In-pile irradiation of rock-like oxide fuels

Five kinds of rock-like oxide fuels were prepared and irradiated using 20% enriched U instead of Pu. The microstructure analyses for irradiated fuel pellets were carried out by ceramography and electron probe microanalysis (EPMA). For MgAl2O4 (spinel)-based fuel, decomposition of the spinel and vaporization of MgO (magnesia) was observed. For Al2O3 (corundum)-based fuels, significant appearance changes were not observed under the irradiation condition of sufficiently high fuel temperature. Fission product (FP) distributions were also analyzed by EPMA. The distributions of Nd and Ba were similar with those of U and Zr. Mo and Pd were found as fine inclusions in the yttria-stabilized zirconia (YSZ) phase. A part of Cs and Xe migrated to the periphery of YSZ particles and to pores in YSZ. The FP distributions of spinel-based fuel were almost similar to corundum-based fuel.