Regarding Requirements to Load Combinations in Case of Evaluation of SSC Seismic Resistance by Indirect Methods

Extension of the list of load combinations that should be analyzed during the nuclear power plant (NPP) components seismic resistance justification is one of the important new regulatory requirements. The paper deals with the thermomechanical equipment for which seismic resistance assessment is performed using operating experience method, in particular the methodology of indirect assessment using the GIP (Generic Implementation Procedure) for the WWER reactors (GIP-WWER procedure). Review of GIP-WWER procedure has been performed. The paper presents the analysis of seismic screening evaluation work sheet based on the example of motor-operated valve. The disadvantages of the GIP-WWER procedure in terms of ensuring compliance with current regulatory requirements for combinations of operating and seismic loads have been identified and the ways of eliminating the revealed disadvantages have been offered. The supporting structures of the equipment in most cases are the metal structures. Impact of different NPP operating modes to the steel supporting structures of the equipment has been considered and the provisions of building codes governing the calculation of steel support structures have been analyzed. A minimum listing of operating and seismic loads combinations has been established, which should be considered in the justification of the seismic strength of steel support structures referred to the first and second seismic categories. The paper is a part of a series of publications devoted to consideration of regulatory requirements to combinations of operational and seismic loads in assessing the seismic resistance of NPP components. (author)