Public/History of SQUG

In December 1980, the U.S. Nuclear Regulatory Commission (NRC) initiated Unresolved Safety Issue (USI) A-46, "Seismic Qualification of Equipment in Operating Nuclear Plants," to address the concern that there had been extensive changes in the requirements for seismic qualification of equipment over the years. The purpose of the USI A-46 program was to verify the seismic adequacy of essential equipment in operating plants that had not been qualified in accordance with more recent criteria.

SQUG Formed

In 1982, SQUG was formed to develop a practical approach for seismic qualification of equipment in operating plants. The approach developed by SQUG was to use experience data from the performance of equipment in power plants and industrial facilities that had been exposed to actual earthquakes as the primary basis for evaluating the seismic ruggedness and functionality of essential equipment in nuclear power plants. In the mid- to late 1980s, SQUG transformed into an EPRI User Group. Today, SQUG membership includes all EPRI Nuclear Members throughout the world as well as a number of other facility owners that have found the experience-based method to be a viable, cost-effective method for seismic qualification of equipment.

NRC Endorses Use of Experience Data

In 1983, the NRC issued NUREG 1018, which includes a general endorsement of the use of experience data for verification of the seismic adequacy of equipment in nuclear plants.

In early 1987, the NRC issued Generic Letter (GL) 87-02 to owners of operating nuclear plants in the United States that were licensed prior to development of modern seismic qualification standards. The recipients of GL 87-02 are referred to as A-46 plants. Essentially, all owners of A-46 plants were members of SQUG. GL 87-02 required owners to take action to verify the seismic adequacy of important equipment in their plants. A number of International utilities with older nuclear power plant also joined SQUG to address the same type of concern that the NRC had for older U.S. nuclear power plants.

GIP Developed

To address the requirements in GL 87-02, SQUG developed the Generic Implementation Procedure for Seismic Verification of Nuclear Plant Equipment. The principal basis for the approach used in the GIP is the successful performance of equipment in dozens of strong motion earthquakes in hundreds of power plants and industrial facilities. This basis was supplemented by results from shake table tests and analyses.

A significant finding of the research upon which the GIP is based is that the conventional electrical and mechanical equipment included in the scope of the GIP will withstand earthquakes that are significantly higher than the design basis earthquakes for eastern U.S. nuclear plants, provided the criteria outlined in the GIP are met. The guidelines in the GIP provide a systematic, controlled, and well-documented method of applying the lessons learned from review of equipment performance during earthquakes and tests. The GIP screens out those types of conventional equipment that have been shown to be insensitive to earthquake motions expected in eastern U.S. plants and focuses on actual equipment and installation vulnerabilities identified in strong motion earthquakes and prior qualification tests. This process has been demonstrated to be cost-effective in identifying risk-significant seismic issues without reducing seismic design margins for the plants.

In addition to addressing the issues associated with USI A-46, the GIP also explicitly addresses the issues associated with methods of analysis for aboveground, flexible, vertical storage tanks identified in USI A-40, "Seismic Design Criteria". Similarly, the GIP explicitly addresses the seismic adequacy of equipment and structures that are in close proximity to important-to-safety equipment identified in USI A-17, "Systems Interactions in Nuclear Power Plants".

SQUG issued several revision of the GIP from 1988 to 1992 with new and improved criteria and guidelines. The version issued on February 14, 1992, (GIP-2) included criteria and guidelines that resulted from extensive discussions and subsequent agreements reached with the NRC staff and the Senior Seismic Review and Advisory Panel (SSRAP). As discussed below, the NRC identified this revision of the GIP as the definitive version for implementing the USI A-46 program.

SSRAP Supported Use of Experience Data

The Senior Seismic Review and Advisory Panel (SSRAP) assisted SQUG and the NRC in reviewing this material and advising how best to apply this experience data for verifying the seismic adequacy of equipment in the older nuclear plants that were subjected to USI A-46. SSRAP produced two technical reports to document their work and recommendations. These reports were later complied into a single document and republished by Sandia National Laboratories, SAND92-0140, UC-523, June 1992. Part I of this report includes the SSRAP report (originally published by SSRAP on 2/28/91) on "Use of Seismic Experience and Test Data to Show Ruggedness of Equipment in Nuclear Power Plants". Part II of the Sandia report includes the SSRAP report (originally published by SSRAP on 3/1/91) on "Review Procedure to Assess Seismic Ruggedness of Cantilever Bracket Cable Tray Supports".

Trial Plant Reviews

One of the key features of the approach used in the GIP is the use of a plant walkdown of each item of equipment by experienced, trained seismic engineers. To demonstrate the effectiveness of this approach, SQUG conducted two trial plant reviews using an early version of the requirements in the GIP. The first trial plant review was performed in 1987 on a PWR using experienced contractors as the review engineers. The second trial plant review was performed in 1988 on a BWR using experienced utilities engineers as the reviewers. Prior to both trial plant reviews, the walkdown engineers were given training on use of the criteria and guidelines in a draft version of the GIP that was available at that time. These trial plant reviews showed that the criteria and guidelines in the GIP could be used successfully by experienced, trained engineers to evaluate the seismic adequacy of equipment and systems covered by the GIP. Both SSRAP and the NRC Staff supported this conclusion.

