The specificity of NPP safety systems is that they must be in a state of constant availability, but they are not used
and, therefore, are not spend the life of the equipment. Verification of readiness through periodic maintenance or testing
can lead to the deterioration of some elements of the system and increases their vulnerability during inspections. Therefore,
the maintenance period of security systems should be optimized with taking into account the quality of maintenance.
A methodology for assessing the reliability of safety systems with taking in account their operating modes and quality of
maintenance, which was implemented as a computer program, is developed. Operational data on the quality of maintenance
of safety equipment of NPPs were used. The results of calculation of the optimal maintenance period for one ofWWERsafety
systems are presented.
Keywords: maintenance, safety systems, maintenance period, reliability, NPP.