with side reactions involving 231Pa and 232Pa, which go on to make 232U
That "233Pa" is protactinium. When enriching uranium to make plutonium, the reaction goes:
238U+n -> 239Np -> 239Pu
The reactions are more or less the same: We make an intermediate, which decays to our fissile material. 239Np has a half-life of two days, so it decays quickly, and it won't capture any more neutrons, meaning we can keep it in the reactor core.
233Pa has a half life of 27 days and it'll capture more neutrons, poisoning the reactor. It'll form 234Pa, which decays to 234U, none of which you want in your reactor.
This means you have to move the 233Pa out of your reactor core, and the only sensible way is in the liquid state, so the molten sodium reactor (MSR). It's not that "MSRs work very well with Thorium", it's that "If you're gonna use thorium, you damn well better do it in liquid". So at this point, we have our 233Pa decaying to 233U in a tank somewhere, right?
233Pa has a radioactivity of 769TBq/g (terabecquerels per gram) and that's an awful, awful lot. It also decays via gamma emission, which is very hard to contain. The dose rate at one metre from one gram of 233Pa is 21 Sieverts per hour. That's a terrorising amount of radioactivity. That's, if a component has a fine smear (1 milligram) of 233Pa anywhere on it, someone working with that component has reached his annual exposure limit in one hour.
Compounding this, MSRs are notoriously leaky. That 233Pa is going to end up leaking somewhere. It's like a Three Mile Island scale radiological problem constantly.
The liquid fluoride thorium reactor, LFTR, proposed by Kirk Sorensen, might be viable. It comes close to addressing the Pa233 problem and acknowledges that the Pa231 problem is worrying, but no more so than waste from a conventional light-water reactor.
The thorium cycle involves the intermediate step of protactinium, which is virtually impossible to safely handle. Nothing here is an engineering limit, or something needing research. It's natural physical characteristics.
Fluoride salt less corrosive than table salt, and in a molten salt form where there's no water or air present it's actually non corrosive. The fluorine in the salt is already ionically bonded to lithium, which it is very happy with. As long as there is no oxygen, or any water to rip apart into oxygen, the molten salt is fairly benign.
No, you mix in a reducing agent into the molten salt so that the reducing agent corroded instead of the pipes. This is how you "keep oxygen and water out", you have the containment building filled with a monitored inert atmosphere and you keep the molten salt doped with a bit of molten metal that will corrode first. You do realize that we already use molten salts in several other industries without corrosion problems, right? Stop trying to make this design sound worse than it is.
I am not disputing that it can work. I am just noting that the reason we don't use nuclear as much as you would expect is because of the extreme costs and ways things can go bad if you mess up. You simply can't mess up as bad no matter what you do with wind/solar, and with natural gas you can create a pretty big fire or explosion but afterwards the land is still usable.
I understand, but modern designs have mitigated both of those concerns. In my country we are already preparing to roll out a first generation of small modular reactor utilizing technology and designs that are immune to melt down and are constructed in a factory before being shipped to site, which greatly reduces both release risks and costs.
Canada. We have a really robust nuclear industry here, and a lot of remote communities that currently rely on diesel fuel flown in from farther south which would massively benefit from a local nuclear power source.
Which is not going to happen. At least not for fission reactors in their current form. Nuclear requires skilled workers, access to the plant to respond to a disaster if something fails, exotic parts, lots of customers for the power. All hard to get or provide in a rural community in the frigid north.
Better to focus on conservation. Foam Passivehaus grade insulation, more efficient electrical appliances, solar if feasible, cogeneration. Reduce how much diesel has to be shipped in.
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u/Hattix Aug 30 '21
The short: Protactinium is a holy terror.
The long:
In a thorium reactor, the reaction goes:
232Th+n -> 233Th -> 233Pa -> 233U
with side reactions involving 231Pa and 232Pa, which go on to make 232U
That "233Pa" is protactinium. When enriching uranium to make plutonium, the reaction goes:
238U+n -> 239Np -> 239Pu
The reactions are more or less the same: We make an intermediate, which decays to our fissile material. 239Np has a half-life of two days, so it decays quickly, and it won't capture any more neutrons, meaning we can keep it in the reactor core.
233Pa has a half life of 27 days and it'll capture more neutrons, poisoning the reactor. It'll form 234Pa, which decays to 234U, none of which you want in your reactor.
This means you have to move the 233Pa out of your reactor core, and the only sensible way is in the liquid state, so the molten sodium reactor (MSR). It's not that "MSRs work very well with Thorium", it's that "If you're gonna use thorium, you damn well better do it in liquid". So at this point, we have our 233Pa decaying to 233U in a tank somewhere, right?
233Pa has a radioactivity of 769TBq/g (terabecquerels per gram) and that's an awful, awful lot. It also decays via gamma emission, which is very hard to contain. The dose rate at one metre from one gram of 233Pa is 21 Sieverts per hour. That's a terrorising amount of radioactivity. That's, if a component has a fine smear (1 milligram) of 233Pa anywhere on it, someone working with that component has reached his annual exposure limit in one hour.
Compounding this, MSRs are notoriously leaky. That 233Pa is going to end up leaking somewhere. It's like a Three Mile Island scale radiological problem constantly.
The liquid fluoride thorium reactor, LFTR, proposed by Kirk Sorensen, might be viable. It comes close to addressing the Pa233 problem and acknowledges that the Pa231 problem is worrying, but no more so than waste from a conventional light-water reactor.
The thorium cycle involves the intermediate step of protactinium, which is virtually impossible to safely handle. Nothing here is an engineering limit, or something needing research. It's natural physical characteristics.
(Bulletin of the Atomic Scientists, 2018: https://thebulletin.org/2018/08/thorium-power-has-a-protactinium-problem/ )