A simple model of the preliminary safety analysis of a high level radioactive waste repository

A simple model has been developed to study the migration of radionuclides from a high level radioactive waste repository (HLRW) which is useful for the preliminary safety analysis during the site survey stage of the repository. The results of such a model would indicate the required refinements in the model and in the data base for the safety analysis during the site selection stage. The host matrix of the repository is modelled as a cylindrical system having a circular fracture at its centre. The migration of radionuclides from the repository is described using two coupled equations; one for the fracture and the other for the host matrix. The processes considered in the fracture are advection, sorption on the fracture surface, diffusive loss to the host matrix and radioactive decay. The governing processes for the host matrix are diffusion, adsorption and radioactive decay. The radioactivity input into the fracture inlet is assumed as an instantaneous area source. The model is simple and performs safety analysis quickly with minimum requirement of computational facilities. A comparison of the results with that of a similar model with leaching source term indicates that the simplicity does not generate undue conservatism. (author)