Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Liquid Fluoride Thorium Reactor

  1. Aug 8, 2011 #1
    New to the forum.

    Currently working on a Masters degree in Nuclear Engineering.

    Has anyone ever heard of the Liquid Fluoride Thorium Reactor (LFTR)?
    It looks like a pretty neet idea. I have been watching some videos by a guy named Kirk Sorensen who is a big proponent for this technology.

    If you want some information on them here is a good 80 minute video on it: http://www.youtube.com/watch?v=AZR0UKxNPh8"

    It would be nice to get peoples views on the technology that are in the industry.
    Last edited by a moderator: Apr 26, 2017
  2. jcsd
  3. Aug 14, 2011 #2


    User Avatar
    Gold Member

    There is considerable discussion of the LFTR on the various forums dedicated to nuclear power.
    There is no question that the concept is very attractive and has been demonstrated to work reliably on a small scale. The challenges that remain are the practical ones, which are much more difficult to solve and reduce to regulation.
    The design will need to be scaled up and either made much more durable or completely rethought. Our experience with large volumes of radioactive molten salts is not huge, but it clearly indicates that everything gets eaten away, valves, pumps, heat exchangers, containers and measuring instruments. Building such a reactor may need a very different design concept, where instead of running a plant for 40 or more years with ongoing maintenance, a three or 5 year and out approach is needed. Fortunately, the very high precision part of the facility, the turbines, only see clean steam from the secondary heat exchanger, so they could serve for decades as before. In the 1950s through the 1980s, aircraft engines for example were managed for decades on the basis of a few hundred to a few thousand hours of service life, so the use briefly and throw away approach is clearly feasible. However, it seriously impacts the expected economic benefits a thorium reactor might provide.
  4. Aug 15, 2011 #3
    From the ORNL reports they published after running a small experimental reactor for 5 years during the 1960's, they stated that corrosion was not extraordinary and that it could be managed without too much issue.

    Also, since this design would run at around 800*C a gas turbine could be used to utilize the Brayton cycle.
  5. Aug 16, 2011 #4
    I am not "in the industry" but I have been following LFTR for a while now. I think it is a great idea. Kirk Sorensen has started a company Flibe Energy their website is flibe-energy dot com
    Their plan is to sell to the military to avoid having to deal with the NRC. The military regulates itself on nuclear matters. There are 200 bases in the US that want to have "base islanding" that is their own on site power supply independent of the civilian grid. Kirk has mentioned first criticality July 2015.
    Last edited: Aug 16, 2011
  6. Aug 17, 2011 #5
    Yes, I have read this. I would love to get involved in this project once I finish my Master's. I found a great forum at http://www.energyfromthorium.com/forum". Lots of information on LFTR.
    Last edited by a moderator: Apr 26, 2017
  7. Aug 18, 2011 #6


    User Avatar
    Staff Emeritus
    Science Advisor

    Besides energyfromthorium, there is a fairly decent page on wikipedia that describes the Molten Salt Reactor Experiment.

    http://en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment (page has some links to ORNL reports)
    Importantly, it was only 7.4 MWth and only operated ~4 years after achieving criticality. Capacity factor would be another critical matter. On the other hand, compact plant of 7 MW might be appropriate for a base or plant.

    Scaling up would not be trivial.

    There are also modern concepts for the MSR.

    According to one colleague, there was a problem of freezing (solidified) salt or plugged lines, and apparently nearly an unintended criticality event. However, I haven't verified this.

    Corrosion, creep and creep fatigue are paricular concerns as operating temperatures increase, particularly above 1/3 of Tmelt.
    Last edited: Aug 18, 2011
  8. Aug 29, 2011 #7
    If scaling up is the big problem causing huge decreases in service life, why even do it? Maybe it would be more economical to build an array of more smaller kW range LFTRs with longer service life than fewer bigger ones with reduced service life (for the same power generation capacity).
  9. Aug 29, 2011 #8


    User Avatar
    Staff Emeritus
    Science Advisor

    Small (kW) LFTRs would be prohibitively expensive, and basically, small fissile systems would be prohibitively expensive from a commercial standpoint due to the security/safety and liability issues. Fissile material is classified as special nuclear material, and there are necessarily stiff regulations regarding control of SNM. Also, compact cores are much more sensitive with respect to control.

