3 ms·

> Waste disposal is an imaginary problem. Ah, so the money a utility spends on its spent fuel is just imaginary? It's not actually being spent? And if more i

> Waste disposal is an imaginary problem. Ah, so the money a utility spends on its spent fuel is just imaginary? It's not actually being spent? And if more is spent (as TRISO fuel would require) that's all financial figments too? What one learns.

credit_guy 2y ago
Are we still talking about China here?
- pfdietz 2y ago
  The considerations I'm talking about are independent of location. Nor does what happened to weapons waste have any bearing on this issue.
  - credit_guy 2y ago
    What exactly is your point? China built 2 reactors that use TRISO fuel. Are you saying it was a bad decision? Good for you. Maybe you should write them a letter and explain to them why it was so, and what to do in the future.
    - pfdietz 2y ago
      I'm pointing out the downsides of TRISO fuel. There are considerable.
  - petre 2y ago
    Not really. China is a big country that's virtually empty above its diagonal. The Nederlands on the other hand is all built up. Imagine opening a nuclear storage facility there in contrast to in some Chinese desert. For China, storage of spent nuclear fuel is a non issue.
    - pfdietz 2y ago
      Yes really. China might or might not be more lax in how it treats spent fuel (due to putting said fuel out near Lanzhou at the southern end of the Gobi Desert), but the larger volume of TRISO fuel means the relative cost of dealing with it will be larger than their cost of dealing with spent LWR fuel. I will add that any graphite moderated reactor will have larger carbon-14 production than a LWR, due to neutron capture on carbon-13 (as well as (n,p) reactions on nitrogen-14 impurities in the graphite.) In the west this renders "spent" graphite into intermediate nuclear waste, even ignoring fission products in the fuel particles. It also means that one cannot just burn off the carbon and release the filtered CO2 in any process that reprocesses TRISO fuel. On the plus side, TRISO fuel doesn't have the same issue with zirconium availability that traditional LWR fuel has.
      - credit_guy 2y ago
        > but the larger volume of TRISO fuel means the relative cost of dealing with it will be larger than their cost of dealing with spent LWR fuel Yes. But the main cost of a reactor comes from the pressure vessel that the reactor is in. A LWR works at a pressure of about 160 bar (i.e. 160 times higher than the atmospheric pressure). The pressure inside a helium cooled reactor is about 50 bar. The cherry on the cake is that helium cooled reactors have much higher thermal efficiency (40% vs 30%). They can in principle even be used to produce hydrogen, in a much more efficient way than water electrolysis. In the US there is the Xe-100 design. But I doubt it will be commercial in less than 15 years. The Kairos design also uses TRISO pebbles, it's a molten salt design. That solves the pressure vessel problem even better. Still 15 years out probably.
        pfdietz 2y ago
        The pressure of a HTGR is lower, but because the temperature is higher, more expensive materials are needed. A LWR pressure vessel is within the creep limit of ordinary steel; HTGR outlet temperature is well above that limit (and I suspect in accident conditions the temperature goes even higher for passive dissipation of decay heat). This especially bites in applications proposing to use that high temperature industrially, such as in thermochemical water splitting. Also, I understand the passive safety of HTGRs is achieved by reducing the core thermal power density (and hence power density of decay heat). So for a given power, that core and pressure vessel will be much larger than in a LWR. If I'm reading a reference properly the ratio of power densities here is more than a factor of ten, which will more than balance the lower pressure and higher thermal efficiency. Material requirements for a pressure vessel scale as pressure x volume.

credit_guy 2y ago

Are we still talking about China here?

pfdietz 2y ago
The considerations I'm talking about are independent of location. Nor does what happened to weapons waste have any bearing on this issue.
- credit_guy 2y ago
  What exactly is your point? China built 2 reactors that use TRISO fuel. Are you saying it was a bad decision? Good for you. Maybe you should write them a letter and explain to them why it was so, and what to do in the future.
  - pfdietz 2y ago
    I'm pointing out the downsides of TRISO fuel. There are considerable.
- petre 2y ago
  Not really. China is a big country that's virtually empty above its diagonal. The Nederlands on the other hand is all built up. Imagine opening a nuclear storage facility there in contrast to in some Chinese desert. For China, storage of spent nuclear fuel is a non issue.
  - pfdietz 2y ago
    Yes really. China might or might not be more lax in how it treats spent fuel (due to putting said fuel out near Lanzhou at the southern end of the Gobi Desert), but the larger volume of TRISO fuel means the relative cost of dealing with it will be larger than their cost of dealing with spent LWR fuel. I will add that any graphite moderated reactor will have larger carbon-14 production than a LWR, due to neutron capture on carbon-13 (as well as (n,p) reactions on nitrogen-14 impurities in the graphite.) In the west this renders "spent" graphite into intermediate nuclear waste, even ignoring fission products in the fuel particles. It also means that one cannot just burn off the carbon and release the filtered CO2 in any process that reprocesses TRISO fuel. On the plus side, TRISO fuel doesn't have the same issue with zirconium availability that traditional LWR fuel has.
    - credit_guy 2y ago
      > but the larger volume of TRISO fuel means the relative cost of dealing with it will be larger than their cost of dealing with spent LWR fuel Yes. But the main cost of a reactor comes from the pressure vessel that the reactor is in. A LWR works at a pressure of about 160 bar (i.e. 160 times higher than the atmospheric pressure). The pressure inside a helium cooled reactor is about 50 bar. The cherry on the cake is that helium cooled reactors have much higher thermal efficiency (40% vs 30%). They can in principle even be used to produce hydrogen, in a much more efficient way than water electrolysis. In the US there is the Xe-100 design. But I doubt it will be commercial in less than 15 years. The Kairos design also uses TRISO pebbles, it's a molten salt design. That solves the pressure vessel problem even better. Still 15 years out probably.
      - pfdietz 2y ago
        The pressure of a HTGR is lower, but because the temperature is higher, more expensive materials are needed. A LWR pressure vessel is within the creep limit of ordinary steel; HTGR outlet temperature is well above that limit (and I suspect in accident conditions the temperature goes even higher for passive dissipation of decay heat). This especially bites in applications proposing to use that high temperature industrially, such as in thermochemical water splitting. Also, I understand the passive safety of HTGRs is achieved by reducing the core thermal power density (and hence power density of decay heat). So for a given power, that core and pressure vessel will be much larger than in a LWR. If I'm reading a reference properly the ratio of power densities here is more than a factor of ten, which will more than balance the lower pressure and higher thermal efficiency. Material requirements for a pressure vessel scale as pressure x volume.