Thorium power plants were a thing that was researched and ultimately abandoned; however, for all intents and purposes, it's safer than any power source we have today.

In our timeline, the first such reactor was built in 1965, but it was a proof of concept only, and all thorium reactors were shut down in 1973. Meanwhile, uranium nuclear reactors have been commercially used since 1954.

What are plausible conditions that would create a situation where thorium power is used to supply at least 1/2 of a major nation's energy needs? Currently uranium-based nuclear energy in the US provides 1/5 of its total needs, while France is almost at 3/4, so we would need to:

  • Increase the share of nuclear power compared to alternatives (fossil, renewable)
  • Increase the share of thorium power plants compared to uranium ones

Let's say the 50% goal should be achieved by 2016, meaning that it may be necessary to push the discovery of nuclear power further back through some events.

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    $\begingroup$ Looking at that wikipedia's article's advantages and disadvantages, it looks to me like it's a question of "how do we incentivize people to choose the option that's better for us in the long run but more costly in the short term?" Maybe I'm a cynic, but history suggests to me that you don't - you simply wait until those short term benefits (especially being cheaper) start dwindling due to decreasing supply and/or the long term disadvantages start having their effects felt. Just look at what we're doing with fossil fuels. $\endgroup$ Commented Oct 10, 2016 at 20:20
  • $\begingroup$ @childofsoong "We discover fossil fuels and hit peak oil sooner, so by 2016 we are already exploring alternatives" is an answer too, as long as you can think of a plausible way to move up the timeline. :) $\endgroup$
    – SPavel
    Commented Oct 10, 2016 at 20:22
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    $\begingroup$ well, by that path, you could just say "we ran out of fossil fuels and uranium quicker". It just seems like a lazy answer on my part. $\endgroup$ Commented Oct 10, 2016 at 20:23
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    $\begingroup$ According to a friend of mine who's a physicist, LFTR reactors work, but research was stopped in the 1960s since they don't have weapons-grade byproducts, which was a key interest then. $\endgroup$ Commented Oct 11, 2016 at 16:12
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    $\begingroup$ What practical issues remain for the adoption of Thorium reactors? $\endgroup$
    – Mazura
    Commented Oct 11, 2016 at 16:25

6 Answers 6


The two primary drivers of Uranium fission reactors are the need for fissile material for nuclear weapons, and the ability to make compact reactors for powering nuclear submarines. Point two also explains why light water reactors are the primary design of existing reactors in the United States; they all evolved from the engineering knowledge and experience gained by building nuclear submarines in the early 1960's.

If WWII had ended with both Nazi Germany and the USSR having collapsed (perhaps the Germans actually won the invasion of the USSR in 1941 to the extent that the Communist government and organizing structures had been destroyed), then the United States would not feel an overwhelming need to push the production of fissile material for bombs and triggers (in practice, Plutonium bred from fission reactors), nor the desire for compact, high energy reactors for submarines.

With fewer incentives to follow a particular path, US nuclear engineers could have worked on a much broader range of reactor designs. Thorium was an obvious choice for civilian power reactors since Thorium is cheap and abundant, and there would be no obvious pressures, pre existing pools of resources and talent or sunk costs to swing the balance towards light water reactors.

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    $\begingroup$ I remember reading the history of our modern nuclear reactors. There are actually more efficient versions but our versions won out because they create weapons grade fission material. The power generation was a side effect... $\endgroup$
    – Nelson
    Commented Oct 11, 2016 at 10:15
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    $\begingroup$ This is not really true. Thorium has concrete disadvantages, most notably, the lack of a naturally occurring fissile isotope. The problems of breeding and reprocessing Thorium into fuel are significantly larger than the problems of enriching Uranium. Uranium was chosen because of economy and safety, the same reasons that pressurized LWRs were chosen over molten salt and other reactor types. $\endgroup$
    – kingledion
    Commented Oct 11, 2016 at 13:43
  • $\begingroup$ @Nelson That is also not true. Efficiency is only one component of nuclear power; by far more important is safety. American nuclear power plants accept significant losses in efficiency to increase safety. The pressurized (light) water reactors (PWR) used in the United States are by far the safest designs in the world. It is very relevant to note that neither Chernobyl nor Fukushima were PWR reactors; while Three Mile Island was. Which reactor would you prefer to have an accident in your town? $\endgroup$
    – kingledion
    Commented Oct 11, 2016 at 16:13
  • $\begingroup$ @kingledion I wouldn't want a reactor of any kind in my town (or any town, really), but I understood that one of the advantages of thorium is that, when something goes wrong, the reactions slows and stops rather than going critical. Is this not true? $\endgroup$
    – gandalf3
    Commented Oct 11, 2016 at 16:58
  • $\begingroup$ @gandalf3 Come talk in chat and I can explain (chat.stackexchange.com/rooms/17213/the-factory-floor). $\endgroup$
    – kingledion
    Commented Oct 11, 2016 at 17:21

Don't have a Cold-War.

