ML20237A817

SER Related to USI A-46 Program GL 87-02 Implementation for Prairie Island Nuclear Generating Plant,Units 1 & 2

ML20237A817
Person / Time
Site:	Prairie Island
Issue date:	08/05/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20237A812	List: ML20237A810 ML20237A817
References
REF-GTECI-A-46, REF-GTECI-SC, RTR-REGGD-01.097, RTR-REGGD-01.100, RTR-REGGD-1.097, RTR-REGGD-1.100, TASK-2.F.2, TASK-A-46, TASK-OR, TASK-TM GL-87-02, GL-87-2, NUDOCS 9808170143
Download: ML20237A817 (12)

Text

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. [pl[tgkt p UNITED STATES g

p ,t j NUCLEAR REGULATORY COMMIS ."ON WASHINGTON, D.C. 206sHo01 O

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO USl A-46 PROGRAM (GL 87-02) IMPLEMENTATION NORTHERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PLANT. UNITS 1 AND_2 9

DOCKET NOS. 50-282 AND 50-306

1.0 BACKGROUND

in December of 1980, the NRC designated " Seismic Qualification of Equipment in Operating Plants" as an unresolved safety issue (USl A-46). The safety issue of concern was that equipment in nuclear plar:ts for which construction permit applications had been docketed before about 1972 had not been reviewed according to the updated licensing criteria for seismic qualification of equipment ,such as Regulatory Guide (RG) 1.100 (" Seismic Qualification of Electric and Mechanical Equipment for Nuclear Power Plants"), IEEE Standard 344-1975, and Section 3.10 of the Standard Review Plan. To address the USI A-46 issue, most of the affected utilities formed the Seismic Qualification Utility Group (SQUG)in 1982.

On February 19,1987, the NRC issued Generic Letter (GL) 87-02 (' Verification of Seismic Adequacy of Mechanical anci Electrical Equipment in Operating Reactors, Unresolved Safety Issue (USI) A-46") to iniplement the resolution to USI A-46, which concluded that the seismic adequacy of certain equipment in operating nuclear power plants should be reviewed against updated seismic criteria not in use when these plants were licensed. On June 10,1987, the SQUG submitted to the NRC a report containing the initial version of the Generic implementation Procedure (GIP) for use by its member utilities. Subsequently, the NRC issued its safety evaluation report on the GIP. The GIP was later revised to incorporate NRC comments. On May 22,1992, the NRC issued Supplement 1 to GL 87-02 including the staff's Supplernental Safety Evaluation Report No. 2 (SSER-2), pursuant to the provisions of 10 CFR 50.54(f), which required that all addressees provide either (1) a commitment to use both the SQUG commitments and the implementation guidance described in Revision 2 of the GIP (GIP-2) as supplemented by the staff's SSER-2, or (2) En attemative method for responding to GL 87-02. The supplement also required that those addressees committing to implement GIP-2 provide an implementation schedule as well as detailed information including the procedures and criteria used to generate the in-structure response spectra (ISRS) to be used for USI A-46.

ENCLOSURE I

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The GlP provides an experience data base, technical approach, generic procedures, and l documentation requirements which can be used by licensees to address the concern of  ;

GL 87-02 for verifying seismic adequacy of the equipment needed for plant safe shutdown I following a safe-shutdown event (SSE) event. Thus GIP-2 and SSER-2 are two documents that I contain acceptable guidance for implementing the resolution of USl A-46. l in a letter dated November 20,1995 (Reference 1), the licensee, Northern States Power Company (NSP) submitted a report summarizing the results of its USl A-46 implementation program, which consists of safe shutdown path selection, equipment selection, equipment seismic evaluation, relay evaluation, and a list of allidentified outliers. In the report, the j licensee stated that it has used the provisions in GIP-2 and SSER-2 during the USl A-46 i resolution and implementation process at the Prairie Island Nuclear Generating Plant (PINGP). l The staff reviewed the report and issued a request for additional information (RAl) on l September 16,1997 (Reference 2). The licensee provided a schedule for outlier resolution in a letter dated December 31,1996 (Reference 3), and responded to the RAI in a letter dated November 17,1997 (Reference 4).

