Oct 31 2013

Thorium Reactors

Thorium is a radioactive element (atomic number 90), discovered by a Norwegian and named after the Norse god, Thor. It is fairly common in the earth’s crust, widely distributed throughout the world, with the largest deposits in Australia, the US, Turkey, and India.

If advocates have their way, you may be hearing more about thorium in the future. It is a potential fuel for nuclear reactors. We have not yet fully developed the technology for building thorium reactors, and the debate is on over whether or not this is a useful investment of energy development funds.

Carbon emissions and global climate change have raised the stakes of this controversy. I am with Bill Nye in advocating searching for the win-wins in combating carbon emissions – rather than asking people to sacrifice, find ways of improving their lives while lowering carbon emissions. The question is, is thorium a potential win-win?

Advocates argue that thorium is abundant and not concentrated in unstable parts of the world. There is about three times as much thorium as uranium in the earth’s crust, and it is more highly concentrated in its ores, making obtaining thorium more cost effective.

A thorium reactor is potentially safer than a uranium reactor. The thorium cycle is not as self-sustaining as uranium – thorium is not fissile on its own. In fact, most concepts use uranium to seed the thorium reaction. Uranium can also be used to keep the thorium reaction going at a higher rate, and disconnecting the uranium reaction (or whatever source of neutrons you are using to get the thorium cycle going) would quickly reduce or stop the thorium reaction when needed.

Thorium also does not create any long-lived radioactive waste. Thorium waste would dissipate its radioactivity in 400-500 years, compared to the uranium cycle which produces various waste products with half-lives ranging from tens of thousands to millions of years. Further, thorium waste could not be weaponized, as uranium waste can be. We can let Iran build thorium reactors without worrying about their weapons program.

Why, then, are we not powering our world with thorium reactors? The most common opinion I have found as to why the US chose uranium over thorium is the fact that the former can be weaponized.  This was thought a beneficial byproduct during the cold war. Whether or not this is true, billions of dollars were invested in developing uranium technology. It’s like the qwerty keyboard – it may not be superior, but we’re stuck with it.

That leaves us with our current dilemma. Thorium seems like an excellent choice for an energy source that does not produce carbon. However, we would need to invest billions in developing the technology. One technological barrier is refining the ore, which requires very high temperatures and is therefore expensive. Reactor designs also need to be developed.

The question is – is this the best way to spend those billions of dollars on energy development?

Renewable energy advocates argue that we would be better off spending that money on wind, solar, and other renewable energies. Some have even argued that if we invested the same money we did in uranium power plants on renewables, we could already run our world on clean energy.

I don’t buy that argument.  Investment certainly accelerates scientific and technological advance, but doesn’t alter the reality when the technology is simply not ready. Sometimes technological progress has to wait for other technological advances, for example in material science, battery design, and nanotechnology. Current advances in wind and solar especially are taking advantage of these technologies, that just were not around 50 years ago.

In any case, the question remains, how do we invest our energy money going forward? These are tough questions as they require predicting the future of technological development. My usual answer to such questions is to do everything, and let the technology sort itself out. Don’t try to pick winners and losers – let the market do it.

American car companies around the turn of the century invested in the coming hydrogen revolution. Japanese car companies hedged their bets and invested in hybrids and a bridging technology. The Japanese won that game, capturing the hybrid market, and leaving American companies in the dust nursing their hydrogen fuel cell dreams.

Wind, solar, and thorium are all clean energy sources. They all have their strengths and weaknesses, none are perfect. They will likely all have a niche in the future of energy production.

But the problem remains that thorium requires a huge investment up front. That is a big hurdle to get over. We can’t dabble in thorium, we would have to invest heavily. From everything I have read it does seem like a good investment to me. Perhaps this needs to be an international project to spread the cost around. In any case I think this is one technology to keep an eye on.

15 responses so far

15 thoughts on “Thorium Reactors”

  1. Deemer says:

    Hi Steve,

    You may be interested to know that a Norwegian company – Thor Energy – which is partially backed by the Norwegian government and one of the the state oil company’s subsids have recently fired up a 4 year test of using thorium as a replacement fuel in an existing, conventional reactor.

