FISSION GAS RE-SOLUTION RATES. Quarterly Report No. 5, July 1--September 30, 1971.

This fifth quarterly.report describes progress in an experimental program to determine the re-solution rates of fission gases in oxide nuclear fuels under irradiation.As-irradiated specimP.ns at burnups of approximately 0.1, 1.2 and 3.2 x 1020 fissionsfcm3 were examined by transmission electron.microscopy.Considerable radiation damage and some dislocations that were not present in the as-fabricated samples were observed.No fission gas bubbles were detected.Annealing of the irradiated specimens in the electron microscope a•t high beam currents produced fission gas bubbles.Specimens annealed at 130a°C for 16 hours exhibited detectable bubbles only on grain boundaries and at dislocations.A specimen which was heated to 157!f'C after ir;adiation showed an essentially uniform concen.tration of bubbles with a log-normal size distribution; the geometric mean diameter was 72 A and the geometric smndard deviation was 1.42.