Talk:Molten-salt reactor

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Molten Chloride Fast Reactor or MCFR[edit]

MCFR currently redirects to this page but not to any section or anchor. I think we should do better than that. There is a little information at TerraPower, whose design this is, but that page needs updating too.

See

https://www.energy.gov/ne/articles/southern-company-and-terrapower-prep-testing-molten-salt-reactor a secondary source
https://www.terrapower.com/our-work/molten-chloride-fast-reactor-technology/ for the TerraPower page on the MCFR, it has been archived on the Wayback Machine but the graphics and relevant text seem to have been lost there somehow

It's an interesting design, maybe not so promising as their Natrium reactor but probably more so than their Traveling Wave Reactor. Andrewa (talk) 15:30, 25 January 2022 (UTC)[reply]

Both MCFR and Natrium are fast neutron reactors. I see no advantage of molten sodium over molten salt, and one clear disadvantage - the flammability of sodium. So I am favoring the MCFR, but I can't get any info from Terrapower for our article in Citizendium. I think Terrapower may be following an under-the-radar strategy on public relations: We got our funding. Let's get our demo up and running before the anti-nukers take notice. David MacQuigg 14:25, 26 May 2022 (UTC)[reply]

Gaseous fission products[edit]

We need a nuclear engineer to clarify what happens with radioactive gases (Xe and Kr) that are produced in fission reactors. It is my understanding that those gases accumulate in solid fuel rods, where they crack the fuel pellets causing voids and absorption of neutrons, which "poisons" the reaction and results in early replacement of the spent fuel. These same gases in a molten salt reactor can bubble out^[1] without causing any damage, thereby greatly extending the life of the fuel. I made a revision to clarify this, and it was reverted. What is the truth? David MacQuigg|David MacQuigg 10:50, 15 April 2022 (UTC)[reply]

@Macquigg I also remembered the same 'bubble-out' statement from my own study of the design for Liquid fluoride thorium reactor#Removal of fission products. It means the design decisions for a 1GWe (1 gigawatt electrical) molten salt fission reactor (called the Can) will have already been made, as in the 2018 Thorcon TMSR-500 proposal to the Indonesian regulatory group (restarted 2022).

The MSRE (Oak Ridge molten salt reactor experiment) had to deal with the same issues, of course. (China, beginning in 2011, followed their own Thorium reactor development path based on the MSRE, and is proceeding on their Thorium molten salt fission reactor scale-up as of September 2021.) I assume your 'without causing any damage' statement is about damage to the prismatic graphite moderator rods (which is evidenced by expansion of the rods). In addition, I am not considering the case of solid fuel. (The MSRE discovered that Hastalloy solved the problem of the piping material. Embrittlement of the grains in the material was observed.) Thorcon's Can contains a Pot with the graphite moderator, and Primary heat exchanger. A Secondary heat exchanger is external to the Cans (the ThorCon nuclear reactor article does not show the Secondary heat exchanger which remains with the power generation building when a Can is recycled). Since China's Thorium reactor scale-up is underway, and since Thorcon was proposing a scale-up in the Indonesian proposal, a search of the Chinese documentation can confirm whether their processing of the byproducts (including Xe and Kr gases) is being handled the same way that Thorcon is proposing. Water is used to absorb the excess heat from the byproducts (Thorcon calls the structure for remediating excess heat from the Can, the cold wall).

The ThorCon_nuclear_reactor#Leakage of radioactivity article appears to cover the chemically-bound byproducts: "iodine-131, strontium-90 and cesium-13" would manifest in the molten-salt mixture; tritium is mitigated in a third salt loop; and the radioactive xenon and krypton gases bubble out of the molten salt into a header tank, where their radioactivity is left to decay away (so those gases can be handled separately, later). Henry's law comes into play for the gases dissolved in the molten salt, such as the Xe and Kr: when the gases are constrained to a container, such as a fuel rod; they would push against the walls of the rod, or TRISO layer, etc. This would manifest as a rip in the containing material, or a void in the solid material in a rod (not applicable to an MSR, of course, in this case, the gases bubble-out of the top surface of the molten salt, where it is not constrained by its holding vessel).

The gaseous fission byproducts in the Thorcon design are simply separated by bubble-out into a separate tank from the molten salt mixture, which remains at high temperature. The byproducts are left to cooldown (to eventually be reprocessed when a Can is swapped out— an alternate Can then receives the molten salt). The remaining molten salt is pumped back upward to the top of the Can to a secondary salt loop, and the heat from the molten salt mixture from both the primary and secondary molten salt loops is harvested to generate steam (this description is simplified: there is another salt loop in this two-fluid design —tritium is mitigated using the oxygen in the CO2 cycle of the supercritical CO2 phase -- the temperature and pressure there suffice to capture the tritium). The steam drives the electrical generation process (Thorcon emphasizes this is then standard electrical power generation technology), and the molten salt flows downward through the Can again, in a cycle. If the process overheats, a freeze plug (at the base of the piping below the Pot and heat exchangers) warms up and opens, which dumps the molten salt mixture into fuelsalt drain tanks by gravity, which stops the reactor, in an automatic fail-safe.

