ML20197K154

SER Granting Request for Approval to Repair Flaws in Accordance W/Gl 90-05 for ASME Code Class 3 Service Water Piping for North Anna Power Station,Per Util 970919 Submittal

ML20197K154
Person / Time
Site:	North Anna
Issue date:	12/18/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20197K139	List: ML20197K134 ML20197K154
References
GL-90-05, GL-90-5, NUDOCS 9801050235
Download: ML20197K154 (5)

Text

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• NUCLEAR REGULATORY COMMIS810N WADMINGTON. D.C. SteeMeet i i\FETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REOUEST FOR APPROVAL TO REPAIR FL AWS IN ACCORDANCE WITH GENERIC LETTER 90-05 FOR ASME CODE CLASS 3 SERVICE WATER PIPING YlRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION. UNIT 1 AND UNIT 2 DOCKET NOS. 50 338 AND 50 339

1.0 INTRODUCTION

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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 x . ' the Code are non Code repairs. However, the implementation of required Com eld) repairs to ASME Code Class 1. 2 or 3 systems is often impractical 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 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 acce) table level of quality and safety in lieu of the Code  :

requirements [1] CFR 50.55a(a)(3)(1)] or if compliance with the Code requirements would result in hardship or unusual difficult compensating 50.55a(a)(3)ii)).

(increase in the level of quality and safety (

10 CFR A licensee may also submit requests for relief from certain Code requirements

• when a licensee has determined that conformance with certain Code requirements is imaractical for its facility [10 CFR 50.55a(9)(5)(111)). 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.

Generic Letter (GL) 90 05. 'Guida.ce 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 31 ping. The staff uses the guidance in GL 90 05 as its criteria for madng its safety evaluation of relief requests for temporary non Code repairs of Code Class 3 piping.

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2.0 BACKGROUND

On August 6. 1997, at the North Anna Power Station. Unit I and Unit 2.

Virginia Electric and Power Company (hereafter referred to as the licensee) identified seven locations with evidence of possible previous leakage. i.e.,

stains, in ASME Class 3 service water system (SWS) lines. In order to reduce the number of entries into action statements and service water manipulations, a repair plan was developed and implemented for the affected lines. All the welds were repaired in accordance with the ASME Code requirements by dovember 4. 1997. By letter dated September 19.-1997, pursuant to 10 CFR 50.55a(g)(6)(1), the licensee reamsted a relief from the ASME Code.Section XI re)lacement re Novem)er 4,1997,quirements for the when the last weld wasperiod of August replaced. The licensee 6,1997.based until the ,

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 Whtph Relief is Reauested Weld # L102). Joint Tvoe Material Egry1C2 t 42A 2" WS80-163 03 Socket Weld SA 312 Type 316L See Note 1 10 2"-WS 948 153A 03 Sc;ket Weld SA 376 Type 304 See Note 2  ;

36 2" WS 954-153A 03 Socket Weld SA 312 Type 304 See Note 3 t 90 4"-WS46-163 03 Butt Weld SA 312 Type 316L See Note 4 3W 4"-WS 56 163 03 Butt Weld SA 312 Type 316L See Note 5

• 4W 4"-WS-56-163 03 Butt Weld SA 312 Type 316L See Note 5 69 4"-WS-F64-163 03 Butt Weld- SA-312 Type 316L See Note 6 The above listed welds are ASME Code Class 3 moderate energy piping in the SWS. j Note 1: Supply to the Unit 1 instrument air heat exchanger (1-IA E-1C) t Note 2: Supply to the Unit 2 chargin i Unit 2 seal coolers (2-CH E1C2A g pumpand 2gear box cooler (2-CH E lCl) and CH E-1C28) .

Note 3: Return from Unit 2 charging pump gear box cooler (2 CH E 1Cl) ard Unit 2 seal coolers (2-CH E-lC2A and 2 CH-E-lC28)

Note 4: Supplies cooling water to the Unit I charging pump lube oil coolers and instrument air compressors Note 5: Return from the Unit I charging pump lube oil coclers and instrument air compressors i Note 6: Return from the Unit I air conditioning condenser The nominal operating pressure is 75 psig a v operating temperature is 957.

3.2- Section XI Edition Unit 1: 1983 Edition of the ASME Code.Section XI including Summer 1983 Addenda.

Unit 2: 1986 Edition of the ASME Code

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. 3 l 3.3 ASME Section XI Code Reauirement l

The ASME Code Section XI requires that repairs or replacements of ASME Code Class components be performed in accordance with rules found in Articles lWA-4000 or 1WA 7000, respectively. The intent of these rules serves 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 1s being sought for the period of August 6.1997. until November 4, i 1997, because not practical. performing The licenseeahad Code repair during that period was determined to be j accomplished permanent Code repairs for all the welds by the end of that period, j

' 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 provisions of 10 CFR  !