In its report on USl A-46 implementation (Reference 1), the licensee indicated its intent to apply the USl A-46 methodology in GIP-2 to future seismic verification of new or replacement equipment or parts. In its RAI (Reference 2), the staff questioned whether future use of GIP-2 may also include equipment covered by RG 1.97 or TMI Action Plan item II.F.2, thus superseding previous licensing commitments as a consequence of GIP-2 incorporation into the licensing basis. In response (Reference 4) to the staff's RAI, the licensee clarified its intent by stating that it will comply with the staff's position in item 2 of Section I 2.2 of the SSER-2.

Therefore, future new and replacement equipment included in the safe shutdown equipment list (SSEL) that are associated with RG 1.97 or TMI Action Plan item II.F.2 will continue to comply with the licensing commitments in the updated plant safety analysis report. The staff finds the licensee's response acceptable. The following is the staff's evaluation of the licensee's submittal and response to the RAl.

2.0 DISCUSSION AND EVALUATION 2.1 Sgismic Demand Determination (Ground Spectra and in-structure Response Spectra)

In Section 3 cf Reference 1, the licensee utilized the licensing design basis Housner ground response spectra (GRS), as defined in the PINGP Final Safety Analysis Report, as the seismic input at the foundation level to devebp ihe ISRS at floor elevations in the Reactor Building, Containment Building, Auxiliary Building, Turbine Building, and Screen House. The GRS of SSE horizontal components have a peak ground acceleration (PGA) of 0.12g. Se corresponding vertical PGA is 0.08g. The GRS and the corresponding ISRS are provided in Appendix B of Reference 1. The method of developing ISRS presented in Reference 5 has been evaluated by the staff ar'd documented in Reference 6.

' In Reference 2, the staff expressed several concerns related to ISRS, and the licensee's  !

response was provided in Reference 4. Brief descriptions of the staff concems and the licensee's response are provided below:

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(a) The staff questioned the possible existence of some ISRS (5 percent damped) that are higher than the 1.5 times the SQUG Bounding Spectrum. The licensee's response indicated that no structures have ISRS (5 percent damped) above 1.5 times the SQUG Bounding Spectrum. Thus the staff's conctm is resolved.

(b) The staff requested justification for not using the possibly higher ISRS if the licensee elected to use method A in Table 4-1 of GIP-2. The response indicated that no equipment falls into this category due to the low amplitude of the ISRS.

.(c) The staff questioned the appropriateness of a direct comparison of the SQUG Bounding Spectrum (defined at free-field) with the plant's SSE ground motion spectrum (defined at the plant foundation level at most other plants) if the plant is founded on shallow soil.

The licensee's response indicated that the PINGP site is underlain by 158 feet - 185 feet of sandy alluvial soil over a 180-foot thick layer of competent sandstone, which is also underlain by other older sedimentary rocks. Thus the staff's concem is resolved since the site is not a shallow soil site.

As noted in each of the above items, the staff determined that the licensee's response has resolved the identified concem and is therefore acceptable.

2.2 Seismic Evaluation Personnel in accordance with the guidance in GIP-2, the licensee's seismic evaluation team designated for determining equipment seismic adequacy should consist of degreed engineers in system.

mechanical, electrical, and structural engineering with adequate experience, SQUG training, and knowledge in nuclear power plant operation, seismic evaluation, equipment and relay functionality, and walkdown procedures.

