On the options for incorporating nuclear data uncertainties in criticality safety assessments for LWR fuel

In view of massive operations with LWR spent nuclear fuel for the forthcoming final geological disposal, as expected, e.g., in Switzerland, needs are growing for exhaustive and enhanced criticality safety assessments to allow optimization of the spent nuclear fuel transportation, storage and disposal strategies. At the Paul Scherrer Institute (PSI) the current base methodology for criticality safety evaluations (CSE) used for Swiss applications is focused, following common practices, on establishing an upper subcritical limit (USL) for the effective neutron multiplication factor (keff), based on a statistical evaluation of the obtained validation results in terms of the calculated-to-benchmark keff values. Recently, new calculation capabilities have been developed at PSI in particular to propagate neutron-nuclear data (ND) uncertainties in calculations with Monte Carlo transport codes in combination with general-purpose ND libraries. The computation tool NUSS for random sampling the ACE formatted ND libraries was developed for that purpose. Thereby, this paper concerns how these new calculation capacities could improve the present PSI CSE methodology and the prospects for its upgrading towards burnup credit applications are consequently discussed.