IIRC the seaborg reactor design uses a "traditional" flouride based salt for the fuel salt. The NaOH is a separate circuit used as the moderator, instead of a g

IIRC the seaborg reactor design uses a "traditional" flouride based salt for the fuel salt. The NaOH is a separate circuit used as the moderator, instead of a graphite block like other thermal spectrum molten salt reactors. Being a liquid, this sidesteps the problem of radiation damage to the graphite with associated swelling, cracking etc. etc.