Application submitted for US molten salt research reactor • Hacker News Board

Re: Application submitted for US molten salt research reactor

#71

Post by pfdietz » Mon, Aug 22, 2022, 8:34 PM UTC

dangerlibrary wrote: post #12

So, in a conventional reactor, you use nuclear fission to heat/pressurize water and then use your hot, slightly radioactive steam turn a turbine. This mostly works because moving even very hot, very high pressure water around is kind of a solved problem in industry. In a molten salt reactor, you use nuclear fission to melt various corrosive salts into a fluid, and this is good because molten salts store a lot more en…

There are a number of obstacles. Neutron damage to the reactor structure is more of a problem, since the fuel is dissolved in salt in direct contact with that structure (unlike a reactor with solid fuel rods, which are separated from the reactor vessel by a thickness of moderator, in the case of LWRs is water.)

See here for a (somewhat old) list of some technical issues:

https://gain.inl.gov/SiteAssets/MoltenSaltReactor/Module2-Ov...

"Nickel-based alloys embrittle under high neutron fluxes at high temperature"

"Over 40% of [fission products] leave core [in offgas]"

"Large fraction of cesium, strontium, and iodine end up in offgas"

"MSRE was approaching end of allowable service life when shut down" (after four years at 40% capacity factor)

Re: Application submitted for US molten salt research reactor

#72

Post by throwaway894345 » Mon, Aug 22, 2022, 8:37 PM UTC

PaulHoule wrote: post #9

marcosdumay wrote: post #2

A 1MW research reactor. Anyway, why is it always a fluoride salt? Is it because of the melting point or because of some nuclear property? I imagine there is some very relevant reason, because a less reactive anion (even chlorine) would be much easier to work with.

Fluoride salts are good for fissile uranium + fertile thorium. If you want to work with a plutonium/uranium 238 cycle then chloride salts are a better choice. Plutonium doesn't dissolve very well in fluorides. Molten chloride reactors can have performance characteristics right out of science fiction, it seems possible for such a reactor to not only breed more fuel but to destroy the long-lived (500 year) fission prod…

> We can produce heat for hydrogen, replacing the need for fossil fuels in heating, transport and industry.

What does it mean to produce "heat for hydrogen"? Why is heating hydrogen a useful property (how does hot hydrogen replace fossil fuels in heating, transport, and industry?)? That seems oddly specific, so I assume I'm misreading something?

Re: Application submitted for US molten salt research reactor

#73

Post by el_nahual » Mon, Aug 22, 2022, 8:38 PM UTC

throwaway894345 wrote: post #43

phire wrote: post #33

Earlier quoted context omitted.

I believe they use active cooling to keep the plug frozen. If the power fails, the cooling fails and the plug melts.

Yeah, I got that (and it seems like a really elegant solution! very cool , pun intended, etc). My question was about how salt (or any other matter, really) can simultaneously be molten and frozen.

Part of it is molten (above the plug), part of it is frozen (the plug).

Think pipes in a house in winter, where one little part of the pipe gets frozen while the rest of the pipes have liquid water in them.

Re: Application submitted for US molten salt research reactor

#74

Post by [deleted] » Mon, Aug 22, 2022, 8:38 PM UTC

politician wrote: post #27

ortusdux wrote: post #18

Earlier quoted context omitted.

Annoyingly, "molten salt reactor" is used to describe two different technologies. What you describe is a traditional reactor that uses molten salt to move heat. This typically leads to higher efficiencies, but does have corrosion issues. Other power generation systems can also benefit from molten salt loops - namely solar energy collectors. In the research field, "molten salt reactors" (MSRs) usually means the other…

One of those safety improvements -- a freeze plug -- passively halts the reaction in the event of a power cut. The reactor sits on top of a vault that has a larger volume separated by a narrow tube containing molten salt that has been frozen into a plug by cryocoolers powered by the turbines themselves. If the pumps stop for any reason, then the plug quickly melts and the molten fluid from the reactor drains into the…

[deleted]

Re: Application submitted for US molten salt research reactor

#75

Post by jacquesm » Mon, Aug 22, 2022, 8:42 PM UTC

ortusdux wrote: post #18

dangerlibrary wrote: post #12

So, in a conventional reactor, you use nuclear fission to heat/pressurize water and then use your hot, slightly radioactive steam turn a turbine. This mostly works because moving even very hot, very high pressure water around is kind of a solved problem in industry. In a molten salt reactor, you use nuclear fission to melt various corrosive salts into a fluid, and this is good because molten salts store a lot more en…

Annoyingly, "molten salt reactor" is used to describe two different technologies. What you describe is a traditional reactor that uses molten salt to move heat. This typically leads to higher efficiencies, but does have corrosion issues. Other power generation systems can also benefit from molten salt loops - namely solar energy collectors. In the research field, "molten salt reactors" (MSRs) usually means the other…

There have been quite a few solar energy concentrator test beds based on molten salt in order to try to get to 24/7 solar power. It is an interesting technology but afaik it's not at the stage where it can be rolled out reliably and maintenance free.

