PSAD: Condition-based maintenance through permanent monitoring

Since the beginning of the French nuclear program, Electricite de France (EDF) has looked for ways to improve the availability and safety of its nuclear units. Therefore, monitoring systems on turbo-generators, reactor coolant pumps, primary circuits and core internal structures were designed by the Research and Development Division and implemented on 56 Pressurized Water Reactor units (PWRs) with technologies available during the 1970ás. The overriding goal of optimizing maintenance costs in power generating plants has led to the design and implementation of the PSAD condition monitoring system. Its main objectives are: Prevent major failures : early and automatic detection of any abnormal behavior in critical equipment (turbo-generators, reactor coolant pumps, inlet valves, ...) using advanced continuous on line vibration, hydraulic and thermal monitoring. Predict and plan maintenance: provide plant maintenance operators and experts with powerful tools to diagnose the wear and other phenomena, identified or not, that characterize aging machinery; this should help them lower costs by reducing current preventive outage schedules. Each component of a nuclear unit is monitored by its own fully autonomous Monitoring Unit. This rack-mounted system performs periodic or event-triggeredacquisitions of plant signals, computes more elaborate data, triggers warning and alarm messages when a malfunction is detectef, and applies intelligent data reduction to archive only significant information. The Diagnosis Workstation centralizes the data storage for all monitoring units through a Local Area Network and provides the user interface to all control and diagnostic functions. Warning messages are processed and sorted by seriousness then displayed in lists to optimize operator acknowledgment. A wide selection of graphical displays and plots let the user view the data in the most suitable and meaningful way. Other tools, such as statistical analysis, rely on the historical database information to detect long-term condition trends. Plant operators can acces monitoring databases covering machine lifetime, dtat import and export capabilities for comparisions and the opinions of experts sharing the data through the PADAS network and thus have the most information available for establishing an accurate diagnosis. Design using Object-Oriented methodology and based on recognized industrial standards, the PASAD is intended to perform over the whole plant lifetime. Its open structure lets it evolve towards new monitoring strategies such as Loose Part Detection in the primary circuit and Core Internal Structure Monitoring, both to be soon integrated. PSAD systems are currently operating on four French nuclear units and it is projected that they be installed in all the other.