EFFECTS OF SOLUBLE FISSION-PRODUCTS ON THERMAL-CONDUCTIVITIES OF NUCLEAR-FUEL PELLETS

Simulated high burnup UO2 and (U, Gd)O-2 pellets, doped with soluble f ission product elements (Sr, Zr, Y, La, Ce, Nd), were prepared. Pellet thermal diffusivities were measured by a laser flash method and their thermal conductivities were evaluated. Thermal conductivities decreas ed with an increase in the total amount of soluble elements at low tem peratures, while they were almost independent of soluble element conte nt at higher temperatures. In the heat transfer process, phonon-phonon scattering was dominant for UO2 and simulated low burnup fuel, while phonon-point defect scattering was more important for higher burnup fu el. By applying Klemens' model, thermal conductivities of UO2 with sol uble fission products was expressed in the form of an empirical equati on. Then with empirical parameters from simulated burnup UO2 and the p revious (U, Gd)O-2 results, thermal conductivity of (U, Gd)O-2 with so luble fission products was expressed as a function of Gd and soluble f ission products contents within a fitting error of +/- 6%.