How efficiently? I’m sure some of the waste products of a conventional reactor (and maybe even some of the waste products of a CANDU reactor) can be refined and put back through a breeder reactor, but (A) it sounds like it’d take more energy to do the refinement than you’d squeeze out of the recycled waste, and (B) what about the radioactive portion of the waste that can’t be recycled?
By the way, have I mentioned that I like the idea of putting our waste-grade uranium and plutonium in CANDU reactors?