Google commits to buying power generated by nuclear-energy startup Kairos Power

While this has some advantages (low pressure, no fission products in the FLiBe), it also some issues.

First, the fuel cycle costs are higher than a LWR. The fuel is dispersed as small encapsulated grains in graphite spheres. Manufacturing the fuel is more expensive, I believe the enrichment needed is higher, and the volume of the spent fuel is considerably larger. All that graphite needs to be disposed of along with the spent fuel.

Second, FLiBe require isotopically separated lithium. Li-6 has a ruinously high thermal neutron absorption cross section so it must be rigorously excluded. It also produces tritium when it absorbs neutrons, which would permeate through the reactor and beyond. But there are no large scale lithium isotope separation plants in operation, and the technology that was used for this in the Cold War (to make Li-6 for H-bombs) has been shut down and cannot be restarted because of mercury pollution (liquid mercury is an inherent part of the process and much escaped down drains at Oak Ridge.)

Kairos has announced operation of a FLiBe purification plant, which sounds promisingly like an isotope separation plant, but it appears it's only a plant for removing other impurities (oxygen, sulfur, iron, etc.) from FLiBe. Isotopically pure Li-7 fluoride would be an input to this plant.

Third, FLiBe is about 11% beryllium. Annual world production of beryllium is just a few hundred tons. There's a limit to how much FLiBe could be made for these reactors (or for fusion reactors, for that matter.)

- "The Kairos Power fluoride-salt-cooled, high-temperature reactor requires highly enriched lithium-7 to support operations. The high enrichment requirements complicate quality and process control due to lack of qualified standards and instrumentation capable of meeting the required precision and accuracy. Currently, enrichment [sic] of 99.95% 7Li is imported to the U.S. in limited quantities."

https://gain.inl.gov/content/uploads/4/2023/10/KairosPower_A...

- "Due to environmental concerns and relatively low demand for enriched lithium, further use of the COLEX process is officially banned in the USA since 1963, which strengthens China’s near unanimous [sic] hold over the market of enriched lithium, followed by Russia.[7]. [...]Although US nuclear industry relies heavily on Chinese and Russian enriched lithium, ecological concerns over the process may impede its future domestic use at industrial scale."

https://en.wikipedia.org/wiki/COLEX_process#COLEX_separation...

(Tangentially, the Chinese FLiBe reactor also uses enriched lithium-7, so I guess they're self-sufficient in that, as both supplier and consumer).

https://en.wikipedia.org/wiki/TMSR-LF1

edit: Found an additional reference,

https://www.gao.gov/products/gao-13-716 ("Managing Critical Isotopes: Stewardship of Lithium-7 Is Needed to Ensure a Stable Supply" (2013))

I believe this is referring to rather small quantities (kilograms) imported for pH control in light water reactors.