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All things being equal TRISO fuel should increase the waste volume. But a fast reactor will tremendously reduce both the waste volume (because it can burn U238)

All things being equal TRISO fuel should increase the waste volume. But a fast reactor will tremendously reduce both the waste volume (because it can burn U238) and its nastiness (it will have virtually no long half life actinides). As for steel. Steel is one of the cheapest materials, with an average price below $1000/ton. Nuclear reactors need to use special steels that are resistant to neutron embrittlement, and even those have a price less than $1000/ton. There are more expensive steels out there (for example those used for tools), but generally the price is less than $3000/ton. But let's say that an alloy of steel that resists both neutron embrittlement and temperatures of 750C is $10000/ton. Then a reactor such as Xe-100 which weighs 700 tons in total will be able to procure the steel at less than $7 million, or $28 million for a group of 4; a powerplant with 4 Xe-100 reactors is estimated to cost $2.4 billion, so this cost would be less than 1% of that. I'm sure there will be 1000 problems that Xe-100 will need to solve before they get their NRC approval and they will be able to economically build their first reactors, but the cost of steel will not be one of them.

pfdietz 4y ago
Does TRISO have higher burnup? Not convinced. Fast reactors that involve reprocessing will greatly increase waste volume due to generation of low level contaminated material in the reprocessing process. Once you let the stuff out of the fuel elements it can get all over things.
- credit_guy 4y ago
  Nothing to do with reprocessing. Fast neutron reactors just use fast neutrons, neutrons that are thousands of times faster than the neutrons used in the current generation of reactors (called thermal neutrons). A thermal neutron is much more likely to hit a nucleus of Uranium. If it hits U-235, it generally makes it undergo fission, but 18% of the time it is just absorbed and becomes the nasty U-236, which is a very long lived radioactive element. If it hits U-238, it's absorbed, eventually becomes Plutonium-239, which in turns may absorb further neutrons, so a bunch of transuranic elements are produced. That's bad on two counts. The transuranic elements are radioactive and tend to be very long lived so the nuclear waste is long lived. And whenever a nucleus just absorbs a neutron and does not undergo fission, it's a shame, it's energy that's not being produced. Fast neutrons solve both problems. They are about 1000 times less likely to hit a nucleus, but when they do they almost invariably trigger fission for U-235 and very often for U-238 as well. That results in a massively higher burnup, and massively lower amount of transuranic elements in the waste. So, not only will a fast reactor produce much less waste for each GWh of electricity, it will be a much nicer type of waste, one that decays to the background radiation level in a few hundreds of years, rather than millions of years. Again, there is no reprocessing. The TRISO particle are not broken or milled at the end. They become nuclear waste as they are, but after they gave a huge amount of energy.
  - pfdietz 4y ago
    TRISO fuels may have higher burnup, but they also have large dead volume in the fuel elements. The fissionable material is surrounded by barrier layers, and these encapsulated particles are embedded in a non-fuel matrix. The volume of spent pebbles will I think be considerably larger than the volume of spent fuel elements from a conventional reactor per unit of produced thermal energy.

pfdietz 4y ago

Does TRISO have higher burnup? Not convinced. Fast reactors that involve reprocessing will greatly increase waste volume due to generation of low level contaminated material in the reprocessing process. Once you let the stuff out of the fuel elements it can get all over things.

credit_guy 4y ago
Nothing to do with reprocessing. Fast neutron reactors just use fast neutrons, neutrons that are thousands of times faster than the neutrons used in the current generation of reactors (called thermal neutrons). A thermal neutron is much more likely to hit a nucleus of Uranium. If it hits U-235, it generally makes it undergo fission, but 18% of the time it is just absorbed and becomes the nasty U-236, which is a very long lived radioactive element. If it hits U-238, it's absorbed, eventually becomes Plutonium-239, which in turns may absorb further neutrons, so a bunch of transuranic elements are produced. That's bad on two counts. The transuranic elements are radioactive and tend to be very long lived so the nuclear waste is long lived. And whenever a nucleus just absorbs a neutron and does not undergo fission, it's a shame, it's energy that's not being produced. Fast neutrons solve both problems. They are about 1000 times less likely to hit a nucleus, but when they do they almost invariably trigger fission for U-235 and very often for U-238 as well. That results in a massively higher burnup, and massively lower amount of transuranic elements in the waste. So, not only will a fast reactor produce much less waste for each GWh of electricity, it will be a much nicer type of waste, one that decays to the background radiation level in a few hundreds of years, rather than millions of years. Again, there is no reprocessing. The TRISO particle are not broken or milled at the end. They become nuclear waste as they are, but after they gave a huge amount of energy.
- pfdietz 4y ago
  TRISO fuels may have higher burnup, but they also have large dead volume in the fuel elements. The fissionable material is surrounded by barrier layers, and these encapsulated particles are embedded in a non-fuel matrix. The volume of spent pebbles will I think be considerably larger than the volume of spent fuel elements from a conventional reactor per unit of produced thermal energy.