Large Scale CFD Simulations of Spent Fuel Pool Accident Scenarios Using a Porous Body Approach

After the accident at the Fukushima Daiichi nuclear power plant, the safety of Spent Fuel Pools moved into the focus of nuclear safety research. For the thermo-hydraulic analysis, system- or severe accident codes are used predomenantly, although simplified assumptions have to be made for the flow paths around the storage racks and inside the reactor building. The present work uses CFD in order to investigate the large scale convective phenomena involved and to examine their influence on the cooling of the individual fuel assemblies. All relevant thermophysical phenomena are discussed together with the corresponding modeling. The Spent Fuel Pool of Fukushima’s Unit 4 with the loading at the time of the accident serves as a test case. The paper gives a first qualitative impression on the emerging flow paths for the scenario of partially as well as fully uncovered fuel assemblies. Finally an outlook is given, how CFD can help to study the safety of Spent Fuel Pools as a standalone tool or by delivering input to one-dimensional codes.