Dislocation Loops in Ceramic Nuclear Fuels

Ceramic nuclear fuels have been widely used in light water reactors and proposed as candidates for advanced reactors. In reactor environments, the degradation of thermal conductivity and mechanical properties of nuclear fuels has been associated with defect generation. Radiation creates point defects (vacancies, interstitials) and extended defects, such as dislocation loops and cavities. Investigating these early-stage microstructural changes is of significance in understanding the performance degradation of nuclear fuels in reactor environments. In this work, we study the evolution of dislocation loops as a function of temperature and irradiation dose in oxide and nitride nuclear fuels using a combination of in situ/ex situ ion irradiation, advanced characterization and modeling. The characteristics and nature of dislocation loops are determined using traditional transmission electron microscopy and atomic resolution scanning transmission electron microscopy techniques. Loop density and diameter are analyzed using a kinetic rate theory that considers stoichiometric loop evolution. The energetics of different dislocation loop types are studied using molecular dynamics simulations.