Statistical approach to safety assessment of WWER reactor pressure vessels

The limit state of a pressure vessel is assessed which may be physically described as the plasticizing of a large area (in the order of m2) of basic material - 15KH2MFA steel owing to quasistatic stress (internal overpressure) under normal operating conditions in the initial period of a WWER 440 reactor operation. The quantitative method was used of assessing the reliability of pressure vessel bodies, i.e., the so-called stress-strength overlap method. The basic principles are given of the method and some of the methodology problems encountered are described. An estimate was made of the probability of plasticizing in the neck area, of the smooth cylinder area and of the pole or the vessel eliptic bottom. The calculated estimates of probability are as follows: for the neck area 1.5x10-13, for the cylinder area 1.1x10-10 and for the pole of the bottom 4.4x10-8. The variability of stress and of the loading capacity of material was also determined. (M.D.)