Precision of moisture quantification in canisters during the vacuum desiccation process prior to the dry storage of spent nuclear fuel

Abstract

This study investigates the complex interplay between canister volume and vacuum pump capacity during vacuum desiccation, revealing critical insights into optimizing drying processes. A high-capacity vacuum pump used with a small-volume canister can cause rapid energy extraction, potentially freezing moisture, while a lowcapacity pump for a large-volume canister extends drying times. Through systematic lab-scale experiments, we found that higher pump capacities increase evaporation rates due to the latent heat consumption during water phase changes, especially evident during boiling due to enhanced surface area. Smaller canisters exhibited lower evaporation before and after boiling but surpassed larger canisters during boiling. Conversely, larger canisters faced delayed boiling and prolonged drying. A cross-analysis of residual moisture measuring tools—comparing initial errors over 10 % between precision mass balances and steam flow meters—achieved error reduction to 1.69 %–6.47 % by applying Magnus relative humidity equations and dew point data. Despite the steam flow meter’s limitations in low humidity and high vacuum, these findings support refining and advancing drying technologies for residual moisture elimination in spent nuclear fuel canisters. Further research into quantification methodologies is recommended to ensure enhanced efficiency and reliability in practical applications of such systems.