutonium and minor actinides recovered from used LWR fuel. It may achieve ridiculously high burn-ups on the order of 700 GWd/t, while bringing Pu-239 down to nil. DOE should just deploy a fleet of HTGR with WG Pu in TRISO pellets. This would be better than wasting money on a MOX plant that will produce fuel that no US commercial operators will want to put in their reactors.

  16. maddy says:

    John E:

    I agree that using TRISO with TRU is more efficient than MOX fabrication, recycling etc. Just so you know, DOE has sponsored studies of using TRISO fueled prismatic block gas reactors for “Deep Burn” where spent nuclear fuel is reused (without PU separations) for TRISO kernels directly. NNSA at DOE has been working with the Russian labs on a weapon Pu burning GTMHR design with GA.

    Folks, The NGNP project has completed studies about the TRISO fuel fabrication costs. Note that a prismatic block fuel design with a Brayton cycle which is over 40% efficient and with full reaching 15% FIMA/burnup is competative with LWR fuel costs. That means 150 MWdays/MT uranium. Remember that LWRs are only 32% efficient, and the burnup is limited to 62 MWdays/MTU…….gas reactors are more efficient, have higher temperatures that allow for process heat and electricity generation, and can have higher burnup fuel…..so the fuel costs are reasonable!

    • Engineer-Poet says:

      Would the recycled SNF be processed to extract fission products, or just physically reformed and repackaged?  If the latter, it’s the gas-cooled answer to DUPIC.

      This TRISO fuel form would be compatible with liquid lead coolant (a la LEADIR), right?

    • Brian Mays says:

      The NGNP project has completed studies about the TRISO fuel fabrication costs. Note that a prismatic block fuel design with a Brayton cycle which is over 40% efficient and with full reaching 15% FIMA/burnup is competative with LWR fuel costs.

      However, it should not be overlooked that the design concept that is being considered by the NGNP Industry Alliance today does not use a Brayton cycle.

  17. Acme says:

    Does is possible to recover and reuse unburnt uranium and other actinides from TRISO particles again?

  18. Engineer-Poet says:

    Coming back to this 2 months late, but…

    What was the enrichment in this TRISO fuel, that allowed it to achieve such high burnup?

      • Engineer-Poet says:

        Nothing that can be used to gauge the breeding ratio, just that it still qualifies as LEU.

        I was hoping to find something that would allow a guess as to the performance with fuels other than LEU, but they may be playing their cards close to the vest.  If the light-water breeder performance could be exceeded with graphite moderation, there would appear to be some major possibilities.

        • Rod Adams says:

          @Engineer-Poet

          The fuel testing conducted so far has been in small batches that can be irradiated in the ATR. Breeding, if possible, would be shown only by large scale testing of specific complete core designs using well-designed operating procedures that minimize neutron capture by control rod poisons.

          My analysis indicates that breeding is a possibility in high temperature gas reactors using TRISO particle fuel, but even a very high conversion ratio may lead to extended life cores.

          • Engineer-Poet says:

            I was pondering the reuse of LWR fuel as seed material for a U/Pu/Th fuel.  If you could achieve even 15% burnup in such fuel, the volume of spent fuel would be closer to the current level with LWRs and the handling would be far simpler.  Given the good neutron economy of graphite moderators, this should be far easier than the light-water breeder experiment at Shippingport.

            Being able to convert spent LWR fuel into TRISO elements and “burn them again” neatly eliminates the “what about the waste?” argument.  You get to answer, “It’s not waste, it’s fuel!” without any mention of scary stuff like liquid sodium.  And if you can get those high burnups, the existing inventory of SNF suffices for a very rapid expansion of the reactor fleet.

            So much I don’t know, but would love to.