Monday, October 24, 2016

On Thorium Reactors for Power Generation

Early this month, I got a link to a discussion of the difference between Thorium and Uranium nuclear reactors.  Whenever the topic of nuclear fission reactors comes up, Thorium reactors are talked about as being a safer technology.  While I'm an advocate of nuclear power, I was familiar with the concept, but not the details.  This article provides a really good overview. 

While reading about them, I did some web searches and found a really good article, by the Slow Facts guy, Rob Morse.  While that previous article is in an engineering magazine and written for folks with that background, the Slow Facts article is more like something you'd present to a friend who is adamantly against nuclear power.  Thorium is two elements below (to the left of) Uranium in the periodic table, but is much more common; about as common as tin.  It's estimated we have about a thousand year supply of Thorium in the US alone.  All current nuclear reactors in this country, at least, are Uranium fission-based reactors.  Comparatively, Thorium reactors:
  • Are safer
  • Produce less radioactive waste, and waste that is easier to provision for
  • Are easier to install, and easier to find a site for
  • Can be smaller and less expensive
  • Are more secure: Thorium can't be used to make a bomb
Unlike conventional light water reactors, cooled by regular water as the name implies, they're cooled by molten fluoride salts (Liquid Fluoride Thorium Reactors - LFTRs).  Molten salt baths are exotic to most folks, but are used in heat treating metals so there's over a century of industrial experience with using them safely.  They are low pressure systems and since there's no steam (no water) a steam explosion is impossible.  As a class, these liquid fluoride reactors are passively safe, which means the system can respond without human intervention.  They can even respond to some things without intervention of any kind at all.  The plant will respond properly even without an active control system.  How?  For example, the molten salt is cooled to keep its temperature at the desired operating point.  As it heats up, the nuclear reactions slow down.  That means an accident caused by loss of cooling is essentially impossible.
Only one reactor has ever been built that could qualify as a reactor representative of the third phase of the plan, and that was the final core of the Shippingport Atomic Power Station in Pennsylvania. The experiment was called the Light Water Breeder Reactor and involved using thorium/U-233 fuel in a repurposed pressurized water reactor. The experiment was a success and showed that just as much U-233 could be produced as was consumed. 
This experiment was in the early 1960s.  1960s!  So why can't we build one now?  The usual: regulations.  Regulations have changed and no developer is going to bet the money required (a billion?  hundreds of millions?) that a politician's promise is any good.  Meanwhile, in the rest of the world, developing Thorium energy is a major goal in India.


  1. I came across similar information several years ago and at the time I heard Bill Gates was interested in them as an alternative to the current generation of reactors and also the safety of the thorium reactor. Supposedly, they could be built small enough to serve small cities of 50,000 population and wouldn't even need an operator...they could be buried in the ground and be much less of a terrorist target. I liked the idea that we wouldn't need the large transformers (EMP vulnerable) currently used as they could be used for local power consumption yet still function as a group to fill in for an off line reactor in an adjacent area. I also thought they would work well for powering the rail infrastructure rather than using the current diesel-electrics. One less petroleum consumer. Because no one seems to be researching the thorium solution is one reason the Dept. of Energy should be closed as they seem to have little imagination or motivation to act. indyjonesouthere

  2. The ONLY reason we have Uranium>Plutonium Reactor Tech. is so the bomb factory's can have a ready supply. The whole IDEA has been about Atomic weapons from its beginning. Power generation is, and always was, a propaganda story to sell the single most likely vector for man made human extinction. Nobody in .Gov WANTS Thorium reactors BECAUSE the fuel cannot be used to make bombs.---Ray

    1. Not true, a Th/U fuel cycle can be used to make bombs.

  3. A few years ago, I wrote a piece here arguing that we should mass produce the A4 reactors the Navy uses on aircraft carriers and use them for the kind of distributed, small power systems Anon 2348 talks about. They're 100 Megawatt reactors, and I figure they'll power about 10 or 15,000 homes.

