ML20199J643

Safety Evaluation Approving Request for Approval to Repair Flaws in Accordance W/Gl 90-05 for ASME Code Class 3 SW Piping for North Anna,Unit 1,as Submitted in ISI Relief Request NDE-46 on 971218

ML20199J643
Person / Time
Site:	North Anna
Issue date:	02/02/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20199J637	List: ML20199J633 ML20199J643
References
GL-90-05, GL-90-5, NUDOCS 9802050373
Download: ML20199J643 (5)

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pa aeg p' At UNITED STATES g , NUCLEAR REGULATORY COMMISSION o WASHINGTON. D.C. - aaat SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION 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 DOCKET HO. 50-338

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 .ihen 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 isolation of the system requiring the repair, and often a shutdown of the nuclear power plant.

Alternatives to Cuae requirements may be used by nuclear licensees when authorizedo'y 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 requests for relief from certain Code requirements when a licensee has determined that conformance with certain Code requirements is impractical for its facility [10 CFR 50.55a(g)(5)(iii)). Pursuant to 10 CFR 50.55a(g)(6)(1). the Con.nission will evaluate determinations of

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ENCLOSURE 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 for the staff in evaluating relief requests submitted by licensees for temporary non Code repairs of Code Class 3 piping. For the purposes of GL 90 05, impracticality is defined to exist if the flaw detected is in a section of

. Code Class 3 piping that cannot be isolated tca completing a Code repair within the-time period pe mitted ir, the limiting condition for operation of the. j affected system as specified in the plant Technical Specifications, and performance of a Code repair would require-a plant shutdown.

2,0 BACKGROUND On October 21, 1997, et the North Anna Power Station. Unit 1, 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, A repair plan was developed and implemented for the affected lines. The three welds were repaired in accordance with_ the ASME Code requirements by November 4. 1997. By letter dated December 18,'1997, pursuant to 10 CFR 50.55a(g)(6)(1), the licensee requested a-relief from the ASME Code.Section XI replacement requirements for the period of i October 21, 1997, through November 4. 1997. The licensee based its request for relief on the results of-a "through wall flaw" evaluation that was performed by- l the licensee 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 Requested

Weld # Line # Joint Tvoe 18W 3"-WS75-163 03 Butt Weld 99 3"-WS-76-163 03 Butt Weld

' 96: 4"-WS-57-163 03 B9tt Weld-The above listed welds are ASME Code Class 3 moderate energy ASME SA-312, type

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."6-L stainless steel piping in the SWS. Lines 3" WS-75 163 03 and 3" WS76-103 03 are return lines from the charging pump lube oil coolers. Line 4" WS 57- ,

163 03 is the return from charging pump oil coolers and instrument air compressors. The nominal operating pressure is 75 psig and operating temperature is 957. t 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.

3.3 ASME Section XI Code Recuirement 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 IWA-7000, respectively. The intent of these rules servec to provide 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 October 21 1997, through November 4,1997, because performing a Code repair during 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 licensee has evaluated the 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 repairs in accordance with the ASME Code during the period October 21, 1997, through November 4, 1997, would have constituted an undue burden (create undue hardehip) 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.

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3.6 Licensee's AlternLtive Proaram During the period of October 21, 1997, through November 4. 1997, the SWS with the identified possible through wall flaws was monitored by the licensee with weekiy visual monitoring of through wall flaws and leakage.

4.0- STAFF EVALUATION AND CONCLUSIONS 4.1 . Doerability Determination. Root Cause Analysis and.,$1ructural Intearity Evaluation This system was constructed in accordance with the requirements of. ASME Code.

Class 3. Based on the radiographic testing (RT) examination data of the welds, the flaws were determined to be small voids surrounded by exfoliat'lon, which is

. typical;of microbiological 1y induced corrosion (MIC). No other type of operationally caused defects were identified by the RT. Because of the inability of both RT and ultrasonic testing (UT) to give reliable through wall depth for MICi alf MIC indications were considered through wall. Thi s --

assumption caused the welds 99 and 18W to fail the assessment requirements of GL 9n-05 -Weld 96 was found structurally acceptable by structural integrity evaluallon. The: disposition of the three welds are: (1) Weld 18W on 3" WS 75-Ifit 03 was removed from service after the weld was radiographed. The weld was rep b m t on November 4. 1997. 1 day after the weld was radiographed and removed from servke. (2) Weld 99 on 3*-WS;/6 163-03 was also removed from service af ter the weld was radiographed. The weld was replaced on October 28, 1997, 1 day af ter the weld was radiographed and removed from service. (3) Even though weld 96 on 4" WS57-163 03 was structurally acceptable it was also removed from service aft.er the weld was radiographed. The weld kn. replaced on October 28.-

199/. 1_ day after the weld was radiographed and removed from service.

- 4.2' Augqtented Insnection-lo assess the overall degradation of the SWS augmented radiographic examination was performed on five additional locations on lines having the same function.

Ali rive welds examined had evidence of MIC. without showing evidence of-through wall leak i.e.. stains. Welds 1W. 3W and 47 on line 3" WS-76 163-03 were found acceptable by radiography and structural integrity evaluation, flowever; welds IW and 3W were replaced _for ease of construction. Weld 2W on line 3" WS-76 163-03 and weld 95 on line 4"-WS57-163 03 failed structural integrity evaluation. and were replaced on October 28.-1997, prior to returning the: lines to service. Because welds.2W 'and 95 had failed the structural integrity evaluation, five additional welds were examined. All five welds had evidence of MIC. without showing evidence of through wall leak. i.e., stains.

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5 Welds 16W, 72 and 73 on line 3" WS-75 163 03 were found acceptable by radiography and structural integrity evaluation. However, these welds were replaced for ease of construction. Welds 15W and 17W on line 3" WS-75 163 03 ,

failed structural integrity evaluation, and were replaced on November 4.1997, prior to returning the lines to service. Because welds 15W and 17W had failed the structural integrity evaluation, five more welds on lines having the same function were examined. None of these welds in the new sample exhibited evidence of MIC on the radiographs. Since all five welds were found acceptable by radiography, the structural analysis was not performed.

4.3 Prooosed Temocrary Non Code Renair and Monitorina Provisions During the period Octber 21, 1997, through November 4, 1997, the licensee performed weekly visual monitoring of all areas with possible evidence of leakago. The areas met the criteria for flooding and spraying consequences 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. During the period of October 21, 1997, through November 4, 1997, the welds were monitored by plant personac1 and the flaws were repaired by November 4. 1997.

Furthermore, the staff finds that performance of an immediate Code repair during the period October 21, 1997, through November 4,1997, 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  ;

t that are otherwise structurally sound and capable of performing their intended safety function. and would not have been in the best interest of plant safety, given the small magnitude of the flaw and the licensee's alternative program.

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

Principal-Contributor: N. Kalyanam Date: February 2. 1998 I

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