Reliability Evaluation of Emergency Diesel Generator Systems (EDGS) for VVER-100/V446 Reactor by Markov Approach

The Emergency Diesel Generator Systems (EDGS) are the emergency electrical source of the nuclear power plants (NPP). These systems work as standby systems in the normal operation of the power plant. In the maintenance of standby system, Surveillance Test Interval (STI) plays as the key role in the reliability evaluation of these systems, living PSA (LPSA) and risk monitoring (RM). Optimum test interval and test duration can reduce the unavailability of the EDGS and the risk and cost of testing. By Markov approach, all the possible condition for EDGS is considered and according to the transition between the states, the optimum test interval and test duration is calculated. To do this, first, the produced states should classify in some groups to analyze the Markov model. The groups are as follow: at least one train work, four trains failed, normal trains in test and failed trains in test. The desired state is state NO.1 with no fail and no test. To compute the optimum test interval and test duration, only group 1 is needed. This article is concluded that the best test interval and test duration is 7 days (168 hours) test duration and 25 days (600 hours) test interval that is similar to experience in the power plant.