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 fission 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 decreased with an increase in the total amount of soluble elements at low temperatures, while they were almost independent of soluble element content 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 fuel. By applying Klemens' model, thermal conductivities of UO2 with soluble fission products was expressed in the form of an empirical equation. Then with empirical parameters from simulated burnup UO2 and the previous (U, Gd)O-2 results, thermal conductivity of (U, Gd)O-2 with soluble fission products was expressed as a function of Gd and soluble fission products contents within a fitting error of +/- 6%.