I think it would be nice if there was a less random/more scalable way to make plutonium later, maybe as a research at the end, after plutonium weapons.

It’s possible to make a net positive plutonium cycle from fuel cell reprocessing, but it takes very strong modules.

Correct me if I'm wrong on my maths, but, it seems you would need 563% productivity across two recipes, to turn 4 plutonium into 22.5

It's three recipes for spent cells -> nuclear waste -> isotopes -> new fuel. On vanilla Aquilo+Cerys, using a cryoplant, this produces an 8% surplus of Pu-239 with maxed out productivity modules.

In thinking about your comment, I realized I'd like space platforms to be able to sustain mixed-oxide reactors (and without maxed out modules). As a result, Cerys 1.4.39 has increased the positivity of the fuel reprocessing loop.