The post-irradiation annealing behaviour of fission gas bubbles in various purities of uranium

Abstract

The gas bubble distribution in irradiated uranium foils subjected to a wide range of annealing treatments has been studied by transmission electron microscopy. The results show that: 1. 1. In the absence of stress, the growth of fission gas bubbles ~ 100 Å diameter in the alpha phase is extremely slow for both pure and adjusted uranium for times up to 1000 h. 2. 2. Post-irradiation annealing at 600 °C of material irradiated at low temperature is not equivalent to irradiation at 600 °C. 3. 3. In the absence of stress, the migration of fission gas bubbles ~ 100 Å diameter at 800 °C for pure and adjusted uranium is slow but measurable. 4. 4. The application of stress during annealing of ~ 100 Å bubbles in the α phase at 600 °C does not noticeably affect the coarsening rate. 5. 5. The gas bubble density increases with dose when the gas bubbles are formed after irradiation but is independent of dose (after very small doses) for high-temperature irradiations.