The United States had to choose a direction in which it would go in terms of nuclear research: Thorium, or Uranium.

Only one of these had the corollary benefit of making bigger bombs. Guess which one got funding from the Defense budget to keep ahead of those pesky Communist Russians?

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    $\begingroup$ This is deceptive. One fuel source was better for bombs AND safer for nuclear power. That was Uranium, so that was developed. Thorium was not developed because it is not safe for commercial power generation. $\endgroup$
    – kingledion
    Commented Oct 11, 2016 at 13:41
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    $\begingroup$ How is it not safer than, say, a BWR? Compared to a pebble-bed reactor, I'll give you that, but not for other varieties. $\endgroup$
    – user6511
    Commented Oct 11, 2016 at 21:14

Thorium people have not stopped their activity, but they suffer from financing issues.

If the question is - "what if history turned another way" - then Reagan could possibly be your point of divergence, as it was a political decision to shut down the process. It had probably bunch of aspects behind the scene, having plutonium sure one of them. Efficient burning was not the goal, but getting specific types of isotopes was.

So a high energy demand, successful breakthroughs in problems, the possibility to make Plutonium, some accidents with solid reactors at early stages like Chernobyl to build public resistance for those types of reactors (so it means actually some serious errors in process of developing nuclear reactors, to be too optimistic and go big too soon)

So significant negative pressure could limit solid reactors to military goals only. And military played significant role in developing those reactor for their purposes.

World's First NUCLEAR SALT REACTOR - Documentary Films pretty interesting history kind video. (they blame Reagan, saying that if he would be more familiar with technology he could decide other way)

Positive factors which could keep a molten salt reactor afloat could include space program like moon base, mars base.

Salt reactor, one of reason to start that program was wish of military to use it in aircraft, and conventional reactor was not capable to do that, but a molten salt reactor could in theory (even if the creator did not believe that it would work in a plane) to be used there.

For use in space, it has advantages too, one advantage being the more efficient use of fuel without expensive and technology intensive processes to recover fuel, to reassemble fuel rods. A lower reactor mass and simpler management are also very significant advantages for use in space.

It is also much easier to deliver the initial fuel - because of how it is packed. There is much less danger in the case of a mishap during launch, because of how it can be packed. It is easier to work with thorium as a main fuel source. There are also pretty significant amounts of it on the surface on the moon (12 ppm is about 70 tonnes per million tonnes of dust, thorium is ca 230 atomic mass, average for moon ca 30 atomic mass, so it is 12 * 7 tonnes per million, my rough estimation, even in the unlikely case that there are no concentrated ores)

According to fast link

  • Thorium reactors deliver 3.6 billion kWh of heat per ton of thorium, which implies that a 1 GW reactor requires about 6 tons of thorium per year, assuming its generators are 40% efficient.

So it would be enough for a 10GW reactor, which will generate 315 GJ of electricity per tonne of ore. On the moon efficiency can be higher overnight, just as a note. Glass production uses 9GJ per tonne of product (mostly for melting), Aluminum production uses 54 GJ per tonne (because of the energy requirements of reduction of Al2O3 into Al). So you basically can melt it (ore) all down, reduce all stuff to pure metals and gases by electricity and it will be something like 20% of what you will produce after extracting the thorium. Not saying it is the way to do, but why not if you need Iron, Aluminum, and Titanium - which are present on the moon: some NASA thoughts about Al on the moon

So a strong lunar program could be one of the factors in favor of molten salt reactors.

One of the factors involved in solid reactors being preferred is investments from the military, they wanted them for a bunch of reasons.

Thorium reactors for a lunar base are an excellent choice, so they may have happened during the Appolo era, if there were other factors enabling moon base. This will aid progress in other areas, not just nuclear related problems, and could be one of the factors that could open perspectives for this technology to be more attractive, or enough attractive to pour money into it, and that is actually all it needed at that time.

