Aren't there some reactors that produce more fuel than they spend?

Deuterium-Tritium fuelled reactors can produce Tritium by wrapping the reactor walls in a "blanket" of lithium. The lithium captures neutrons and transmutes into Tritium. It should be possible to produce an more tritium then the reactor requires, but no one has actually done it yet for fusion reactors. Fission "fast" reactors can do something similar by turning uranium into plutonium. This has been demonstrated by several countries but so far has been uneconomic.

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.

Thanks for the details. I don't think I even have to confess that my knowledge here is rudimentary. I just finished Atomic Awakening and I remember the phrase popping up a few times.