Performance indicators Quantifying the Contribution of Safety Functions to the Confinement of Radionuclides in a Geological Repository System

The main indicators for the safety evaluation of a geological repository are the dose or risk estimated for a sufficiently representative set of possible evolution scenarios. In recent years complementary sets of safety and performance indicators have been developed within national geological disposal programmes and international projects. Whereas safety indicators give an indication on the level of safety provided by the repository system, performance indicators aim at illustrating how the repository system works. Most sets of performance indicators introduced hitherto are related to the multi-barrier concept; they quantify or illustrate the contribution of the main engineered and natural barriers to the confinement of the radionuclides within the geological repository system. However, the application of the defence-in-depth principle to geological disposal led to the introduction of safety functions in safety cases. Because of the paramount role played by the multi-safety-functions concept in recent safety cases, we have derived performance indicators that quantify the contribution of the main safety functions to the confinement of radionuclides in the geological repository system. The considered safety functions are containment, limitation of release and retardation. The proposed performance indicators are based on time-integrated fluxes of radionuclides released from the main successive compartments of the repository.