The
minor actinides are the
actinide elements in used
nuclear fuel other than
uranium and
plutonium, which are termed the
major actinides. The minor actinides include
neptunium,
americium,
curium,
berkelium,
californium,
einsteinium, and
fermium. The most important isotopes in
spent nuclear fuel are
neptunium-237,
americium-241,
americium-243,
curium-242 through -248, and
californium-249 through -252.