Abstract:

Hydrogeological condition is one of the most important factors in the site selection and site safety assessment for the disposal of high-level radioactive waste (HLW). Furthermore, groundwater recharge research is of importance in the study of hydrogeology. Beishan area in Gansu Province, China is a preselected priority region for disposal of China’s HLW. Beishan area locate in the north of Hexi Corridor, Gansu Province, about 70 km south of Yumen Town In order to find out the groundwater recharge in this area, this paper used the chloride mass balance (CMB) method in the unsaturated zone as well as the saturated zone. Considering the thickness and the lithology of the unsaturated zone, the typical profile and the available fieldwork, four typical profiles were carried out in Beishan area. They are located in Suanjingzi, Shazaoyuan and Xinchang respectively. In addition, this experiment successfully collected 45 samples of shallow groundwater. The groundwater level of most wells are less than 10 meters. The distribution of the wells is relatively evenly. The result indicated as follows: (1) In general, the applicability of the CMB method in Beishan area is good. The groundwater recharge rate ranges from 0.07 mm·a^-1 to 2.05 mm·a^-1 based on unsaturated CMB method, where all the profiles were located in the gully basin with relatively larger permeability. The groundwater recharge rate is approximately 0.26 mm·a^-1 based on saturated CMB method, which accounts for only 0.40% of the average annual precipitation. (2) The CMB method based on the unsaturated zone is limited where the background value is high. Therefore, other methods should be considered in these areas, such as the artificial tracer method, ³H, Br, water-table fluctuation method, water-budget models method. (3) The chloride concentration in atmospheric precipitation has a great effect on the results as the background input data. (4) Due to the complexity and uncertainty of the groundwater recharge research, it is suggested that other methods should be studied on the basis of this study, such as artificial tracer method, water-table fluctuation method, Darcy method, and so on. Through this research, the groundwater recharge rate in Beishan area was obtained for the first time. These achievements can be useful for the site selection and site safety assessment of the HLW repository. Moreover, it can also be helpful for the construction of the underground laboratory in the future.

Key words: groundwater recharge, high-level radioactive waste disposal, environmental tracer, chloride mass balance (CMB) method