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Move over uranium here comes Thorium

  1. Aug 9, 2010 #1
  2. jcsd
  3. Aug 9, 2010 #2


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    Well, the use of thorium has been considered for quite some time. It was used in the Shippingport reactor, but as (U,Th)O2.

    Unfortunately, the articles contains hype.
    High efficiency would necessarily require higher temperatures than a conventional LWR, and yes, that means more severe corrosion, and it is not a trivial problem. Corrosion is essentially an Achilles heel of any reactor design. As mentioned, any material needs to be demonstrated over the plant design life. If the system plans to generate power from steam turbines, then one will need a 'special alloy' that will keep the secondary (water) side coolant from the primary fluoride side. If one insists on liquid fuel, then issues like delayed neutrons need to be considered, and this has an effect on the reactor kinetics.

    The NRC and utilities will not accept a 'chaotic' system - with the possible exception of a bounded chaotic system. If one referes to the title 10 of the Code of Federal Regulations (10 CFR), and particularly 10 CFR 50, and the attendant Reg. Guides and NUREGS, nuclear reactor and fuel design is all about integrity and predictability. If one cannot predict the behavior of a reactor design and the nuclear fuel with an acceptable degree of certainty or margin to established limits, the design is unacceptable.

    A new reactor design requires new infrastructure for its production, as well as the production of it's fuel - and that is not trivial. So in addition to the capital costs of the plant, there will be costs associated with the reactor and component fabrication supply chain, as well as the fuel supply chain.

    As for proliferation - that will be a concern with respect to the residual U-233.
  4. Aug 15, 2010 #3
    Very interesting thoughts Astronuc. I have another thought then. What about traveling wave reactors (TWR)? I am not well studied on the topic, but I viewed a TED Talk given by Bill Gates a few months back, where he presented the idea as an alternative to the current system. I think Terrapower is the only company investing in the TWR technology at this point, but it seems to have potential?

    Also I think thorium reactors still need to be researched, even with their current drawbacks. Just my 2c....
  5. Aug 15, 2010 #4


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    Thorium certainly needs exploration, but it does have proliferation issues like U-235 and Pu-239. Apparently the Russion VVER design (triangular or hexagonal lattice) is rather well suited to Th-cycles.

    I've heard that the TWR concept has been reconfigured from it's original concept. I'm skeptical of it based on claims I've heard.
  6. Aug 16, 2010 #5
    I believe the fact that several countries are doing more than "looking into it," but have already formed cooperative enterprises (US-India's 1-2-3 Agreement), it stands to reason that both research and progress into the several designs (India's AHWR, the HT3R Project in Texas) will continue.
  7. Aug 20, 2010 #6


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    Issues, but not like U-235 and Pu-239.

    I don't see these statements as being very useful in the context of the OP. Yes of course Th has some route to a weapon and thus has proliferation 'issues'. It seems to me however that the difficulty of making a weapon from Th as opposed U is higher, I think much higher. For instance, U-233 requires a greater critical mass for a bomb and has a higher rate of spontaneous fission than U-235. In general I'd say that any fertile fuel, Th or depleted U, has a more difficult path to a weapon than say raw U, with a reactor required somewhere in the loop to produce fissionable fuel, and then a difficult process for separating out the fissionable material.

    My point is that I believe Th does has proliferation advantages. I fear that these advantages are being ignored with mindsets something like "the engineering knowledge for making weapons grade material from Th is out there, and that given time and resources any state can make a bomb with Th too, so don't bother me about proliferation advantages over U-235/PU."
  8. Aug 23, 2010 #7


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    One concept -

    Thorium-Based Fuel Design for Incineration of Excess Weapon Grade Plutonium in Existing PWRs

    The problem with this concept is that it would need modification of upper reactor internals, otherwise the assembly would have to reside in a non-controlled (unrodded) location, which has been done.
  9. Sep 3, 2010 #8


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    Last edited by a moderator: Apr 25, 2017
  10. Sep 5, 2010 #9
    A (single) bomb using 233U has already been built and successfully detonated. This was in the early years of nuke weapons, so it can't be hugely difficult. And against proliferation, "more difficult" isn't enough. So, consider that thorium proliferates.

    Separating 233U when it's the only abundant isotope avoids isotopic separation, one difficulty less.

    And as in most breeders, the user has plutonium in his reactor. The phase between loading and operation is especially critical, with this plutonium more easily graspable. So exporting a breeder looks really risky.
  11. Sep 5, 2010 #10


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    One, and only one. With regards to the early years, many things in the nuclear field that were difficult then still are - making HEU for instance.

