- High-temperature operation naturally presents design challenges.
- LFTR technology base has largely stagnated for 40 years.
- LFTR technology is very different from the water-cooled, solid-fueled reactors that are the basis for current nuclear power generation, and is not yet fully understood by regulatory agencies and officials.
“Only Single Fluid graphite designs do not require new materials to be verified in a strong neutron fluance.” LeBlanc TEAC3
“The design weakness of the two-fluid design [at Oak Ridge National Labs in the 1960s] was its complex plumbing. The design used brittle graphite pipes to hold the fuel salt. The pipes separated the fuel salt and breeding salt, so they were essential. The problem is that graphite expands under intense neutron bombardment. So, graphite pipes would change length, crack and become very leaky… In modern research, copper-reinforced graphite fiber cloth seems theoretically suitable, but no physical tests have been done.” Wikipedia
We have computer modeling, design, and testing methods not available in the 1960s; we’ll likely find a better material and/or better core designs.
[So at worst, we go with graphite and the reactor would be periodically shut down, like current reactors needing to be refueled? “Typical graphite lifetimes of 4 years” — while we’d love to have a reactor that runs non-stop for 50 years, would 4 years be okay? These pipes would only be in the reactor core. So drain the fuel, swap in new pipes (are designs so would be easy), and start it up again. These graphite pipes cracking wouldn’t be catastrophic, they are only separating liquid salt containing uranium (and reaction byproducts) from liquid salt containing thorium, primarily for ease in separating out reaction byproducts.]
Solving the “two fluid plumbing problem” that ORNL had in the 1960’s: Make the reactor core a small (less than 1 meter diameter) elongated cylinder. A single barrier separates core and blanket regions (not intermixing regions in the core with complex pipes). The entire volume of the core is power-producing salt; the carrier salt itself is a fairly effective moderator, so no graphite moderator is needed. Increase power generated without intermixing by extending the length of the core.
This reactor design has a “potential lower limit of start up fissile inventory of a mere 150 kg/GW(e) with 400 kg/GW(e) being a more conservative goal. For comparison ORNL Two Fluid work was about 700 kg/GW(e), ORNL Single Fluid 1500 kg/GW(e), an LWR is 3-5 tonnes/GW(e) and liquid metal cooled fast breeders 10-20 tonnes/GW(e).” A reactor with a 70 cm wide cylindrical core 6.6m long with a steam cycle generator, gives 224MW electricity. “Including a meter thick blanket and outer vessel wall still results in a simple to manufacture design that can fit within a tractor trailer for transport”. D. LeBlanc / Nuclear Engineering and Design 240 (2010) p. 1644-1656
Need more research on materials for in the core, or improvements on the Hastelloy-N alloy for use in the reactor core: “It is likely though that Hastelloy N has a limited lifetime if used within the full neutron flux of the core. Use in the outer vessel walls and heat exchangers should pose little problem but substantial work will be required in order to qualify any new alloys for ASME Section III use.” D. LeBlanc / Nuclear Engineering and Design 240 (2010)
“Potentially a much superior metal barrier is a high molybdenum alloy which is known to have a much greater tolerance to neutron damage (Zinkle and Ghoniem, 2000).” D. LeBlanc / Nuclear Engineering and Design 240 (2010)
There is a long Core-Blanket barrier materials discussion at D. LeBlanc TEAC3
“…the Oak Ridge National Laboratory prototype LFTR showed some signs of corrosion after four years’ operation. Hence this would be a technical challenge that needs to be addressed if LFTRs are to be constructed and have an expected 50-year operational lifetime… The corrosion problems are potentially soluble simply by employing sufficiently thick pipe and chamber walls fabricated from Hastelloy-N, or alternatively developing further improved corrosion-resistant metal alloys, says Dr. Norris.” [Dr. Timothy Norris, European Patent Attorney at Norway’s ACAPO] — Nuclear Energy Insider
What is Needed Short Term: Fuel Salt chemistry and corrosion studies of various carrier salts and materials for heat exchangers or potential 2 Fluid barriers. Non-nuclear component testing of pumps, valves, heat exchangers etc. LeBlanc TEAC3
