ABSTRACT: We review the processes used in managing protective system equipment failures in the commercial nuclear power setting.&nbsp;We find that managing the efficacy of protection is governed by maintenance policy that includes system modification, maintenance inter-arrivals as a function of time, and upset inter-arrivals arrivals as a function of time. The observations described in this article bear on the impact of time-dependent activities&nbsp;associated with maintenance policy as&nbsp;they relate&nbsp;to endogenous and exogenous upset inter-arrival times. We describe why methods evaluating maintenance policy reliant on combinatorial logic, such as Probabilistic Risk Assessment (PRA), fault trees, or event trees, may lead to misunderstanding protective system efficacy; the development we follow demonstrates why this is true. Recommendations for maintaining effective protections, and connections to engineering maintenance practice and regulations, are made based on the implications that come from our observations. The importance of the investigation described is that relationship of design, maintenance, and repair policies&nbsp;must be properly understood and taken into account by process owners, operators, and investors, as well as the regulators&nbsp;who manage protections in hazardous processes.SELECTED FROM INTRODUCITON:&nbsp;We are concerned with two broad categories of hazardous technological systems, one we call a production system, and the second we call a protective system. The categorical differences between protective systems and production systems is that we categorize protective systems as those under regulation and production systems as those that meet commercial standards. Our interest in production systems primarily focuses on the extent to which they affect protective systems. Equipment failures can be operative in either category and can be said to be related to failures that affect systems in such a way as to result in upsets that challenge the protective system.We are concerned that the understanding of maintenance policy as seen through the lens of current&nbsp;risk quantification methods is unsatisfactory from a scientific point of view and lacks practical applicability in risk management. The&nbsp;investigations we have found in the literature that rely on risk quantification may mislead readers interested in, or responsible for, maintenance policies on protective systems. For one example, Duthie et al. in their development of a method to combine Reliability Centered Maintenance (RCM) with PRA, overlook the process of root cause analysis and resultant changes to&nbsp;equipment, and/or&nbsp;the maintenance and operational policies, following in-service failures.We assert that quantification of failure probability is an important activity and should be carried out. However&nbsp;the failure probability, which we distinguish as being different than the concept of risk&nbsp;quantification in PRA, of equipment located in a protective system, is under continuous review and subject to maintenance policies that go well beyond the classic process of RCM and the processes contemplated in the logic&nbsp;construction of PRA. That is, failure of&nbsp;protective system equipment is subject to root cause analysis and subsequent maintenance policy revision that would remove the cause of failure in the future. Representation of such processes are not available to the PRA except&nbsp;ex post.

Nuclear Power: On PRA and Protective System Maintenance

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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