Feasibility study for the criticality calculations of the LEU+ with ATF fuels

This study evaluates the criticality safety of Accident Tolerant Fuel (ATF) and LEU+ (5–10 wt% U-235) in the APR-1400 spent fuel pool (Region 1) and new fuel storage vault (NFSV) using SCALE 6.3.1's CSAS6/KENO-VI module. It was confirmed that simply increasing fuel enrichment above 5 wt% significantly raises criticality risk. To solve this risk, neutron absorber plates should be added to existing storage racks. By adding absorbers, ATF enriched up to 8 wt% in Region 1 and 10 wt% in the NFSV remained safely subcritical. Compliance with NRC guidelines necessitates such absorber modifications, especially considering boron areal density, flux trap characteristics. Consequently, although higher enrichment elevates criticality risks, the proper design of absorber plates can ensure sufficient safety margins. These findings are expected to aid in designing and operating storage facilities for future adoption of LEU+ and ATF.