Radiation damage in uranium dioxide

Abstract

Point defect clusters and dislocation loops produced in bulk uranium dioxide by fission damage have been observed and studied by transmission electron microscopy. Clusters 25 Å in diameter are first observed at a dose of 4.3 × 10¹⁵ fissions cm⁻³. With increasing dose, these clusters quickly grow into resolvable prismatic dislocation loops which have been shown to be formed from interstitial atoms. They lie on {110} planes and have a ½ 〈110〉 Burgers vector. Evidence of the evaporation of small loops traversed by fission fragment tracks is given, and used to explain the rapid growth of the loops. At high doses the loops grow and coalesce to form a network of dislocations, but at a dose of 1.6× 10²⁰ fissions cm⁻¹ and a post-irradiation anneal at 1100°c, a new set of dislocation loops is observed to form between the existing dislocation network. The second set of dislocation loops is thought to be formed from the collapse of platelets of vacancies.