Quantification of the safety status of PWR steam generators

The operational safety of components is affected during the period of operation (e.g., by loads and environmental effects). Additionally, changes in codes and standards can affect the safety margin of a component. In order to determine a quantitative status of the safety, the existing status of the component and the actual knowledge have to be regarded and evaluated. Differences (deficits) with respect to actual demands must be balanced by use of redundant measure to guarantee safety. The procedure is demonstrated using the steam generators of GKN 1 (German nuclear power plant--in operation since 1975) as an example. The existing status of the component regarding design and construction, material, load history (results of monitoring), the results of nondestructive testing and operational experience is determined and related to the actual regulatory and code compliance and to the state of the art in technics. Non-specified loads were measured in operation. Stress and fatigue analysis computations are performed on the base of realistic load patterns (results from monitoring). Thus the safety status can be quantified. Finally the GKN-concept of measures to guarantee the reliability and the safety of the component in future operation is discussed.