ML20217E187

SER Approving Request for Approval to Repair Flaws in Accordance W/Gl 90-05 for ASME Code Class 3 Service Water Piping,Virginia Electric & Power Co,North Anna Power Station,Units 1 & 2

ML20217E187
Person / Time
Site:	North Anna
Issue date:	09/24/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20217E179	List: ML20217E174 ML20217E187
References
GL-90-05, GL-90-5, NUDOCS 9710060376
Download: ML20217E187 (5)

Text

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION i

REQUEST FOR APPROVAL TO REPAIR FLAY,S IN ACCORDANCE WITH GENERIC LETTER 90 05 FOR ASME COLiE CLASS 3 SERVICE WATER PIPING VIRGINIA ELECTRIC AND POWER COMPANY l

l NORTH ANNA POWER STATION. UNITS 1 AND 2 l DOCKET NOS. 50 338 AND 50-339

1.0 INTRODUCTION

10 CFR 50.55a(g) requires nuclear power facility piping and components to meet the applicable requirements of Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (hereafter referred to as the Code).Section XI of the Code specifies Code-acceptable repair methods for flaws that exceed Code acceptance limits in piping that is in-service. A Code repair is required to restore the structural integrity of flawed Code piping, independent of the operational mode of the plant when the flaw is detected. Those repairs not in compliance with Section XI of the Code are .1cn-Code repairs. However, the implementation of required Code (weld) repairs to ASME Code Class 1. 2 or 3 systems is often impractical for nuclear licensees since the repairs normally require an isolation of the system requiring the repair, which could result in entries into action statements and manipulations of the system or even a shutdown of the nuclear power plant.

Alternatives to Code requirements may be used by nuclear licensees when authorized by the Director of the Office of Nuclear Reactor Regulation if the proposed alternatives to the requirements are such that they are shown to provide an acceptable level of quality and safety in lieu of the Code requirements [10 CFR 50.55a(a)(3)(1)]. or if compliance with the Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety [10 CFR 50.55a(a)(3)(ii)].

A licensee may also submit recuests for relief from certain Code requirements when a licensee has determinec that conformance with certain Code requirements is imaractical for its facility [10 CFR 50.55a(g)(5)(iii)]. Pursuant to 10 CR 50.55a(g)(6)(1), the Commission will evaluate determinations of impracticality and may grant relief and may impose alternative requirements as it determines are authorized by law.

Generic Letter (GL) 90-05. " Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2 and 3 Piping." dated June 15. 1990, provides guidance ENCLOSURE 9710060376 PDR 970924 P ADOCK 05000338 pop

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2 for the staff in evaluating relief requests submitted by licensees for temporary non-Codo repairs of Code Class 3 31 ping. The staff uses the )

- guidance in GL 90-05 as its criteria. for-ma cing its safety evaluation of

-relief requests for temporary non-Code repairs of Code Class 3 piping.

2.0- BACKGROUND On February 10, 1997, at the North Anna Power Station. Unit 1 and 2. Virginia Electric and Power Company (hereafter referred to as the licensee) identified three locations with evidence of possible previous leakage i.e., stains in three ASME Class 3 Service Water System (SWS) lines. At the time the evidence of the leaks was identified, both Units 1 and 2 were in operation.

By letter dated March 19, 1997, pursuant to 10 CFR 50.55a(g)(6)(1), the ,

licensee requested a relief from the ASME-Code Section XI requirements for the period of February 10. 1997, through March 18, 1997. The licensee based its i

request for relief on the results of a "through-wall flaw" evaluation that was performed by the licensee in accordance with the guidelines and acceptance l

criteria contained in GL 90-05.

3.0 LICENSEE'S RELIEF REQUEST

.3.1 Comoonents for Which Relief is Reauested Unit 1 Unit # Weld # Line # Joint Tvoe 1 6 2"-WS-C82-153A-03 1

Socket Weld 19W 4"-WS-57-163-03 Butt Weld 2 Base metal adjacent 2"-WS-776-163-03 2" pipe weld 56 -

The above listed welds are ASME Code Class 3. moderate energy piping in the SWS. The piping provides cooling water from the SWS to instrumer.t air-compressors and charging pump lube oil coolers for both units and returns service water back to return headers. Normal flow is 20 to 100 gpm at an operating pressure temperature is 150*F.of 100 psig. The design pressure is 150 psig and design 3 . 2..Section XI Edition for North Anna 1 and 2 North Anna Unit 1 - 1983 Edition of the ASME Code.Section XI including Summer-1983 Addenda.

North Anna Unit 2 - 1986 Edition of the ASME Code.Section XI.

