Uncertainty and sensitivity analysis for the modeling of transients with interaction of thermal hydraulics and neutron kinetics

The GRS methodology to assess the uncertainty of the calculation results of computer simulation codes was applied to the coupled code system DYN3D/ATHLET, consisting of a 3D neutron kinetic core model and a thermal hydraulic system code. It was used to make a statistical analysis of the result parameters from the output data of the DYN3D/ATHLET-calculation. A number of variation calculations with randomly distributed input parameters within given boundaries was carried out. On that basis, time-dependent rank correlation coefficients were calculated showing the influence of the varied parameters on the output parameter under investigation. The most interesting output parameters are the physical parameters for which experimental data are available. The calculation results allowed also the determination of time-dependent tolerance intervals for given coverage and confidence. The comparison of the experimental data, the (best-estimate) reference solution and the tolerance intervals showed how the agreement between experiment and calculation could be quantified. In most of the cases the tolerance intervals include the experimental curves. A compiled list of the most important input parameters based on the rank correlation coefficients shows, which input parameters and models are responsible for the deviations.