Adds processing of plutonium, excess product from nuclear reaction. Plutonium can be used to make ammo (even plutonium atomic bomb) and to generate energy as MOX fuel.
I would love to see the zircalloy plates added to your MOX and breeder reactors recipes if the above is installed, because they do go into the vanilla reactor, which does very much follow real life reactor construction. (Zirconium does not absorb neutrons)