6.40. A related term is the robustness of a disposal system, which addresses the robustness of individual components as well as their interactions. This is conceptually broader than the robustness of a system component only. The assessment of the robustness of a disposal system relies on several elements:@@- Demonstration of the robustness of individual barriers and their safety functions;@@- Evaluation of the concept of defence in depth, i.e. the presence of multiple diverse safety functions, to ensure that the overall performance of the disposal system does not rely on a single safety function, the failure or unexpected poor performance of which would lead to unacceptable radiological consequences (see paras 6.29-6.37);@@- Verification that good engineering practices (demonstrability and feasibility) have been applied;@@- Demonstration that safety is achieved through passive means.