Radon attenuation characteristics of compacted soil layer for uranium mill tailings pond subjected to drying-wetting cycles.

Compacted soil layer (CSL) is generally designed for uranium mill tailings (UMTs) pond to form the radon seals, whereas it is usually affected by drying-wetting environmental conditions. To summarize the radon attenuation degradation performance of CSL subjected to drying-wetting cycles, an experiment with the application of meteorological data was developed. This paper focuses on the evolution of the soil apparent porosity, soil integrity and radon attenuation characteristics of CSL during continuous drying-wetting cycles. Image processing and a nonmetal acoustic wave detector were applied to analyze variations in the soil surface and internal defects, and the radon concentration was measured to reveal the radon attenuation performance of the CSL. The results reveal that with successive drying-wetting cycles, the soil apparent porosity increased, and the soil pores were enlarged. The soil integrity underwent dynamic recombination or reorganization and eventually reached a steady state. Moreover, it was observed that the saturated state of the uppermost soil led to a sharp increase in radon concentration (capping effect), and the decrease in accumulated radon concentration during the initial period resulted from the coupling effect of soil moisture, temperature and ambient pressure. The observations confirm that the drying-wetting environmental conditions markedly affect the radon migration channels and environment in the CSL, which provides a theoretical foundation for UMTs pond governance and radiation safety management.