… we believe a small prototype plant should be built to provide experience in all aspects of a commercial plant. The liquid nature of the molten salt reactor permits an unusually small plant that could serve the role just so that the temperatures, power densities, and flow speeds are similar to that in larger plants. A test reactor, e.g., 10 MWelectric or maybe even as small as 1 MWelectric would suffice and still have full commercial plant power density and therefore the same graphite damage or corrosion limited lifetime. Supporting research and development would be needed on corrosion of materials, process development, and waste forms, all of which, however, are not needed for the first prototype. Thorium-Fueled Underground Power Plant, Moir and Teller, 2005
We need to show adequate long corrosion lifetime for nickel alloy resistant to the tellurium cracking observed after the past reactor ran for only 4 yr. If carbon composites are successful, corrosion will likely become less important. We want to prove feasible extraction of valence two and three fluorides, especially rare earth elements, which will then allow the fuel to burn far longer than 30 yr (200 yr). We need to study and demonstrate an interim waste form suggested to be solid and liquid fluorides and substitute fluorapatite for the permanent waste form of fission products with minimal carryover of actinides during the separation process. This solution holds the promise to diminish the need for repository space by up to two orders of magnitude based on waste heat generation rate. We need a study to show the feasibility of passive heat removal from the reactor after-heat and stored fission products to the atmosphere without material leakage and at reasonable cost. Another study needs to show that all aspects of the molten salt reactor can be done competitively with fossil fuel. Thorium-Fueled Underground Power Plant, Moir and Teller, 2005
Can someone direct me to information about salt-to-salt and salt-to-water heat exchangers? It seems to me that the construction of a salt-to-salt heat exchanger would be radically different than LWR heat exchangers because there would be no phase change. Also, the reactor salt might eat the heat exchanger metal. The corrosion problem would be worse in the heat exchanger than the reactor vessel because the heat exchanger wall needs to thin to facilitate heat transfer while the reactor wall can be as thick as needed for safety. I am looking for the name of type of heat exchanger used for salt-to-salt. Also, whether the computer codes have been written to describe the salt-to-salt exchanger.
While in general, salts tend to corrode metals, specifically, there are metals that corrode minimally, for each salt that would work as a coolant in a nuclear power plant. The MSRE used one combination that materials testing, and reactor operation, showed work. Materials testing still needs to be done for modern materials that should work at much higher temperatures (more efficient heat exchange and electric generation, and for more industrial heat uses).
(LWR heat exchangers have to deal with high pressure 350C water, which is corrosive to many metals. High pressure is non-existent in MSR.)
Not sure about “needs to be thin”, though of course “thin is in”. What thickness does this wall here need to be for strength and corrosion over 60 years under these temperature (and radiation, for heat transfer from reactor to salt without radioactive material) conditions? What size then does the exchanger need to be, to transfer the desired amount of heat?
Ask on Thorium Energy Alliance for who is working on exchangers or the computer simulation codes.
Due to the nature of the grid, even in the most free-market sceonries, RMR contracts will still provide the majority of baseload and even peaking load sceonries. If not RMR then very flexible day-ahead and 10 min. incremental contracts. I can’t see everything “up for bid” at least not for base load, which is handled now, but both RMR contracts (basically year contracts for being *available* for loading) and day ahead markets. Sometimes plants can have *part* of their load capacity put toward various segments of the market, like 50% RMR the rest divided between day ahead and say, hourly.The point is that the LFTR can handle this stuff pretty easily, regardless of how it is dispatched.
