Environmentally friendly application of hydrides to nuclear reactor cores

As new environmentally friendly techniques, hydride materials have been proposed to be introduced to fast reactor (FR) cores in this paper. Hydrogen atoms in metal hydride can efficiently moderate fast neutrons. Based on this fact, some metal hydrides have been investigated for their potential environmentally friendly application as nuclear materials to be used in FR cores. Two types of utilisation of metal hydrides in FR cores are discussed in this paper. One is the application of hafnium hydride as neutron absorber in FR cores. The core design has been carried out to examine its characteristics as well as to evaluate the cost reduction effect. Demonstration of the fabrication of hydride pins has been performed using hydride pellets and stainless steel claddings. The coating technique of the inner cladding surface has also been developed to reduce the permeation of hydrogen through the stainless steel cladding. The physical and chemical properties of the pellet have been measured for the purpose of designing a hafnium hydride pin. Irradiation test of the hydride pins has been performed in the experimental FR, JOYO, Japan Atomic Energy Agency. The other application is the utilisation as a transmutation target of long lived nuclear wastes. Hydride fuel containing ²³⁷Np, ²⁴¹Am and ²⁴³Am has been studied for a candidate transmutation target to be used to reduce the radioactivity of long lived nuclides contained in the nuclear wastes, which are obtained after reprocessing spent fuels.