The majority of uranium mill tailing impoundments in the southern part of China are located in humid subtropical regions where persistent rainfall and rapid evaporation of water after rain often occur. Under the prolonged influence of alternating wet and dry conditions, the covering soil layer of uranium mill tailing impoundments develops cracks, leading to the issue of degradation or even failure of the radon retardation effect. A beach surface of uranium mill tailing impoundments in the southern part of China is selected as the research object. Through use of a self-made simulation test device, a degradation experiment of uranium mill tailing covering soil models under wetting–drying cycles was conducted indoors. The experimental results indicate that with a constant amplitude of wetting–drying cycles, microcracks characterized by a narrow width and high abundance were mainly generated in the early-to-mid-stage of wetting–drying cycles. The main cracks, characterized by their wide width and less abundance, were mainly formed in the mid-to-late stage of wetting–drying cycles. After seven wetting–drying cycles, the total length of cracks showed a “stair-step” increase and the surface crack ratio exhibited a trend of moving from rapid growth to stable growth and then to a slight decline. The cumulative damage degree showed a rapid increase to stable growth with an increase in the number of wetting–drying cycles. Grey relational analysis revealed that, compared to other surface crack indicators, radon exhalation rate was the most closely correlated with the surface crack ratio. With a constant amplitude of wetting–drying cycles, the radon exhalation rate underwent four stages as the number of wetting–drying cycles increased: stage I witnessed a rapid increase, stage II witnessed a rapid decrease, stage III witnessed a gradual increase, and stage IV witnessed a stable or even slight decrease. With a constant number of wetting–drying cycles, the radon exhalation rate correspondingly increased with the amplitude of wetting–drying cycles, particularly noticeable when the alternation amplitude was 30 ± 20%. From the early mid-stage to the late stage of wetting–drying cycles, the curves of the radon exhalation rate, surface crack ratio, and cumulative damage degree tended to be consistent, showing a gradual increase. The research provided in this study offers valuable insights into radon control measures and environmental assessments on the beach surface of uranium mill tailing impoundments.

中文翻译：

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干湿循环对铀厂尾矿库覆盖土裂缝发育和氡阻滞影响的试验研究

我国南方地区的铀厂尾矿库大部分位于湿润的亚热带地区，经常出现持续降雨和雨后水分快速蒸发的情况。在干湿交替条件的长期影响下，铀厂尾矿库覆盖土层出现裂缝，导致氡阻滞效果下降甚至失效。选取我国南方铀矿尾矿库滩面作为研究对象。利用自制的模拟试验装置，在室内进行了干湿循环下铀厂尾矿覆盖土模型的降解实验。实验结果表明，在干湿循环幅度恒定的情况下，宽度窄、丰度高的微裂纹主要产生于干湿循环的早中期。主裂缝主要形成于干湿循环的中后期，宽度较宽，数量较少。经过7次干湿循环后，裂纹总长度呈现“阶梯式”增长，表面裂纹比例呈现出由快速增长到稳定增长再到小幅下降的趋势。随着干湿循环次数的增加，累积损伤程度呈现快速增加至稳定增长的趋势。灰色关联分析表明，与其他表面裂纹指标相比，氡析出率与表面裂纹率的相关性最为密切。在干湿循环幅度恒定的情况下，随着干湿循环次数的增加，氡析出率经历了四个阶段：第一阶段快速增加，第二阶段快速下降，第三阶段逐渐增加，第四阶段IV 平稳甚至小幅下降。在干湿循环次数一定的情况下，氡析出率随着干湿循环幅度的增大而相应增加，特别是当干湿交替幅度为30±20%时尤为明显。从干湿循环前期中期到后期，氡析出率、表面裂纹率、累积损伤度曲线趋于一致，呈现逐渐增加的趋势。本研究提供的研究为铀厂尾矿库海滩表面的氡气控制措施和环境评估提供了宝贵的见解。