So it may be not a big stretch, that history of molton salt reactors could be different.

P.S. as people have mentioned the Russians, so will I. Greater successes for their moon program could be also one of the factors supporting an expanded US moon program, without collapsing it. So moon base race could be an enabling factor too.


read in case factual incorrectness feeling. disclaimerTM, do not build it at homeTM, make your own research before buildingTM, call me if u didTM

In this answer I rather project words of other, who are optimistic about thorium reactors and who thinks that problems can be solved.

Also it is not mention explicitly, answer keep in mind one particular type of possible types of Thorium reactors, molten salt with in situ utilization.

Packing benefits assumes packing fuel pellets, like in Pebble bed reactor, and relays on possible advantages dividing fuel in to small packages, encapsulating them in robust shell which can withstand fall from orbit if needed, where shell may be actually non radioactive part of future fuel(same thorium actually). It may be non radioactive (as Thorium non radioactive, not as completely non radioactive) in case of some kind of ADS(accelerator-driven system) as starter for whole process. There is difference with uranium rods, which I think can be exploited to our advantage.

Each reactor development includes lot of work behind the scene. This is complex work, which includes solving non obvious for the public or outsiders set of problems. If everything would be easy and simple, then it would be solved in the past, and we would not have question may or may not it to be solved. It wasn't, and question is valid.

Simplicity of main concept, does not mean that solution will be simple, it does not mean it is possible at all, at least at some technological level, which looks sufficient for solving that problem, but in fact, it is not sufficient and needs involving of more advanced technologies, to make it working or just working.

Some examples for better illustration:

Examples of such, which comes in my mind right now, as example knife. It is very old design, stone age old, but really good results where achieved after work with metal became more usual practice.

Another relatively simple idea as Space Elevator, with less obvious problem not exactly but like - to have easy access to space, u have lift huge amount of stuff or build that in space - both looks like easy access to space help here. Obscure/contrast it a bit more - to get easy access, u better have easy access. Even it almost technically possible to build such cable as just rope, u need more advanced rocket systems, or another and better launch technology it is possible, but would u need elevator then?

3He as fuel in thermonuclear reactor there are objections based on speed of reactions which would have place in such reactor.

Launch loop where main problem is reliability at current level of tech.

So there are interesting and promising things which looking good, but do not work at current tech level, for understandable reasons. How advanced we should be to solve them, who knows? Those who knows about thorium dividing in 2 categories believers and non believers, but none of them can prove that other side is wrong. One side not failed yet, but also do not have great success. Other side can point those 2 facts, but can't state it is not possible, exactly because of those 2 facts, but they try to make their reactors better, just in case(for reasons of waste). So this race is not ended yet.

Interesting links

play scientists, investigate isotopes chains - periodictable.com, isotopes, Th

Thorium optimists site energyfromthorium.com, they recommend this video 2h video "NASA" - Thorium remix 2016 to watch, I expect it to be at least interesting, but have not watched it yet.

Thorium fuel cycle, and specially "List of thorium-fuelled reactors"

Molten salt reactor concepts in general, https://en.wikipedia.org/wiki/Molten_salt_reactor

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    $\begingroup$ This post needs to be edited for spelling and grammar. I can't really understand that much of it, but what I do understand seems to be factually inaccurate. Equating molten salt reactors with Thorium primary mistake. Even if molten salt reactors had be developed into commercial viability, that doesn't solve the problem of processing Thorium fuel, so those salt reactors would be using a Uranium fuel. $\endgroup$
    – kingledion
    Commented Oct 11, 2016 at 13:46
  • $\begingroup$ @kingledion Spell checker do not shows something useful to me, feel free to edit grammar or mark sentences with italic - I can try to reword them for better understanding and grammar. Not much hope in success but we can give a shot for that idea. As for factual correctness I added note section. Based on your answer I see u talking about closed cycle reactors, I'm not big fan of them. Although I'm not against any type of reactors which do not blowup by themselves. Also for space implementations I'm even not against nukes as energy source, so basically I do favor anything that gives energy $\endgroup$
    – MolbOrg
    Commented Oct 11, 2016 at 20:04
  • $\begingroup$ I've done a fairly drastic grammar and spelling edit, feel free to roll back areas where I've incorrectly parsed something. A lot of it is still hard to understand, those are areas where I couldn't figure out what you meant and thus left it alone. This still needs a lot of work, but I hope this is an improvement. $\endgroup$
    – Gryphon
    Commented Nov 18, 2019 at 11:23
  • $\begingroup$ @Gryphon-ReinstateMonica thanks, appreciate it very much, looks better) $\endgroup$
    – MolbOrg
    Commented Nov 18, 2019 at 15:40

Just a practical way of harnessing its power.

