THERMOCHEMICAL PREDICTION OF CHEMICAL FORM DISTRIBUTIONS OF FISSION-PRODUCTS IN LWR OXIDE FUELS IRRADIATED TO HIGH BURNUP

Based on the result of micro-gamma scanning of a fuel pin irradiated t o high burnup in a commercial PWR, the radial distribution of chemical forms of fission products (FPs) in LWR fuel pins was theoretically pr edicted by a thermochemical computer code SOLGASMIX-PV. The absolute a mounts of fission products generated in the fuel was calculated by ORI GEN-2 code, and the radial distributions of temperature and oxygen pot ential were calculated by taking the neutron depression and oxygen red istribution in the fuel into account. A fuel pellet was radially divid ed into 51 sections and chemical forms of FPs were calculated in each section. In addition, the effects of linear heat rating (LHR) and aver age O/U ratio on radial distribution of chemical form were evaluated. It was found that approximately 13 mole% of the total amount of Cs com pounds exists as CsI and virtually remaining fraction as CS2MoO4 under the operation condition of LHR below 400 W/cm. On the other hand, whe n LHR is beyond 400 W/cm under the transient operation condition, its distribution did not change so much from the one under normal operatio n condition.