Towards a direct comparison of practical CSE with BUC approaches. Benchmark for a pseudo-application case with user-defined NCS criteria

This paper aims to introduce the recently initiated OECD/NEA/WPNCS subgroup (SG13) calculation benchmark exercise. The SG13 objective is to provide a comparison of existing Nuclear Criticality Safety (NCS) approaches in application to final disposal canisters loaded with used nuclear fuel (UNF). An output of such a study would inform/support practical applications for UNF safe transportation and final disposal, by enabling a better understanding of important aspects of the loading curve determination methodology, such as the Upper Safety Limit (USL) definition, and providing further insight into the expected methodological uncertainties. Furthermore, this study would provide very valuable information for nuclear waste management organizations to facilitate and optimize the designing process of the UNF disposal canisters and geological repositories. The scope of the envisioned required computations will be limited to criticality calculations, optionally complemented with the nuclear data (ND) uncertainty propagation, in accordance with the participants' implementation. The requested result is the loading curve (LC) in the form of the required burnup (BU) vs. the initial U-235 enrichment. The participants' task is to determine the BU values at which the model k_eff meets the NCS criteria for each initial enrichment by performing their own criticality calculations (i.e. following their own methodologies). Based on this determination, the participants will obtain the loading curves, which represent the final result of the task. The NCS criteria are to be defined by the participants individually, whereby a common administrative margin for subcriticality equal to 5% (Δk_eff) will be used. (author)