[DugFin]

>closing the fuel cycle loop in a way that is proliferation resistant

Isn't simply using a non-PUREX reprocessing method sufficient? Realistically, a "nuclear club" nation like the US/France/GB only needs to ensure that the reprocessed fuel contains enough non-Pu239 isotopes that any attempt at a bomb with stolen Pu would necessarily fizzle. The fact that the nation itself could (theoretically) produce Pu239 via the process and cause "proliferation" seems far fetched in the absence of the Cold War level rivalry that was the original proliferation impetus. Warheads are expensive. Nobody who already has a bunch of them already is really interested in making more.