    Economies of scale are partly driven by the necessary safety considerations associated with maintaining control and retention of fission products, i.e., keeping fission products from the environment.
  10. Sep 21, 2011 #9
    I could imagine that Thorium reactors will have the same basic problems as any other fast breeder reactors.They are terribly radioactive and in case of Thorium mean not only fast neutrons but also terrible gamma radiation as part of its cycle.It will recuire huge lead protector and expences.Also it means terrible induced radioactivity and degrading of reactor walls and materials and necessity of expensive and frequent repairs.
    I know that in USSR molten salt rectors (though not necessary Thorium) were found to be without perspectives.Also since then techics may go much forward,I guess that economy just will not work it out for now.
  11. Sep 22, 2011 #10
    Actually the nice thing about thorium cycle is that one does not need to use fast spectrum neutrons - Th/U cycle works well in thermal spectrum too, unlike the U/Pu cycle. This is explained in the OP Google lecture. This means low fissile loads, slow reactor periods, and low neutron damage to structural materials. Indeed the molten salt reactors allow for much lower fissile loads than even the light water reactors, as the major neutron poisons (Xe135 and other volatile FPs) are continuously removed by He sparging, and the ionicly bonded fluid fuel form allows unlimited burnup and continuous refueling, thus eliminating the need for large excess reactivity on every batch refueling common in solid fuel reactors.

    Th/U cycle does not produce any more gammas than any other chain reaction fission, and any reactor needs to be designed to take that.

    The only two MSRs ever operated were ARE (1954) and MSRE (1964-1969), both at ORNL. USSR never built a molten salt reactor, nor did any other country to this date.

    Power scaling is also easier than suggested above. The issue is power density (hence neutron flux, thus the lifetime of primary barrier) not total power, and this was thoroughly investigated by ORNL research following the completion of the MSRE experiment. This was discussed by David LeBlanc, a physicist from University of Ottawa, see his talk given last year at ORNL here: http://www.viddler.com/explore/ThoriumHammer/videos/1/ [Broken]

    I would recommend that people first to take time to familiarize themselves with this technology, as it is very much different from both either water moderated rectors or the fast breeders, before voicing strong opinions either way. The good place to start are talks and discussions at
    I would like to recommend this interview in particular for popular audience, Dr. Kiki's Science Hour:

    Concerning economics, there were four detailed estimates of cost of a large 1GWe MSR plant done in the past, and when corrected for inflation they come to $1~2/We at current costs. Obviously the proof is in the pudding.. See the talk of Robert Hargraves at his website for details. https://sites.google.com/site/rethinkingnuclearpower/aimhigh

    A short 16 minute primer is here:
    If you want to study the technology in detail, most of the original ORNL's papers were scanned and can be downloaded, along with other relevant publications, here: http://energyfromthorium.com/pdf/

    Currently there is active research of MSRs within GenIV International Forum, mainly in the US, France, and the Czech Republic. Recently Chinese announced a large and high profile national program to develop thorium MSRs, but without any international cooperation - they intend to keep the related intellectual property to themselves. http://energyfromthorium.com/2011/01/30/china-initiates-tmsr/
    There are also several commercial companies (Flibe, ORLY, Thorenco, Transatomicpower)in the US recently established to pursue this technology, and other independent commercial efforts centered in Japan and South Africa.
    Last edited by a moderator: May 5, 2017
  12. Sep 22, 2011 #11
    There seem to be a huge issue with Uranium 232 which is part of Thorium cycle and which is
    terribly gamma radioactive.Proponents of Thorium power plant say it is advantage which will prevent nuclear weapon prolifiration.But in the same time which protection mesures are suggested and how much will they cost?
    Last edited: Sep 22, 2011
  13. Sep 22, 2011 #12
    Stanley, the gamma radioactivity from U232 decay chain is only an issue if someone wants to isolate the uranium bred in the reactor and run away with it - then there is additional protection in the Th/U cycle which is not necessarily present in U235 or U238/Pu239 based fuels.

    As long as the uranium stays in the reactor (as it should), this activity is insignificant compared to all the "regular" gammas associated with the fission process and FP decays. Therefore there are no additional measures or costs due to U232 activity.