As indicated in Section 4.3 and Appendix C of the Summary Report (Reference 1), the seismic capability engineers involved in walkdowns and seismic evaluation consisted of a group of personnelirom NSP, Wisconsin Public Service Company, and Stevenson & Associates, which served as 1 contractor to the licensee. The staff reviewed their resumes and found that they all have SQUG training and appeared to have adequate educational background in engineering and worbng experience in seismic evaluation. In addition, the staff also reviewed resumes of perstmnel involved in relay evaluation, shutdown path selection, and establishing of equipment list, and found that they have adequate background and experience in plant systems, equipment functionality, and plant operation procedures. Thus the staff concludes that the personnel involved in the USl A 46 program implementation have met the qualification provisions in GIP-2 in regard to educ? tion, experience, and training, and are therefore j scceptable, i 2.3 Safe Shutdown Path  !

1 In its submittal of Reference 1, the Uconsee accounted for the following plant safety functions:

, reactor reactivity control, pressure control, inventory control, and decay heat removal. A primary and an attemate safe shutdown success path with their support systems and ,

instrumentation were identified for each of these safety functions to ensure that the plant is ,

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4 capable of being brought to, and maintained in, a safe shutdown condition for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> following a safe shutdown earthquake. Attachment D to Reference 1 provides the safe shutdown success paths.

The reactos decay heat removal function is accomplished by relieving steam from the steam generator via the steam generator power-operated relief valves. Makeup water to the steam generator will be supplied by the turbine-driven auxiliary feedwater pump which takes suction from the safeguards cooling water system. The motor-driven auxiliary feedwater pump is available as the alternate success path. The cooling water system has two diesel-driven pumps which are common to both units. Only one cooling water pump is required for the safe shutdown of both units. Each diesel-driven pump is provided with both local and control room manual controls. The Mississippi River is the source for the cooling water system.

The plant operations department reviewed the safe shutdown success paths and concluded that the plant operating procedures and operator training were adequate to direct the plant to the safe shutdown using the systems identified in Attachment D.

The staff concludes that the licensee's approach to achieve and maintain safe shutdown for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> following a seismic event is acceptable.

2.4 Seismic Screenina Verification and Walkdown for Mechanical and Electrical Eauloment At the PlNGP, the procedure used by the licensee for performing the seismic screening verification and walkdown for mechanical and electrical equipment is based on guidelines in GIP-2 and SSER-2, which consist of comparison of seismic capacity with demand, conformance with specific caveats, adequate anchorage, and proper consideration of seismic interactions. The following are staff evaluation results on these aspects.

2.4.1 Equipment Seismic Capacity Compared to Seismic Demand in Section 4.1.1 of the Summary Report (Reference 1), the licensee indicated that it developed horizontal ISRS for one horizontal direction only and applied it to both horizontal (North-South and East-West) directions.

The licensee stated that generally, the GRS of the SSE was used as a seismic demand and that it was compared to the seismic capacities defined by the " Bounding Spectrum" (BS) in accordance with

• Method A" of GIP-2 for equipment within 40 feet above the effective grade.

Fo ~ ?quipment located above 40 feet from the effective grade, the licensee used " Method B" (1.5xBS) of GlP-2 to establish the seismic capacity for equipment that was compared to the ISRS as the required seismic demand. The licensee also stated that the " Generic Equipment Ruggedness Spectra (GERS)" were not used. The staff considers that the licensee's use of Methods A and B in Table 4-1 of the GIP-2 has yielded adequate verification of seismic capability of equipment for the resolution of USl A-46 at the PINGP.

l in Attachment 2 of Reference 4, the licensee indicated that, for outlier resolutions, analyses of actual installations were conducted to verify that the in structural seismic demand is less than i

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the capacity. Alternatively, vendor's specifications were reviewed to verify that the seismic capacity is greater than the demand for specific equipment. The staff reviews found that the ]

licensee's determination on meeting seismic demand is generally acceptable.

2.4.2 Assessment of Equipment Caveats According to the GIP, caveats are defined as the set of particular inclusion and exclusion rules that identify the important characteristics and features that a specific class of equipment should have in order to verify its seismic adequacy. A summary of caveats for each earthquake experience equipment class is described in Appendix B of the GIP-2.

