Conditions, consequences and prevention ways of behind-the-casing flow in deep well injection disposal of liquid waste sites

Abstract

The main detection methods, signs, geotechnical conditions, factors and potential consequences of liquid radioactive waste (LRW) behind-the-casing flow are described in the paper. Based on the modeling results for the real LRW components behind-the-casing flow, the mechanism of behind-the-casing flows evolution in the intervals of wells with increased permeability of cement stone are presented. The concentration of LRW components in these intervals changes significantly in time and depends not only on their current concentration in the waste and the permeability of the rock, but also on the pressure gradient, the direction and absolute value of which are determined by the well operation mode and natural hydrogeological conditions. It is noted that behind-the-casing flows of groundwater and LRW components are formed primary in injection wells, above its filter and top of aquifer used for LRW disposal (operational aquifer). The behind-the-casing flows lead to technogenic changes in the geological environment, which are local in space and time, and reduce the safety of such facilities as deep-level disposal sites for LRW (DDF LRW). The vertical channel of increased permeability around injection wells and behind-the-casing flows may be prevented by improving the design and construction materials of wells, adjustment of the LRW disposal mode and other methods, including the use of new sealing materials and clarifying technical solutions.