Thorium power-plants need to go a long way it before being commercially interesting. Not because Thorium is expensive or hard to use, but because we don't really have a easy way to tap on its power — yet.

People are driven by necessities. If coal and oil (the "easy" power sources) are getting rarer and more expensive, people will turn to other, "harder to use" energy sources, like nuclear power, hydroelectric or wind-based.

However, as you use something, you learn its limitations. This provides a good base to future research, which in turn makes it easier to use as new, more efficient stuff is discovered about that something. It was the same with computers, with the Architecture change — people didn't swap to x64 right away because it was easier to keep using x86, even if x64 was way better. Nowadays, you only find x86 computers on some really outdated offices and on a few grandfather's houses. Heck, it's HARD to find x86 machines anymore!

So, yeah. It's mostly time. Once you find a way to make use of Thorium, just keep up researching and making it easier to use, and eventually people will embrace it.

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    $\begingroup$ Every x64 computer is an x86 computer. $\endgroup$
    – user6511
    Commented Oct 10, 2016 at 21:07
  • $\begingroup$ Note: see the edits I made to your post, for future reference. $\endgroup$
    – JDługosz
    Commented Oct 10, 2016 at 21:28
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    $\begingroup$ @user6511 not really, and the fact that most PCs can run both x86 and x64 code is not really relevant to this answer. I'm sure everyone gets what Thales meant. $\endgroup$
    – Mołot
    Commented Oct 10, 2016 at 21:47
  • $\begingroup$ Better tell that to the x86 operations that still exist in the x64 (as in all of them) $\endgroup$ Commented Oct 11, 2016 at 17:36
  • $\begingroup$ All x64 computers are x86 machines. The instructions are still there and they will work perfectly find with no x64 operations ever being processed. (that isn't to say all 64bit machines are x64 is a particular type of 64bit processor.) And it's not an emulation. $\endgroup$ Commented Oct 11, 2016 at 18:01

The requirements for developed theorium reactors are not that tough: easy access to thorium, limited access to uranium and other sources of power and no incentive to develop a nuclear arsenal (and this last point is perhaps not even true; there are some that claim that the uranium 233 that is the actual fuel in a thorium-based cycle is viable as bomb material).

Thorium is today seen as a less viable choice because it would need different reactor technology than what is used in most of the world to be most effective. However, this is not in itself a major problem. The Soviet union, Canada and the UK uses or has used reactor designs that significantly differ from the US-designed LWRs.

I will give you one possible scenario: Sweden had it's own program for building heavy water reactors, with uranium mined in Sweden (Sweden has a lot of uranium, but not very concentrated). Had the large thorium deposits found in Norway been on the other side of the border, it is possible it would have choosen designs based on thorium instead, and gotten so far before the non-proliferation treaty that it would have decided to not buy american LWR designs but instead continue with the domestic design. At the peak, Sweden's reactors produced slightly less than half of the electricity used, so that requirement is not much of a stretch.

  • $\begingroup$ Now if only we could get Sweden to be a major nation... $\endgroup$
    – SPavel
    Commented Oct 11, 2016 at 13:02
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    $\begingroup$ Energywise, it's fairly large; total electricity consumption is on par with that of Egypt. In terms of nuclear energy, Sweden had for a long time the highest production per capita. The number of nations where nuclear power is responsible for about half or more of the total production is extremely limited, the only one that is without a doubt a "major nation" is France. $\endgroup$
    – andejons
    Commented Oct 11, 2016 at 13:23
  • $\begingroup$ This (I'm not sure what everyone else's going on about; TL;DR y'all). Have thorium; run out of everything else; ignore the nonproliferation idiots; done. Also, France is awesome; they DGAF ;) $\endgroup$
    – Mazura
    Commented Oct 12, 2016 at 3:48

Thorium is not a practical nuclear fuel

Uranium contains 0.72% by mass of U-235, which is capable of sustaining a fission chain reaction, yet it does not produce high radiation by itself. So a block of Uranium can be refined to 3-4% U-235 by mass. At this point, it can sustain a fission chain reaction, and can be used for fuel.

