Quality Assurance and Reliability

Leland G. Marquis and Ivan M. Jacobs

11- 1.1 Definition of Terms

Quality assurance comprises all those planned and syste­matic actions necessary to provide adequate confidence that a structure, system, or component will perform satisfactorily in service Quality assurance includes quality control, which comprises those quality assurance actions related to the physical characteristics of materials, struc­tures, or systems which provide a means to control their quality to predetermined requirements

Reliability is the probability that a system, channel, or component will perform a specified function under given conditions for a specified period of time without failure For instrument channels this probability is normally a function of time because few one-shot measurements are considered in nuclear power plants

A product may meet all design specifications When first tested, but, if components of the product are overstressed, they will fail sooner than expected As a result, a product that passes stringent quality-control requirements may not necessarily be reliable This relation between the two terms should be kept in mind even though they are treated separately here

10- 1.2 Quality and Reliability Requirements in Reactor Instrumentation

In the past few years a great deal of effort has gone into the generation of definitive specifications, standards, and regulatory requirements concerning all aspects of quality for the purpose of establishing universal guidelines for all nuclear-reactor systems and components manufacturers and their vendors, as well as nuclear-reactor architect—engineers and owner/operators

Those organizations and personnel concerned with design, construction, and operation of systems and compo­nents for domestic power plants are bound by the 18 quality-assurance criteria in Appendix В of Title 10, Part 50, in the Code of Federal Regulations This docu­ment, which was promulgated by the AEC, has created an atmosphere within the nuclear energy industry of extreme concern for the quality of systems and components that are important to safety

Another document, also issued by the AEC, but much more comprehensive, is the standard used by organizations and personnel concerned with reactor development and test facility projects The objective of this document, RDT-F2 2T, Quality Assurance Program Requirements, “is to assure that structures, components, systems, and facili­ties are designed, developed, manufactured, constructed, operated, and maintained in compliance with established engineering criteria ”

Certain instrumentation devices, such as in-core detec­tors and penetration seals, which when placed into service become an integral part of a pressure boundary, are required to meet Sec III of the ASME Boiler and Pressure

Vessel Code, which addresses itself to Nuclear Power Plant Components Article NA-4000 of this section, titled Qual­ity Assurance, “sets forth the requirements for planning, managing, and conducting quality-assurance programs for controlling the quality of work performed under this section of the Code ”

In addition to the above-mentioned documents, the American National Standard Institute (ANSI), under the sponsorship of the ASME, is issuing a whole series of standards (N45 2 series) for the purpose of guiding organi­zations and personnel involved in design, construction, and operation of nuclear-power-plant systems and components in proper performance of the quality-related aspects of each phase of the total scope of activities

There has never been any question about the need for a high level of quality and reliability in nuclear instrumenta­tion, especially since it represents such a visible segment of the nuclear safety system These documents attempt to describe the contents of an acceptable quality-assurance program, and it is up to the industry to develop such a program and still remain competitive The remainder of this chapter endeavors to deal with this theme

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