Radionuclides migration in the far field of geological repositories: a numerical example

Radioactive wastes can be classified according to their activities and their half-life period: high activity and/or long half-life may cause severe hazards to people and environment for thousands and thousands of years. For repositories of such dangerous wastes classified as Category III by Italian law and as High Level Waste (HLW) by IAEA - the geological repository technology is the preferred technology. As one can imagine, most of the volume of these wastes are spent nuclear fuel and products of nuclear reprocessing plants. To permanently isolate HLW from the biosphere, the segregation of wastes in geological repositories, several hundred meters below the surface, is now under way in many countries where large, compact and impermeable geological formations, not exposed to the seismic risk, exist. Safety conditions associated with these repositories must be guaranteed also in the case that the secular contact of the waste canisters with the groundwater allows the radionuclides to migrate to the external environment. In the present article the first results of a numerical simulation made using PMWIN (Processing Modflow), one of the most complete groundwater simulation codes, are presented to assess the migration process of radionuclides in the far-field of a geological repository to study the influence of two important parameters, the distribution coefficient and the hydraulic gradient, on the numerical results.