Advanced vacuum drying technique for residual water removal from damaged spent fuel rods

This study presents a novel vacuum drying methodology specifically designed for damaged nuclear fuel, addressing the limitations of conventional non-stop and step-hold depressurization methods. Experimental investigations were conducted using simulated damaged nuclear fuel specimens with varying pinhole sizes (0.3–2.0 mm), comparing traditional approaches with the newly developed method. The innovative technique employs strategic pump capacity modulation, initially operating at 600 L/min before reducing to 100 L/min near the phase change boundary, effectively maximizing evaporation while preventing ice formation. Results demonstrate superior water removal efficiency, achieving complete drying (100 % removal) for 2.0 mm crack cases, compared to maximum 68.99 % removal using traditional methods. The new approach achieved up to 2.314 times greater evaporation rates than conventional methods, with significantly improved removal efficiencies across all pinhole sizes (33.14–100 % versus 14.32–68.99 %). While requiring longer processing times (7512 s versus 4536.3 s), the enhanced water removal capability justifies this trade-off. The study establishes critical parameters for damaged fuel drying, including optimal pinhole size requirements (≥2.0 mm) and phase change boundary manipulation techniques. These findings provide crucial insights for improving spent nuclear fuel dry storage safety, particularly in preventing long-term corrosion risks from residual moisture.