TABLE OF CONTENTS A general agreement exists that classification of systems, structures and components of a plant from the point of view of safety and from the point of view of resistance to external actions (earthquake, and so on) is necessary to make decisions on the following: AR17
Adequate design, construction and operation provisions for each class.
System characteristics, such as redundancy, emergency power supply, qualification for environmental conditions.
Systems to be considered available or not in the deterministic analysis of the Postulated Initiating Events (PIE) (EUR, Chapter 18).
Gradation of the QA measures, to be proportioned to the importance of the safety component but also to the characteristics of the component such as its complexity and degree of technological innovation.
In general, the following classifications should be defined:
Classification on the basis of the safety function, with reference to the requirements above. Classification for pressure components, on the basis of the mechanical complexity and the pressure level.
Classification for the resistance to earthquakes, with reference to the need that the component continue to be undamaged or functional during and after an earthquake of a certain severity, taking into account the aftershocks and therefore the possible incremental damage.
Classification of the instrumentation and control systems, on the basis of their safety function, which may be different from that of other system types because of the existence of classification schemes specific to their field and commonly used.
Classification for QA requirements.
The various national approaches to the classification systems strongly differ from each...