    They're a standardized product with a stellar safety record. When the Navy needs one, they just cut a proposal for one A4. The companies that can build them bid on the contract. The only thing you could say against widespread use of these is that the Navy has a dedicated, well-trained group of sailors to run it, and the idea of Thorium reactor with much smaller crew (or, possibly, no crew!) is clearly better.

    With the advantages of going small and local, LFTRs really need to be examined. Why support multi-thousand mile, extremely high voltage transcontinental power lines when the power can be generated locally? That's a 1930s fix that is as outdated as 1930s movies.

  4. I wrote the book, THORIUM: energy cheaper than coal. I'm now engaged with a near-term project to develop and market hybrid thorium/uranium liquid fuel fission power plants. We are planning the first one for Indonesia. We are very focused on being cheaper than coal, and getting this done soon. Please explore our website, and visit the Facebook page .

    1. Thanks for stopping by. I'm going to turn your URL into a link to make it easy for others. I hadn't heard of this effort to get LFTRs going elsewhere in the world, and the idea of keeping the cost below that of coal is so filled with winning, it's hard to describe. It just removes any objection except for the reflexive anti-nuclear zealots.

      As an aside, I personally don't do Facebook because I find many of their business practices despicable. I think other folks who drop by here feel the same way. I can see the advantage to a company in reaching a wide audience, but I don't see any advantage to being data mined like they do. A website link like that is easier, and anything you post to FB could be a Blog page or News page or something like that on your website.

    2. Yet another "thorium is great" private entitiy misleading the unwashed masses by purporting to be creating a new technology and implementation method while not crediting the people who did it before.

      I would love to debate the efficacy of your technology in detail.

      Also, your modular block design a la shipyard construction is rather clever...or at least I thought so when I published it in both MIT thesis form and at ANS conferences 12 years ago. And I'm sure the MIT IP office would -love- to take a better look at your lack of citation to work performed there on modular reactor construction methods.

      But hey, if the "claiming its your idea" shoe fits, strap that thing on and run with it.

    3. This comment has been removed by the author.

  5. Fascinating. I've been following these for some time now. I think I first heard of them over 10 years ago, and wondered why they weren't The Next Big Thing.

    Oh, yeah.....Big Gov doesn't like them, and all the Greenie Weenies have completely closed minds to ANY type of nuclear power.


  6. As a practicing nuclear engineer, who has done many architecture comparisons for both private and public institutions, I'm going to have to Fisk this:
    Are safer
    --only because of the technology (eg molten salt), not because of the specific fuel mix, and the technology can be used in U/Pu cycles as well

    Produce less radioactive waste, and waste that is easier to provision for
    --not true/partially true--the waste is EXTREMELY radioactive (that's why it's proliferation resistant), and the only reason it's "less" is because a Th/U cycle is by definition a breeder, and thus has a lower volume of actual waste per unit MWhr--the same would be true for a U/Pu once through breeder or a U/Pu cycle done through reprocessing.
    --while they do result in fewer ultra-long life isotopes being produced (eg Pu isotopes) the same can be true for high burnup U/Pu breeders

    Are easier to install, and easier to find a site for
    --only because of the safety issue and potential size, which are no different (and in some cases worse) than comparative tech used with a U/Pu cycle

    Can be smaller and less expensive
    --same as above, has nothing to do with fuel, other than thorium is technically cheaper than raw uranium...but the raw fuel ore price has effectively nothing to do with the end cost.

    Are more secure: Thorium can't be used to make a bomb
    --actually, the ACTUALLY fuel used in a "thorium" reactor is Uranium...specifically U-233, which can be made into a nuclear weapon (and one can tweak the cycle to yield greater U-233 and lower 232. But even with 232 present, it's still bomb-capable, since 232 doesn't cause predetonation.
    --and actually, the plutonium generated by a high burnup U/Pu breeder can't be used in a bomb (as increasing burnup results in more Pu-240/241 which does cause predetonation, so this is both true of both systems, or not true for both systems.

