Evaluation of silver transport through SiC during the German HTR fuel program

For direct cycle gas cooled high-temperature reactor designs operating conditions may be limited as a result of excessive maintenance dose rates caused by the 110mAg source term on the turbine. The accurate prediction of silver fission and activation products’ release during normal operation is required to ensure regulatory compliance and economic viability of planned power plants. Fuel qualification programs should provide satisfactory results to ensure correct analyses, but will not be available for many years. In the meantime data from the German fuel development program are utilized to develop and validate analyses methods. Previously, from primarily material and fuel component test results, transport models and parameters through all the fuel materials and components were derived. Good verification of silver transport in fuel materials and components were achieved with the exception of SiC. An earlier study of all German fuel irradiation tests identified a set of applicable tests to be used to evaluate silver transport through high-quality SiC. Simplified first estimate analyses were performed on different transport models. This was followed by an in depth study with a more complete diffusion model on all applicable irradiation test results to derive new transport parameters for silver in SiC. These new parameters were applied in an evaluation of some heat-up tests of irradiated fuel spheres to assess the range for which they are valid.