5 ms·

Is that the right metric? You wouldn't need to build a huge containment structure around it like you would for a PWR, so I'd imagine the power density of the pl

Is that the right metric? You wouldn't need to build a huge containment structure around it like you would for a PWR, so I'd imagine the power density of the plant as a whole wouldn't be anywhere near 40x worse. Why focus just on the primary reactor vessel?

pfdietz 5y ago
Because the rest of the power plant will be similar (or also worse for fusion; consider the tritium handling facility or the robotic equipment for maintaining the fusion reactor). You would need a confinement structure, just to keep the tritium in (which will leak all over even in normal operation). So if you swap out a cheap PWR reactor for a much larger, and hence much more expensive, fusion reactor, you get a power plant that costs more than a fission power plant. Viewed another way: if you could make a fission reactor with a power density as low as ARC, it would have so much thermal inertia that meltdowns would be essentially impossible. You should then ask why such fission reactors are not built.
- apendleton 5y ago
  I guess I still just don't really see it... like, coal plants are also much less energy-dense than nuclear fission. So is solar, so is wind. We build all of those anyway. There are lots of things other than power density that contribute to whether or not a particular generation technology is economical. As to why massive fission reactors aren't built: there are plenty of already-available passively-safe/meltdown-proof fission designs (many gen-IV designs qualify), and from what I can tell, the reasons they're not built are as much political as anything -- people don't like them, and the consequent regulatory regime has made any fission projects prohibitively expensive regardless of their size. None of this need be the case with fusion. As to tritium: I think you're overstating the tritium risk. They're only dealing with grams at a time, and even if it all leaked out, it would rapidly diffuse such that risk to the public would be infinitesimal as compared to normal background radiation (plus its half-life is only something like 12 years). ITER has a safety page: https://www.iter.org/mach/safety https://www.iter.org/mach/safety that essentially says as much.
  - pfdietz 5y ago
    Power (not energy) density matters in comparison of fission and fusion because the rest of the power plant is very similar. It's not relevant to the comparison of PV solar and fusion because this is not true. But we don't need to make that comparison, since we CAN compare those directly with fission by looking at actual costs, and then conclude they should be cheaper than fusion (because that will be more expensive than fission). Tritium will be handled in such large quantities in a fusion reactor that even small leaks will be problematic. As I like to point out, the tritium made and burned in a 1 GW(e) DT fusion reactor in one year would contaminate 2 months of the entire flow of the Mississippi River above legal limits for drinking. Even small leaks could cause serious harm to property values (sorry, your ground water can't be drunk for the next 50 years.) Gen-IV reactors aren't built not for political reasons, but because nuclear has become such an economic orphan that there aren't stakeholders to drive the construction of these things. The money isn't there because the ROI isn't there.

pfdietz 5y ago

Because the rest of the power plant will be similar (or also worse for fusion; consider the tritium handling facility or the robotic equipment for maintaining the fusion reactor). You would need a confinement structure, just to keep the tritium in (which will leak all over even in normal operation). So if you swap out a cheap PWR reactor for a much larger, and hence much more expensive, fusion reactor, you get a power plant that costs more than a fission power plant. Viewed another way: if you could make a fission reactor with a power density as low as ARC, it would have so much thermal inertia that meltdowns would be essentially impossible. You should then ask why such fission reactors are not built.

apendleton 5y ago
I guess I still just don't really see it... like, coal plants are also much less energy-dense than nuclear fission. So is solar, so is wind. We build all of those anyway. There are lots of things other than power density that contribute to whether or not a particular generation technology is economical. As to why massive fission reactors aren't built: there are plenty of already-available passively-safe/meltdown-proof fission designs (many gen-IV designs qualify), and from what I can tell, the reasons they're not built are as much political as anything -- people don't like them, and the consequent regulatory regime has made any fission projects prohibitively expensive regardless of their size. None of this need be the case with fusion. As to tritium: I think you're overstating the tritium risk. They're only dealing with grams at a time, and even if it all leaked out, it would rapidly diffuse such that risk to the public would be infinitesimal as compared to normal background radiation (plus its half-life is only something like 12 years). ITER has a safety page: https://www.iter.org/mach/safety https://www.iter.org/mach/safety that essentially says as much.
- pfdietz 5y ago
  Power (not energy) density matters in comparison of fission and fusion because the rest of the power plant is very similar. It's not relevant to the comparison of PV solar and fusion because this is not true. But we don't need to make that comparison, since we CAN compare those directly with fission by looking at actual costs, and then conclude they should be cheaper than fusion (because that will be more expensive than fission). Tritium will be handled in such large quantities in a fusion reactor that even small leaks will be problematic. As I like to point out, the tritium made and burned in a 1 GW(e) DT fusion reactor in one year would contaminate 2 months of the entire flow of the Mississippi River above legal limits for drinking. Even small leaks could cause serious harm to property values (sorry, your ground water can't be drunk for the next 50 years.) Gen-IV reactors aren't built not for political reasons, but because nuclear has become such an economic orphan that there aren't stakeholders to drive the construction of these things. The money isn't there because the ROI isn't there.