Experimental study on the radon barrier performance of cover materials under frozen and unfrozen isothermal conditions

Seasonal temperature variations, particularly frozen and unfrozen conditions, exert a considerable influence on radon exhalation from the surfaces of uranium tailings impoundments. To evaluate the radon barrier performance of cover materials under frozen and unfrozen isothermal conditions, three indoor-cured materials-pure laterite, a laterite-bentonite mixture (1:1 mass ratio), and a laterite-zeolite powder mixture (1:1 mass ratio)-were tested across five temperature setpoints (-20 °C, -10 °C, 0 °C, 10 °C, and 20 °C) in a temperature-controlled test chamber, using bare uranium tailings as a control. The results indicate that: (1) At a cover thickness of 15 cm, the radon barrier efficiencies of pure laterite, the laterite-zeolite powder mixture, and the laterite-bentonite mixture ranged from 89.07% to ∼100%, 81.99% to ∼100%, and 98.59% to ∼100%, respectively, with barrier efficiency gradually increasing as temperature decreased. (2) For all materials, the rate of change in radon barrier efficiency with temperature was lower above 0 °C than below 0 °C. The temperature sensitivity followed the order: laterite-zeolite powder mixture > pure laterite > laterite-bentonite mixture, demonstrating that the laterite-bentonite mixture maintained the most stable performance across thermal fluctuations. Additionally, preliminary empirical piecewise equations were established to describe the relationship between barrier efficiency and temperature across frozen and unfrozen regimes. Overall, this study demonstrates that radon exhalation barrier by cover materials depends not only on their intrinsic physical properties and ambient temperature, but also exhibits distinct behavioral shifts between frozen and unfrozen states.