Microstructural Evolution in Cerium Dioxide Irradiated with Heavy Ions at High Temperature

Abstract

Formation of subdivided grains and coarsened bubbles in uranium dioxides under high burn up conditions in nuclear power plants deteriorate the performance of nuclear fuels. To clarify its mechanism, heavy ion irradiations in cerium dioxide followed by Raman spectroscopy, X ray diffractometry and electron microscopy (SEM) were performed. At the early stage of irradiations, increase in the lattice constant and shift in the F 2g peak position were observed presumably indicating accumulation of oxygen vacancies. Further irradiation enhanced recombination or clustering of vacancies depending on the irradiation temperature. The behaviors affect the surface morphology of the sample as well. Especially above 1000K, characteristic changes in Raman spectra and surface features were detected, presumably attributable to remarkable diffusion of vacancies. The relation between displacement of F 2g position and electronic energy deposition of incident ions was observed, suggesting the role of electronic excitations on the formation of oxygen vacancies in cerium dioxide.