Benefits of a systematic approach to maintenance for safety and safety related systems

For safety and safety-related systems, nuclear plants have to balance the requirements of demonstrating the reliability of each system, while maintaining the system and plant availability. With the goal of demonstrating statistical reliability, these systems have extensive testing programs, which often results in system unavailability and this can impact the plant capacity. The inputs to the process are often safety and regulatory related, resulting in programs that provide a high level of scrutiny. In such cases, the value of the application of a Systematic Assessment of Maintenance (SAM) process, such as Reliability Centered Maintenance (RCM), is questioned. The special case of Standby-Safety systems was discussed in a previous paper, where it was demonstrated how SAM techniques provide useful insight into current system performance, the impact of testing on component and system reliability, and how PSA considerations can be integrated into a comprehensive Maintenance, Surveillance, and Inspection (MSI) strategy. Although the system reliability requirements are an important part of the strategy evaluation, SAM techniques provide a systematic assessment within a broader context. Testing is only one part of an overall strategy focused on ensuring that component function is maintained through a combination of monitoring technologies (including testing), predictive techniques, and intrusive maintenance strategies. Each strategy is targeted to known component degradation mechanisms. This thinking can be extended to safety and safety related systems in general. Over the past 6 years, AECL has been working with CANDU utilities in the development and implementation of a comprehensive and integrated Plant Life Management (PLiM) program. As part of developing a comprehensive plant asset management approach, SAM techniques are used to develop a technical basis that not only works towards ensuring reliable operation of plant systems, but also facilitates the optimization and integration of component maintenance, surveillance, and inspection (MSI) strategies. These strategies can be tailored to mitigate risk in combination with the most optimal operational approach. This becomes particularly valuable when considering the operation of redundant components, such as normally found in safety systems. The optimal approach is not always obvious. The answer lies in understanding the relative risk of different options and the cost of applying the strategy. The relative risk is by definition related to the ultimate reliability of the component. This paper considers the application of Systematic Assessment of Maintenance (SAM) to standby safety and safety related systems. Recently completed studies provide useful insight into the important value added of the systematic assessment approach for these systems. The paper considers how the results of the SAM process demonstrate that the analysis can be used to assist in the optimization of the testing program dictated by reliability while also taking better advantage of the testing through condition monitoring and predictive maintenance techniques. Further, the results illustrate the importance of identifying and linking the different plant activities with a well integrated plant culture. (author)