Fuel types of most of the earliest fast breeder reactors were focused on metallic fuels, composed of U, Pu or U-Pu alloys. The main reason is that metallic fuels have the best breeding performance as high fuel density and hard neutron spectrum. But the in-core experiences later indicated that the swelling of metallic Fuel types of most of the earliest fast breeder reactors were focused on metallic fuels, composed of U, Pu or U-Pu alloys. The main reason is that metallic fuels have the best breeding performance as high fuel density and hard neutron spectrum. But the in-core experiences later indicated that the swelling of metallic