Technogenesis and its effect on radionuclide migration on near-surface storage sites

Abstract

Information on the conditions of near-surface storage sites for radwastes in the central region of the country and scenarios for possible migration of radionuclides with a liquid phase is presented for sections located in different geographic-climatic zones. The distinguishing features of the geologicalhydrogeological conditions of the locations of near-surface storage facilities are shown. It is noted that there is a possibility and danger of radionuclides escaping into the environment by "overflowing" during the spring months, irrespective of the regional location of the radwastes.Sections for siting near-surface radwaste storage were chosen at the beginning of the 1960s [1]. The main criterion for choosing them was preventing radionuclide migration through the aeration zone into the first zone from the surface of a water-bearing stratum as a result of vertical flow infiltration. On the basis of this criterion, most near-surface storage sites were tied to the surrounding rock, mainly clayey rocks which possess low water permeability and high sorption capacity. The closest water-bearing horizon used for various needs, depending on the geographic region, was located at depths 10-60 m from the base layer of the radwaste repository [2, 3].However, experience in building and operating near-surface type storage facilities has shown that technogenic actions (technogenesis) change the initial properties of the geological and engineering barriers [4,5]. Ultimately, technogenesis can change the main migration paths for radionuclides, including the direct flow onto the surface in the altered sections [6].The present work examines for several sites at the Radon special works scenarios for possible escape of radionuclides with a liquid phase into the environment; these scenarios can be used to optimize the siting of near-surface storage facilities. The following were done for this: 1) the data from multiyear geological-hydrogeological and nature-climate studies along the sites were analyzed and generalized in order to validate the main migration paths of radionuclides into the environment;2) these were used as a basis for outlining the natural conditions, calculating the paths for radionuclide transfer into the environment by various scenarios with an evaluation of the importance as compared with other possible ways of escaping into the environment; and3) the role of technogenesis was evaluated. Five sites in the Central, Povolozhie, and Southern regions were chosen for investigation: Moscow, Samara, Saratov, Volgograd, and Rostov special works. These sites are tied to clayey deposits (heavy sandy loams and quaternary loams), but they are located in different nature-climate conditions (Tables 1, 2; Fig. 1).The thickness of the rocks in the aeration zone and the average slope of the surface were obtained from geological and topographic-geodesic research at the beginning of the 1960s and the coefficients of filtration and water yield were obtained under field and laboratory conditions (filling of test pits and individual well...