The design criteria and methods for the seismic qualification of mechanical and electrical equipment in nuclear power plants underwent significant changes during the course of the licensing of commercial nuclear power plants. Consequently, it was believed that the margins of safety provided in equipment to resist seismically- induced loads and to perform their intended safety functions could vary considerably. Therefore, to ensure the ability of plants to achieve a safe shutdown condition when subject to a seismic event, the seismic qualification of equipment in operating plants had to be reassessed.
The objective of this issue was to establish an explicit set of guidelines that could be used to judge the adequacy of the seismic qualification of mechanical and electrical equipment at all operating plants, in lieu of attempting
to backfit existing design criteria to new plants. This guidance was to address equipment required to safely shut down a plant as well as equipment whose function is not required for safe shutdown but whose failure could result in adverse conditions that might impair shutdown functions. Also, explicit guidelines were to be established for use in requalifying equipment whose qualification was found to be inadequate. The issue was declared a USI
in February 1981 and published in NUREG-0705.[1] A detailed action plan for resolving the issue was published in NUREG-0649,[2] Revision 1.
Resolution of the issue was based mainly on work completed by the Seismic Qualification Utility Group (SQUG) and EPRI using the seismic and test experience data approach[3] that was reviewed and endorsed by
the Senior Seismic Review and Advisory Panel (SSRAP) and the NRC staff. The scope of the review was narrowed down to equipment required to bring each affected plant to hot shutdown and maintain it there for a minimum of 72 hours. A walk-through of each plant was deemed necessary to inspect equipment in the scope. Evaluation of the equipment was to include: (a) adequacy of equipment anchorage; (b) functional capability of essential relays; (c) outliers and deficiencies (i.e., equipment with non-standard configurations); and (d) seismic
systems interaction. Work completed on the issue resulted in the publication of NUREG/CR-3017,[4] NUREG/ CR-3875,[5] NUREG/CR-3357,[6] NUREG/CR-3266,[7] NUREG-1030,[8] and NUREG-1211.[9] The issue
was RESOLVED when requirements were issued in Generic Letter 87-02.[10] Verification of licensee actions was pursued with Generic Letter 87-03.[11]
[1] NUREG-0705, "Identification of New Unresolved Safety Issues Relating to Nuclear Power Plant Stations," U.S. Nuclear Regulatory Commission, March 1981.
[2] NUREG-0649, "Task Action Plans for Unresolved Safety Issues Related to Nuclear Power Plants," U.S. Nuclear Regulatory Commission, February 1980, (Rev. 1) September 1984.
[3] Letter to Seismic Qualification Advisory Committee (SQAC) and Meeting Attendees from G. Sliter and R. Vasudevan (EPRI), "Summary of the EPRI Seismic Equipment Qualification Research Coordination Meeting at ANCO Engineers, Inc., Los Angeles, California, September 19 & 20, 1984," October 10, 1984
[4] NUREG/CR-3017, "Correlation of Seismic Experience Data in Non-Nuclear Facilities with Seismic Equipment Qualification in Nuclear Plants (A-46)," U.S. Nuclear Regulatory Commission, August 1983.
[5] NUREG/CR-3875, "The Use of In-Situ Procedures for Seismic Qualification of Equipment in Currently Operating Plants," U.S. Nuclear Regulatory Commission, June 1984.
[6] NUREG/CR-3357, "Identification of Seismically Risk Sensitive Systems and Components in Nuclear Power Plants," U.S. Nuclear Regulatory Commission, June 1983.
[7] NUREG/CR-3266, "Seismic and Dynamic Qualification of Safety-Related Electrical and Mechanical Equipment in Operating Nuclear Power Plants," U.S. Nuclear Regulatory Commission, September 1983.
[8] NUREG-1030, "Seismic Qualification of Equipment in Operating Nuclear Power Plants," U.S. Nuclear Regulatory Commission, February 1987.
[9] NUREG-1211, "Regulatory Analysis for Resolution of Unresolved Safety Issue A-46, `Seismic Qualification of Equipment in Operating Plants,'" U.S. Nuclear Regulatory Commission, February 1987.
[10] Letter to All Holders of Operating Licenses Not Reviewed to Current Licensing Criteria on Seismic Qualification of Equipment from U.S. Nuclear Regulatory Commission, "Verification of Seismic Adequacy of Mechanical and Electrical Equipment in Operating Reactors, Unresolved Safety Issue (USI) A-46 (Generic Letter 87-02)," February 19, 1987. [ML031150371]
[11] Letter to All Licensees, Applicants and Holders of Operating Licenses Not Required to be Reviewed for Seismic Adequacy of Equipment Under the Provisions of USI A-46, 'Seismic Qualification of Equipment in Operating Plants,' from U.S. Nuclear Regulatory Commission, "Verification of Seismic Adequacy of Mechanical and Electrical Equipment in Operating Reactors, Unresolved Safety Issue (USI) A-46 (Generic Letter 87-03)," February 27, 1987. [ML031140317]
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