ION-IMPLANTATION STUDIES OF UO2 AND UN

Ion implantation of fission products (rare gases Kr and Xe, volatiles Te, I, Rb, Cs) in UO2 and UN has been used to perform separate effect studies to investigate formation and recovery of radiation damage as well as the behavior (lattice location, diffusion, release, precipitation, etc.) of the fission products. Both radioactive beams to provide tracers for release measurements and inactive beams were used, with widely varying doses between approximately 10(11) and 10(17) ions/cm2 at energies between 40 and 500 keV. The implantation temperatures were varied between 5 and 770 K and furnace anneals were performed up to 2070 K. The analytical techniques applied were Rutherford backscattering (RBS) channeling supported by electron microscopy (TEM, SEM) and conventional counting methods for the tracers. A very large data base on damage formation and recovery for both UO2 and UN and on fission product behavior has been obtained and is summarized. A large fraction of the damage formed is shown to recover instantaneously, helping to explain the structural stability of the fuels and the absence of amorphization. Half of the remaining metal defects (the interstitials) migrate to sinks below room temperature in both UO2 and UN. Also, channeling results indicating coherent precipitation of volatiles even at room temperature are reported together with new data on low temperature release of these impurities.