Thorium power has a protactinium problem
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Countermeasures are to make sure there's some U-238 around to blend it down (but then it makes Plutonium and minor actinides), use faster neutrons (not as affected by the Pa), or install safeguards around the reactor.
I'm a huge proponent of nuclear reactors but I have yet to see a design that is truly proliferation-proof. All reactors require safeguards. It's still well worth getting that low-footprint 24/7 clean energy, which nukes alone can produce.
Thorium is great. It doesn't automatically solve all issues in nuclear. Here are the highlights of modern common Thorium Misconceptions: https://whatisnuclear.com/thorium-myths.html
'Just getting' some of these is the story of modern proliferation, the theft of the tech specs from Europe by AQ Khan, and his/Pakistan's subsequent proliferation to Iran, Libra and North Korea. Because without good centrifuges, the SWU (separation work) per electrical energy is very poor -- more than 100 times more energy.
[1] https://en.wikipedia.org/wiki/Separation_of_isotopes_by_lase...
I assume this statement is limited to nuclear power generation? You wouldn't extend that to, say, that one Iraqi research reactor?
One point, that is often ignored, about Uranium 232 is that it is super easy to find. Meaning its incredibly easy for the IAEA to say that something containing Uranium 232 was used anywhere or to validate that it did not leave the reactor site.
That said, a lesser known program after the Molten Salt Breeder Experiment at Oak Ridge National Laboratory was the Denatured Molten Salt Reactor, that was specifically designed to be more proliferation resistant (they hope proliferation resistant research would keep their program alive, and it did for a little bit).
This work actually lives on and the company furthers ahead in building a Molten Salt Reactor (Uranium) is the Canada based Terrestrial Energy. They are building the Integrated Molten Salt Reactor.
In both designs you avoid some of these problems you have if you do separation, but rather you just switch to a burner design and burn it all in one big reactor, no piping, no chemical plants and so on.
The problem is once you go to a burner, the primary reason why Thorium is an interesting fuel cycle (>2 neutron fission rate) is lost in a burner. That means the extra work to prove that Thorium is safe is just more work that you have to prove safe to the regulator. Pretty much all Molten Salt companies, even when they have met at a Thorium conference (as Terrestrial Energy did), switch to Uranium because of this issue.
For those interested, here are some of the presentations about the current companies working on Molten Salt Reactors:
- Stable Molten Salt Reactor (https://youtu.be/TvXcoSdXYlk?t=2m40s)
- Integrated Molten Salt Reactor (https://www.youtube.com/watch?v=OgTgV3Kq49U)
- Longer term Liquid fluoride thorium reactor (https://www.youtube.com/watch?v=R3lcIvS7cO0)
The primary problem with the metal is actually just qualifying that it is actually the case. The material they used in the original Molten Salt Experiment was great at resistance but re-qualifying this (or anything) to modern standards is incredibly difficult.
The 'Stable Salt Reactor' for Moltex actually have a solution where they use a slightly different salt that they can put some metal into and the chemistry works out that it will corrode that metal first and the piping is fine.
I however primary believe that for the last 40 years, regulatory approve and path to market were the primary issues. In the molten salt reactor experiment they solved many of these problems in relatively short time with a tiny team of people.
Because of regulations you basically can not develop a test reactor, and all of the nuclear companies basically design directly to production because it would be way to expensive to build a test reactor. Building a tiny research reactor would be an option, but those are limited to sizes that are to small to actually validate your design.
Care to elaborate? Looks like a very interesting problem.
The material they developed for the MSR was called Hastelloy N and showed a lot of promise.
Sadly, because its primary benefit was working with salts, it was not further developed and the use it saw does not qualify it for use in a modern nuclear reactor.
Therefore you have to do a complete re-qualification of the material under advanced neutron flux. Nuclear regulations are so incredibly strict that doing that alone would probably blow most development timelines.
[1] https://en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment...
So not just regulations are at issue. We'd need a 2nd test reactor to really iron out the kinks and fully vet the whole process in real life, and then we can start getting approval for commercial plants. As I've said elsewhere, thorium reactors are very exciting and we should be funding experiments on them. But we are still at the 'funding experiments' phase of this endeavor, and so even at peak funding we're still a ways out from viable thorium grid power.
The way the regulation works at the moment makes building a test reactor basically impossible for a company to do that's why pretty much every single nuclear company produces directly to a production model.
Thorium breeding was proven, but not in the MSR. So that does not necessarily need validation.
The 2-fluid reactor design would need a test reactor, but there are other reactor designs, like the IMSR that really would not need much further research.
However, if you don't go to a fuel breeder with online refueling thorium does not buy you much. Uranium is fine and does everything you want and that's why most MSR companies use Uranium.
Molten sodium is used in the coolant loop of some fast reactors, but it doesn't develop any long-lived radioactive byproducts, so it (and the various parts and fittings that it inevitably corrodes) can be disposed of relatively easily. They don't really have solutions to keep it contained, it eventually eats through everything. You just have to keep it from contacting water and exploding.
Re-qualifying that material would be tricky and costly, but there are companies doing it.
For the MSR style modern 2 fluid reactor your main problem is the chemical plant that needs to live in the reactor itself.
Secondly Thorium has absolutely no regularly support, and given the way nuclear regulation works its basically impossible to get a new fuel and type of reactor to market.
There is Thorium fuel for LWR coming to the market very slowly, but the advantages of that are very limited.
- hot corrosive sodium
- heat exchanged with water for steam turbine
- water+sodium = boom
was always going to be problematic.
The world does not need an excuse to stop research into nuclear power for another fifty years.