    You can see details here – http://www.thorenergy.no – and here – http://www.extremetech.com/extreme/160131-thorium-nuclear-reactor-trial-begins-could-provide-cleaner-safer-almost-waste-free-energy

    I hadn’t previously noticed that Westinghouse is involved as well, in such things the more the merrier, no?

    I think it’s the way forward.

    I also note that the UK is getting itself in a terrible mess with wind farms not working at all as expected and the electricity grid failing spectacularly to manage the unfortunate fact that “green” energy is both lumpy and is often most easily generated at the very times that you don’t need it (locally).



  2. My understanding is that the primary impediment in using Thorium as a fertile material for reactors is the problem of of U-232 via n,2n reaction with the fissile U-233 breeding products of Th232 and Pa232. U-232 has strong gamma emitting isotopes in its decay chain, which does limit weapons proliferation concerns, but it also makes handling the fuel more problematic. There are also other technical concerns which I think make U-235 & U238-Pu239 less technically challenging, but I think U232 generation is the bigee.

    Also While Thorium/U-233 is less easier to weaponize that U-235 & U-238-Pu239, it is apparently not totally un-weaponizable, and Ihas been used in weapons tests.

    I wouldn’t go so far as to say ,”We can let Iran build thorium reactors without worrying about their weapons program.” Thorium reactors breed U-233, which is fissile. The unavoidable presence of U232 makes using it for weapons problematic, but not necessarily impossible.

  3. steve12 says:

    I’ve also read a little about the placement of reactors – that they can be buried deepl in bedrock and designed such that the waste simply stays there.

    It just seems absurd to me that we’re not further developing (improving and making safer) nuclear energy considering the threat of global warming and a waning oil supply.

    My only misgiving is the oversight. The NRC has a bad enough history. Considering the libertarian fetish that’s overcome the US I can’t imagine that getting better. So my only misgiving is political – that a profit seeking venture will not be properly regulated, leading to safety issues.

    I think the science and tech, though, has the potential to literally save the world.

  4. Please look past how poorly edited my comment was. I wrote it in a very big hurry, and it ended up a minor mess well below my personal standards. Never comment in a hurry. 🙂

  5. petrossa says:

    This pdf contains interesting short overview of current thorium situation https://dl.dropboxusercontent.com/u/1828618/thorium.pdf

  6. bachfiend says:

    OK, I’m a pedant. One of the advantages of thorium is that it’s an energy source that doesn’t produce carbon dioxide, not that it doesn’t produce ‘carbon’ (as written). One of the (sillier) arguments global warming deniers use is that carbon dioxide isn’t pollution. Using ‘carbon’ supposedly inviting the image of soot in the air, which is pollution.

  7. Ribozyme says:

    The first time I heard about thorium reactors was through this video (a TEDx Talk). What do you think, Dr. Novella, too good to be true?


  8. Ribozyme says:

    To add a little information, the video is about thorium molten salt reactors.

  9. jmkorhonen says:

    Thank you for this post – it is nice to see that educated people begin to notice the untapped possibilities of advanced nuclear power.

    Thorium fuel cycle indeed shows considerable promise, so much so that the relatively small funding its R&D requires are definitely good investments. However, may I suggest you to take a second look into alternatives, such as the Integral Fast Reactor?

    The IFR technology, based on uranium-plutonium cycle, was designed to – modestly – eliminate or considerably alleviate EVERY problem associated with nuclear power. Even according to its critics, it largely succeeded in this before its funding was cut for purely political reasons in 1994. IFR eats even depleted uranium and current nuclear waste, spitting out electricity and a very small amount of waste products that are safe to handle after 300 years. It is passively safe, relying purely on the laws of physics rather than operator actions or mechanical devices: the reactor has actually been tested in conditions as severe or more so than anything that has occurred with any nuclear plant ever. That’s including Chernobyl.

