4.28. The safety strategy should address a number of key elements, namely: the provision of multiple safety functions and defence in depth, containment and isolation of the waste, the adoption of passive safety features, robustness of the disposal system, demonstrability of safety related features and aspects8, and interdependences with the predisposal management of the waste. It should also address the approach that will be taken to management of uncertainties, with a view to ensuring that the approach to safety described in para. 4.17 will be respected. @@8) Such demonstrability may be ensured by means of assessment, testing or other physical demonstration of functionality.