Annihilation processing method for transuranium element

In a FBR type reactor, TRU assemblies containing a great amount of transuranium elements (TRU) having an atomic number of 93 or greater are disposed at the outer side of a reactor core to operate an FBR type reactor. Then, neutrons leaked from the reactor core are irradiated to the TRU assemblies. As a result, less fissionable nuclides are converted into easily fissionable nuclides. Subsequently, the TRU assemblies are disposed again to the inside of the reactor core to operate the FBR type reactor. With such procedures, undesired effects on neutron economy upon loading the TRU to the reactor core can be reduced, the amount of the TRU oaded to the reactor core can be increased and nuclear transformation can be conducted. Further, the breeding property of reactor fuels is improved. Furthermore, the amount of fuels such as plutonium required for reactor operation can be reduced or saved. (I.S.)