As indicated in Section 4.1.2 of the Reference 1, the licensee performed seismic adequacy evaluation and walkdown for items of equipment contained in the SSEL and determined '

whether specific seismic concems addressed by the caveats were met. The licensee indicated that, at Prairie Island, most items of equipment contained in the SSEL do meet the GIP-2 caveats, except for a small number of SSEL items that were judged to meet the intent, but not the exact wording, of certain caveats. Table 5-1 of Reference 1 contains a listing of cases depicting instances where the intent of the caveat was met in each case. In most cases, engineering judgement, analysis or simple test, such as a " tug test," was used by the licensee's Seismic Review Team (SRT) to determine whether the intent of a caveat was met.

The staff reviewed information provided in Table 5-1 of Reference 1. According to the provisions of GIP-2, meeting intent of a caveat is permitted on a case basis provided that ,

interpretation of a specific approach and measures taken are justifiable. In Reference 2, the staff selected two cases in which engineering juogement was used and requested further explanations from the licensee. The staff found that the licensee's response reflected sound engineering judgement and is therefore acceptable.

2.4.3 Equipment Anchorages The staff reviewed the guidelines stated in the Section 4.1.3 of the Summary Report (Reference 1) and found that they are in conformance with the rules in GIP-2 for verifying  !

seismic adequacy of equipment anchorages.

As indicated in Section 4.1.3 of the Summary Report (Reference 1), the licensee verified equipment anchorage adequacy by comparing the anchorage capacity to the seismic demand.

Anchorage installations were ' inspected to verify that they are free of gross installation defects and to ensure adequate stiffness and strength in the anchorage load path. Analyses were performed using guideline

• in Appendix C of the GIP for determining normal capacities and reduction factors. In some cases, engineering judgement or a simple test was used to

- determine whether the scecific seismic concern addressed by the caveat is met.

During the walkdowns, the SRT inspected the seismic adequacy of the anchorage installation i and its connection to the base of the equipment and determined the allowable capacity of the

! anchoraga used to secure the equipment. The inspection consisted of visual checks and l

measurements utilizing plant documentation and drawings and an anchor bolt tightness and embedment check for concrete expansion anchors. The SRT determined the seismic demand

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imposed on the equipment and identified outliers for anchorages that did not have enough capacity when compared to the demand. Table 8.1 of the Summary Report (Reference 1) shows the list of the equipment outliers identified during the A-46 walkdowns at PINGP. Amcng 28 equipment outliers identified, approximately 29 percent of the outliers were related to anchorage deficiencies including insufficient anchor capacity, unacceptable anchorage edge distance, and potential bolt bending concerns. The licensee committed to resolve all of the outliers as discussed in Section 2.9 below.

In Appendix D of the Summary Report, Screening Verification Data Sheets (SVDS) were provided and contained a specific check on evaluation of equipment anchors. Conformance with GIP screening guidelines was evaluated for each anchor and identified in the SVDS. In Section 5 of the Summary Report, anchors that meet the intent of specific caveats were listed along with an explanation for their acceptance. In Attachment 2 of the licensee's response to staff's RAI (Reference 4) on the licensee's USl A-46 implementation program, the resolution method and status of all outliers were provided, including the resolution of anchorage outliers.

Based on the above discussion, the staff concludes that equipment anchorages are generally in conformance with the guidelines of GIP-2 and SSER-2 and are therefore acceptable.

2.4.4 Seismic Spatial Interaction Evaluation As indicated in Sections 4.1.4 and 4.3 of the Summary Report (Reference 1), several walkdowns were performed by the SRT, which included seismic cepability engineers to determine whether adverse seismic spatial interactions with nearby equipment exist.

Guidelines in Appendix D of the GIP were used for the walkdowns. The licensee's walkdowns considered the following concerns: (1) proximity effects, (2) structural failure and falling, (0) flexibility of attached lines and cables, (4) overhead piping and ductworks, and (5) any other possible interactions.

