5 ms·

The notable thing here is that it's a molten salt reactor design, where the fuel is dissolved in a molten salt (FLiBe). This allows online continuous processing

The notable thing here is that it's a molten salt reactor design, where the fuel is dissolved in a molten salt (FLiBe). This allows online continuous processing of the fuel, unlike with solid fuel rods sealed inside a pressure vessel. This unlocks a lot of options for the fuel cycle, including the use of thorium. This work builds on a previous molten salt reactor experiment at Oak Ridge, decades ago. There's a whole lore about MSRs.

JumpCrisscross 11mo ago
> notable thing here is that it's a molten salt reactor design Notable, but not unique. The unique bit is it burns thorium.
- AtlasBarfed 11mo ago
  It breeds thorium to fissionable uranium from a starting fissionable uranium starter fuel. It doesn't directly use thorium for fuel. What people need to understand about the cycle efficiency is that when you mine uranium, the fissionable part of uranium (U-235) is only 1% of that uranium, the rest is nonfissionable U-238. Thorium is about twice as abundant as Uranium (all isotopes). The MSR uses Thorium to create U-233, a fissionable but not naturally occurring Uranium isotope. So the "unlimited energy aspect" is that about 200-300x more breedable Thorium exists than fissionable U-235. A MSR nation could also try to breed U-238 into plutonium, which would provide another 100x more breeding stock, although LFTR never talked about U-238 breeding. IIRC the plutonium may be difficult to handle because of gamma rays, but I don't recall exactly. While I don't have confidence that even LFTR/MSR reactors can get economical enough to challenge gas peakers, it may be possible to make truly price-competitive MSR electricity with the right modular design. I wish the Chinese the best of luck, because if they do it will spur the rest of the world to adopt this about-as-clean-and-safe-as-it-gets nuclear design.
  - rhoads 11mo ago
    That's what you learn playing factorio
  - JumpCrisscross 11mo ago
    > Thorium is about twice as abundant as Uranium China has thorium, and while less than others [1], it’s better than they do with uranium [2]. > it may be possible to make truly price-competitive MSR electricity with the right modular design Yes. But probably not in the near term with thorium. This isn’t designed to be cheaper. It’s designed to be more available to China than being dependent on Russian deposits. [1] https://www.nature.com/articles/492031a https://www.nature.com/articles/492031a [2] https://www-pub.iaea.org/MTCD/Publications/PDF/Pub1800.pdf https://www-pub.iaea.org/MTCD/Publications/PDF/Pub1800.pdf
    - mikhailfranco 11mo ago
      Geoneutrino surveys show the Tibetan plateau and western China are full of uranium and thorium: https://en.wikipedia.org/wiki/Geoneutrino https://en.wikipedia.org/wiki/Geoneutrino Economic recoverable reserves are another matter, but there's plenty there.
  - cryptonector 11mo ago
    Eh, U-235 is .7%, not 1%, but also U-238 can be bred into Plutonium. What makes Thorium interesting -besides its abundance- is that U-233 is very difficult to work with, so proliferation concerns are mitigated.
- fmajid 11mo ago
  Not really, the US bred several tons of U-233 from thorium in the 60s. https://en.wikipedia.org/wiki/Thorium-based_nuclear_power https://en.wikipedia.org/wiki/Thorium-based_nuclear_power
bilsbie 11mo ago
What absorbs the neutrons then?
- lazide 11mo ago
  The thorium cycle is generally neutron negative.
  - JumpCrisscross 11mo ago
    > thorium cycle is generally neutron negative Source for the fuel cycle? Thorium 232 -> 233 is neutron negative. But after that you get all kinds of nonsense.
    - lazide 11mo ago
      Thorium 232 is the thorium in the cycle yes. And all kinds of nonsense is correct for the daughter products. But in general, to actually use do anything with thorium you need excess neutrons. Even the daughter uranium 233 only produces on average 2.48 neutrons per fission, so it’s very difficult even in a combined lifecycle process to have enough - thorium doesn’t produce uranium 233 immediately (takes almost 30 days), neutron capture with that low a ratio requires a LOT of thorium, which is going to mostly just suck up all neutrons and you won’t have any extra for addition uranium 233 fissions, etc. It’s quite difficult (impossible?)to have actually work without a source of a large amount of additional neutrons.
      - JumpCrisscross 11mo ago
        > to actually use do anything with thorium you need excess neutrons Unless 100% of those neutrons is being absorbed by the thorium, this means you'll have neutron flux at the boundary. Which, for a liquid moderator, means all the pipes and tanks and pumps.
        lazide 11mo ago
        It’s almost like there is a reason why it’s not commonly used despite all the hype.
pfdietz 11mo ago
MSRs have some attractive features, but they also have significant drawbacks. The most pressing is that fissionable material is spread throughout the fluid, so fission and decay of fission products is occurring right up to the edge of the fluid. The walls and pipes containing the molten salt, and anything dipped into the salt, are exposed to unmoderated neutrons. One can shield using (say) graphite, but then damage to that (and soaking up of radioactive materials) become issues. The Molten Salt Reactor Experiment at Oak Ridge was near the end of its radiation exposure lifetime when the program ended. Contrast this to light water reactors. These are designed so that no lifetime component sees unmoderated neutrons. There's a thick barrier of water between the fissioning fuel and the reactor vessel wall and the support structures for the fuel bundles. The bundles themselves are exposed, but they are replaced for refueling and are not lifetime components.
- cyberax 11mo ago
  To add to this, even with the shielding provided by water in light water reactors, the neutron exposure is _the_ limiting factor for the reactor vessel. The metric to look for is called "DPA" (displacements per atom), the number of neutron collisions that a material can tolerate before losing enough structural integrity to fall below the acceptable limits. The best modern reactor steels are at 150-180 DPA. And a lot of potentially cool reactors like TWR (travelling wave reactor) end up being logistically impossible because lifetime-limited components will be exposed to multiple hundreds of DPAs.
  - jabl 11mo ago
    Many old LWR's have had their reactor vessels heat treated during a maintenance break to undo some of that neutron radiation damage and extend the life of the reactor. Not sure whether it would be possible to do something similar to a liquid fueled reactor, including all the hot pipework. Maybe, but yet another cost. Notably some of the recent MSR projects propose replacing the entire reactor every now and then (Terrestrial or whatever they were called, not sure if they are still around).
    - 11mo ago

