Severe accident code-to-code comparison for two accident scenarios in a spent fuel pool

•Benchmark of 6 SA codes (14 participants) for two accident scenarios in a Spent Fuel Pool.•Differences in draining velocity induced scattering in the onset of fuel heat-up (LOCA scenario).•For both scenarios, important spreading in the heating rate and hydrogen production.•Discrepancies due to differences in physical models and in the representation of the storage racks.•Criticality risk assessment by 5 participants with a rather good agreement of the results. Spent fuel pools (SFPs) are large structures equipped with storage racks designed to temporarily store irradiated nuclear fuel removed from the reactor. SFP severe accidents have long been considered as highly improbable since the accident progression is slow (in comparison with reactor core accidents) and let time to corrective operator actions. However, the accident at the Fukushima Dai-ichi Nuclear Power Plants has highlighted the vulnerability of nuclear fuels that are stored in SFPs in case of prolonged loss-of-cooling accidents and consequently renewed international interest in the safety of SFPs. In this context, the AIR-SFP project, funded by the Euratom 7th FP in the frame of the NUGENIA+ project, was launched in May 2015 with 15 participants. One of the objectives was to assess the applicability of Severe Accident (SA) codes, which were initially developed for reactor applications, to the calculation of transients in SFPs. To reach this objective, a benchmark, including a criticality risk assessment, was carried out. The degradation progression was computed by 14 participants with 6 different SA codes and 5 have participated to the criticality risk assessment. Main results are presented as well as conclusions that have been drawn concerning SA codes readiness to address these “beyond-scope” scenarios.