Talk:Molten salt reactor
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[edit] Molten salt
What is a molten salt ?. Can any give soma examples ?. And an inert metal ? Thanks in advance --HybridBoy 13:34, 22 May 2007 (UTC)
- Just what it says: Salt so hot it melted and is a fluid. (Yes, table salt melts; in a gas flame it vaporizes.) A picture of the molten salt is here. The most similar substance in every-day life is water, which is likewise an ionically-bonded substance that forms a polar fluid. Like water, a molten salt dissolves a lot of things easily, and conducts electricity pretty well. Because of these two traits, it can get pretty corrosive. Water (and molten salts) carry heat away pretty well (in fact, the specific heat is similar). A big difference: The BeLiF carrier salt mixture melts at 346C and vaporizes at 1400C! So, the liquid will burn one's skin something like molten lead or a soldering iron. Very nasty. 346C is not nearly hot enough to visibly glow, however. The colors are different: melted BeLiF is a clear, rather pretty blue-green fluid, about the viscosity of... water. It also has a meniscus like water, because it has similar inter-ionic forces. Unlike water, it shrinks when it freezes. Fluorides and Beryllium compounds are generally poisonous, so don't eat it. Hope that helps. Ray Van De Walker 02:09, 1 June 2007 (UTC)
- Inert metal? See galvanic corrosion. Generally an "inert metal" is one that's "more noble" so that it doesn't dissolve in the presence of other metals that are touching conductive solvents. Classic examples are Gold, Platinum, maybe Nickel and somewhat copper. Ray Van De Walker 02:09, 1 June 2007 (UTC)
[edit] Working fluid vs coolant
The article currently states that the working fluid would be a molten salt, whereas it is in reality the primary coolant that is a molten salt. The working fluid (the fluid used to convert heat into work in the plant's turbine ) would most likely be light-water, or possibly helium in VHTR designs. It appears very unlikely that the reactor would use a salt as a working fluid since the working fluid would have to be boiling for the turbine to achieve a high efficiency ( and you really don't want a boiling salt as primary coolant ). 137.205.192.27 02:04, 18 September 2006 (UTC)
[edit] Corrosion
Could we have some references on the corrosion issues with the Flibe environment? I've looked for references to problems encountered during the live run of the MSBR experiment at Oak Ridge, but from everything I've read they didnt encounter any of these issues during the years that they ran the reactor.
Indeed from a Usenet post several years ago, Bruce Hogolund adressed these concerns, and the corrosion issues were due to tellurium fission products reacting with the Hastelloy-N rather than any corrosion due to Cr migration by itself:
---
As for corrosion of the pipes & reliability; an excellent question, as a leak is the only real accident a MSR can have. Hastelloy-N was chosen & represented a large part of the early research on the MSR, due to its total compatability with the salt up to ~700 C; thus the limit on its operating temperature. You can go higher, but then the corrosion rate rapidly rises from unmeasurable at 700 C. Of course some people unfamiliar with negative temperature control then question what happens if the temperature were to rise. With a MSR, the only way to increase the temperature is to add more fissile fuel because the amount of fissile determines the outlet temperature of the salt due to its total control via its large negative temperature coefficient. So it can not get too hot unless you add hundreds of kilograms of very expensive fuel to the MSR & never look at the output temperature guage!
There was one (& believe it or not, only one) surprise during the entire MSRE operation, and this was not at first detected due to its subtlety; the tellurium fission product disolves the chromium from the surface of the Hastelloy-N. This was noticed when Hastelloy-N samples, that had been in the MSR during its entire operation were stress tested (pulled apart) & it was noticed that there were tiny cracks (>0.1 mm) in the surface. This minor problem was later solved on 2 fronts: improving the alloy (Hastelloy-N is now modified with 1-2% titanium and/or niobium & is usually called "Titantium modified Hastelloy-N", catchy, isn't it! } & by maintaining the UF4/UF3 ratio (whose explaination are somewhat complicated, and better discussed in the reference below). --[unkown]
--- Many of the corrosion issues I discused were fixed by placing a Be rod in contact with the solution to drive down the electrochemical potential of the solution thereby negating many of the corrosion issues. I wrote most of this very quickly, and many of the things arn't applicable to the MSRE which used flibe. Using other salts would bring this problem back though, but for the sake of simplicity I think the whole article should be rewritten, especially the technicological issues section. I wrote that section when I was researching some other molten fluoride corrosion issues at temperatures in excess of 800C and they kinda crept in, mainly because they haven't solved the problem yet for flinak, however there are several ideas. I have lots of references on the ARE, MSRE, and other molten fluoride and chloride reactors, but I see no point in adding 100 plus references for an article that is a generalization. FLIBE may not be used in all molten fluoride systems, nor even a fluoride, which is why the technological issues thing included corrosion. For a reference here, see reference 2 by W.D. Manely, it is one of the more readilly available references, from what I understand he was a big wig in the MSR development community for a while. If you disagree, ask for a more pointed reference (i.e. molten fluoride corrosion, temperature driven mass transport, etc...). But I caution you, most of the references you must find offline as they are government reports, or were in journals and are copyrighted. The few online sources of info I've found usually aren't all that good. I looked at Bruce Hoglund's website and think there may be the potential for POV from him, refering to published ORNL work would be much better. I'll try to leave some of the more relevent sources below. The national lab abbreviation is first, followed by the report number (I think). Feel free to change some of the things, I know its not that good now, I can always change them back if I disagree, but I won't as long as it improves the article. Lcolson
