Interrelation between in-service inspection and structural integrity in reactors residual lifetime assessment

The object of this paper is to show that in-service inspection (ISI) is of a great importance in structural integrity provision of NPP equipment as it permits: to assess material properties degradation during operation, to describe production flaws propagation under operating factors influence, to detect flaws appearance from structural concentrators and corrosion damages and to observe their development, to verify material loading conditions in structure depending on operating damages. It is presented the detailed scheme of possible production and operating flaws development during structure lifetime. The following flaws distribution function are considered in the schema: distribution probability of detected flaws (detectability), distribution density of actual flaws, distribution density of detected flaws. On the basis of stated above functions it is performed the selection of reference flow size and its outline (surface and internal flaws, cracks in cladding). (author)