    While it may be theoretically possible to use it in a nuclear bomb program, the composition of the fuel makes this exceedingly difficult if not impossible; and plutonium proliferation concerns are already largely outdated, because widely available modern centrifuge technology for uranium is in almost every way the superior route to the bomb – especially for states that do not already have experience building the damned things. (By the way, this also applies to concerns about thorium fuel cycle. No sense to use the extra difficult and hazardous U-233 route when you can centrifuge U-235 in any desired quantity and far more easily from safe to handle natural U feedstock. The bomb is a political, not a technological problem.)

    And IFR is probably at least not much more expensive than current reactors, and has the potential to be much cheaper: the reactor is designed cost-consciously and it can be manufactured from modular, factory-built parts, rather than having to be built on site.

    Finally, the fact that, in my opinion, puts it ahead of thorium reactors is that it is also nearly ready for deployment; GE-Hitachi already offers its offspring, the S-PRISM reactor, to the British government for the destruction of British plutonium stockpile. The last I heard, this would have not induced any financial risk to the taxpayer: GE-Hitachi has offered to provide the reactor and charge only on a basis of plutonium actually destroyed. Dr. David MacKay, who I believe is the government’s scientific advisor, calculated that plutonium stocks alone would suffice to provide ALL electric power to the United Kingdom for the next 500 years.

    Yes, I’m aware that this all sounds too good to be true. But while skepticism is a healthy attitude, I implore anyone who is interested in the climate change fight to take a hard look into technology and at least consider the possibility that this might be what fusion has promised to be: almost unlimited energy source that has very few environmental or safety issues, small footprint and no issues with variability.

    The best book about the IFR is “Plentiful Energy: The Story of the Integral Fast Reactor,” written by the two guys who were responsible for developing it, Charles E. Till and Yoon Il Chang of Argonne National Laboratory. There is also lots of stuff available on-line, the best resource probably being collected by prof. Barry Brook under the heading “IFR Facts and Discussion” here:


  10. daedalus2u says:

    There are several reasons why uranium was chosen for light water reactors. The primary advantage of light water reactors is that hydrogen is a good moderator (actually it is the best moderator) and so the neutrons in a light water reactor are mostly “thermal”, that is at ~ the temperature of the reactor, less than 1 eV. The neutrons released during fission are “fast” neutrons with energies ~ few MeV. MeV neutrons move much faster than thermal neutrons and so can escape from the reactor much more easily.

    If you want a small reactor (as for a submarine), you want to use light water to minimize neutron loss. The power rating of a reactor is independent of its size (approximately). Once a reactor is critical, the power level can be increased to any level. The first power reactors were for submarines and they were light water reactors. Later power reactors used the same technology because it was cheaper to do so in the short term. No one knew (or even cared) what the long term costs were.

    If you are using fast neutrons, then you have to use a coolant that doesn’t contain hydrogen. Canada uses deuterium, liquid sodium can be used, Chernobyl used graphite (as a moderator, not as a coolant). The Soviets used a graphite moderated design for Chernobyl because it was a modified Pu breeder (the design they already had).

    Then your reactor needs to be larger so that fewer neutrons are lost. This makes a containment building more expensive (because it has to be larger). The faster neutrons are more effective at causing fissions, so the transuranics are fissioned rather than accumulated (as in a slow neutron reactor). The transuranics are the source of the long time radioactivity, they eventually decay into uranium and thorium which are very long lived.

    I think the “problem” with radioactive waste is a political problem and not a technical problem. The fission products are intensely radioactive, but nothing can be both intensely radioactive and radioactive for a long time. Those are mutually exclusive properties. If you take spent fuel from a light water reactor, it is intensively radioactive, but if you wait 700 years it becomes less radioactive than the ore from which the uranium was mined (which is ~19x more radioactive than uranium because of the uranium daughter products including radium, radon and polonium).

    U235 can be used to make nuclear weapons, but only the US and South Africa ever did so (South Africa dismantled them before ending Apartheid. U235 has a critical mass of ~50 kg, which is inconveniently large for a warhead that you would like to send somewhere on a missile, or to use as the primary of a thermonuclear device. Pu239 has a critical mass of ~10 kg which is much more convenient.