The licensee performed an interaction evaluation for the equipment contained in the SSEL and verified the equipment accep%bility and conformance with the GlP guidelines in the SVDS b Appendix D of the Summary Report.

In Table 8-1 of the Summary Report, specific outliers identified during the final A-46 walkdown were listed, including some items wid an interaction concern. Resolution of outliers was presented in Attachments 2 and 3 of the licensee's RAI response in Reference 4. In addition, an independent eval 9ation and peer review of the walkdown process was also performed by the SRT to ascertain completeness and conformance of the licensee's USl A-46 walkdowns to applicable GIP provisions. During the walkdowns, the SRT identified one issue involving overhead lighting fixtures. Overhead fluorescent lights were found to be connected by open S-hook supports that could potentially be released during a seismic event. The findings were identified as outliers and the licensee stated that a work order was issued to crimp the S-hooks as part of an outlier resolution. The work was completed as a general maintenance activity.

This is acceptable.

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7 The staff reviewed the spatial interaction guidelines used by the licensee's seismic review team for their walkdowns to verify their conformance with the provisions in GIP-2. The check list in the SVDSs is comprehensive, and the specific outlier descriptions contained in Table 8-1 of Reference 1 and outlier resolutions explained in Attachments 2 and 3 appear reasonable and reflect sound engineering judgement. The third party peer review also meets the provisions of GIP-2, and is therefore acceptable.

2.5 Ignks and Heat Exchanaers The licensee stated that it reviewed the tanks and heat exchangers at PINGP in accordance with the rules and procedures described in Section 7 of GlP-2. The licensee identified 10 tanks and heat exchangers as outliers out of the entire outlier population of 62. Four out of the ten tanks were declared as outliers since the SRT was not able to determine the flexibility of buried pipes, which are connected to the tanks, from available documentation. The SRT proposed a detailed analysis of the buried pipes including sufficient soil-structure interaction analysis as an outlier resolution (Reference 4). The proposed analysis of the buried piping was subsequently performed, and its related outliers were resolved. The remaining outliers (two vertical tanks, two horizontal tanks and two horizontal heat exchangers) were resolved by detailed analysis and/or technical justifications by the SRT. The licensee stated that the seismic margin methodology, described in the report Electric Power Research Institute (EPRI) NP-6041, was not used in any manner in the PINGP USl A-46 program. The staff determined that the licensee's implementation of GIP-2 provisions relating to tanks and heat Lchangers is considered adequate for the resolution of USI A-46 at PINGP.

2.6 Cable and Conduit Raceways in Section 7 of the licensee's Summary Report, the I!censee stated that it has followed the ,

guidelines and inclusion rules provided in Section 8 of GIP-2. Based on the walkdown results, l the licensee concluded that no anomalies in design or construction were identified, and PINGP l meets the Cable Raceway inclusion Rules of GlP-2 in their entirety without exception. In

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addition, the SRT inspected the raceway systems for the caveats relating to "Other Seismic l Performance Concerns" and " Seismic Interaction Review." The licensee stated that no findings f were noted with respect to "Other Seismic Performance Concerns" and only one finding was l noted with respect to " Seismic interaction Review." The SRT identified unrestrained exercise  !

equipment in the operators exercise room in the Auxiliary Buildir j . ' elevation 735 as a {

potential cause of seismic interactions with safety-related condub. The finding was classified l as an outlier that was subsequently resolved.

In accordance with GlP-2 guidelines, the licensee selected 10 raceway supports for a limited l analytical review (LAR) as shown in Table 7.2 of the Summary Report (Reference 1). The L.AR  !

evaluations checked dead load stresses, ductility, and vertical capacity. The results shown in i Table 7.3 of the Summary Report indicate that all 10 cable tray and conduit supports chosen for l the LAR met the guidelines as set forth in Section 8 of GlP-2.

f The staff concluded that the licensee's activities were adequate to resolve the cable and I conduit raceway supports issue for the resolution of USl A-46 at PlNGP.