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3 3.3 ASME Section XI Code Reauirement The ASME Code Section XI requires that repairs or replacements of ASME Code Class components be performed in accordance with rules found in Articles IWA-4000 or 14A-7000, respectively. The intent of these rules serves to prnvide an acceptable means of restoring the structural integrity of a degraded Code Class system back to the original design. requirements.

3.4 Content of the Relief Reauest Relief is sought from performing a repair or replacement of the service water piping per the requirements of Article IWA-4000 or IWA-7000, respectively.

Relief is being sought for the period of February 10, 1997, through March 18, 1997, because not practical. performing a Code repair during that period was determined to be The licensee had accomplished permanent Code repairs for all welds by the end of that period.

3.5 Basis for Relief Request for relief has been submitted and alternatives to the Code requirements have been proposed by the licensee. The NRC staff revi ued the

$0.55a(g)(6)(i).roposed alternatives for compliance3rovisions of 10 with theCFR guidance provided Thein GLlicensee 90-05. has evaluated tie flaws in accordance with the Based upon the evaluation, it was established that the discovered flaws satisfy the criteria for non-Code repair as described in GL 90-05 and performing permanent repairs in accordance with the ASME Code during the period February 10. 1997, through March 18,1997. would have constituted an undue burden (create undue hardship) upon the licensee since the repairs would have necessitated the unnecessary isolation of po-tions of SWS that are structurally sound and thus reduce the margin of shfety of the SWS.

3.6 Licensee's Alternative Proaram During the period of February 10, 1997, through March 18. 1997, the SWS with the identified possible through-wll flaws was monitored by the licensee as follows:

1. Weekly visual monitoring of through wall flaws and leakage.

2. Radiographic examination of butt weld 19W was done. Weld 19W was analyzed and found to be acceptable. Radiographic examination of the area adjacent to weld 56 on line 2"-WS-776-163-03 indicated unacceptable amount of microbiologically influenced corrosion (MIC) and the weld was repaired.

Radiography of socket weld 6 was not attempted since radiographs of socket welds do not yield meaningful results. The weld was also repaired 9 days after the evidence of leakage was detected and before a complete structural integrity analysis could be performed.

4 4.0 STAFF EVALUATION AND CONCLUSIONS 4.1 Opfrability Determination. Root Cause Analysis '

and Structural Intearity Evaluation The licensee determined that the three locations on the SWS had "through-wall" flaws and analyzed them in accordance with the position stated in GL 90-05.

This system was constructed in accordance with the requirements of ASME Code, j Class 3. Based on the radiographic testing (RT) examination data, the flaws l

were determined to be small voids surrounded by exfoliation, which is typical of MIC. No other type of operationally caused defects were identified by the RT. The licensee performed an operability determination of the SWS in the "as-found" condition and determined the following: (1) butt weld 19W on line 4"-WS-776-163-03 was analyzed and found acceptable: (2) weld 56 on line 2"-WS-776-163-03 showed the possibility of MIC for 77 percent of the circumference.

This length exceeded the established allowable limit and the weld was declared inoperable. The line was isolated and the weld was repaired prior to returning the line to service: and (3) radiography of socket weld was not attempted since radiographs of socket welds do not yield meaningful results.

Therefore' once the evidence of leakage was detected the weld was monitored weekly for additional leakage until the the repair was done.

4.2 Auamented Insoection To assess +he overall degradation of the SWS, augmented radiographic and visual examinations were performed on five additional locations on lines having the same function. This sample group also identified welds degraded by MIC. Any indication was treated as a through-wall defect and analyzed for structural integrit in accordance with the guidance 3rovided in GL 90-05.

Allaugmentedweld{iocationswerefoundtobeaccepta)le.

4.3 ProDosed Temocrary Non-Code Reoair and Monitorina Provisions During the period February 10, 1997, through March 18, 1997, the licensee performed weekly visual monitoring of all areas with possible evidence of leakage. The areas met the criteria for flooding and spraying and for structural integrity.

4.4 Staff Conclusions The staff has determined that the licensee's flaw evaluation has been consistent with the guidelines and acceptance criteria of GL 90-05. The staff therefore finds the licensee's structural integrity and operability assessments to be acceptable. The licensee had repaired all flaws by March 18, 1997. During the period of February 10, 1997, through March 18, 1997, the welds were monitored by plant personnel.

Furthermore, the staff finds that performance of an immediate Code repair during the period February 10. 1997 through March 18. 1997, would have resulted in hardship without a compensating increase in the level of quality and safety. An immediate repair would have necessitated the isolation of portions of the SWS that are otherwise structurally sound and capable of

h performing their intended safety function. Isolation of portions of the SWS is not in the best interest of plant safety, flaw and the licensee's alternative program. given the small magnitude of the Accordingly, relief is authorized pursuant to 10 CFR 50.55a(a)(3)(ii).

Principal Contributor: G. Georgiev Date: September 24, 1997 I