Testing Safety and Performance Indicators for a Geological Repository in Clay

The main indicators for the evaluation of the safety of a geological repository are the dose or the risk that are estimated for a sufficiently representative set of possible evolution scenarios. However, the uncertainty in dose rate calculations increases with time, especially in the aquifer system surrounding the host formation and the biosphere. Therefore, it is desirable to develop additional indicators that can improve the reliability of the results of the safety assessment. For increasing the confidence of various stakeholders in the results of the safety evaluations, it is essential to develop indicators that explain the functioning of the repository system by quantifying the contribution of its main barriers or safety functions; such indicators are called performance indicators. Four main groups of performance indicators can be distinguished: indicators based on inventories, fluxes, integrated fluxes and transport times. Because of the paramount role played by the multi-safety-functions concept in recent safety cases, performance indicators quantifying the contribution of the main safety functions to the confinement of radionuclides in the geological repository system have also been developed.