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2.7 Essential Relays As indicated in the Relay Evaluation Report (Reference 1), the licensee considered any electrical contact as a relay for the purpose of initial screening, from which a total of 1786 relays were found. A further screening identified 420 essential relays. The essential relays are those relays for which chatter of its electrical contacts resulting from SSE motion could adversely

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impact the safe shutdown function of components associated with the SSEL. The essential relays were reviewed in accordance with the guidelines of GlP-2 to establish that their seismic capacity is not exceeded by the seismic demand, and that each related component housing essential relays is adequately anchored and not subject to adverse interaction during seismic motion. Outliers were identified for essential relays not meeting the GIP-2 guidelines. In Attachment ! of the Relay Evaluation Report,49 outliers were identified, including some relays with known low ruggedness and with missing model numbers. However, the report of Reference 1 provided neither resolution nor proposao methods for resolution of these outliers, in response to the staff's RAI (Reference 2), methods used by the licensee to resolve outliers along with descriptions of implemented resolutions for relay outliers were presented in Attachment 3 of Reference 4. Of the 49 identified outliers,28 have been already resolved and the remaining 21 were scheduled to be resolved by December 1997 during the Unit 1 outage.

As described in Section 2.9, below, these have been resolved. The staff has reviewed the methods and resolution descriptions provided in Reference 4, which generally included performing analysis to verify that the seismic capacity is not exceeded by the seismic demand, conducting modification of operation procedures to restart a component after a seismic event 4 and replacing those relays 'known to possess low seismic ruggedness or insufficient experience regarding their stismic ruggedness. The staff found that the described resolution of relay outliers, although brief, is in general conformance with guidelines of GIP-2, and thus I acceptable. I 2.8 Human Factors Aspects The licensee provided information that outlined the use of the " desk-top" and simulator evaluation methods by the operations department to verify that existing normal, abnormal, and -

emergency operating procedures were adequate to mitigate the postulated trant,ient and that operators could place and maintain the olant in a safe shutdown condition. The staff verified that the licensee had considered its operator training programs and verified that its training was sufficient to ensure that those actione specified in the procedures could be accomplished by the operating crews. The licensee stated that the shutdown path selected for USl A-46 and included in the SSEL was verified to be capable of achieving hot shutdown conditions using the normal control room ste* find levels. The licensee developed two special scenarios based on a seismic event concurrent with a loss of offsite power as part of this verification. The present l

level of operator training is sufficient to assure that the operators are proficient in the procedures to assure the selected success path will be used.

In addition, the staff requested verification that the licensee had adequately evaluated potential ,

challenges to operators, such as lost or diminished lighting, harsh environmental conditions, l potential for damaged equipment interfering with the operators tasks, and the potential for l placing an operator in unfarailiar or inhospitable surroundings. The licensee provided

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9 information regarding its evaluations to substantiate that operator actions could be accomplished in a time frame required to mitigate the transient. In addition to the anticipated recovery actions, the licensee determined that the operators would potentially have to restart a control room chiller unit if the relays associated with the seal-in circuits tripped as a result of the seismic event. The licensee modified the abnormal procedure for earthquakes and verified through actual operation of the unit that this could be accomplished in a time frame necessary to maintain the control rootn environment. The licensee also verified that the procedures and cperator training were adequate to ensure the operators could perform the required actions credited in the submittal. The licensee verified that hazards to the operators, such as the potential for light diffusers to fall in the control room, were analyzed and actions were taken to restrain the equipment. Therefore, the potential for physical barriers resulting from equipment or structural earthquake damage that could inhibit operator ability to access plant equipment is not considered to be a significant hazard. The licensee has provided the staff with sufficient information to demonstrate conformance with the NRC-approved review methodology outlined in the SQUG GlP and is, therefore, acceptable.

2.9 Outlier Identification and Resolutions The licensee used the GlP screening guidelines as a generic basis for identifying outliers.

