In-depth analysis of water evaporation in damaged spent nuclear fuel after vacuum drying

• Analyzed pump suction rate, crack size, and water temperature to enhance vacuum drying for damaged spent nuclear fuel rods. • Higher pump suction rates significantly reduce drying times but can complicate the final stages of complete water removal. • Larger crack sizes facilitate greater water expulsion but prolong drying times due to complex secondary evaporation effects. • Increased residual water temperatures hinder removal efficiency by causing vapor entrapment despite high evaporation potential. • Provided key insights for optimizing vacuum drying protocols, essential for managing high-burnup fuel storage scenarios. The objective of this study is to quantify and interpret residual-water evaporation/retention behavior in a simulated damaged spent-fuel cladding during vacuum drying as a function of key operational and geometric parameters. A lab-scale vacuum-drying facility was used to conduct a parametric investigation by varying vacuum pump suction capacity (100–600 L/min), defect diameter (0.3–2.0 mm), and initial water temperature (20–80 °C), and by evaluating water removal after the vacuum-drying criterion was satisfied. The results show that increasing suction capacity to 600 L/min reduced the time to meet the drying criterion by more than 50% compared with 100 L/min, while rapid cooling at high suction could hinder complete removal. Circular defect geometry strongly governed bulk discharge: a 2.0 mm defect achieved up to 75% removal, whereas a 0.3 mm defect yielded ∼ 15%. Higher initial water temperature (80 °C) did not improve removal as expected; instead, vapor entrapment associated with buoyancy reduced removal efficiency relative to 20 °C. Contour mapping indicated residual-water retention spanning 24.80–88.80% across the tested conditions, with defect size as the dominant factor. These findings provide experimentally grounded guidance for interpreting and optimizing vacuum-drying performance for damaged fuel configurations, including conditions relevant to high-burnup thermal loads.