Operational behavior of FBR mixed oxide fuel pins

To predict the behavior of the mixed oxide fuel pins to be used in the DeBeNe fast reactor prototype SNR 300, irradiation experiments were carried out up to burn-up values of about 100,000 MWd/tHM. The fuel pins were mainly irradiated under fast flux conditions either in KNK II or in the Phoenix reactor, and the main parameters examined were the behavior of the mixed oxide fuel and of the austenitic stainless steel used as a cladding. Three different fuel types were irradiated: mixed oxide fuel with a low density, prepared by a dry blending procedure of the oxides, and highly dense, mixed oxide, prepared either by coprecipitation or comilling. Examples of changes in microstructure, plutonium-and fission-product distribution, and the mechanical and chemical interaction between the fuel and the cladding for the high burn-up values are discussed. With respect to the austenitic cladding materials, the results of the dimensional changes owing to swelling and in-pile creep of the DeBeNe reference material 1.4970 are presented