JumpCrisscross 11mo ago

> notable thing here is that it's a molten salt reactor design Notable, but not unique. The unique bit is it burns thorium.

AtlasBarfed 11mo ago
It breeds thorium to fissionable uranium from a starting fissionable uranium starter fuel. It doesn't directly use thorium for fuel. What people need to understand about the cycle efficiency is that when you mine uranium, the fissionable part of uranium (U-235) is only 1% of that uranium, the rest is nonfissionable U-238. Thorium is about twice as abundant as Uranium (all isotopes). The MSR uses Thorium to create U-233, a fissionable but not naturally occurring Uranium isotope. So the "unlimited energy aspect" is that about 200-300x more breedable Thorium exists than fissionable U-235. A MSR nation could also try to breed U-238 into plutonium, which would provide another 100x more breeding stock, although LFTR never talked about U-238 breeding. IIRC the plutonium may be difficult to handle because of gamma rays, but I don't recall exactly. While I don't have confidence that even LFTR/MSR reactors can get economical enough to challenge gas peakers, it may be possible to make truly price-competitive MSR electricity with the right modular design. I wish the Chinese the best of luck, because if they do it will spur the rest of the world to adopt this about-as-clean-and-safe-as-it-gets nuclear design.
- rhoads 11mo ago
  That's what you learn playing factorio
- JumpCrisscross 11mo ago
  > Thorium is about twice as abundant as Uranium China has thorium, and while less than others [1], it’s better than they do with uranium [2]. > it may be possible to make truly price-competitive MSR electricity with the right modular design Yes. But probably not in the near term with thorium. This isn’t designed to be cheaper. It’s designed to be more available to China than being dependent on Russian deposits. [1] https://www.nature.com/articles/492031a https://www.nature.com/articles/492031a [2] https://www-pub.iaea.org/MTCD/Publications/PDF/Pub1800.pdf https://www-pub.iaea.org/MTCD/Publications/PDF/Pub1800.pdf
  - mikhailfranco 11mo ago
    Geoneutrino surveys show the Tibetan plateau and western China are full of uranium and thorium: https://en.wikipedia.org/wiki/Geoneutrino https://en.wikipedia.org/wiki/Geoneutrino Economic recoverable reserves are another matter, but there's plenty there.
- cryptonector 11mo ago
  Eh, U-235 is .7%, not 1%, but also U-238 can be bred into Plutonium. What makes Thorium interesting -besides its abundance- is that U-233 is very difficult to work with, so proliferation concerns are mitigated.
fmajid 11mo ago
Not really, the US bred several tons of U-233 from thorium in the 60s. https://en.wikipedia.org/wiki/Thorium-based_nuclear_power https://en.wikipedia.org/wiki/Thorium-based_nuclear_power

