Application of CFD towards the thermo-hydraulic analysis of Spent Fuel Pool accidents

The thermo-hydraulic analysis of Spent Fuel Pool accident scenarios is predominantly carried out using one-dimensional codes. This implies that simplified assumptions have to be made for the flow paths around the storage racks and inside the reactor building. Here, CFD is employed to investigate the convective phenomena involved and to examine their relevance for the cooling of the individual fuel assemblies, which themselves are modeled as porous bodies. The paper includes a discussion of relevant thermohydraulic aspects and the modeling on the fuel assembly scale as well as the reactor building scale. First preliminary large scale simulations are presented, using the design of Fukushima’s Unit 4 with the corresponding Spent Fuel Pool loading as a test case. A loss of coolant due to the outage of the cooling system and subsequent boil-off is assumed, leading to partially or fully uncovered fuel assemblies. The emerging flow paths are described qualitatively. This ongoing work gives an outlook how CFD can help to study the safety of Spent Fuel Pools as a standalone tool or by delivering input to one-dimensional codes.