A CHANNELING STUDY OF ION-IMPLANTATION DAMAGE IN UO2 AND UN

Radiation damage in UO2 and UN implanted with different doses of light (Kr) and heavy (Te, Xe, Cs) fission product ions in the energy range of 40-500 keV was studied in the as-implanted state (at 77 K and at room temperature) as well as following isochronal anneals up to 1440° C with Rutherford backscattering (RBS)/channeling techniques and with transmission electron microscopy (TEM). The largely ionic UO2 showed a damage peak coinciding with the range profile of the implanted ions. No long range migration of the defects was seen. In contrast, the largely metallic UN showed the dechanneling knees known from metals proving the migration of U atoms into the undamaged crystal, even at liquid N2 temperature. The number of displaced U atoms in UO2 per implanted ion decreased with ion dose and approached ~ 1, indicating important instantaneous defect recombination. The thermal recovery showed stages which can be interpreted in terms of the defect structure observed in TEM. The defect structure was also investigated by measuring the energy dependence of RBS (for UN). TEM showed the development of a dislocation network between the distorted and the virgin regions of UN crystals. The lattice location of the heavy ions was also determined. The implication of these results for the use of UO2 and UN as nuclear fuels is discussed. © 1990.