Directions for performing reliability analyses of equipment important for nuclear safety of nuclear installations

The basic terms are given for the description of the objects, aims and means of structural reliability analysis, as is the general principle for the implementation of the analysis with a view to the failure tree. The demands are summed up on reliability analysis with regard to the initial systems analysis, the safety criteria, the methods of determining limit values of selected reliability indexes for individual pieces of equipment and demands on input data. The procedure is recommended as is the methodology of analyses involving uncertainty in the formulation of the problems and objectives of the analyses and uncertainty caused by the approximative character of reliability analyses. The demands are described placed on the mathematical model and calculation means; the individual stages of the reliability analysis are also described. The presentation of results must contain documentation on the individual stages of the analysis, must define undesirable system behaviour, the representation schemes used, etc. The Boolean model of reliability is given, as are graphical models for drawing the failure tree, complex reliability indexes of safety systems, and the method of calculating characteristic time intervals. (J.C.)