ML20217E070

Safety Evaluation Granting Licensee ASME Section XI Relief Request NDE-33 at Plant,Unit 1

ML20217E070
Person / Time
Site:	North Anna
Issue date:	09/24/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20217E068	List: ML20217E063 ML20217E070
References
NUDOCS 9710060285
Download: ML20217E070 (4)

Text

!

O ae4

, - f/ t UNITED STATES g

j NUCLEAR REGULATORY COMMISSION o, WASHINGTON. D.C. 30866 4 001

% . . . . . ,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RE0fJEST 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 NO. 50-333

1.0 INTRODUCTION

10 U R 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 isolation of the system requiring the repair, and often a shutdown cf the nuclear power plant.

Alternatives to Code requirements may be used by nuclear licensees when 4

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 i 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 imaractical for its facility [10 CFR 50.55a(g)(5)(iii)]. Pursuant to 10 CFR 50.55a(g)(6)(1), the Commission will evaluate determinations of impracticality and may grant relief and may impose alternati- 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 aiping. 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.

ENCLOSURE En 188"! 7J888saa P PDR

2

2.0 BACKGROUND

On January 8.1997, at the North Anna Power Station, Unit 1. Virginia Electric and Power Com)any (hereafter referred to as the licensee) identified three locations wit 1 evidence of possible previous leakage, i.e., stains in three ASME Class 3 service water system (S4S) 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 January 23. 1997. By letter dated March 3. 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 January 8,1997, through January 23. 1997. The licensee based its 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 criteria contained in GL 90-05.

3.0 LICENSEE'S RELIEF RE0 VEST 3.1 Comoonents for Which Relief is Recuested Weld,# line # Joint Tvoe '

68 4"-WS-F63-163 03 Butt Weld 97 3"-WS-74-163-03 Butt Weld 1 2"-WS-C81-153A-03 Socket Weld The above listed welds are ASME Code Class 3. moderate energy piping in the SWS, The piping arovides cooling water from the SWS to instrument air compressors and clarging pump lube. oil coolers for both units ard returns service water back to return headers, Normal flow is 20 to 10 jpm at an operating pressure of 100 psig. The design pressure is 150 p. g and design temperature is 150 F.

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

3.3 ASME Section XI Code Reauirement The ASME Code Section XI requires that repairs or replacements of ASME Code Class com>onents be performed in accordance with rules found in Articles IWA-4000 or 14A-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 alping per the requirements of Article IWA-4000 or IWA-7000, res)ectively.

Relief is being sought for the period of January 8.1997, througl January 23, 1997, because not practical. performing The licensee a Code repair duringpermanent had accomplished that oeriod wasrepairs Code determined for all to be welds by the end of that period.

3 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 c proposed alternatives for compliance with the 3rovisions of 10 CFR 50.55a(g)(6)(1). The licensee has evaluated tie flaws in accordance with the guidance provided in GL 90 05. B m d 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 January 8, 1997, through January 23, 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 safetf.

3.6 Licensee's Alternative Proaram During the period of January 8. 199/, through January 23, 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 butt welds.

_. 4. 0 STAFF EVALUATION AND CONCLUSIONS 4.1 Doerability Determination. Root Cause Analysis and Structural Intearity Evaluation The licensee determined that three locations on the SWS have a "through-wall flaw" 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.

Class 3. Based on the radiographic testing (RT) examination data, the flaws were determined to be small voids surrounded by exfoliation, which is typical of microbiologically induced corrosion (MIC). No other type of operationally caused defects were identified by the RT. -The licensee evaluated the structural integrity of the welds based on the radiogra) hic examination and determined the following: (1) butt weld 68 on line 4"-43-F68-163-03 was analyzed and found to be acce) table: (2) butt weld 97 on line 3"-WS-74-163-03 indicated the possibility of AIC over 89 percent of the circumference. Since-the-length of MIC exceeded the allowable limit, the weld was declared inoperable. The line was isolated and the weld was repaired )rior to returning the line to service: and (3) radiography of the soccet weld was not performed since it would not yield meaningful results and the flaws cannot be effectively characterized. The socket weld was replaced 9 days after the evidence of leakage was detected and before a structural integrity analysis with a postulated 3/4" hole could be completed.

4.2 Auamented Insoection To assess the overall degradation of the SWS, augmentea radiographic

4 examination was performed on five additional locations on lines having the same function. Two of the five welds. weld numbers 60 and 71 on 4"-WS-F63-163-03, had evidence of HIC but showed no evidence of through-wall leakage.

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

All augmented weld locations were found to be structurally acceptable.

4.3 Prooosed Temocrary Non-Code Reoair and Monitorina Provisions During the period January 8, 1997, throuah January 23, 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.

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 January 8.1997, through January 23, 1997. the welds were monitored by plant pers 'inel and the flaws were repaired by January 23, 1997.

Furthermore, the staff finds that performance of an immediate Code repair during the period January 8,1997 through January 23, 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 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 CFR 50.55a(a)(3)(11).

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

- _ _ - _ _ _ _ _ _ _ _ _ _