Study of Rock-like Oxide Fuels under Irradiation

Abstract

To evaluate the irradiation behavior of the rock-like oxide fuel, irradiation experiments were carried out. Three fuels were prepared; a single phase fuel of yttria-stabilized zirconia containing UO 2 (U-YSZ) and two types of particledispersed fuels of U-YSZ particles in spinel or corundum matrix. U-YSZ particle sizes were about 100 -200 µm. These fuels were irradiated in Japan Research Reactor No.3 for about 280 days. The burnups were about 11% FIMA. The fission gas release rate (FGR) was determined by puncture test and gas analysis. Corundum-based fuel showed extremely high FGR (88%). The irradiation behavior of spinel-based fuels in conditions avoiding the spinel decomposition was superior to corundum-based fuels, in view of their retention of FP gases. The temperature of U-YSZ single-phase fuel pellets was highest among the fuels, because of its low thermal conductivity. Nevertheless the U-YSZ single-phase fuel showed very low FGR (5%). Microstructure analyses of irradiated fuel pellets were carried out by ceramography and electron probe micro-analysis (EPMA). The restructuring of fuel pellet was not observed in the spinel-based fuel irradiated below 1400 K. Significant appearance changes were not also observed for corundum-based fuel, in the range of about 800 K to 1900 K, where the irradiation tests were carried out.