According to the GIP, an outlier is defined as an item of equipment or relay that does not comply with the GIP screening guidelines. By conducting USl A-46 walkdowns and seismic review, the licensee identified 93 outliers in 20 classes of equipment, which were described and listed in Table 8-1 of the Summary Report in Reference 1. In addition,49 relay outliers were also identified and discussed in the Relay Evaluation Report in Reference 1.

For equipment outliers, concerns were generally related to the following: (a) seismic demand exceeding the capacity, (b) inadequate anchorage, (c) seismic spacial interaction, and (d) equipment not in the experience database. As for relay outliers, concerns were generally related to (a) seismic demand exceeding the capacity, (b) no applicable GERS, (c) relay model number unavailable, and (d) low ruggedness reported in EPRI document.

The staff review of Reference 1 found that no resolution of these outliers was provided in the report, and that neither schedules nor methods were proposed to resolve these outliers. In the licensee's letter of December 31,1996 (Reference 3), the licensee provided an outlier resolution schedule which indicated a time frame ranging from end of 1996 to the spring of 1999, depending on the determination whether a specific outlier will be resolved by analysis or by modification with or without plant outage. Subsequently, in an RAI (Reference 2), the staff I expressed its concern regarding potential safety implication of continued plant operation in light of a prolonged resolution schedule and requested information regarding the methods that will be taken for resolving these outliers.

1 In a letter dated November 17,1997 (Reference 4), the licensee indicated that the GlP-2 l screening criteria are not part of the licensing basis at the PINGP, and as a result, the existence of outliers that do not meet the GlP-2 screening criteria does not constitute a plant operability or l design-basis concern. In Reference 4 the licensee provided updated lists of outlier resolution methods and schedules. As indicated in Attachment 3 of Reference 4,28 out of a total of 49 relay outliers were resolved, and the remaining 21 outliers were scheduled for resolution in

10 December 1997. Methods for resolution were described, which generally include performing analysis to justify seismic capacity meeting demand, conducting procedure modification to restart a component after a seismic event, or simply replacing the relays with doubtful seismic ruggedness. The staffs eval"ation concluded that the descriptions provided regarding the methods employed for ret outlier resolution, although brief, were generally reasonable.

Also, as indicated in Attachment 2 of Reference 4, out of the 93 equipment outliers listed, 61 were resolved and 28 were scheduled for resolution by December 1997. Only 4 out of the 93 equipment outliers remain unresolved and are scheduled for resolution during the Unit 2 outage in December 1998 and the Unit 1 outage in May 1999. These four items of equipment required either additional welds to strengthen a support connection or rerouting to maintain minimum clearance to avoid potential seismic-induced interactions. Methods used or proposed to resolve outliers were individually described. The staff evaluation found that the descriptions on resolution methods, although brief, were generally reasonable in terms of good engineering practice. On March 24,1998, the staff was informed by the licensee that those outliers that were scheduled for resolution by the end of December 1997 were already resolved as projected. Thus only four outliers remain to be resolved. Considering that a significant number of equipment outliers have already been resolved, and that the remaining four outliers will require a plant outage for implementing the desired equipment modification, the staff concludes that there is no remaining safety concern regarding outlier resolution for relays and equipment, and, therefore, the licensee has satisfactorily addressed and resolved the outliers to allow the staff to close this issue.

3.0

SUMMARY

OF MAJOR STAFF FINDINGS The staff's review of the licensee's USI A-46 implementation program, as provided for each area discussed above, did not find any significant or programmatic deviation from the GIP-2 regarding the walkdown and the seismic adequacy evaluations at PlNGP.

