Some important issues in evaluating the availability of passive systems

In some countries new reactor concepts based on a broader use of passive safety features are under development. The term 'passive' as used here refers to systems which rely heavily on natural heat transfer process such as natural circulation to perform their function rather than on decidedly 'active' components like pumps. The paper deals with important issues in evaluating the availability of passive systems, e.g. the assessment of the active components, the assessment of passive components and structures and the probabilistic assessment of the physical function of the natural processes. Based on an outlined assessment process for the entire system and on an exercised simulation process for the assessment of passive components e.g. pipes insights and important issues are presented. A follow-up study will refine and expand the concept to a full scope assessment procedure of passive systems. (author)