History of SQUG

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. Today, SQUG membership includes U.S. utilities with nuclear power plants that had been subject to USI A-46. In addition, SQUG membership includes international utilities 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 [Reference 1] 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” [Reference 2]. 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” [Reference 3].

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 [Reference 4]. 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” [Reference 5]. 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” [Reference 6].

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 GIP-2 (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 [Reference 7]. 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 [Reference 8]. The NRC commented on SQUG’s understanding in a letter and enclosure dated 10/2/92 [Reference 9]. 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 [Reference 10]. 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 [Reference 11 ]. 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 [Reference 12].

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.

SEQUAL Formed
In 1995, a sister organization, called SEQUAL, was formed to extend the use of the SQUG method to the newer nuclear power plants in the U.S. (i.e., the non-A46 plants). In 2003, SQUG and SEQUAL began operating together as a single organization and are now referred to simply as SQUG.

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) [Reference 13].

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 [References 7 and 13]. 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) [Reference 15] as incorporated into Revision 4 of the NARE Guidelines [Reference 18].

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) [Reference 20].

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 (Reference 15). The NRC reviewed this document and provided comments, including clarifications, on the application of the GIP method for NARE (Reference 16). SQUG accepted the NRC’s clarifications, produced Revision 4 of the NARE Guidelines, and sent these guidelines to SQUG members on 7/25/00 (Reference 18 ). Subsequently, SQUG updated the NARE Guidelines in Revision 5 to reference GIP-3A and make other improvements (Reference 19 ).

For SQUG members to use the GIP method for seismic qualification of new and replacement equipment (NARE), it is advisable, if not necessary, to modify the plant licensing basis to allow use of the GIP as an alternative (see NRC letter to SQUG dated 6/19/98, Reference 14). To assist members in changing the plant licensing basis, SQUG prepared Revision 0 of a 50.59 Template (Reference 17). This template is based upon the NEI guidance available at the time for preparing 50.59 safety evaluations (NEI 96-07, Revision 0). Specifically, Section 3 of the template offers suggested language to answer the seven questions from NEI 96-07, Revision 0. The template also reflected the guidance provided by the NRC in their letter to SQUG (Reference 14) in which the NRC agreed that the 50.59 process is an acceptable method to adopt the GIP, based on their expectation that a detailed comparison of a plant’s licensing basis with comparable elements of the GIP will be performed to support the 50.59 evaluation. Appendix A of the template compares typical elements in the licensing basis for A-46 plants to comparable elements in GIP-3. This comparison is intended to show that there is no reduction in the plant safety margin. Appendix B of the template provides suggested language which may be included in the plant’s USAR for adopting the GIP method as an alternative seismic qualification method.

Subsequently, SQUG updated the 50.59 Template to Revision 1 (Reference 19) to make it consistent with the amendments made by the NRC to 10 CFR 50.59 that became effective March 13, 2001, and the NEI guidance for applying this new 50.59 process, as contained in NEI 96-07, Revision 1. The 50.59 Template was also revised to reference GIP-3A and make other improvements.

SQUG’s Future
As discussed in the Mission Statement, 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.

References

1. Generic Letter 87-02, “Verification of Seismic Adequacy of Mechanical and Electrical Equipment in Operating Reactors, Unresolved Safety Issue (USI) A-46,” U.S. Nuclear Regulatory Commission, Washington, DC, February 19, 1987.

2. USI A-40 “Seismic Design Criteria Short-Term Program”, USNRC, Washington, D.C.

3. USI A-17 “Systems Interactions in Nuclear Power Plants” USNRC, Washington, D.C.

4. Sandia National Laboratories Report SAND92-0140, UC-523, June 1992, containing two reports originally published by the Senior Seismic Review and Advisory Panel (SSRAP) on (1) Use of Seismic Experience and Test Data to Show Ruggedness of Equipment in Nuclear Power Plants, and (2) Review Procedure to Assess Seismic Ruggedness of Cantilever Bracket Cable Tray Supports.

5. Part I of Sandia Report SAND92-0140, UC-523 [Reference 0 above]: SSRAP Report, “Use of Seismic Experience and Test Data to Show Ruggedness of Equipment in Nuclear Power Plants,” originally published by SSRAP on 2/28/91.

6. Part II of Sandia Report SAND92-0140, UC-523 [Reference 0 above]: SSRAP Report, “Review Procedure to Assess Seismic Ruggedness of Cantilever Bracket Cable Tray Supports,” originally published by SSRAP on 3/1/91.

7. Generic Letter 87-02, Supplement No. 1, Transmitting Supplemental Safety Evaluation Report No. 2 (SSER No. 2) on SQUG Generic Implementation Procedure, Revision 2, as Corrected on February 14, 1992 (GIP-2), U.S. Nuclear Regulatory Commission, Washington, DC, May 22, 1992.

8. SQUG (N. Smith) letter to NRC (J. Partlow), dated 8/21/92, describing SQUG’s understanding of SSER No. 2.

9. NRC (J. Parlow) letter to SQUG (N. Smith), dated 10/2/92, with enclosure containing NRC Staff comments on SQUG’s 8/21/92 letter.

10. SQUG (N. Smith) letter to NRC (J. Partlow), dated 3/26/93, forwarding Revision 2A of the Generic Implementation Procedure (GIP-2A) along with a description of how SQUG addressed the NRC comments in SSER No. 2 (Enclosure 2) and an explanation of the clarifications made in GIP-2A (Enclosure 3).

11. NRC (W. Butler) letter to SQUG (N. Smith), dated 5/24/93, NRC Response to SQUG Letter Dated March 26, 1993, on GIP-2A.