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Not exactly. Nuclear reactors have a difficult time following the load because of Xenon poisoning. Xenon generated during the fission reactions absorbs neutrons

by lven 4y ago

Not exactly. Nuclear reactors have a difficult time following the load because of Xenon poisoning. Xenon generated during the fission reactions absorbs neutrons that could have been used for fissions. Luckily, it decays away over time. If you turn down the reactor power, you have to wait hours or day for for Xenon buildup to decay so that you can turn the reactor back on. Some reactors manage to load follow more easily by adding lots of excess reactivity (more potent control rods) which is less safe overall. Smaller reactors will have the exact same issue. The amount of Xenon poisoning is proportional to the power density. NuScale reactors run at even higher power density than normal light water reactors, so they will have even worse Xenon poisoning. They won't be load following. One exception where this isn't true is micro gas-cooled reactors that have so low a power density that they have negligible xenon poisoning and can follow loads easily if necessary. Even then, it's not a great idea because of thermal cycling issues.

panick21_ 4y ago
Some reactors can also more effectively let xenon escape. That is one of the reasons why Alvin Weinberg wanted a liquid molten salt reactor, you can let the xenon bubble out like CO2 in a soft drink.
- pfdietz 4y ago
  And if you do that, then the 137Cs ends up in the off gas storage rather than in the molten salt. A good fraction of the fission products escape the salt, which kind of shoots down one of the main selling points of MSRs. https://gain.inl.gov/SiteAssets/MoltenSaltReactor/Module2-OverviewofMSRTechnologyandConceptsML17331B114.pdf https://gain.inl.gov/SiteAssets/MoltenSaltReactor/Module2-Ov... (see slide 23)
Manuel_D 4y ago
Nuclear can modulate it's output by more aggressively cooling the water. There's no xenon poisoning since the reactors output is the same. This is undesirable because it's essentially wasting fuel, by deliberately reducing the efficiency of the steam turbine. But it can be done, and fuel is not a big driver of nuclear cost.
- ncmncm 4y ago
  Modulating nukes' output make each kWh even more expensive, when they are already not competitive.
  - Manuel_D 4y ago
    Most of a nuclear plants' cost is in construction. It doesn't really affect operating costs. Furthermore nuclear is the most competitive decarbonized energy source, because wind and solar rely on fossil fuels.
    - ncmncm 4y ago
      During the ten years it takes to build a nuke, 100% of the power it is hoped to displace is supplied by fossil fuel. The thousands of tons of concrete are produced by cooking limestone with, again, fossil fuel. And the thousands of tons of steel are refined and smelted with, again, fossil fuel. Most of a nuke plants' cost is in construction, but that is not because its operating cost is low. It is just insanely expensive to build. Then, its operating cost is high. Each moment it is not producing at 100% rated power, its per-kWh cost increases accordingly. Its operating cost does not decrease proportionally when it operates at below rated maximum power, so the operating cost per kWh is multiplied by the difference. And, operating at below rated capacity, the construction cost is amortized over fewer kWh, again making the per kWh cost greater. You already well understood all of the above, but evidently hope readers will not.
      - Manuel_D 4y ago
        > During the ten years it takes to build a nuke, 100% of the power it is hoped to displace is supplied by fossil fuel. By comparison gas turbines will always emit carbon dioxide, and there's no realistic plan to run a solar and wind grid without fossil fuel backing. No, there is no realistic plan to store electricity despite your incessant insistence to the contrary. > The thousands of tons of concrete are produced by cooking limestone with, again, fossil fuel. And the thousands of tons of steel are refined and smelted with, again, fossil fuel. Both of these can be replaced with thermochemical processes powered by nuclear power. > Most of a nuke plants' cost is in construction, but that is not because its operating cost is low. It is just insanely expensive to build. Then, its operating cost is high. Incorrect, nuclear power is quite cheap once the plants are constructed.
projektfu 4y ago
I mean that loads can be shared geographically and the reactors can maintain relatively consistent output.
nobody9999 4y ago
I may be missing something important here, but I'm not a nuclear fission SME. Please do correct me if I'm not making sense. Doesn't the modularity (multiple 60MW reactors in a single installation) in the NuScale design obviate the "Xenon poisoning" issue, since shutting down one or more reactors doesn't mean halting power generation as it would with a single, larger reactor? Presumably the reactors can be shut down and powered up independently so addressing the "Xenon poisoning" issue should be just a matter shutting down, then powering up some fraction of the reactors, scheduled to maintain the base load required, no?

