Analysis of the inherent response of nuclear spent fuel pools

Highlights: • The impact of the SFP fuel assembly arrangement is more limited than expected. • The offload power does not present a crucial role in fuel damage progression. • User effects on the building modelling greatly impacts the SFP response. - Abstract: This work performs an analysis of the inherent nuclear spent fuel pool response to a loss of pool cooling accident. The influence of fuel offload times, fuel assembly arrangement, fuel assembly binning for modelling, and building compartmentalization are evaluated. These impacts are assessed through sensitivity calculations performed with the MAAP code. Results are compared in terms of selected significant safety quantities such as fuel uncovery time, hydrogen generation, building temperature, relocated mass to the floor, and integrated total radiological dose at 1 km distance from the spent fuel pool. According to the results, the impact of the fuel assembly arrangement on the output safety quantities is more limited than initially expected. Also, the offload power (as a function of elapsed time between shutdown and removal from the reactor pressure vessel to the spent fuel pool), relevant in the pre-uncovery phase, does not present a crucial role in fuel damage progression. Somewhat unexpectedly, user effects on the building modelling hosting the pool significantly affect its inherent response. This is due to the large influence that natural circulation currents of gas have on mitigating fuel damage as such currents significantly rely on the modelling of the building in terms of nodalization, thermodynamic imposed conditions and heat sinks configuration. Follow-on work is identified to address uncertainties in the calculation of natural convective flows and heat transfer.