    While I like thorium cycles, (and have consulted on the design and business aspects of them as well) they are always argued for in this way, which is honestly not correct. What is also left off is "thorium" reactors are ACTUALLY uranium reactors...thorium isn't directly fissionable, but needs to be converted into uranium-233. But that is left off to make it seem more different than it is.
    And there are a variety of other things.

    Also, with respect to using naval reactor designs for mass produced power...there are HUGE issues with that...namely the type of fuel used in them and their enrichment levels...

    TL;dr. Thorium is used PURELY as a marketing strategy to make it seem different than a U/Pu cycle...and the "new" technologies proposed are basically betting that the reason we don't have more nuclear power is some sort of technology limit, instead of ignorance and I guess you can say thorium is a great approach, if only because it takes advantage of that ignorance.

    1. Marc,

      I can't thank you enough for coming by with these contributions.

      I think it should be obvious to readers from that large figure in the middle that Thorium is a minority species in a Thorium reactor; it should be obvious that there's plenty of Uranium and Plutonium in there. I'm simply not prepared to fisk the engineering claims I see for LFTRs because of my lack of engineering experience with them.

      I also recall hearing good things about a (U/Pu?) system that encased the metals in ceramic spheres, so that they were supposedly much safer, too. I think they used the same argument that they could run dry and steam explosions weren't possible with that system either. Do you have any feedback on those?


  7. Both pebble bed and HTGR systems use ceramic encased microspheres.
    If you google my name and MPBR, or the South African PBMR (I worked closely with those guys down there...and its your old stomping grounds.) you can find a bunch on the gas cooled gen-IV reactors.

    Between the MSR's and the HTGR (high temperature gas cooled reactor) they each have their advantages and disadvantages when it comes to a variety of different aspects, so there really isn't a clear winner per se (I've designed all 4 combinations of MSR/HTGR combined with Th/U or U/Pu systems).

    Both are far safer than current systems, BUT honestly, current systems can't really be any safer.
    Fukushima was effectively a worst worst case (for systems with a containment, I.e. Not Chernobyl) and there, the biggest problem wasn't the reactors, but the spent fuel...which wouldn't have been present if it was a good reprocessing/recycling fuel cycle using either Th/U or U/Pu. And even then, it was actually more dangerous to be in the surrounding city due to the non-nuclear disaster, than it was to be working at the plant AND working the cleanup.
    TMI here in the US was a true meltdown and its death toll Period.

    Nuclear has been safe (at least western nuclear) for decades. Like I said, it's not a technology problem.

    Random fun fact: per MWhr, and INCLUDING Chernobyl, wind power kills more people than nuclear...because it's dangerous to climb up and build tall stuff. Food for thought...

    1. It seems an inescapable fact of life in the last 50 years that there's a group of people who just simply freak out when "the R word" is used. They think radioactive waste will simply kill everyone near it for thousands of years. I recall working with a guy in the early '00s who was talking about the awful problem of radioactive waste and had never heard of vitrification as basically solving it. He was an engineer even older than me, so it surprised me.

      I think Dave Barry's line about Chernobyl was something along the lines of "a nuclear reactor built by a country that can't build a working clock radio", which seems to be only a slight exaggeration. The reaction to Fukushima was totally out of scale to what really happened, and I've got to think that it's because we can detect such very low levels of radioactivity. I remember writing about it. To quote from one of them: "Every time I eat a bag of potato chips I think of Fukushima. This 12-ounce bag of chips has 3500 picoCuries of gamma radiation in it, and the number of bags I eat a year gives me a dose as high as what I would receive living in much of the evacuated zones around Fukushima. But unlike the Fukushima refugees, I get to stay in my home."

      And BTW, I have no knowledge of South Africa; that's Peter at Bayou Renaissance Man. No big deal, of course.

    2. Crap, sorry for confusing you with Peter, I just finished reading his blog for today when I switched over to here. My bad.