Swift heavy ion and fission damage effects in UO2

Abstract

Irradiations of uranium dioxide, UO2 with different swift heavy ions were performed using wide ranges of energies and fluences from 72 MeV to 2.7 GeV in the range 5×109–1017 ions/cm2. The ions were Zn, Mo, Cd, Sn, Xe, I, Pb, Au and U. The threshold energy loss for formation of visible tracks in UO2 could be determined to be in the range 22–29 keV/nm. Fission products of fission energy are below this threshold but nevertheless form thermal spikes in UO2. Observable tracks are only found at the surface. By using 127I-beams of 72 MeV energy the consequences of fission product impact, i.e., lattice parameter increase, fission gas bubble formation, resolution of fission gas from bubbles and fission-enhanced diffusion were all observed and measured. The swelling of UO2 was confirmed to be small and the technologically important process of polygonization (grain subdivision, also called rim-effect in operating UO2-fuel) could be simulated. The results obtained are important in understanding the operating behavior of UO2, today’s fuel in nuclear electricity-producing power stations.