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4.0 CONCLUSION

The licensee's USI A-46 program at PINGP was established in response to Supplement 1 to GL 87-02 through a 10 CFR 50.54(f) letter. The licensee conducted the USI A-46 implementation in accordance with GIP-2 and the staff's SSER-2. The licensee's submittal on the A-46 implementation indicated that the SSEL contains 1100 components of which 680 equipment and 420 relays were reviewed to verify their seismic adequacy by conducting walkdown and document evaluation. A total of 93 equipment outliers and 49 relay outliers were identified. As indicated in Section 2.9, the licensee had resolved all outliers by December 31, 1997, except for four equipment outliers, which the licensee is committed to resolve during the Unit 2 outage in December 1998 and the Unit 1 outap in May 1999. As described in Section 3.0, the staff's review did not identify any r.reas where the licensee's program deviated from GIP-2 and the staff's SSER-2 on SOUG/ GIP-2 issued in 1992.

The staff concludes that the licensee's A-46 implementation program has, in generai, met the purpose and intent of the criteria in GIP-2 and the staffs SSER-2 for the resolution of USl A.-46.

The staff has determined that the licensee's already completed actions will result in safety enhancements, in certain aspects, that are beyond the originaliicensing basis. As a result, the

11 licensee's actions provide sufficient basis to close the USl A-46 review at the facility. The staff also concludes that the licensee's implementation program to resolve USI A-46 at the facility has adequately addressed the purpose of the 10 CFR 50.54(f) request. Licensee activities related to the USl A-46 implementation may be subject to NRC inspection.

Regarding future use of GIP-2 licensing activities, the licensee may revise its licensing basis in accordance with the guidance in Section 1.2.3 of the staff's SSER-2 on SQUG's GIP-2, and the staff's letter to SQUG's Chairman, Mr. Neil Smith, on June 19,1998. Where plants have specific commitments in the licensing basis with respect to seismic qualification, these commitments should be carefully considered. The overall cumulative effect of the incorporation of the GIP-2 methodology, considered as a whole, should be assessed in making a determination under 10 CFR 50.59. An overall conclusion that no unreviewed safety question is involved is acceptable sn long as any changes in specific commitments in the licensing basis have been thoroughly evaluated in reaching the overall conclusion. If the overall cumulative assessment leads a licensee to conclude an unreviewed safety question is involved, incorporation of the GIP-2 methodology into the licensing basis would require the licensee to seek an amendment under the provisions of 10 CFR 50.90.

Principal Reviewers: S. Hou Y. S. Kim Date: August 5, 1998 r ,

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5.0 REFERENCES

1. Letter, Northern States Power Company to U.S. NRC, " Response to Generic Letter 87-02, " Verification of Seismic Adequacy of Mechanical and Electrical Equipment in Operating Reactors, USI 4-46" with attached Summary Report on equipment evaluation and Relay Evaluation Report, for Prairie Island Nuclear Generating Plant, Units 1 and 2, November 20,1995.

2. Letter, U.S. NRC to Northern States Power Company, " Request for Additional Information on A-46 Resolution, Prairie Island Nuclear Generating Plant, Units 1 and 2,"

September 16,1997.

3. Letter, Northern States Power Company to U.S. NRC, " Followup Response to Generic j Letter 87-02, Verification of Seismic Adequacy of Mechanical and Electrical Equipment '

in Operating Reactors. USl 4-46," which proposed a schedule for outlier resolution, December 31,1996.

4. Letter, Northern States Power Company to U.S. NRC, " Response to Request for Additional Information on the Prairie Island Nuclear Generating Plant, Units 1 and 2, Resolution of USl A-46," November 17,1997.

5. Letter, Northern States Power Company to U. S. NRC, "NSPC Response to Supplement l

No.1 to Generic Letter 87-02 on SQUG Resolution of USI A-46, Prairie Island Nuclear i Generating Plant Unit Nos.1 and 2," September 21,1992.

6. Letter, U.S. NRC to North States Power Company, " Prairie Island Nuclear Generating )

Plant Unit Nos.1 and 2,120-day Response to Supplement No.1 to Generic  !

Letter 87-02," November 30,1992.

i l

l l

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_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ . _ _ _ _ _ _ _ . _.__ _ _ _ _ . _ . _ _ _ _ _ _ _ _ _ _ _ _ . ___ _ _ . ._ )