Thermal Conductivity and Emittance of Solid UO2. A Critical Review and Analysis of the Literature.

Abstract : Significant and important variations can be observed in material composition and properties of various species of U02, depending especially on the manufacturing process, mechanical and thermal treatment, and on the irradiation in the reactor. Consequently, substantial differences in porosity, uranium-to-oxygen ration, and, of course, impurities have an important influence on the thermal conductivity. The results on thermal conductivity measurements (some 300 publications) are compared with respect to both experimental conditions and condition of the samples used. The thermal conductivity of stoichiometric U02 with nearly theoretical density is well known up to the melting point with a maximum uncertainty of 15%. For the porosity dependence of the thermal conductivity predictive models can be used, taking into account the shape and distribution of the pores. It is difficult to find agreement between the calculated and the experimental results, for it is not possible to describe exactly the real pore stereometry by a distinct model. In many cases sufficient basic data required for numerical calculations are not given. Hence, a simple empirical formula for the porosity dependence of the thermal conductivity is given in this work. (Author)