Iodine Release and Bubble Formation in Oxide Fuels

Abstract

Iodine, rubidium, and krypton were ion-beam implanted into specimens of thoria, simulated high burnup thoria, and urania. Release of iodine from the thoria specimens was examined from 250 to 1700 degrees C, and the results were compared with those from similar tests with xenon, reported previously. Differences between iodine and xenon behaviour in thoria are interpreted as evidence either for different intragranular mobilities or for surface influences on iod1ne. Release of iodine, rubidium, and krypton from simulated high burnup thoria fuel was not enhanced compared to release from fresh thoria. Transmission electron


microscopy showed cube-shaped bubbles or bubble-like precipitates in urania implanted with iodine and heat treated at 900 degrees C. Morphology changes in the bubbles at higher temperatures are described.