Re: Application submitted for US molten salt research reactor

#76

Post by pfdietz » Mon, Aug 22, 2022, 8:42 PM UTC

marcosdumay wrote: post #2

A 1MW research reactor. Anyway, why is it always a fluoride salt? Is it because of the melting point or because of some nuclear property? I imagine there is some very relevant reason, because a less reactive anion (even chlorine) would be much easier to work with.

Because fluorine has a low neutron capture cross section.

Chlorine has a rather high capture cross section for thermal neutrons, so it could only be used in fast reactors.

Re: Application submitted for US molten salt research reactor

#77

Post by throwaway894345 » Mon, Aug 22, 2022, 8:52 PM UTC

powerhour wrote: post #57

2OEH8eoCRo0 wrote: post #48

Earlier quoted context omitted.

They are up against big fossil fuel tycoons like the Kochs. If we are strictly talking corporate propaganda, the fossil fuel industry has plenty of that.

It seems to me that companies like GE and Westinghouse have tons of money. Add that to the billions pro-nuclear folks have in SV and you've got quite the war chest to fund effective pro-nuke campaigns.

Those folks might not want to waste that money in a propaganda race against the entire fossil fuel industry and the emerging renewable energy industry. GE and Westinghouse are large and successful companies, but is nuclear a major part of their portfolio such that they would take such a big risk (compared to fossil fuel industry which views clean energy as an existential threat)?

Re: Application submitted for US molten salt research reactor

#78

Post by kenned3 » Mon, Aug 22, 2022, 8:55 PM UTC

HPsquared wrote: post #68

ortusdux wrote: post #53

Earlier quoted context omitted.

You are correct about the corrosion issue. I've done some work developing molten salt resistant claddings. The main culprit is chromium leaching, which de-alloys most of the metals approved for reactor design. The leeching happens at the grain boundaries, so you will hear 'intergranular attack' as a research focus. A close second problem is the radiation itself. Elements in both the containment vessel and salt transm…

Does it even need to be a metal? (Since the pressure is so low strength requirements are lower)... How about ceramic or glass (or quartz), or something else non-metal?

non-metals have their own problems and glass tends to have some really weird properties.

I would think a major one would be their failure mode. Metals flex and expand before they eventually fail. Glass/ceramic is fine until suddenly it isn't and has a total failure.

Think of a window being hit. If it were metal it would probably deform but if it is glass it shatters.

Next would be joining them on-site. If needed, metal piping can be bent and welded in-place. what do you do with a glass pipe that needs a join? what do you do if there is a small variation in the plans and the pipe needs an adjustment?

I think there are a host of reasons why glass is not used for pipes.

Re: Application submitted for US molten salt research reactor

#79

Post by Turbots » Mon, Aug 22, 2022, 8:59 PM UTC

kenned3 wrote: post #78

HPsquared wrote: post #68

Earlier quoted context omitted.

Does it even need to be a metal? (Since the pressure is so low strength requirements are lower)... How about ceramic or glass (or quartz), or something else non-metal?

non-metals have their own problems and glass tends to have some really weird properties. I would think a major one would be their failure mode. Metals flex and expand before they eventually fail. Glass/ceramic is fine until suddenly it isn't and has a total failure. Think of a window being hit. If it were metal it would probably deform but if it is glass it shatters. Next would be joining them on-site. If needed, met…

what about glass pipes encased in said metals :-)

Re: Application submitted for US molten salt research reactor

#80

Post by robotresearcher » Mon, Aug 22, 2022, 9:03 PM UTC

throwaway894345 wrote: post #43

phire wrote: post #33

Earlier quoted context omitted.

I believe they use active cooling to keep the plug frozen. If the power fails, the cooling fails and the plug melts.

Yeah, I got that (and it seems like a really elegant solution! very cool , pun intended, etc). My question was about how salt (or any other matter, really) can simultaneously be molten and frozen.

Think of a lake in the winter. Just the top layer of water is frozen, exposed to the cold air above the lake. Some of the lake water is frozen and some is liquid, depending on its position in the lake.