Performance of Uranium-Plutonium Mixed Carbide Fuels Irradi ated to Low Burnup

Four pins of U-Pu mixed carbide fuel, which is one of potential advanced fuels for FBRs, were irradiated in JRR-2 up to burn-ups of 1.5% FIMA without any pin failure. In spite of irradiations at relatively low linear heat powers of 42 and 64kW/m, the change in the sizes of pores and grain size was observed. Pellet density and carbon content appreciably influenced to irradiation fuel performance, such as restructuring, cracking and FP gas release. It was revealed in the γ-spectrometry that Cs behaved similarly to FP gases and condensed at the plenum. A slight carburization was observed at the inside of 316 stainless steel cladding.