6.50. For any given time in the evolution of the disposal facility and its environment, emphasis in the safety case should be placed on those safety functions that are expected to be most effective, and on those arguments that are considered to be the most convincing. For example, initially it may be confidently expected that canisters provide complete containment of the waste, and safety arguments may emphasize evidence supporting the integrity of the canisters for a certain period of time. At later times, complete containment cannot be relied upon, and arguments based on, for example, the stability of the waste forms, geochemical immobilization, the slow rate of groundwater movement and the stability of the geological environment should be used to show that any releases of radionuclides to the environment will nevertheless be small [36].