A contribution to the NPP equipment strength and service life assessment

The sections of the paper are as follows: Introduction; Basic structure of A.S.I. Technical Standards Documentation (TSD) for NPPs; Effect of multiaxial stress on fatigue; Demonstrating the material damage level for NPP components; and Conclusions. The following recommendations are presented: (i) Further development of A.S.I. documentation should be directed so that it should be applicable to the determination of WWER component damage level usable when submitting application for NPP lifetime extension; (ii) The Manson-Coffin fatigue strength curves should be measured for materials and their welded joints from more than one melt and add them to A.S.I. Documentation Section II; (iii) The strength reduction factors should be determined for the materials and their welded joints during the isolated as well as combined action of various material damage mechanisms; (iv) Methodology should be developed for experimental measurements and for fatigue assessment during simultaneous medium pressure and temperature change and also during a thermal shock during which the stress from pressure can be regarded as the constant mean cycle stress. A body test should be designed to enable the result of fatigue tests during multiaxial stress to be generalized for use for different geometric defects of real bodies; (v) A draft list should be set up of basic dimensions of screw systems for the calculation pressure at a calculation temperature and pressure test ensuring the required joint leaktightness. (P.A.)