Concept for long-time integrity assurance illustrated by a steam generator and the volume control system of the nuclear power plant Neckarwestheim

Ensuring integrity of safety-relevant components or systems over their serviceable life is a legal requirement. A decisive factor within the established system for integrity assurance is whether there is sufficient information available about inservice degradation mechanisms, and whether this information is taken into account in component or system designing. The design relies on existing specifications or data reflecting the then current knowledge. This is why existing knowledge has to be updated in response to new knowledge obtained from plant operation, and negative effects revealed have to be eliminated by appropriate measures. Damage to components is caused by real loads occurring during operation, or real local conditions in the system, so that inservice monitoring of local conditions and causes leading to damage is a priority task. The information obtained from monitoring can be taken as a basis for modifying the operating mode and documenting the current status of the system. Another redundant measure is monitoring of the consequences of a degradation during operation, this task primarily relying on non-destructive examinations. The efficiency of this measure decisively depends on the available knowledge of possible damaging mechanisms, i.e. monitoring of causes. A comprehensive concept for ensuring long-time integrity will encompass the above quality monitoring and evaluation activities, operation-induced impact and damage monitoring and documentation, and updating of the data representing current knowledge. (orig./CB)