50.55e(g)(6)(1). Radiography of socket welds 42A, 10. and 36 were not ,

attem)ted because radiographs of socket welds do not yield meaningful results  :

and tie flaws cannot be characterized for socket welds. Lines 2" WS-80 163-03, 2" WS 948-153A-03 and 2" WS 954 153A 03 weie removed from service and socket welds were re) laced by August 20. 1997. The radiography of weld 90 was i unable to give reliaale through wall depth for microbiologically induced corrosion (MIC) indications and, with a conservative through wall asssumption.

the weld failed the assessment requirements of GL 90 05. Therefore, weld 90 on line 4" WS 46163 03 was removed from service and repaired on August 14, 1997. Even though welos 3W and 4W showed evidence of acceptable MIC as  :

determined by radiography and structural integrity analysis, the two welds  !

were replaced on August 12. 1997. Weld 69 on line 4" WS F64 163 03 also i showed evidence of acceptable MIC as determined by structural integrity analysis and was replaced on November 4. 1997. One of the two options allowed by GL 90 05 is leaving the piping as-is if there is no leakage and the flaw is ,

found accepatable by the through wall flaw approach and, subject to i monitoring, meeting the criteria for cosequences and for structural integrity until replaced. .

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 93 05 and performing permanent re) airs in accordance with the ASME Code during  ;

the period August 6.1997, througl November 4.1997. 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 i structurally sound and thus reduce the margin of safety. (

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4 4.0 -STAFF EVALUATION AND CONCLUSIMS 4.1- Doerability Determination. Root Cause Analysis ADA.S.tructural Intearity Evaluation The licensee determined that four locations on the SWS have a "through wall  !

flaw" and analyzed them in accordance with the position stated in GL 90 05. i This system was constructed in accordance with the requirements of ASME Code.

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 l RT. The licensee evaluated the structural integrity of the welds based on the radiographic examination and determined the following: (1) butt welds 3W and 4W on line 4" WS 56 163 03 which were analyzed and found to be acceptable were ,

replaced on August 12, 1997. Butt weld 69 on line 4"-WS F64 163 03 which was  !

also analyzed and found to be acceptable was replaced on November 4, 1997:

(2) the butt weld 90 on line 4" WS 46 163-03 did not meet the assessment requirements of GL 90 05 and the line was removed from service and the weld was replaced on August 14. 1997: (3) radiography of socket welds 42A on line 2" WS 80 163 03. 10 on line 2"-WS 948 153A '23 and 36 on line 2" WS-954 153A 03 were not done since radiographs of socket welds do not yield meaningful results. The lines were removed from service and the welds were replaced on August 20. 1997. 14 days after the evidence of leakage was detected.

4.2 Auamented Insoection i To assess the overall degradation of the SWS, augmented radiogra) hic examination was performed on five additional locations on lines laving the same function. Any indication was treated as a through wall defect and analyzed for structural integrity in accordance with the guidance provided in GL 90 05. Two welds. 2W on line 4"-WS56-163 03 and 94 on line 4"-WS-46 163- '

03. had evidence of MIC but showed no evidence of through wall leakage. Weld 2W was found structurally acceptable by radiography and structural integrity -

evaluation and was not replaced. Weld 94 failed the structural integrity  ;

evaluation and was replaced on August 14. 1997. Welds 68 and 85 on line 4"-

WS F64-163 03 which did not show evidence of MIC were not replaced. Weld 6W on line 3" WS-75 163 03 was replaced for ease of construction. Because weld 94 in the augmented inspection scope failed structural integrity evaluation,

- five additional locations on lines having the same function were examined usirg radiography. All five weld locations were found to be accepatable by radiography and structural integrity analysis.

4.3 Prooosed Temocrary Non Code Reoair and Monitorina Provisions During the period of August 6. 1997, through November 4. 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 for structural integrity.

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• * . i 5 l 4.4 Staff Conclusions  !

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- The staff has determined ' hat the licensee's flaw ,1 valuation has been  :

consistent with the guidelines and acceptance criteria of GL 90-05. The 4 staff, therefore, finds the licensee s-structural integrity and operability i assessments to be acceptable. Durin the period of August 6, 1997, through November 4. 1997 the welds were mon tored by plant personnel and the flaws  !

were repaired by November 4,1997.

furthermore, the staff finds that performance of an imediate re> air during the period of August 6. 1997, through November 4. 19m , would lave resu'Ited 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 SW. that are otherwise structurally sound and capable of 3 performing their intended safety function, and would not have been in the best i 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 50.55a(a)(3)(11).

Principal Contributor: S. Heu Date: December 18, 1997 i

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