by lven 4y ago

panick21_ 4y ago

Some reactors can also more effectively let xenon escape. That is one of the reasons why Alvin Weinberg wanted a liquid molten salt reactor, you can let the xenon bubble out like CO2 in a soft drink.

pfdietz 4y ago
And if you do that, then the 137Cs ends up in the off gas storage rather than in the molten salt. A good fraction of the fission products escape the salt, which kind of shoots down one of the main selling points of MSRs. https://gain.inl.gov/SiteAssets/MoltenSaltReactor/Module2-OverviewofMSRTechnologyandConceptsML17331B114.pdf https://gain.inl.gov/SiteAssets/MoltenSaltReactor/Module2-Ov... (see slide 23)

Manuel_D 4y ago

Nuclear can modulate it's output by more aggressively cooling the water. There's no xenon poisoning since the reactors output is the same. This is undesirable because it's essentially wasting fuel, by deliberately reducing the efficiency of the steam turbine. But it can be done, and fuel is not a big driver of nuclear cost.

ncmncm 4y ago
Modulating nukes' output make each kWh even more expensive, when they are already not competitive.
- Manuel_D 4y ago
  Most of a nuclear plants' cost is in construction. It doesn't really affect operating costs. Furthermore nuclear is the most competitive decarbonized energy source, because wind and solar rely on fossil fuels.
  - ncmncm 4y ago
    During the ten years it takes to build a nuke, 100% of the power it is hoped to displace is supplied by fossil fuel. The thousands of tons of concrete are produced by cooking limestone with, again, fossil fuel. And the thousands of tons of steel are refined and smelted with, again, fossil fuel. Most of a nuke plants' cost is in construction, but that is not because its operating cost is low. It is just insanely expensive to build. Then, its operating cost is high. Each moment it is not producing at 100% rated power, its per-kWh cost increases accordingly. Its operating cost does not decrease proportionally when it operates at below rated maximum power, so the operating cost per kWh is multiplied by the difference. And, operating at below rated capacity, the construction cost is amortized over fewer kWh, again making the per kWh cost greater. You already well understood all of the above, but evidently hope readers will not.
    - Manuel_D 4y ago
      > During the ten years it takes to build a nuke, 100% of the power it is hoped to displace is supplied by fossil fuel. By comparison gas turbines will always emit carbon dioxide, and there's no realistic plan to run a solar and wind grid without fossil fuel backing. No, there is no realistic plan to store electricity despite your incessant insistence to the contrary. > The thousands of tons of concrete are produced by cooking limestone with, again, fossil fuel. And the thousands of tons of steel are refined and smelted with, again, fossil fuel. Both of these can be replaced with thermochemical processes powered by nuclear power. > Most of a nuke plants' cost is in construction, but that is not because its operating cost is low. It is just insanely expensive to build. Then, its operating cost is high. Incorrect, nuclear power is quite cheap once the plants are constructed.

projektfu 4y ago

I mean that loads can be shared geographically and the reactors can maintain relatively consistent output.

nobody9999 4y ago

I may be missing something important here, but I'm not a nuclear fission SME. Please do correct me if I'm not making sense. Doesn't the modularity (multiple 60MW reactors in a single installation) in the NuScale design obviate the "Xenon poisoning" issue, since shutting down one or more reactors doesn't mean halting power generation as it would with a single, larger reactor? Presumably the reactors can be shut down and powered up independently so addressing the "Xenon poisoning" issue should be just a matter shutting down, then powering up some fraction of the reactors, scheduled to maintain the base load required, no?