Lithium hydroxide from Li-7 as used in thermal reactors

[artis]

So I read that lithium hydroxide made from Li-7 is used as an anti-corrosion additive in light water reactors purely for the "longevity" and "well being" of the vessel and structural auxiliary elements like steam pipes etc.

Lithium separation is a rather chemically "nasty" task if using the COLEX process , I see there are others as well but much less effective. Given US no longer operates Li separation facilities where do US reactors get their Li-7 needed inventory?
I would assume Russia and China.
And why only Li-7 is used but not ordinary Lithium containing both the Li-6 and Li-7 stable isotopes?
Is it because Li-6 in a neutron rich environment (the core) would produce too much Tritium?, Because chemically I would suspect that using ordinary Lithium instead of Li-7 for the lithium hydroxide solution would make no difference in the chemical anti corrosion properties?

Comments are welcome, thanks.

 

[Astronuc]

LiOH is used as a buffer for soluble H₃BO₃ in PWR primary coolant. The goal is to achieve a pH > 6.9, and preferably ~7.1 to 7.4 (at ~300°C), in order to prevent dissolution of Ni from steam generator tubing (and stainless steel cladding on carbon steel PV and other components) as well as crud deposition in the core. Zn is also injected into the coolant to suppress Ni dissolution.

Li in LiOH is enriched in ⁷Li for the reason one cited above, that ⁶Li experiences (n,α) reaction resulting in T production.

Russia is a source and China is a potential source. There is currently a program in the US to enrich Li, or rather produce separate streams of ⁶Li and ⁷Li.

Russian VVER systems have used KOH for the same purpose.

One can reduce the demand of LiOH by reducing the required concentration of H₃BO₃ through enrichment of ¹⁰B in the boric acid. However, one must weight that against hypothetical boron dilution events and the reactivity insertion accidents.

Some background
http://www.world-nuclear.org/information-library/current-and-future-generation/lithium.aspx