Spent Nuclear Fuel Heatup Calculations Supporting Emergency Planning Exemption Using CFD Code

One of the important criteria of the emergency planning (EP) exemption for nuclear power plant (NPP) decommissioning is a minimum of 10 h available before any spent nuclear fuel (SNF) cladding temperature reaches 900°C after a complete loss of the spent fuel pool (SFP) water inventory with no heat loss (adiabatic). This study used the computational fluid dynamics (CFD) code to analyze the cladding heatup time of the SFP for a boiling water reactor. First, the developed CFD local model of the SFP was compared with the U.S. Nuclear Regulatory Commission’s (NRC’s) report on SFP heatup calculations, NSIR-2015-001. The CFD results were similar to the theoretical calculations and MELCOR results for cases with and without racks. The results also indicated that racks can significantly delay the heatup time. This study also performed sensitivity studies to identify the effects of fuel burnup, hottest assembly, and fuel loading configurations. After validation of the CFD local model against MELCOR, a whole-pool CFD model of the Chinshan SFP was developed and successfully applied to analysis for the EP exemption of the Chinshan NPP. The results predicted using the whole-pool CFD model of the Chinshan SFP agreed well with the MELCOR results. Additionally, the required 900°C heatup times were calculated based on the actual decay heat of each cycle and fuel loading at the Chinshan SFP. The required 900°C heatup times were 19.1, 54, and 64.6 h for the Chinshan SFP at 1, 5, and 10 years after shutdown, respectively. The actual fuel loading and decay heat of the Chinshan SFP met the requirements for the EP exemption after 1 year of shutdown. The main purpose of this study is to demonstrate that the CFD code can be used as a tool to calculate SFP fuel assembly heatup times for the EP exemption. The advantage of using the CFD code instead of MELCOR is that the whole-pool SFP model can be developed based on the actual decay heat of each cycle and fuel loading and to determine more realistic fuel assembly heatup time for the EP exemption.