Since Thorium is fertile, but not fissile, the neutron flux that is slowed down by the graphite moderator amplifies the conversion of Thorium into fissionable fuel. The MSR article states that Xe absorbs neutrons. Thorium needs all the slow neutrons so it can convert into fissionable fuel. Thus control of the purification process of the molten salt in its cycle (removal of any Xe, Kr, tritium, etc.) would actually stabilize the operating temperature for a Thorium molten salt reactor. Understanding the conditions to maintain the operating temperature is good for electical power generation, not for conversion into weapons materiel, which is the danger for a fast neutron process. The power generation process simply consumes the weaponizable materiel and produces heat for four years, the design life of the Can. The electric power vendor can then recycle the Can, for compensation, with much less waste than coal (a factor of thousands, at least). --Ancheta Wis (talk | contribs) 15:41, 15 April 2022 (UTC)[reply]

^ See discussion of xenon and krypton at https://thorconpower.com/safety/

Drain tank[edit]

Extended content

What happens after an emergency stop by which all salt ended up in the drain tank, and how does it differ from possible other systems? --Wickey (talk) 13:30, 16 April 2022 (UTC)[reply]

My short answer is in the references of the latest edit to the article. A more helpful reply is that fission stops immediately. Please see the Thorcon Safety page. I don't have the time right now for a longer answer. --Ancheta Wis (talk | contribs) 12:15, 17 April 2022 (UTC)[reply]

I know that the untested theory is that the nuclear reactions will stop. My question is actually what will happen with the system after that. --Wickey (talk) 14:35, 17 April 2022 (UTC)[reply]

I don't understand why you would call it an "untested theory". If the fuel is drained from the reactor, the reaction stops. It does not take a degree in engineering to understand the inherent safety of the design. That is one advantage of an MSR over solid-fuel designs. Read that page suggested by Ancheta Wis, and let me know if that doesn't answer your question. David MacQuigg 12:38, 14 May 2022 (UTC)[reply]

The honest answer is:

If in case of emergency the temperature in the reactor becomes too high, a frozen plug at the bottom will melt – if this feature is built-in – and all highly radioactive fuel and cooling salts will end up in the drain tank. No one knows what will happen then, as this has never been tested and reality is always worse than theory.

The result will be a complete shutdown and the power plant will have to be decommissioned. Virtually all promotional articles will stop at this point. --Wickey (talk) 13:19, 24 May 2022 (UTC)[reply]

Wickey, this is astonishing. Others have made substantive and honest accounts of what is believed will happen in this case, but YOU claim to know definitively what will happen--something different and drastic and awful. Are you harboring some special expertise that you've been hiding from the rest of us? Please stick to actual science. I see no reason why fission would not stop immediately, and that seems like a really good thing as compared with older reactor designs. Harborsparrow (talk) 18:09, 24 May 2022 (UTC)[reply]

You see no reason and others believe honestly they wil be save. Fact is that there has never been an MSR working for a longer time and currently there exists not a single one, so it could never be tested. This, while they have an inherent safety risk due to corrosion problems. I still do not have an answer to my initial question. --Wickey (talk) 13:20, 25 May 2022 (UTC)[reply]

Wickey, The answer to your question what happens after the molten salt is in the drain tank is simple, the heat is absorbed by the "Cold Wall" in the ThorCon design. Other reactors have similar schemes. Please follow the links you have been given. They will answer your questions. We have been warned to keep this topic discussion to a minimum, and I see the entire discussion of safety has now been deleted, including the acknowledgement of the source. This is why I avoid writing for Wikipedia. David MacQuigg 15:25, 1 October 2022 (UTC)[reply]

Though everyone may have his own opinion, I don't think MSRs will ever be commercially used. AFAIK, drain tanks are not included in every design. Anyway, if after an emergency stop all radioactive stuff has been sunk into the drain tanks, they are no longer functioning. There is nothing else left than nuclear decommissioning, followed by complete dismantling of the reactor, right? --Wickey (talk) 11:41, 2 October 2022 (UTC)[reply]

Please read WP:NOTAFORUM. Please confine commentary to direct discussion of article improvement. Speculation, criticism, how is this or that done, etc, are not the purpose of the article talk page. If you have changes that you think are needed in the article, and have reliable sources to support them, please do so. Otherwise, this is not a productive discussion. There are other venues to chat about this stuff. cheers. anastrophe, an editor he is. 18:48, 2 October 2022 (UTC)[reply]

[1] See discussion of xenon and krypton at https://thorconpower.com/safety/

[1]