THE EMANATION OF RADON 220 FROM SINTERED UO$sub 2$ POWDERS AND PLATES

The emanation of thoron (Rn/sup 220/) from sintered UO/sub 2/ powders and plates was measured as a function of temperature. The uranium oxide samples were indexed with radiothorium by coprecipitation and coevaporation techniques. The emanation measurements were performed in a flow system, using an alpha scintillation detector and a helium-hydrogen carrier gas mixture. Both the radiothorium concentration (5 to 100 mu C/g UO/sub 2/) and the uranium oxide density (71 to 99 percent TD) were varied. The surface areas and densities of the UO/sub 2/ plates were measured by krypton gas adsorption and liquid immersion techniques, respectively. Assuming a diffusion mechanism, diffusion coefficients for thoron in sintered UO/sub 2/ were calculated as a function of temperature. The data were represented by an equation of the form, D = D/sub O/ exp (-Q/RT). An apparent increase in both activation energy (Q) and D/sub O/ with density was observed for the 1100 to 1450 deg C temperature range. For some samples the thoron emanating power could be measured at temperatures as low as 400 deg C. Log D versus 1/T plots from 400 to 1450 deg C gave intersecttng straight lines with different activation energies. One intersection occurred near the Tammann temperature. The emanation of Rn/sup 220/ from UO/sub 2/ apparently involves several types of diffusion processes. (auth