Improving spent nuclear fuel vacuum drying efficiency via pump modulation at the liquid–vapor phase transition

• This study proposes phase-boundary pump modulation that “surfs” the liquid–vapor transition to sustain vigorous boiling and accelerate vacuum drying. • Controlled pump modulation prevents interfacial icing, avoiding the transport penalties and measurement bias associated with rapid deep pull-down. • Compared with conventional stepwise depressurization, the approach achieves higher evaporation efficiency by shaping pressure descent and residence near the transition. • This study validates the mechanisms using multi-channel diagnostics, including gravimetry, condensate tracking, dew-point/flow monitoring, and near-surface thermocouples. • Applicability is confirmed in a drainage-hole simulant under conditions aligned with dry-storage acceptance criteria. This study explores advanced vacuum drying strategies for spent nuclear fuel, focusing on thermodynamic optimization through precise pump modulation at phase transition boundaries. Utilizing a high-capacity vacuum pump within a 98-liter canister, the research underscores the critical role of dynamic pump performance in enhancing drying efficiency. A salient finding is the elevated average evaporation rate of 33.703 mg/s achieved by fine-tuning pump flow from 400 L/min near 10 torr to below 5 torr before finally setting at 100 L/min—surpassing direct transitions to 100 L/min. This demonstrates the potential for further optimization by exploiting sub-10 torr pressures, thus mitigating ice formation risks and boosting efficiency through targeted modulation. Comparative analysis illustrates improvements up to 3.486-fold when employing dual pump transitions, highlighting the transformative potential of adaptive pumping. Results confirm that strategic modulation fosters robust moisture removal, ensuring complete drying with pressures below three torr for 30 min, marking a significant advancement in nuclear fuel storage methodologies.