NRC Accepts Use of GIP-2

After lengthy discussions between SQUG, SSRAP, and NRC Staff, agreement was reached on the criteria and guidelines to be used for resolution of USI A-46. These agreements were incorporated into GIP2 (GIP Revision 2, Corrected 2/14/92). The NRC Staff reviewed the revision of the GIP and issued Generic Letter 87-02, Supplement 1 including Supplementary Safety Evaluation Report No. 2 (SSER No. 2) in which GIP-2 was accepted as the basis for SQUG members’ use in resolving USI A-46. The SQUG approach embodied in the GIP was explicitly recognized by the NRC as the preferred method for accomplishing the objectives of the USI A-46 program. Nevertheless, the NRC identified certain clarifications, interpretations, positions, and exceptions to the requirements in GIP-2. SQUG’s understanding of the clarifications, interpretations, positions, and exceptions in SSER No. 2 were provided to the NRC in a letter dated 8/21/92. The NRC commented on SQUG’s understanding in a letter and enclosure dated 10/2/92. SQUG members committed to using GIP-2 plus SSER No. 2 as the basis for resolving USI A-46 at their plants.

GIP-2A Issued

In March 1993, SQUG issued Revision 2A of the GIP (GIP-2A) to assist members in applying GIP-2 in light of the clarifications, interpretations, positions, and exceptions identified by the NRC in SSER No. 2. This augmented revision of the GIP combined into a single document the guidance contained in both GIP-2 and SSER No. 2. Use of GIP-2A helped users avoid inadvertent errors that would result from omitting or misinterpreting the NRC’s clarifications, interpretations, positions, and exceptions as contained in SSER No. 2. SQUG forwarded this augmented revision of the GIP to the NRC for review and approval on 3/26/93. The NRC declined to formally review and approve GIP-2A, stating that GIP-2 plus SSER No. 2 was adequate for implementation of USI A-46. Nevertheless, SQUG advised its members that they should use GIP-2A as a working level document in their day-to-day seismic verification of equipment to avoid making inadvertent errors and omissions during resolution of USI A-46.

SQUG Training Program

Since the criteria and guidelines in the GIP included new methods and approaches, compared to the tradition methods for seismic qualification of equipment, SQUG developed the following six training courses to help users properly apply the various guidelines and tools developed by SQUG:

• Safe Shutdown Equipment Selection Training Course
• Relay Screening and Evaluation Training Course
• Walkdown Screening and Seismic Evaluation Training Course
• Add-On Seismic IPE Training Course
• New Replacement Equipment and Parts (NARE) Training Course
• SQUG/NARE Awareness Training Course

More details on these courses and access to the training material associated for some of them are posted on SQUG Training section of this web site for use by members.

GIP-3 Issued

In May 1997, SQUG issued Revision 3 of the GIP (GIP-3) to incorporate new information that became available between 1992 and 1995 and to apply lessons learned during implementation of the USI A- 46 program up to that point in time. This revision included three additional restrictions beyond those in GIP-2, namely: (1) use of lower allowable pullout capacities for certain types of concrete expansion anchors, (2) increase in the cutoff frequency from 11 Hz to 13 Hz for use of the in-cabinet amplification factor of 4.5 for certain types of equipment containing essential relays, and (3) correction of an equation for calculating allowable anchorage capacity for horizontal tanks and heat exchangers. GIP-3 also included editorial and typographical changes that clarified the meaning of the guidance in GIP-2. The NRC reviewed and accepted GIP-3 in Supplementary Safety Evaluation Report No. 3 (SSER No. 3).

GIP-3A Issued

In December 2001, SQUG issued an augmented revision of GIP-3 (i.e., GIP-3A) to assist members in applying GIP-3 plus the clarifications, interpretations, positions, and exceptions identified by the NRC Staff in SSER No. 2 and SSER No. 3. . GIP- 3A also includes changes to address the issues identified by the Staff in their review of the plant-specific implementation of the USI A-46 program at the SQUG member plants and in their review of SQUG's guidance on use of the GIP for New and Replacement Equipment (NARE) as incorporated into Revision 4 of the NARE Guidelines.

By using GIP-3A, SQUG members have a better chance of avoiding inadvertent errors that would result from omitting or misinterpreting the NRC’s clarifications, interpretations, positions, exceptions, and issues that are included in the two SSERs and their letter to SQUG on the NARE Guidelines. SQUG recommended that members use GIP-3A as a working level document for their day-to-day seismic qualification of equipment in their plants, including New and Replacement Equipment (NARE),

In developing GIP-3A, SQUG endeavored to incorporate the NRC clarifications, interpretations, positions, exceptions, and issues in a manner that it believes would be acceptable to the Staff without adding new, substantive criteria or guidance into the document. Therefore, even though GIP-3A has not been formally reviewed and approved by the NRC Staff, SQUG considers this document to be an additional statement of the accepted criteria and guidance, not a change to the criteria and guidance provided in the baseline documents that had been reviewed and approved by the NRC Staff.

NARE Application

In addition to resolving USI A-46, the GIP method may continue to be used at USI A-46 plants for seismic qualification of new and replacement equipment (NARE). To assist members, SQUG prepared a set of guidelines for applying the GIP for NARE and sent a summary of the guidelines to the NRC Staff for review and approval. The NRC reviewed this document and provided comments, including clarifications, on the application of the GIP method for NARE. SQUG accepted the NRC’s clarifications, produced Revision 4 of the NARE Guidelines, and sent these guidelines to SQUG members on 7/25/00. Subsequently, SQUG updated the NARE Guidelines in Revision 5 to reference GIP-3A and make other improvements.

SQUG’s Future

SQUG continues to maintain the validity of and support and broaden the use of earthquake experience data as a cost-effective method for seismic qualification. Various programs and projects continue to be pursued to support this mission.

The SQUG Walkdown process is also used in Seismic Margin Assessments and Seismic Probabilistic Risk Assessments as the best way to assess the as-installed equipment and identify any important seismic interactions.