Safety assessment of a subsurface radwaste repository in the region of the Leningradskaya NPP

Abstract

The propagation of radioactive contamination in non-head, near-surface, water-bearing strata is modeled in order to analyze the safety of a possible subsurface radwaste repository in the region of the Leningradskaya NPP. The propagation of radioactive contamination along the top water-bearing complex formed by Quaternary and Lower Cambrian deposits is studied. A map model approximation is used. The main contamination components are assumed to be 137 Cs, 90 Sr, and 60 Co. The propagation of contamination over 50 years is predicted. It is shown that the contamination of rocks by 137 Cs, 90 Sr, and 60 Co propagates only in the direct proximity of the section where they leak from the repository (at a distance not exceeding 10 meters). Effective handling of radioactive wastes is a necessary condition for the development of the nuclear energy complex [1, 2]. Analysis of the implementation possibilities and the safety and economic efficiency revealed that the most promising strategy is long-term or permanent placement of conditioned radwastes in subsurface repositories [3‐6]. It is thought that in the north-west of the Russian Federation such a repository could be located in direct proximity of the principal enterprises of the nuclear complex in the region: the Leningradskaya NPP and the Leningradskoye division of Radwaste Handling Enterprise (RosRAO), because this will make it possible to avoid the additional risk of radioactive contamination of the biosphere during transport of wastes from their production locations to the repository [7]. The main mechanism of the propagation of radioactive contamination from such a repository is transport of radionuclides by subsurface waters. Reliable isolation of wastes in a repository is achieved by an engineered barrier, which prevents radionuclides from migrating out of the wastes placed in the repository into subsurface waters, and natural (geological) barrier ‐ rock mass separating the repository from the biosphere [8]. The wastes can remain dangerous for the environment for hundreds of years. Partial degradation of the engineered barrier can occur over this time, so that special importance is attached to the reliability of the geological barrier [1]. It can be regarded as adequate if over the migration time from the repository to the biosphere the radionuclide concentration in the subsurface waters decreases as a result of the radioactive decay to an environmentally safe level. In the present work, methods are presented for analyzing the protective properties of the rocks for the example of a subsurface repository in the region of the Leningradskaya NPP and the results of modeling of the transport of radionuclides which hypothetically have migrated from the repository into the subsurface waters. The geological structure of the subsurface medium on the section of the proposed site for the repository is described