Abstract A monitoring plan is an important part of a disposal programme. Monitoring a deep geological repository for the disposal of radioactive waste faces several challenges. These may arise from the technically demanding environment in which the monitoring equipment must operate or from the potentially long period of time during which they must operate. Over the past decades, a lot of experience has been gained in monitoring experiments in underground research laboratories (URL). Since the HADES URL became operational in the 1980s, thousands of sensors have been installed. To document the experience gained in this context, ONDRAF/NIRAS launched a research project to evaluate the performance of the monitoring equipment implemented in the HADES URL. This required developing a method to assess the performance of sensors in a consistent way. The methodology is explained in this paper and illustrated for the instruments installed to monitor the THM response of Boom Clay to the large-scale PRACLAY in situ experiment.

Abstract A safety concept and a safety demonstration concept for the disposal of high-level radioactive waste in German clay formations have been developed. The main safety objective is to retain the radionuclides inside a ‘Containment Providing Rock Zone’. Thus, the radionuclide transport should be restrained by adequate safety functions of the geological and geotechnical barriers. The compliance with legal dose constraints has to be demonstrated for probable evolutions and less probable evolutions. As a basis for system analysis, generic geological reference models, disposal concepts and repository designs have been developed for northern and southern Germany. All data relevant for future system evolution were compiled in two FEP (features, events and processes) catalogues. They provide information on FEP characteristics, their probabilities of occurrence, their interactions and identify ‘initial FEP’ that impair the safety functions of relevant barriers. A probable reference scenario has been deduced systematically from the probable ‘initial FEP’, and from probable processes relevant for radionuclide mobilization and transport. Four different starting points to develop alternative scenarios (i.e. less probable evolutions) were identified. The scenario development methodology is applicable to different kinds of host rock and therefore may be a basis for the preliminary safety analyses necessary in the future site selection process in Germany.