The process by which uranium is enriched is by attaching Uranium atoms to Florine atoms to create Uranium Hexaflouride gas. This is then spun in a centrifuge; the heavier U-238 atoms are separated from the lighter U-235 atoms. Once enough of the U-238 is removed, the UH$_6$ gas is converted to UO$_2$ for use in reactors. The excess U-238 becomes depleted uranium. While the UH$_6$ gas is highly toxic, the radiation exposure of people and equipment from this process is negligible. Almost all reactors in the world (~90%) use this process to generate power.

The remaining 10% are Pressurized Heavy Water Reactors. These reactors do not use enriched Uranium, but rely on heavy water (D%_2$O). Heavy water does not absorb neutrons as readily as regular water; it thus reflects more neutrons back into uranium fuel as it moderates and allows natural Uranium to become fissile. The trade off for the reduced fuel cost of natural Uranium is the high costs of heavy water and reduced energy density of the fuel.

A Thorium reactor would work on a different principle altogether. It would 'breed' productive U-233 fuel from Th-232. The U-233 must then be removed from the thorium and concentrated to use as fuel for the reactor. Once a U-233 reactor is set up, Th-232 can be inserted into it to breed more U-233.

The problem with U-233 comes with separating it from the Thorium. This can be done chemically; since Th and U are different elememnts, they react with different chemicals making it easy to dissolve one but not the other. However, a byproduct of breeding U-233 is U-232, which is extremely radioactive, having an extended decay chain that releases multiple MeV gammas per atom that decays. That is the showstopper.

Remember, that enrichment of U-235 takes place from a material whose radiation level is barely above background. Instead, when trying to separate fissile material from Thorium, you are trying to remove fissile material from highly radioactive nuclear waste, and within the usable product is more highly radioactive nuclear waste. High energy gammas require the separation process be done in a sealed, shielded room; but they also will disrupt electronics in that room.

The damage to electronics is key; if electronics (i.e. robots) are damaged by gamma radiation, the entire process must be stopped and radiation levels allowed to drop until equipment can be replaced or repairs made. These work stoppages would make the Thorium fuel cycle uneconomic. The only alternative is to expose workers to high radiation levels to limit reliance on robots. Radiation exposure of that level is obviously not feasible in Western countries, as the liability to lawsuits of nuclear power companies would be prohibitive.

Fissile material cannot be economically refined from Thorium due to high radiation levels of the 'bred' Thorium and the mixture of highly radioactive U-232 into the U-233 fuel. An engineering solution to this may eventually be possible, but currently there is no way to use Thorium as a fuel without accepting high levels of radiation to workers.

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    $\begingroup$ Except that Thorium power plants are already a thing. There were a few working prototypes around the world, and India is about to put a few major Thorium power plants in use. Check this: en.wikipedia.org/wiki/… $\endgroup$
    – Mermaker
    Commented Oct 11, 2016 at 15:27
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    $\begingroup$ @ThalesPereira My primary reference is personal expertise. I already linked a paper talking about use of plutonium; here is an article that mentions a ratio of 880kg plutonium to 1100kg thorium for the Indian plants. Here is one talking about using low-enriched uranium. Thorium only reactors have not gotten off the drawing board; don't let Wikipedia fool you. $\endgroup$
    – kingledion
    Commented Oct 11, 2016 at 15:55
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    $\begingroup$ No one is saying that they would be thorium only. But thorium would be the primary fuel source once they are started. better still you could take all the nuclear trash sitting in cooling ponds around existing reactors and use it as fuel instead of an environmental disaster waiting to happen. $\endgroup$ Commented Oct 11, 2016 at 17:42
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    $\begingroup$ They've already been done in test reactors. And no thanks on the chat. I perfer the comments section of these sites. $\endgroup$ Commented Oct 11, 2016 at 17:46
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    $\begingroup$ from your plutonium link: The criticality starts by k∞ = ∼1.48 for both fuel compositions. A sharp decrease of the criticality has been observed in the first year as a consequence of rapid plutonium burnout. The criticality becomes quasi constant after the second year and remains above k∞ > 1.06 for ∼20 years. After the second year, the CANDU reactor begins to operate practically as a thorium burner. Cite END; Also I do not understand that wish to extract that U-233, let that radioactive pile burn, use ADS if neutron economy isn't so good, eventually they all break up and give energy $\endgroup$
    – MolbOrg
    Commented Oct 11, 2016 at 20:22

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