LEAK-BEFORE-BREAK CRITERIA AND STRENGTH MONITORING IMPLEMENTATION IMPACT ON IN-SERVICE INSPECTION OF RBMK PRIMARY CIRCUIT COMPONENTS

Major scientific and technical tasks of strength monitoring and survei llance in NPP RBMK operation are considered proceeding from the presen t-day requirements to safety insurance based on the circuit integrity concept. The application of the ''Leak-Before-Break'' Concept in the m ost complete and systematic definition corresponding to the approaches adopted in the U.S.A. will permit, in the case of success, to assess the compliance of RBMK primary circuit components with still more rigi d requirements to the integrity and safety in comparison with the regu latory requirements acting at present in the R.F. nuclear industry. Pr ocedures for evaluation of allowable size defects in pipelines with Dy 800 depending on the loading levels are viewed. It is shown that the a pplication of the LBB Concept criteria and the implementation of a str ength monitoring system as a means of continuous operation quality con trol permit to assess the requirements to the sensitivity of metal con trol devices and to support NPP utilities to optimize ISI schedule.