35 Functionality and Operability Criteria
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Chapter 35, the functionality was initially authored by Guy Deboo for the previous two editions. This third edition has been updated by Stephen R. Gosselin who revised the discussions pertaining to and operability criteria, which address evaluations for operating plant systems, structures, or components (SSCs) found to be degraded, nonconforming, or subjected to unanalyzed conditions during nuclear plant operation. This revision discusses the methodologies and acceptance criteria applicable to these evaluations. Gosselin introduces typical SSCs that may require operability assessments and functionality evaluations and discuss methods and assessments, failure modes, functionality and operability, and as-built conditions divergent from design. He covers, with the aid of figures, tables, and references, Code requirements as well as short-term and long-term operability acceptance criteria for valves, pumps, snubbers, piping, reactor vessels, tanks, heat exchangers and supports (including component standard and linear supports as well as spring hangers), structural bolts, concrete expansion anchors, and integral welded attachments.
The current practice involves a process of consensus among the regulator viewpoints; plant-specific Technical Specification (TS) requirements; and applicable Codes, Standards, rules, and other licensing-basis compliance requirements. Guy discusses the role of related agencies and committees, such as the U.S. NRC, the ASME Code Committees, and the ASME O&M Code Committees. This chapter includes basic concepts, definitions, evaluation methods, and acceptance criteria from these documents. In this chapter, the scope of SSCs is limited to mechanical systems and their components and supporting structures. Authors discuss the role of the CFR-facility TSs as they relate to the topics of this chapter. Authors provide examples of specified safety functions, operating conditions, and events to be considered for some SSCs and piping. The discussions elucidate the often complex, and sometimes non-uniform nature of operability concepts and criteria.