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I like the sodium fast reactor: low pressure, moderate temperature, sodium is dirt cheap, high burn-up of non-uranium/plutonium products ("waste"), and plutoniu
by Daniel_Newby 17y ago
I like the sodium fast reactor: low pressure, moderate temperature, sodium is dirt cheap, high burn-up of non-uranium/plutonium products ("waste"), and plutonium need never be separated from other reaction products.
The article doesn't say, but because molten salt reactors use liquid fuel, they release the radioactive xenon gas produced by uranium fission. (In fact this is sold as a benefit, since xenon absorbs neutrons better used for the chain reaction.) Xenon is a noble gas and therefore volatile, so the reactor will need strenuous containment measures. Loss of the gas seal would result in significant radioactivity release.
Helium-cooled reactors may be constrained by shortages of helium, which is rather rare and difficult to extract on Earth. You'd hope that government program managers would have worked out the logistics of this, but they tend to not see things that would get their funding cut. (Argon is plentiful but might not be a substitute because it reacts with neutrons a lot more than helium does.)
- sp332 17y ago> Xenon is a noble gas and therefore volatile This must be some definition of "volatile" I'm not familiar with.
- Daniel_Newby 17y agoEvaporating easily. Xenon boils at -108 deg. C. Given the chance, it would tend to rapidly escape from liquid fuel at reactor temperatures.
- elblanco 17y agoWe're probably both thinking of "prone to explode" vs. "prone to evaporate".
- elblanco 17y agoWell, if had said "nonvolatile" it would have been boring.
- sketerpot 17y agoIn the case of liquid fluoride thorium reactors, I don't think the xenon-135 is what you need to be worrying about; worry about the fluorine gas instead! It's very reactive. Xenon, on the other hand, is chemically stable because it's a noble gas. And it's larger than helium, so it's easier to contain. Also, I'd like to point out that pebble-bed reactors, while usually cooled with helium, could also be cooled with nitrogen that we just pull out of the air. It's more reactive than helium and it forms carbon-14 when you expose it to neutron flux, but those issues are both fairly minor. I think they're going with helium now because they want to get something working as quickly as they can, and they don't want to go mucking with what works.
- Daniel_Newby 17y agoThey use the relatively-nonvolatile fluoride ion (F-), not the gaseous molecular fluorine (F2). Fluoride is corrosive in higher concentrations, but nowhere near as dangerous as the oxidative toxicity of fluorine gas. Re. nitrogen, the radiation would turn it into ionized nitrogen radicals. Any info on how much damage that would cause to the graphite and metals? Also, carbon-14 is preferentially concentrated into living things, so a release would provoke a political panic similar to strontium-90.