APPLICATION OF TSUNAMI AND TSURFER FOR VALIDATION OF BURNUP CREDIT IN THE CRITICALITY SAFETY ANALYSIS OF A TRANSPORT CASK

In up-to-date criticality safety analysis of spent nuclear, fuel modern calculation methods are applied to take into account the reduction of reactivity of nuclear fuel due to the burnup process. The use of these methods has to be validated by comparison to experimental data and usually this leads to a bias, which has to be considered in the neutron multiplication factor keff. Applying the so-called burnup credit, this task is complex since any fission products and actinides considered in the calculation have to be validated by adequate experiments. However, for typical applications like a spent fuel transport cask there are no public available experimental data which directly match the conditions of an application and include all the fission products typically being used. Thus the user is obliged to validate the fission products separately by choosing experimental data which match the conditions of the application at least partially and include one or more of the fission products of interest. Since 2009 new tools in the latest version 6 of the American code package SCALE (“Standardized Computer Analyses for Licensing Evaluation”) from Oak Ridge National Laboratory have been provided to study and quantify the bias and uncertainty of an application calculation based on the validation calculations of experiments. E.g., a dedicated analysis tool named TSUNAMI can be used to quantify the similarity of an experiment to the respective application. We are applying these tools, amongst those especially TSUNAMI and TSURFER, to a generic cask model and study their potential with regard to a possible validation. The experimental data used are taken from the International Criticality Safety Benchmark Evaluation Project (ICSBEP), an internationally supported benchmark database of high quality. TSURFER is intended to allow for the determination of the bias of a computation even if no experiment exactly matching the application condition is available. Special attention will be drawn to the influence of the fission products on the bias and the reliability of this bias in dependence on the available experiments.