Thermal diffusion kinetics of cesium in ceramic microcell UO2 fuels for accident-tolerant fuel

Abstract

This work investigates the diffusion kinetics of cesium in ceramic microcell UO2 fuels at temperatures ranging from 650 to 1200 degrees C to predict its release behavior under actual fuel circumstances. Diffusion couples containing ceramic microcell UO2 pellets with silica-based cell wall compositions (with and without Al) were prepared and subjected to a heat treatment with abundant gaseous cesium source. From the experiment, kinetic data were obtained in the form of an Arrhenius equation: the addition of Al lowers the degree of cesium diffusivity. The favorable contribution of Al may stem from the formation of the cesium compound as a solid form of Cs-Al-Si-O. The findings here provide a diffusion model describing diffusion mechanism of cesium in the cell wall. Also, this study suggest an evaluation method that can be used in UO2 fuels with trapping agents from a kinetic standpoint.