Relocation of Fission Products and PU in Irradiated UO₂ Pellet

Abstract

Distribution of fission products (¹⁴⁴Ce, ¹⁰⁶Ru, ¹³⁷Cs, ⁹⁵Zr-⁹⁵Nb and ⁸⁵Kr) and Pu were examined in UO² pellets which were irradiated at high temperature (∼3,000°C). Two capsules, each containing six natural uranium UO² pellets were irradiated in GETR at 0.05 and 0.10% burnup respectively. The UO² pellets were completely fused into a single rod, and a big void was formed along the length of the rod as a result of the high temperature. Analysis was made by direct γ-scanning along the length and across sections of the rods, as well as by samples scraped off from the rods. Pu and Ru were found to be distributed fairly regularly, while Cs was markedly concentrated at both ends of the rod where the temperature was lower than the middle part. Zr-Nb was found to be concentrated in the inner portions which were the hottest parts. About 2% of the ⁸⁵Kr remained in a sample of 0.05% burnup, though only a trace amount in that of 0.1% burnup. Distribution of γ-activity along the length of the rods was quite irregular, having wide depleted sections, which might be explained from the exposure to high temperature.