Temperature Variation and Ice Formation in Nuclide-Contaminated Sandy Soil: Implications for Artificial Ground Freezing

This study addresses the critical challenge of optimizing parameters for artificial ground freezing (AGF), a technology used for the emergency containment of nuclear-contaminated water leaks. Through systematic freezing tests and nuclear magnetic resonance (NMR) analyses, the temperature variation patterns and ice formation characteristics in nuclide-contaminated (Cs, Sr, I) sandy soils were elucidated. The main findings are as follows: Sr2+ compresses the electric double layer due to its high valence state, resulting in the highest free water content. The soil nucleation temperature (Tsn) is 0.8°C lower, and the supercooling duration (ts) is extended by 47% compared to Cs+, necessitating enhanced freezing below −35°C. Cs+ exhibits minimal ice formation resistance due to strong adsorption, making it suitable for conventional AGF (‒25°C to ‒35°C). A fines content of 20% represents the optimal threshold, reducing the ts by 33% and decreasing the average curvature of the temperature curve (κa) by 50% through ice-nucleation effects, whereas excessive fines (40%) inhibit thermal conduction via thickened bound-water films. In the sandy soil stratum, ‒35°C represents the critical temperature for stable freezing efficiency. Nuclide concentrations > 5 g/L cause a 0.5°C Tsn reduction without significant ts variations, highlighting the priority of ion migration control in high-concentration strata. NMR confirms that the latent heat release during phase transition in Sr2+-contaminated soils is minimal, leading to a maximum κa value during the continuous cooling stage, which requires thermal compensation measures. The developed fine-particle modulation, staged freezing, κ-monitoring technical framework provides both theoretical foundations and engineering design methodologies for nuclear leakage disposal through freezing barriers.