ORNL-5694: 1981-01
Comparative Evaluation of Pebble-Bed and Prismatic-Fueled HTGRs
ORNL-5176: 1977-02 Engineering Tests of the Metal Transfer Process from MSBR Fuel Salt
ORNL-4829: 1972-11 Intergranular Cracking of INOR-8 in the MSRE
ORNL-2387: 1958-02-04 Aircraft Nuclear Propulsion Program: Quarterly Progress Report for Period Ending September 30, 1957
ORNL-TM-8298: 1982-12 Thermal-Convection-Loop Study of the Corrosion of Fe-Ni-Cr Alloys by Molten NaNO3-KNO3
ORNL-TM-5783: 1977-05 Compatibility Studies of Potential Molten-Salt Breeder Reactor Materials in Molten Fluoride Salts
ORNL-TM-5325: 1976-04 Evaluation of Alternate Secondary (and Tertiary) Coolants for the MSBR
ORNL-TM-4286: 1972-12 Alloy Compatibility with LiF-BeF2 Salts Containing ThF4 and UF4
ORNL-CF-60-12-111: 1960-12-13 Homogeneous Molten-Salt Reactors
I think that this article should be broken into several sections to avoid confusion.
one on the molten salt reactor with fuel bearing salt, the second on the molten salt reactor which uses the salt for coolant only. Finally, the ARE and MSRE should get their own sections, or their own articles. Lcolson
[edit] corrosive fluoride salts?
What's that comment about the dangers of floride salts? No molten fluorides are used "to extract aluminium", a fluoride (kryolithe) is used to get the melting point of aluminium oxide down for the electrolysis. This is done at higher temperatures than 700°C in graphite vessels, and they don't burn down. Mentioning the oxidizing power of fluoride is comparable to calling sodium chloride aka table salt toxic, because it contains chlorine.
This second paragraph of "technological" issues is better revoved altogether. --[unkown]
---
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- lets go through the points in this paragraph one by one.
The primary reason this concept has not taken off relates to the corrosion issues
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- Salts with any moisture or oxygen in them lead to rapid corrosion... especially in Ti, Al, and Cr containing metals.
difficulty with working with highly radioactive fluids
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- The salt will likely have a fair amount of tritium in it from the lithium, but this is a trait shared by almost all cooling fluids except for maybe helium
the added expense of having to heat all piping prior to start-up
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- this and refueling is likely to be the largest problem of the concept, all those heaters for the piping will be expensive evin if they are only needed during start-up and shut-down and for maintenance
lack of industry support
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- What company would want to produce this if they loose their fuel manufactering business. Also, why compete with eixisting technology which doesn't have the monitary risk.
and lack of government support.
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- The DOE has stated that while the MSR is a gen IV concept, it is not being actively researched in the US
Fluoride salts can be extremely corrosive,
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- This is just restating the already mentioned stuff and could be taken out
in fact, molten fluorides are used in the aluminum industry to aid in the extraction of aluminum,
and fluorine is a better oxidizer than oxygen.
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- The molten salt will have to be clean to be used, a process which is neccessary to avoid corrosion issues. Fluorination is the only process I know of that can do this, and this requires fluorine gas. If there is excess free fluorine in the system afterwords, this could react with various metal constituents in the alloys.
Another issue for the MSR, at least for the designs that rely in fuel dispersed in graphite, is that the fuel-salt must be a liquid during refueling.
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- this is big, I don't think anyone has come up with a widely accepted method of doing this yet, but it probably can be done.
Furthermore, I put this paragraph in here because I think there should be some mention for why the msr has not ever become used outside of a research setting. Just saying that its because lwr's are so much more economic kinda misses the point, there is some reason lwrs are much more economic. As for the paragraph heading, and how it is actually written, well nothings perfect, in fact, I know my writings pretty bad. If you think you can do a better job, go ahead, this is wikipedia after all, you don't need anyones permision to change things. That being said, I do not want this article mearly to turn into an advertisement for msr's, this is not a "perfect" technology, it has issues. Lcolson
...which is the reason why I first discuss it, then change it. An edit war is nothing pretty, you know? We'll see. Anyway, what you write is largely true, but misleading. Especially:
- Free oxygen, free fluorine and moisture surely will corrode the metallic walls. However, the chemical potential of the salt has to be controlled anyway so it is slightly on the reducing side, containing some trivalent uranium. So any free oxygen or fluorine will oxydize the uranium ions, not the metal structure. Moisture will be driven out with the off-gas at working temperatures. All this is pretty much a non-issue.
