Safety achievement linked to operational experience and R and D results accumulated till now

In the past, most of the safety considerations aimed at the improvement of design provisions for safety. Lateron, as a considerable number of power reactors were constructed during a relatively short period, emphasis passed to questions of commissioning. More recently, with a large and still increasing number of nuclear power plants in operation, interest has shifted towards operational issues. From a technical point of view these aspects can be considered as three basic constituents of nuclear reactor safety: A sound design provides a high safety level of the projected plant. Construction and commissioning should assure that the quality of the real plant corresponds to that of the design. Plant operation should maintain the built-in safety level, eliminate deficiencies, and optimize the performance where possible. It is quite obvious that these components of safety are interrelated and that the degree of safety reached by this concept depends much on how research and experience are used to stimulate a dynamic feedback process. Positive and negative lessons from commissioning and operation can be used for plant specific and generic improvements. Research provides a deeper understanding of the experience and permits the investigation of problems not directly accessible to observation. In the following I will take a few examples in order to indicate where this dynamic process is standing now. Even though my point of view relies to a large extent on experience from the Federal Republic of Germany, I will nevertheless try to give emphasis to aspects of international interest