Study of radionuclides' migration parameters for waste repository performance evaluation

The article concerns the mathematical model of radionuclide mass transport in a multilayer system of natural and artificial barriers. This model is realized in a specialized ''Masstrans'' software program. The software helped to assess the radionuclides' dispersion in an environment for the repository of solid radioactive wastes with low and intermediate radiation. These repositories are the units, Ukrainian State Association ''Radon'' and Enterprise ''Mayak'' (Russia). The repositories are located in different geological mediums. They are characterized by different rates of protective barrier's irrigation and by the technological modes of waste's piling in a repository. The appropriate mathematical model was composed for each repository. The calculation of dispersion extent of radionuclides (3H, 90Sr, 60Co, 239Pu, 226Ra) was carried out for a multilayer system of protective barriers. Retrospective calculations for 30 years and forecasts for 50 years were carried out. Calculated data were compared with data from natural inspections. As a result of the calculations and the following evaluation, it was determined that radiation in the repositories is complicated during storage by the unreliability of the repository's constructive elements. In some repositories it was found via data processing that radionuclides, such as 3H, 137Cs, 239Pu, and 226Ra are outside artificial protective barriers in concentrations, that exceed the safety standards. Thus, the computer simulation allows them to evaluate the working state and the environmental impacts of the repository