The problem is that reactors that can do enriching are also the ones you want to ensure fuel safety - as they can run on natural (not enriched) uranium. If you

The problem is that reactors that can do enriching are also the ones you want to ensure fuel safety - as they can run on natural (not enriched) uranium. If you need enriched uranium to start, then you need enrichment plants, which have 0 difference between making fuel or bomb core (about only real difference being that U-235 as bomb core is somewhat low efficiency option compared to plutonium or thorium fuel cycles). Meanwhile plutonium produced from reactors can be milled together with uranium to produce MOX fuels to be burnt again, often in reactor not capable of breeding fuel. P.S. Thorium doesn't fix any of that, it just was IIRC a bit more complex to use for power generation and for bomb making plutonium won by slight difference.