IN-PILE MEASUREMENT OF THE ELECTRICAL RESISTIVITY AND THERMOELECTRIC POWER OF SINTERED UO$sub 2$

Two thin plates of high-density UO/sub 2/ were sandwiched together with thermocouples between them and pressed against the outer surfaces. The thermocouples were used as electrodes and the electrical resistivity of the UO/sub 2/ measured by the potential drop method using corresponding arms of the thermocouples as current lead-in wires and potential probes. The UO/sub 2/ was heated by its own fission heat and the electrical resistivity measured at temperatures from 50 to 972 deg C. Preirradiation measurements were made using an electric furnace to obtain temperatures to 750 deg C. Electrical resistivity did not change with irradiation up to about 10/sup 1//sup 8/ nvt, at which point the resistivity decreased by a factor of 3. The resistivity ranged from 8.75 x 10/sup 3/ ohm-cm at room temperature (before irradiation) to 0.4 ohm-cm at 773 deg C (after nvt > 10/sup 1//sup 8/). The activation energy was 0.5 ev during irradiation as compared with 0.65 ev before irradiation. The temperature between the plates was higher than the outside temperature during irradiation. This thermal gradient created a thermoelectric emf between the UO/sub 2/ and the platinum thermocouples. The thermoelectric emf for the Pt-UO/sub 2/-Pt system ranged from 130 mu v/ deg C at 162 deg C to 29 mu v/ deg C at 900 deg C. The UO/sub 2/ behaved lixe an n-type conductor during irradiation. (auth)