Reliability centre maintenance: An experience at TAPS 1&2

Tarapur Atomic Power Station-1&2 (TAPS # 1&2) is a twin Boiling Water Reactor (BWR) Nuclear Power Station, each unit operating at 160 MWe. Both the units were commissioned in November 1969 and completed more than 40 years of operation. Nuclear Power plant operation requires reliable and continuous operation of equipments confirming to its design intent. TAPS has adopted Reliability Centered Maintenance (RCM) policy for all plant equipments. To execute RCM, performance data such as operating parameters, vibration, temperature, noise level, current, failure frequency, failure mode etc are monitored and documented. A reliability centered maintenance (RCM) approach requires identification of the critical components of the systems. Identification of those components on the quantitative basis is based on reliability (or unavailability) models developed using fault trees. In the RCM process, the PSA was used as a source of information for System functions and functional failures. Component failure modes, Component failure probability, System reliability model. The PSA model provided the initial input information for the risk characterization process. It uses two PSA importance measures: risk achievement worth (RAW) and Fussell-Vesely (FV), as screening tools to identify potentially safety-significant components/systems. Based on this information, condition and reliability assessment of equipments is done. This enables to incorporate possible changes in design, maintenance strategy and surveillance requirements to avoid unplanned outages. It is typically much more safe and cost effective than allowing the machinery to fail suddenly. By following these tools TAPS has been able to operate in safe, efficient and economical manner. TAPS has solved many uncommon problems of equipments during its 40 years of operation such as failure of reactor level control valves etc. This paper depicts an overview of TAPS-1&2 reliability centered maintenance strategy with some experiences.