Assessment of Defence in Depth for Nuclear Power Plants considering Long Term Operation

Defence in depth is a comprehensive and systematic approach to safety that has been developed by the nuclear power community to assure with high confidence that the public and the environment are protected from any hazards posed by the use of nuclear power for the generation of electricity. Moreover, the concepts of defence in depth and safety culture have served the nuclear power community well as a basic philosophy for the safe design and operation of nuclear power plants (NPPs). The historical development of the concept of defence in depth led to a general structure of multiple physical barriers and complementary means to protect the barriers themselves, the socalled levels of defence. Defence in depth is implemented through NPP lifetime to provide a graded protection against a wide variety of transients, incidents and accidents, including equipment failures and human errors within the NPP and events initiated outside the NPP.