    I don’t see any compelling need for nuclear power for Earth based electricity generation. Wind and solar are pretty cheap. They would be cheaper than any fossil fuel if fossil fuel energy production had to pay its fair share of the costs of CO2 in the atmosphere.

    What we need to do is scale up wind and solar, and then use the off-peak electricity for things that are not time sensitive, like ammonia production.

  11. Nitpicking says:

    Wind and solar are cheap for values of “cheap” that mean “incredibly expensive”.

    India is starting up Thorium reactors now. Hard to argue that other not-yet-constructed technologies are ahead of one that’s operating.

  12. BillyJoe7 says:


    A quote from wiki (not sure how reliable it is)

    “India’s plans for thorium cycle

    With huge resources of easily-accessible thorium and relatively little uranium, India has made utilization of thorium for large-scale energy production a major goal in its nuclear power programme, utilising a three-stage concept:

    Pressurised heavy water reactors (PHWRs) fuelled by natural uranium, plus light water reactors, producing plutonium.

    Fast breeder reactors (FBRs) using plutonium-based fuel to breed U-233 from thorium. The blanket around the core will have uranium as well as thorium, so that further plutonium (particularly Pu-239) is produced as well as the U-233.

    Advanced heavy water reactors (AHWRs) burn the U-233 and this plutonium with thorium, getting about 75% of their power from the thorium. The used fuel will then be reprocessed to recover fissile materials for recycling.

    This Indian programme has moved from aiming to be sustained simply with thorium to one ‘driven’ with the addition of further fissile plutonium from the FBR fleet, to give greater efficiency. In 2009, despite the relaxation of trade restrictions on uranium, India reaffirmed its intention to proceed with developing the thorium cycle.

    A 500 MWe prototype FBR under construction in Kalpakkam is designed to produce plutonium to enable AHWRs to breed U-233 from thorium. India is focusing and prioritizing the construction and commissioning of its sodium-cooled fast reactor fleet in which it will breed the required plutonium. This will take another 15-20 years and so it will still be some time before India is using thorium energy to a significant extent.”

    Unless I’m misreading this, it’s going to take 15-20 years to complete stage two of a three stage program to produce energy from thorium reactors.
    In other words, there is a long lead time, and this is assuming no unforeseen complications.

  13. BillyJoe7 says:

    My ipad won’t let me copy and paste twice???
    Here’s the link:


  14. BillyJoe7 says:

    Also here:


    “Speaking to reporters in the sidelines of the first graduation ceremony of National Institute of Science Education and Research (NISER), Sinha said the country already has the technological know-how to use thorium. However, for large-scale use of thorium, the country will need two decades. “We have to assess the thorium-powered reactor on various aspects in the long-term before replicating similar models in bigger ways,” the AEC chief said”

  15. daedalus2u says:

    The problems with nuclear power are not technical, they are human.

    All large human organizations operate from a top-down control perspective. The person at the top cannot know everything that is going on, and promotion to the top (usually) does not occur due to technical expertise. It is very rare for the individual at the top to prioritize safety over profit. The only example I can think of is Rickover in the US Nuclear Navy.


    “Rickover’s substantial legacy of technical achievements includes the United States Navy’s continuing record of zero reactor accidents, as defined by the uncontrolled release of fission products subsequent to reactor core damage.”

    Of course demanding performance over profits made him enemies in the military industrial complex and eventually they got rid of him.

    I don’t doubt that India has the technical expertise to design, make and use safe nuclear reactors of any type, thorium, uranium, plutonium. I doubt that India has the political will to prioritize safety over profits. India certainly didn’t 30 years ago.


    I don’t think the US has the political will to prioritize safety over profits. We certainly can’t deal with global warming, we can’t deal with antibiotics in animal feed, we can’t deal with neonicotinoid insecticides, we can’t deal with banking fraud, we can’t deal with CAM.

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