With attention focusing towards modular LFTR for spatially distributed power generation around the 50 MW to 100 MW scale, much more analysis is needed for the accident and failure modes of LFTR. To think that LFTR will never fail in operation is naive. The Japanese thought the safety systems at Fukushima Dai’ichi were invincible and that the inner containment would never be breached; how very wrong the designers in Westinghouse (GE) were in practice. [Not accurate. Gov’t regulators knew TEPCO hadn’t followed basic safety precautions, including inadequate sea wall and backup generators in basement where could be flooded. Other reactor sites where this was done are undamaged. — George] Three reactor cores have melted down at Fukushima Dai’ichi,
with spontaneous criticalities occurring continuously at the time of writing, with the molten cores burning via their own lava tubes towards the water table below the stricken reactors. Fukushima Dai’ichi will take centuries to sort out, if at all, long after the Second World War is long forgotten; 50 years of nuclear power in Japan, 500000 years of nuclear contamination.[No, fission can’t take place in the concrete subfloor. ] As Einstein said, “… nuclear power is one hell of a way to boil water”. Fukushima Dai’ichi is rapidly becoming hell on Earth, namely a radioactive swamp,In comparison, on account of the fuel salt being very radiologically active in a LFTR, cleanup after a major LFTR failure would be particularly hazardous. [No, the salt, chemically bound to most fission products, would quickly cool to solid; it doesn’t dissolve in water or interact with air, it will remain in place even if it got outside the radiation containment (e.g. a bomb exploded). The “radiologically active” material is fission products, same as in LWR, with a very short half life; even one year later the radiation would be much lower. MSR doesn’t have the problems LWR has, since there is No Water.]
I write above so that readers appreciate that Thorium LFTR is potentially a great improvement, but not be considered “… looking through rose-tinted glasses”. Thorium LFTR will create its own set of technical and environmental problems, and these should be anticipated to achieved a balanced view on matters.
[Fukushima problems deleted. This is not a Fukushima blog, stop multiple-posting about them on pages about other topics.]
However, on a positive note, apparatus developed for handlign the Fukushima Dai’ichi situation will be able to survive high radiation flux, and should be suitable also for coping with leaks and other problems with Thorium LFTR when in operation. MSR (incl. Thorium LFTR) will develop technical faults in operations, from time to time, and to think otherwise would be rather naive.
[Yes, and with no water, no high pressure, most fission products chemically bound to the salt, technical faults with Molten Salt Reactors will be much easier to repair and to clean up than any LWR faults. — George]
LFTR Technology Status
Are we really 30 years away from even STARTING the review process for LFTR technology? I can’t believe our government is so stupid and slow. Yet at another website, it mentions the NRC is planning to set up protocols for review by 2025. This is unbelievably slow. Why? What is going on?
I believe, from my readings, that much of that 30 year start-up period is largely, as you indicate, imposed by regulatory constraints. Regulatory constraints probably are due to an abundance of caution and, likely, encouraged by self-interest of LWR factions. Alvin M. Weinberg, one of the inventors of LWR, was researching a type of LFTR in 1969 at Oak Ridge National Laboratory and saw this as potentially superior to LWR. However, President Richard M. Nixon chose LWR over LFTR as LWR research was more advanced and could more quickly be used for commercial production of electricity, thus justifying the massive infrastructure expenditure. The impact of this building program on the economy helped Nixon’s re-election. Due to the withdrawal/diverting of funding, Weinberg stop his research in the mid-1970s. The LFTR research data was made available to anyone who wanted it. India, Russia and China have extensive programs in place for research and implementation of LFTRs.
[George’s comments] India is doing solid-fueled thorium reactors; I don’t know if they are doing much with molten-salt reactors. Russia’s economy is heavily oil-based, and several oligarchs are wealthy from oil, so I doubt they will do much in MSR development. There are companies in many countries that are doing MSR design and testing, or materials testing for MSR. China is going to have MSR ready for production in very little time, and sell them to the world, much like they are leading the world in solar photo-voltaic production. I think Nixon’s picking LWR was because he talked to his “friends in the energy industry”, fossil fuel experts, who knew Molten Salt Reactors would ruin the oil/gas industry, and LWR wouldn’t. We have direct evidence (audio tape) Nixon picked his “southern California buddy’s” favorite design, over other fast-spectrum reactor designs, and then none of those fast-reactors ever became widely used.