Quantification of retention processes in the Konrad waste repository for airborne activity released from waste packages in normal and accident conditions

A safety assessment has been performed for the operating phase of the Konrad waste repository. For normal operation conditions this includes the demonstration that activity releases will be kept below specified limits in order to ensure adequate radiation protection for the operating staff and the public. For this reason a numerical model has been derived to describe the activity transport from sealed emplacement rooms to the environment. Besides the material properties of the sealing barrier, the emplacement rooms and the ventilation systems, the combined effects of the following transport mechanisms have been considered: convection of residual air from the emplacement rooms into air-conditioned galleries by residual volume reduction (convergence), diffusion through the barrier, and convection from and into the emplacement rooms by pressure fluctuations in the mine atmosphere. The results allow specifications to be formulated for the design of the barrier which ensure the desired retention properties. For accidental releases of radioactivity from the repository the off-site consequences have been analysed. Essentially, the established regulatory practice adopted in the Federal Republic of Germany for nuclear power plants has also been applied to the operating phase of the repository, and a number of supporting experimental investigations have been carried out to contribute to this new field of safety analysis. The paper reviews the main features and results of an experimental programme to determine the retention of accidentally released radioactive aerosols within the repository. These experiments proved to be important in the determination of source terms released to the environment from design basis accidents within the repository, such as the dropping of waste packages from a height of several metres. (author). 3 refs, 7 figs, 2 tabs