- Cryolithe. Yes, aluminium is produced by electrolysing alumina with cryolithe. This can be considered a mixture or solution of sodium flouride, aluminium fluoride and aluminum oxide, certainly a molten salt. But the cryolithe is really only a fluxing agent, it is chemically non-agressive and it doesn't extract aluminium or something. You hinted that it does, which is really misleading.
- Heating is not a technological issue. Sure, it adds to the cost, but other than that there's no problem. A power reactor would run quite some time without ever being cooled down, refuelling is done by adding some molten or even solid salt, without shutdown, cooling or heating.
- But tritium is a problem. To slow down tritium formation, the lithium in the salt has to be almost pure Li-7, and even then tritium will form. Tritium in the salt is no problem, it doesn't attack metals. Tritium migrating from the salt is a problem. ORNL says, they were able to chemically trap the tritium in the secondary cooling loop. A problem, yes, but nothing major.
And of course there are the political issues. An MSR doesn't fit into the "razor-blade" business model currently employed, research is still needed, and that is expensive, waste reprocessing is currently illegal (though this is stupid when also applied to pyroprocessing), and uranium is too cheap these days to make a breeder economically viable.
(Yes, if we can find some agreement, I'll summarize this and move it to the article proper.)
--[unkown]
-- You make several good points, perhaps the essence of the paragraph should be moved under a different heading. Perhaps under advantages-disadvantages, then bulleted and explained. Inaddition to the other advantages and disadvantages of course.
I was just thinknig... It seems like you know quite a bit about this concept, its history, and the issues involved, so you could probably give this article a much more thorough treatment then I've given it. I wrote the majority of this article from what little I learned about the concept researching something else. Therefore its got several holes in it, its definetly not going to become featured status in its current form. Before I expanded it it was a pretty sorry stub, I think it said:
Molten salt reactors are reactors that use molten salts... or something similiar
I would have no problems if you wanted to completely rewrite this article to make it more technically correct. I think I've already done it twice. There are several concepts and parts of its history which I'm sure are probably incorrect. I've tried not to include stuff that I wasn't positive about, but sometimes sources are contradictory. Lcolson
[edit] Political Issues
I thought the law against reprocessing was repealed under Reagan.
And I thought the point of the Molten Salt Reactor reprocessing was to only filter out the fission fragments, and leave the actinides circulating in the fuel. I don't see how there is any risk of a plutonium economy there.
Maybe "only filtering out the fission fragments" came about with the Generation IV initiative, though. I don't know the early history of the reactor concept very well. Oralloy 08:06, 20 December 2005 (UTC)
- President Reagan lifted the ban on reprocessing on October 8, 1981:
- Note:
- "(3) I am lifting the indefinite ban which previous adminstrations placed on commercial reprocessing activities in the United States. In addition, we will pursue consistent, long-term policies concerning reprocessing of spent fuel from nuclear power reactors and eliminate regulatory impediments to commerical interest in this technology, while ensuring adequate safeguards."
- "It is important that the private sector take the lead in developing commercial reprocessing services. Thus, I am also requesting the Director of the Office of Science and Technology Policy, working with the Secretary of Energy, to undertake a study of the feasibility of obtaining economical plutonium supplies for the Department of Energy by means of a competitive procurement. By encouraging private firms to supply fuel for the breeder program at a cost that does not exceed that of government-produced plutonium, we may be able to provide a stable market for private sector reprocessing and simultaneously reduce the funding needs of the U.S. breeder demonstration program."
- http://www.reagan.utexas.edu/archives/speeches/1981/100881b.htm Oralloy 09:30, 21 December 2005 (UTC)
The ban on reprocessing is lifted, however investors in the commercial reprocessing plants lost billions of dollars when the ban was originally created. I believe they see the cost/benefit to be too low to for something they consider to be very volatile in the market place. The incentive for the utilities to reprocess, at this time, is low because there is a glut of uranium and because the spent fuel created by powerplants is by law, the government's problem, not the utility's. There also may be some policy issues with reprocessing, but I'm not sure about that. Ajnosek 21:18, 5 January 2006 (UTC)
MSR reprocessing is backwards, compared to PUREX. The fission products are removed from the salt, all actinides remain in there. There is of course absolutely no way to extract pure plutonium, let alone weapons grade; the same goes for U-233. No try and explain that to a self proclaimed "nuclear critic". He'll still tell you that reprocessing will be used to construct weapons. Political resistance isn't based on logic, unfortunately.
[edit] Section refactor needed
Some good comments above. Lots of WP:SIGN:unsigned posts but enough meat to refactor the section... which is badly needed IMO! Present section contains much weasel-talk and speculation, mixed with some good information. Andrewa 17:50, 15 May 2007 (UTC)