    Unless someone can somehow demonstrate a full proof proliferation-free nuclear fuel & reactor design, then comparative difficulties are the only choice.

    More easily than in an low enriched U235 LWR design? How so?
  12. Apr 5, 2011 #11
    Regarding proliferation. Being completely proliferation proof is impossible and insisting on such a standard is simply another way of saying no nuclear power ever. There are many flavors of Liquid Fluoride Thorium Reactors - among them is the denatured molten salt reactor which both the US and England deemed the most proliferation resistant of any reactor.

    Regarding corrosion. The measured corrosion rates from 50 years ago were miniscule and this was not considered an issue when plans were being made for future reactors.

    Regarding "... unsettling". Yes it is different and that is definitely a hinderance, both because regulators are unsure what to do with it and established players would be threatened by its success. But if we started with LFTRs and then someone proposed an LWR you would think they were crazy. I can just imagine the conversation:
    "You want to put enough excess fuel in there to last three years? You want to run this at 70 atmospheres? You want to put water inside the reactor vessel?"
    These are all difficult things to control that we have proven we can do. By comparison, controlling a LFTR is easy.
  13. Apr 11, 2011 #12
    Last edited by a moderator: Apr 25, 2017
  14. Apr 13, 2011 #13
    The "advantage" regarding proliferation in the thorium cycle is that the 233U is mixed in with 232U, which decays into some species which emit some pretty mean gammas. That would wreak havoc with any electronic components or primer explosives in a putative bomb, and at one dalton difference in weight it's quite a bit harder to separate in a centrifuge than the three daltons which separate 235U and 238U.

    Personally, I think that liquid-core reactors like the LFTR/TMSR are the way of the future. The system has a strong negative temperature coefficient, which means that if the temperature rises too much, the salt expands, becomes less dense and the core loses criticality. In an accident like in Fukushima, even without power a MSR would simply heat a bit, melt the freeze-plug (a section of solid salt which is continually refrigerated to remain below the melting point for the fluoride; when power is lost, the plug melts, and the core is evacuated to a large, shallow pool where the reaction stops) and empty the core such that there would have been no explosion, and no meltdown (only a solidification). Of course, working at atmospheric pressure is a big plus, as well, since it removes a source of explosions.

    I guess the biggest technical hurdle for the MSR would be the engineering of the wall that separates the core from the fertile blanket, which captures the neutrons with thorium to create more uranium and protects the rest of the plant installation from neutron damage. The inner wall needs to handle the high temperatures and have a small reaction cross-section to avoid neutron damage while letting the stuff pass on through the blanket.
  15. Apr 17, 2011 #14
    Is there still a phase in the production of the fuel that requires another reactor to produce?
    Last edited: Apr 17, 2011
  16. Apr 30, 2011 #15
    Concerning proliferation: Where is all this thorium now? I gather that it is currently seen as a waste product for those mining for other materials, so is it sitting in someone's garbage somewhere? Or is it currently in a state unusable to terrorists?
  17. Apr 30, 2011 #16
    Last edited by a moderator: May 5, 2017
  18. Apr 30, 2011 #17

    According to the links, thorium power has very real potential to solve all our energy needs practically forever, just like fusion, but compared to fusion it is far easier to achieve it. And why are we not already using it? Cold war politics (huge preference of uranium power because of bomb fissile material production), established uranium nuclear industry inertia, "ecoterrorism" preventing real nuclear innovation etc.. according to this interesting study:

    Liquid fluoride thorium reactor features:
    - passively safe
    - very efficient fuel utilization, temperatures allowing high generation efficiency turbines (45%)
    - produces only very small amount of shortlived waste (300 years to achieve non-dangerous levels)
    - thorium breeder reactor produces more fuel than it consumes, and there is much more thorium than uranium on Earth
    - no need for expensive fuel fabrication
    - easily scalable from small submarine or carrier units to multigigawatt powerplants
    - nuclear weapons proliferation resistant
    - molten salt fuel reactors are not experimental. Several have been constructed and operated flawlessly at 650 °C temperatures for extended times, with simple, practical validated designs, using 60s technology. There is no need for new science and very little risk in engineering new, larger or modular designs.

    LFTR thorium power plant design explained in one minute:


    When I read these links it seems almost too good to be true, especially when one considers we are still not using it for some reason, and its been here for 50 years.. Are really all comparative disadvantages of LFTRs just that it is in principle a "chaotic system" (but still managed to be run for 6 years without problems, even in experimental stage) and some corrosion due to molten salt fuel (again, didnt seem to be a huge issue even with 60s materials)?
    Last edited by a moderator: Sep 25, 2014
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