ABSTRACT
Safety classification of structures, systems and components of nuclear power plants shall be based on the functional importance of the items. One challenge with the nuclear safety classification is that different classification systems are used in different countries and standards. Even if certain classification scheme can be agreed upon, it is not straight-forward how the classification should be carried out for various components, e.g., in electric and automation systems. At higher plant and system level, the safety importance of functions can be defined directly, but the classification of smaller components requires further assessments. In principle, a component’s safety class follows its functional importance. Downgrading is possible if mitigative factors and reliability arguments can be shown. The importance of finding correct safety class is that it determines the QA requirements for the component. The paper will outline a risk-informed safety classification approach for the components, based on both probabilistic and deterministic assessments. Emergency diesel generator system will be used as an example.