    Now all MSRs likely need to be operated in a hotcell in a double containment to provide for enough independent barriers to fission products. I would expect however that the cost of that would be significantly smaller than the containment costs of water cooled reactors, as there is no high pressure steam or other pressure/chemical driver to take the core out in the MSR, so the containment can be much smaller and close fitting - it just needs to be leak-tight and protect against external events, it does need to hold enormous pressures from the inside.
  14. Sep 22, 2011 #13
    What is major issues with LFTR reactor then and why they are still not build everywhere?

    Some proponents of Thorium power also propose to burn in such reactors Uranium 238 (altogether with Thorium).
    Will it require fast neutron mode then or it still could be done with thermal neutrons only?

    Could you convert it into $/kW-h?And compare with price of coal power and usual Uranium power plants?
    Last edited: Sep 22, 2011
  15. Sep 22, 2011 #14
    Thorium molten salt reactors were initially tossed on the shelf after the ORNL experiments in the 60's due to LWR's already having heavy national and private investment. This was a big driver for the government to end the liquid thorium program and never let it demonstrate its potential.

    I believe one of the largest issues why they aren't being built right now is that it is a completely different way to go about nuclear power. The industry doesn't want the change and if it turns out to be a cheaper, safer way to do nuclear, than the coal industry is highly likely to be against it as well so they would hedge their bets and rail against it immediately.

    The anti-nuclear crowd still see's it as nuclear and can attach the radioactive term to it and sell it as just another way to kill millions of people when a commonly occurring nuclear accident occurs at a plant (sarcasm). This influences politicians who want to ride the 'green' energy wave while its hip because it is a safer bet in terms of votes. In the end, no big push for advancing nuclear technology results (a.k.a. funding for research, etc.).

    A lot of people in the nuclear industry (from my experience) only have a vague knowledge of molten salt reactors and most likely have never heard of a liquid fluoride thorium reactor. If they have, it has usually been incorrect information. This doesn't help progression of the technology.

    But the biggest reason I see as for why no one is building them is no one has ever built a fully functioning Liquid Fluoride Thorium Reactor. China, as tt23 stated, announced a program to design and build thorium MSR's in January. Hopefully that will help ignite a spark for this technology and maybe get something built here.
  16. Sep 22, 2011 #15
    The basic issue is regulatory. This technology is completely different from everything that the NRC and nuclear engineers know. No water, no steam, no solid fuel, no high pressures,..

    This argument can be used against literately any progress of any kind. There is a long list of reason which I could give you, but none of them is neither very good nor convincing, at least in the current paradigm (which mind you changed dramatically since early 1970s).

    The principal reason why was this abandoned in the early 1970s was that Alwin Weinberg, then director of ORNL, started to publicly question safety and sustainability of the light water reactors. Mind you he was one of the inventors of this design, which made matters worse obviously. He got consequently kicked out of ORNL, and the molten salt program - his brainchild - was abruptly killed shorty thereafter.

    ORNL was the only lab which was pursuing this, nobody else really knew much about it, and it fell into obscurity. As the concept was reviewed within GenIV nearly 3 decades later, some European groups went to ORNL and made private copies of the research papers, and resumed their own (small scale - dozens of people maximum) research within GIF.

    Kirk Sorensen managed to get NASA funding to scan and PDF most of these documents, and put them on the web in late 2006. Since then the information is publicly available with ease. I would say that the fact that Chinese started a high priority $1B national effort to build these reactors on their own within few years after this information became available, speaks rather favorably about merits of the concept.

    There are reasons why to use "denaturated" molten salt reactor, that is with U238 in the core. The principal one is further enhancing proliferation resistance, such as if you want to sell these reactors to potentially unsafe countries. The original DMSR is a converter with breeding ratio ~0.8, so it needs some fissile fuel to keep going. This is still much better than light water reactors with BR of 0.2-0.3.

    It is possible to go to fast(er) spectrum by eliminating the graphite moderator (which is currently favored by the French research), using less moderating salt than FLiBe, and/or increasing the fraction of heavy metal (nuclear fuels) dissolved in the salt. There are limits to the last one, as the solubility of tri-fluorides (mainly PuF3) is limited, so to run U/Pu cycle in molten salt we either need to increase salt temperature to ~800C, or to use different salt. Chloride salts are excellent for fast MSRs, but much less proven than Fluoride ones.

    I do not think we need to consume U238 in MSRs, at least not in the next centuries, there is plenty unused thorium, as a waste from rare earth mining, so we can let the chloride reactors as a task for future.

