ML20217E241

SER Accepting 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,Unit 1

ML20217E241
Person / Time
Site:	North Anna
Issue date:	09/24/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20217E237	List: ML20217E232 ML20217E241
References
GL-90-05, GL-90-5, NUDOCS 9710060405
Download: ML20217E241 (4)

Text

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P NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30M64001 k*..../

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION i REQUEST FOR APPROVAL TO REPAIR FLAWS IN ACCORDANCE WITH GENERIC LETTER 90-05 FOR ASME CODE CLASS 3 SERVICE WATER PIPING VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION. UNIT 1 QQCETNO.50338 1.0 JNTRODUCTION 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 non 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 isoletion of the system requiring the repair, and often 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 compen ating increase in the level of quality and safety [10 CFR 50.55a(a)(3)(11)).

A licensee may also submit requests for relief from certain Code requirements when a licensee has determined that conformance with certain Code requirement; is imaractical for its facility (10 CFR 50.55a(g)(5)(114)]. Pursuant to 10 CFR 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.

ENCLOSURE NR DO Ob33G P PDR

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Generic letter (GL) 90 05. "Guidai.ce for Performing Temporary Non Cade Repair of ASME Code Class 1. 2 and 3 Piping." dated June 15, 1990, provides guidance for the staff in evaluating relief requests submitted by licensees for temporary non Code repairs of Code Class 3 )iping. The staff uses the guidance in GL 90 05 as its criteria for macing its safety evaluation of relief requests for temporary non Code repairs of Code Class 3 piping.

2.0 BACKGROUND

On March 19, 1997, at the North Anna Power Station. Unit 1. Virginia Electric and Power Com)any (hereafter referred to as the licensee) identified five locations wit 1 evidence of ossible previous leakage. i.e., stains in a 4" line of the Service Water S stem (SWS),

By letter dated April 29. 1997, pursuant to 10 CFR 50.55a(g)(6)(1), the I licensee requested a relief from the ASME Code.Section XI replacement requirements for the period of March 19. 1997, through May 15.-1997 The licensee based its request for relief on the results of a "through wall flaw" evaluation that was performed in accordance with the guidelines and acceptance criteria contained in GL 90-05.

3.0 LICENSEE'S RELIEF REQUEST 3.1 Comoonents for Which Relief is Reauested Weld # line # Joint Tvoe 13 4"-WS F63 163 03 Butt Weld 16 4"-WS F63 163 03 Butt Weld '

61 4" WS F63-163 03 Butt Weld 64 4" WS F63-163 03 Butt Weld 66 4" WS F63 163 03- Butt Weld The above listed welds are ASME Code Class 3. moderate energy piping in the i SWS. The piping provides cooling water to the Unit 1 control room chillers.

Normal flow is 237 gpm at an operating pressure of 80 psig and operating temperature of 95*F. The design pressure is 150 psig and design temperature is 125'F.

3.2- Section XI Edition for North Anna 1 1983 Edition of the ASME Code.Section XI ucluding Summer 1983 Addenda.

3.3 ASME Section XI Code Reauirement The ASME Code Section XI requires that repairs or replacements of ASME Code Cla;s components be performed in accordance with rules found in Articles IWA-

-400) or IWA 7000, respectively. The intent of these rules serves to provide an sci.eptable means of restoring the structural integrity of a degraded Code Class system back to the original design requirements.

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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 40')0 or IWA 7MO. respectively Relief is being sought for the period of March 19. 1997, throughMay15.i997.

because performing a Code repair dt. ring that period was determined to be not practical. 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 reviewed the proposed alternatives for compliance with the )rovisions of 10 CFR '

50.55a(g)(6)(1). The licensee has evaluated tie flaws in accordance with the guidance provided in GL 90 05. 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 re) airs in accordance with the '

ASME Code during the period March 19. 1997 througi May 15. 1997 would have constituted an undue burden (create undue hardship) upon the licensee since the repairs would have necessitated the unnecessary isolation of portions of SWS that are structurally sound and thus reduce the margin of safety.

3.6 Licensee's Alternative Proaram ,

During the period March 19. 1997 through May 15. 1997.-the SWS with the identified possible through wall flaws was monitored by the licensee as  ;

follows.

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

2. Radiographic examination of all welds.

4.0 STAFFEVALVATIONANDCONCLUS{QE 4.1 Doerability Determination. Root Cause Analysis

- and Structural Inteority Evaluation Based on the radiographic testing-(RT) examination data, the flaws were determined to be small voids surrounded by exfo11ation, which is typical of microbiological 1y induced corrosion (MIC). No other type of operationally caused defects were identified by the RT. However, because of the inability for either radiography or ultrasonic techniques to determine the extent of wall degradation the structural assessment considered each indication to be through wall. The licensee evaluated the structural integrity of the piping using.theguidanceofGL9005. Based upon the evaluation. it was determined that the fiawed piping satisfied the criteria of GL 90 05 and the integrity of the piping would be maintained.

4.2 Auamented Insoection To assess the overall ' degradation of the SWS. augmented radiographic and

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visual examinations were performed on five additional locations on lines having the same function. Three out of the five were also degraded by MIC.

Any indication was treated as a through-wall defect and analyzed for structural integrity in accordance with the guidance >rovided in GL 90 05.

All augmented weld locations were found to be accepta)le, 4.3 Proposed Temocrary Non Code Renair and Monitorina Provisions During the period March 19. 1997, through May 15, 1997, the licensee performed weekly visual monitoring of all areas with possible evidence of leakage. The areas met the criteria for flooding and spraying consequences and structural integrity.

4.4 Staff Conclus,1gns 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. During the period of March 19. 1997, through May 15, 1997, the welds were monitored by plant personnel and the flaws were repaired by May 15. 1997.

Furthermore, the staff finds that aerformance of an immediate Code repair during the period March 19, 1997 tirough May 15, 1997, would have resulted in hardship without a compensating increase in the level of quality and safety.

An immediate re) air would have necessitated the isolation of portions of the SWS that are otlerwise structurally sound and capable of aerforming their intended safety function, and would not have been in the 3est interest of plant safety, given the small magnitude of the flaw and the licensee's alternative program.

Accordingly, relief is authorized pursuant to 10 CFR 50.55(a)(3)(ii).

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