Complex sentence: Fission of the nuclear fuel in any reactor produces neutron-absorbing fission products, and because of this it is necessary to reprocess the fertile material from a breeder reactor if one is to fully utilize the ability to breed as much or more fuel than is consumed.
Split into simpler sentences: Fission of the nuclear fuel in any reactor produces neutron-absorbing fission products. This step is required if one is to fully utilize the ability to breed as much or more fuel than is consumed.