Isotopic Study of Deep Groundwater in Jijicao Preselected Site for China's High Level Radioactive Waste Disposal Repository

At present,deep geological disposal scheme is widely accepted for high level radioactive waste disposal in the world.The precondition of high level radioactive waste safe disposal for this scheme is to select a feasible site.The feasibility of a site mainly depends on the hydrogeological conditions.A potential site for high level radioactive waste disposal needs very low-permeability rock body to isolate the waste.The use of classical and conventional methods is limited for the research of very low-permeability rock body.But isotope hydrology techniques can be particularly valuable when used in conjunction with other hydrogeological methods.This paper,taking Jijicao preselected site of high level radioactive waste disposal repository in our country at present stage as an example,mainly studied the isotopic methods used in site hydrogeological research in granite body.According to the environmental isotopic component characteristics of groundwater in different depths and combined with hydrogeological conditions,the origin of groundwater was recognized and the main factors controlling the velocity of groundwater movement and alternation in the site was explored.The results show that 14~C age of deep groundwater in the area can reach about 8000years which indicates the deep groundwater movement and alternation is very slow.But the deep groundwater also contains some tritium which indicates it is recharged mainly byold coming from lateral flow and thenew waterrecharged from infiltration of local rainfall if little in the deep groundwater.In addition,through comparison of 14~C age of deep groundwater with percentage of core recovery of water sampling section in the boreholes,it is known that the factor controlling the velocity of groundwater movement and alternation in the granite body in the site area is fissure characteristics,but not