Thermochemical Prediction of Chemical Form Distributions of Fission Products in LWR Oxide Fuels Irradiated to High Burnup

摘要

Based on the result of micro-gamma scanning of a fuel pin irradiated to high burnup in a commercial PWR, the radial distribution of chemical forms of fission products (FPs) in LWR fuel pins was theoretically predicted by a thermochemical computer code SOLGASMIX-PV. The absolute amounts of fission products generated in the fuel was calculated by ORIGEN-2 code, and the radial distributions of temperature and oxygen potential were calculated by taking the neutron depression and oxygen redistribution in the fuel into account. A fuel pellet was radially divided into 51 sections and chemical forms of FPs were calculated in each section. In addition, the effects of linear heat rating (LHR) and average O/U ratio on radial distribution of chemical form were evaluated. It was found that approximately 13mole% of the total amount of Cs compounds exists as CsI and virtually remaining fraction as Cs2MoO4 under the operation condition of LHR below 400W/cm. On the other hand, when LHR is beyond 400W/cm under the transient operation condition, its distribution did not change so much from the one under normal operation condition.