    However, it is possible to use small amounts of transuranics - the problematic waste from current reactors - as a fuel in regular MSRs, as a means of waste disposal. Chloride salt reactors would be better at that potentially, but are not necessary.

    PS: All your questions are answered in better detail in the resources linked in my first post.

    Perhaps one more, a well written first hand account of the original research:
    H. G. MacPherson: The Molten Salt Reactor Adventure

    Check the slides and the talk by Robert Hargraves I linked above.
    Last edited by a moderator: Apr 26, 2017
  17. Sep 22, 2011 #16
    Unfortunately Thorium plants still will need Uranium 235 as a supplement and therefore
    this technology is still limited by small reserves of Uranium 235.
    There is another option to use particle accelerator but efficiency and costs are still prohibitive.Also,what materials are able to withstand molten salt temperatures and corosion?
  18. Sep 22, 2011 #17
    No they do not - molten salt reactors/LFTRs that is. It is possible to use thorium as a solid fuel in light water reactors (see Lightbridge corp., Radowski design, etc.), where it only saves 5-10% of the mined uranium, but that is a completely different beast from the LFTR/MSR approach we discus here.

    LFTR/thorium-MSR needs a fissile "kindling" to start the reaction off, but that kindling can be any fissile - U233, U235, or trans-uraninuim elements (TRUs) from the existing light water reactor's spent nuclear fuel. There is plenty of fissile to start the reaction with. Actually the problem now is that we bread too much of TRUs, and we do not know what to do with them, see the Yucca Mountain controversy.

    Yes indeed, this would be nuts.

    Clean halide-fluoride salts are not corrosive to begin with - they are very stable being what they are. There are issues with some fission products though, such as tellurium. A compatible material must be selected, and reductive environment must be maintained (typically by UF3/UF4 ratio of ~0.02). High nickel alloys such as Hastelloy-N or MoNiCr are the most common candidates, qualified up to 704C.

    Other options were investigated by fusion research - stainless steel (for low temperatures), amorphous carbon, Si-C composite, high molybdenum alloys such as TMZ, and tungsten. There is a slide showing the respective temperature windows in LeBlanc's talk somewhere.
    Last edited: Sep 22, 2011
  19. Sep 22, 2011 #18
    Do you want to tell that we don`t need to add Uranium 235 in LFTR on a regular basis?
    Because in one place I`ve read that Thorium is converted to U233 during cycle but not in sufficiet quantity to sustain complete self reproduction.
    I think that Thorium power plants could be good solution to stop burn natural gas and coal
    but in this case situation might be a bit controversal.Because when we burn coal,we dont burn carbon ferever and with time it is recycled somehow in nature.But when we burn Thorium or Uranium,we burn chemical element forever.And it will gone until the end of the Universe.
    So nuclear energy is least renewable from all.And what will say our descendants in few hundred of years when they will need Thorium for some reason?And how energy will be produced after all recoverable Thorium will gone?
  20. Sep 22, 2011 #19
    > Because in one place I`ve read that Thorium is converted to U233 during cycle but not in sufficiet quantity to sustain complete self reproduction.

    This is incorrect - it applies to U/Pu cycle in thermal spectrum, not to Th/U cycle, which is the main point.

    Specifically U233 fission in thermal spectrum produces 2.3 neutrons per neutron absorption. 1 neutron is needed to keep the chain reaction going, another 1 neutron to breed U233 from Th232, and 0.3 neutrons to take care of parasitic absorption and leakage. Plenty.

    Any energy source is finite (see elemental thermodynamics). Thorium will easily last for tens of thousands of years, consume long lasting TRU waste, and produce on-demand energy without emissions of any air pollution or green house gases. I'd say that is good enough.

    Is geothermal energy renewable? If you think it is, thorium energy is renewable - most geothermal heat originates from thorium decay.
    Last edited: Sep 22, 2011
  21. Sep 22, 2011 #20
    Well,probably you could build reactor which is designed to work few decades on the same pieces of Uranium and Thorium and you don`t need to add more Thorium or Uranium dyring its cyclelife.But when you decomission old reactor and build a new one you still need a new kindling made from Uranium.I guess you can`t firestart new reactor from an old one.
    Therefore there should always be some amount of rare Uranium isotope per certain amount of
    Thorium.I think it is not going to work for tens of thouhand of years because rare Uranium isotopes such as U 235 will not last for so long...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook