Interesting. Seems a big engineering challenge is the corrosivity of the sodium fluoride coolant.
It is a key issue on the road to proving the LFTR design is commercially viable. Hastelloy N seems to be the current alloy of choice. Try this search for discussion/references on Hastelloy N at Energy from Thorium.
Kirk Sorenson posted on the WIRED thorium article on 12/21/2009, going directly after the corrosion issue:
Also, with regards to the article, it’s important for me to mention a few things. First of all, fluoride salt is NOT highly corrosive if it’s put in the right container material. The high-nickel-alloy Hastelloy-N was proven by Oak Ridge scientists and engineers to be compatible with fluoride salt at the elevated temperatures at which LFTR would operate. Discovering Hastelloy-N and proving it would work was one of their great accomplishments.
Earlier Kirk wrote “it isn’t a problem” in a reply to a comment-critic in 2006
Corrosive properties of floride salts and UF4
As I’ve stated on here repeatedly, and can be verified by examining the actual test documents, which are here as well, the right salt combination with the right material doesn’t lead to corrosion. This is an issue that keeps coming up even though the data is there to show that it isn’t a problem.
In another Energy from Thorium post Charles Barton reviews some of the history of the IFR and LFTR
In his 1982 UCLA dissertation by E. H. Ottewitte, who had participated in the Swiss study stated:
Molten salts compete favorably with liquid metals: (…)
Chemical stability and corrosion of molten salts are fairly predictable. Low vapor pressure of the salts enhances safety and permits low pressure structural components
In a May 2009 post Charles Barton supplies quotes from several ORNL reports — in response to Scty Chu statements in hearings of The Senate Energy subcommittee:
Secretary Chu: A3: The “liquid-fluoride thorium reactor,” otherwise known as a molten salt reactor (MSR), where molten salts containing fissile material circulate through the reactor core, is not part of the Office of Nuclear Energy’s research program at this time. Some potential features of a MSR include smaller reactor size relative to light water reactors due to the higher heat removal capabilities of the molten salts and the ability to simplify the fuel manufacturing process, since the fuel would be dissolved in the molten salt. One significant drawback of the MSR technology is the corrosive effect of the molten salts on the structural materials used in the reactor vessel and heat exchangers; this issue results in the need to develop advanced orrosion-resistant structural materials and enhanced reactor coolant chemistry control systems. In addition, operational practices would have to address the fact that the liquid salts solidify between temperatures of 300 C to 500 C, thereby requiring the use of special heating systems when the reactor is not operating. From a non-proliferation standpoint, thorium-fueled reactors present a unique set of challenges because they convert thorium-232 into uranium-233 which is nearly as efficient as plutonium-239 as a weapons material. A cost per kilowatt hour estimate has not been developed.
The pasting of ORNL text seems a bit dodgy in spots, but here is a relevant bit quoted from ORNL/TM-6415 (1979):
The second likely solution involves the chemistry of the fuel salt. Recent experiments indicate that intergranular attack on Hastelloy N is much less severe when the fuel-salt oxidation potential, as measured by the ratio of U4+ to U3+, is less than 60, the possibility that the superior titanium-modified Hastelloy N could This discovery opens up be used for MSRs through careful control of the oxidation state of the Fuel salt.
Bath (sic) of the above solutions appear promising, but extensive testing under reactor conditions would be required before either could be used in the design of a future MSR.
I read that last paragraph from the 1979 report as indicating the Hastalloy N alloy is not yet proven.
Since we haven’t built commercial scale LFTRs we don’t what the problems/economics are. If I were King I would pull a few scrap Obama billions from the flood of money being wasted on “renewables” and wasted on the whole arena of “global warming foorah”. How much would cost to build a full scale IFR to the PRISM design? If we have to do only one Gen IV commercial scale proof, then I would pick IFR due to big volume of work already completed + the scientists with all the knowhow are getting old.
But if I were King I would look very hard at paralleling a LFTR program. For both projects I would try to organize to maximize private skin in the game – e.g., GE/Hitachi for the PRISM #1 unit. Science prizes might help for some segments of the design.