On the uncertainty and sensitivity analysis of experiments with supercritical water with TRACE and SUSA

This study was performed at the Institute for Neutron Physics and Reactor Technology at Karlsruhe Institute of Technology and is addressed to establish the combined usage of the best-estimate code TRACE and the uncertainty and sensitivity analysis tool SUSA, for safety related investigations of current and future nuclear energy systems. In the frame of this paper the applicability to supercritical water related investigations is covered. Several Nusselt correlation for the heat transfer to supercritical water are available and have been evaluated in previous investigations but not one of them gave satisfying results. Hence, the consideration of uncertainty and sensitivity measures applied to the topic of heat transfer seems to be an appropriate way. In a first step a post-test analysis of an experiment was conducted. Results showed that with the help of uncertainty and sensitivity methods parameters which affect the results most could be identified. The most important parameter was of course the Nusselt correlation. In addition to the identification of important parameters, the experimental results were enveloped by the calculated results. That means, in the sense of safety related evaluation of designs for reactors operated with supercritical water, that key parameters (cladding temperature) can be calculated with a certain confidence.