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Comment by brrt | Hacker News Reader

Have you heard about xenon poisoning? Load following with a nuclear power plant is much more complex than it seems

The LWR is a difficult case for xenon poisoning (compared to other reactors) because of the thermal spectrum and the lack of homogenization (it's not just a temporal problem but a spatial problem) but if you add reactivity swing it can be managed. It's a problem for going from 0-100% quickly but not a problem for following loads across the day, see

https://www.oecd-nea.org/upload/docs/application/pdf/2021-12...

This already makes a large assumption about the type of reactor you are using. For example, a liquid fluoride thorium reactor (LFTR) does not suffer from the xenon poisoning issue, as do many other designs.

I don’t believe there are any commercial LFTR plants?

It's an interesting thing that pro-nuclear people always talk about "Gen X" power plats with no issues and just a big fat gogo stamp on them, but when you ask about any commercial examples they all come up short.

I'm pro nuclear, but I don't think using hypotheticals and futures is how to convince people nuclear is good, it's good because it works and it doesn't poison the planet (Yes there have been accidents and they have been dramatised but count deaths and it becomes as irrational as being afraid of flying)

It takes decades to turn on a new plant which is why you won't see the latest and greatest commercially deployed anytime soon.

Molten Salt reactors are designs from the 60s-70s and afaik no one ever built on commercially. No one was willing to take a gamble on building a new design when we had working reactors already and approval for those was already difficult enough.

AFAIU the corrosion problems are still not solved from a commercial PoV. Ie, without having to shut down and replace piping too often for it too be viable.

I had not, but TIL about xenon poisoning and that it was a major contributing factor in the Chernobyl accident (the tl;dr is they did a test where they reduced the fission rate; there was a buildup of Xenon 135 because of that, which caused the reaction to not start back up as fast as the operators thought it should. They removed the control rods almost completely, and when the Xenon stopped doing its thing they had a runaway reaction on their hands.

The xenon poisoning is why they took the control rods all the way out, but the runaway reaction was probably caused by the graphite tips on the ends of the control rods. As the control rods were scrammed these tips passed through areas of high neuton flux and caused a spike in power which probably caused the explosion.

There were a lot more factors at play in the chain, but the burnoff of the xenon wasn't itself the proximal cause of the explosion.

Complex or not, it's doable as the nuclear power plants in France are doing. Germany used to do it as well, until they shut down all their nuclear plants.

Though due to the xenon poisoning, they apparently use the reactors which at the moment have the freshest fuel for the load following, as they have more excess reactivity available to overpower the xenon. They can ramp at something around 5% of rated capacity per minute between around 30-100% of full power.

Most other countries with nuclear power plants have a much lower share of nuclear in their grids, so they haven't needed to do it, as due to the economics of nuclear it makes the best sense to run flat out as much as possible in order to recoup capital costs.

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