IRRADIATION-INDUCED PHASE CHANGES IN ZrO$sub 2$-UO$sub 2$ FUELS

After comparatively small amounts of neutron irradiation, multiphase mixtures in the ZrO/sub 2/--UO/sub 2/ binary system combine into a single phase. Above 8 x 10/sup 20/ fissions/cc, this single phase is cubic. This cubic phase is apparently continuous from UO/sub 2/ to ZrO/sub 2/. The cell edge varies linearly with molar composition, but not significantly with radiation exposure. It is postulated that there exists a hightemperature cubic phase which cannot be quenched using ordinary furnace techniques at compositions with less than 70 wt% UO/sub 2/. (auth)