bilsbie 11mo ago

What absorbs the neutrons then?

lazide 11mo ago
The thorium cycle is generally neutron negative.
- JumpCrisscross 11mo ago
  > thorium cycle is generally neutron negative Source for the fuel cycle? Thorium 232 -> 233 is neutron negative. But after that you get all kinds of nonsense.
  - lazide 11mo ago
    Thorium 232 is the thorium in the cycle yes. And all kinds of nonsense is correct for the daughter products. But in general, to actually use do anything with thorium you need excess neutrons. Even the daughter uranium 233 only produces on average 2.48 neutrons per fission, so it’s very difficult even in a combined lifecycle process to have enough - thorium doesn’t produce uranium 233 immediately (takes almost 30 days), neutron capture with that low a ratio requires a LOT of thorium, which is going to mostly just suck up all neutrons and you won’t have any extra for addition uranium 233 fissions, etc. It’s quite difficult (impossible?)to have actually work without a source of a large amount of additional neutrons.
    - JumpCrisscross 11mo ago
      > to actually use do anything with thorium you need excess neutrons Unless 100% of those neutrons is being absorbed by the thorium, this means you'll have neutron flux at the boundary. Which, for a liquid moderator, means all the pipes and tanks and pumps.
      - lazide 11mo ago
        It’s almost like there is a reason why it’s not commonly used despite all the hype.

pfdietz 11mo ago

MSRs have some attractive features, but they also have significant drawbacks. The most pressing is that fissionable material is spread throughout the fluid, so fission and decay of fission products is occurring right up to the edge of the fluid. The walls and pipes containing the molten salt, and anything dipped into the salt, are exposed to unmoderated neutrons. One can shield using (say) graphite, but then damage to that (and soaking up of radioactive materials) become issues. The Molten Salt Reactor Experiment at Oak Ridge was near the end of its radiation exposure lifetime when the program ended. Contrast this to light water reactors. These are designed so that no lifetime component sees unmoderated neutrons. There's a thick barrier of water between the fissioning fuel and the reactor vessel wall and the support structures for the fuel bundles. The bundles themselves are exposed, but they are replaced for refueling and are not lifetime components.

cyberax 11mo ago
To add to this, even with the shielding provided by water in light water reactors, the neutron exposure is _the_ limiting factor for the reactor vessel. The metric to look for is called "DPA" (displacements per atom), the number of neutron collisions that a material can tolerate before losing enough structural integrity to fall below the acceptable limits. The best modern reactor steels are at 150-180 DPA. And a lot of potentially cool reactors like TWR (travelling wave reactor) end up being logistically impossible because lifetime-limited components will be exposed to multiple hundreds of DPAs.
- jabl 11mo ago
  Many old LWR's have had their reactor vessels heat treated during a maintenance break to undo some of that neutron radiation damage and extend the life of the reactor. Not sure whether it would be possible to do something similar to a liquid fueled reactor, including all the hot pipework. Maybe, but yet another cost. Notably some of the recent MSR projects propose replacing the entire reactor every now and then (Terrestrial or whatever they were called, not sure if they are still around).
  - 11mo ago