CONCEPTUAL AND MATHEMATICAL MODEL FOR LIQUID FLOW AND RADIONUCLIDE MIGRATION THROUGH UNDERGROUND STORAGE OF RADIOACTIVE WASTE

摘要

At a structure for underground storage of radioactive waste, one of the most important questions is the possible migration of radionuclides from the zone of storage to its surroundings. Revealing the nature of possible flow of underground waters through a storage facility with dissolved radioactive substances will allow more objective estimation of the reliability of waste isolation. As an example, waste disposal is investigated in the production space and mine complexes of uranium mines. With this purpose in mind, a conceptual and mathematical model is developed for flow of a liquid and associated migration of radioactive substances in the environment. The model is developed for the case of one-dimensional transient radial flow of a liquid, in which there is hydraulic connection of the waste zone with an aqueous horizon in a geological section. Unlike many analyses conducted for the evaluation of the safety of repositories, steady-state flow is not assumed, permitting an assessment of flow and transport under non-equilibrium conditions. In developing the model, a certain idealization of the physical phenomena is used and some assumptions are applied which do not alter the essence of the physical processes. The ultimate goal of this model is the evaluation of the depth of penetration of radionuclides into the surrounding environment at any moment of time. The problem is complicated by the presence of an initial disequilibrium in hydrodynamic head between the repository and its surroundings. Proceeding from a stipulation of continuity of flow, it is possible to solve for the dynamic level of underground waters, following which it is easy to evaluate the flow of underground waters through the repository. Depending on the ratio of pressure in the repository and in an adjacent aqueous horizon, the flow of underground waters through the repository and in the surroundings can be determined. The progress of the front of radioactivity will lag behind the water by a delay factor, which is determined by the sorption of radionuclides on rocks.