Determination of Thermal Accommodation Coefficients of Inert Gases on a Surface of Vitreous UO₂ at ∼35°C

Estimation of gap conductance in nuclear reactor fuel rods requires values for thermal accommodation coefficients of several gases on Zircaloy, uranium-dioxide, stainless steel, and other surfaces. These values for UO₂ have now been obtained by observing cooling rates of a UO₂ sphere suspended in the several gases in a manner similar to the authors’ previous work on Zircaloy-2. These measurements are on so-called “engineering” surfaces, and no special attempt other than mild baking under high vacuum pumping was used to clean the surfaces.