Breeder reactors are possible because elements above the atomic weight of iron are storing a lot of energy that's released if you can bust them up (fusion.) Iro

Breeder reactors are possible because elements above the atomic weight of iron are storing a lot of energy that's released if you can bust them up (fusion.) Iron is the least (stored) energetic state, so below iron, fusion releases energy. It's a real nasty process to control, though since neutron radiation tears the shit out of container metals over time.