ML20198M343

SER Accepting Util Request for Relief from ASME Code Repair Requirements for ASME Code Class 3 Piping for South Texas Project,Unit 2

ML20198M343
Person / Time
Site:	South Texas
Issue date:	12/28/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20198M342	List: ML20198M339 ML20198M343
References
NUDOCS 9901050315
Download: ML20198M343 (4)

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g<lc ui UNITED STATES j

g NUCLEAR REGULATORY COMMISSION l WASHINGTON, D.C. 20066-0001  ;

h[.....lt SAFETY EVALUATION Sy THE OFFICE OF NUCLEAR REACTOR REGULATION l

RELATED TO THE INSERVICE INSPECTION PROGRAM REQUEST FOR REL[R FROM ASME CODd REPAIR REQUIREMENTS FOR ASME CODE CLASS 3 PIPING STP NUCLEAR OPERATING COMPANY SOUTH TEXAS PROJECT. UNIT 2 )

DOCKET NO. 50.492 1

1.0 INTRODUCTION

10 CFR 50.55a(g) requires nuclear power facility piping and components to meet the applicable i

requirements of Section XI of the American Society of Mechanical Engineers (ASME) Boiler i 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 of the nuclear power plant.

Attematives to Code requirements may be used by nuclear licensees when authorized by the Commission if the proposed alternatives to the requirements are uch that they are shown to ,

provide an acceptable level of quality and safety in lieu of the Code requirements (10 CFR I 50.55a(a)(3)(i)), 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)(i), the Commission will evaluate determinations of impracticality and may grant relief and may impose altcrnative requirements as it determines is authorized by law and will not endanger life or property or the common defense and security and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements wore imposed on ine facility.

9901050315 981228 fDR ADOCK 05000499 ENCLOSURE PDR

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Generic Letter (GL) 90-05, entitled " Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1,2 and 3 Piping," and 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 purpose of this generic letter, impracticality is defined to exist if the flaw detected during plant operation is in a section of Class 3 piping that cannot be isolated for completing a Code repair within the time period permitted by the limiting condition for operation of the affected system as specified in the plant technical specifications, and performance of Code repair necessitates a plant shutdown.

2.0 BACKGROUND

During plant operation on July 13,1998, the licensee discovered a small discolored area on the exterior of a 3-inch flange that is part of the cast aluminum-bronze screen wash booster pump located in the Train "C" Unit 2 Essential Cooling Water intake Structure. The Essential Cooling Water System (ECWS) is a low pressure system with normal operating pressures of approximately 50 psig and the design pressure is 120 psig. The c'ealloying appeared to be localized at the takeoff point for a %-inch seal water flow line attached to the pump body flange.

The discoloration was about 1/16 inch in diameter with no visible leakage. The pump body 4 material was identified to be aluminum-bronze (ASME SB 148 CA954 material). By letter dated l September 30,1998, the licensee requested relief from the .ASME Code,Section XI repair or replacement requirements under the provisions of 10 CFR 50.55a(g). The licensee based its request for relief on the results of a flaw evaluation that was performed by the licensee in . I accordance with the guidelines and acceptance criteria contained in GL 90-05. I 3.0 LICENSEE'S RELIEF REQUEST l 3.1 Comoonents for Which Relief is Recuested ASME Code Class 3 ECWS, Train "C," screen wash booster pump flange.

3.2 Section XI Edition for South Texas Proiect. Unit 2 1983 Edition including Summer 1983 Addenda of the ASME Code,Section XI.

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 IWA-7000, respectively. These rules serve 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 a dealloying spot on a Unit 2 3-inch flange which is part of the Train "C" screen wash booster pump, per the requirements of Article IWA-4000 or IWA-7000, respectively. Relief is being sought until the next South Texas Project, Unit 2 refueling outage which was scheduled to take place during October of 1998.

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3.5 Basis for Relief Request for relief hn been submitted by the licensee under 10 CFR 50.55a(g) and alternatives to the Code requirements have been proposed by the licensoo. The licensee has evaluated the i flaw in accordance with the guidance provided in GL 90-05. Based upon the evaluation, the '

licensee established that the discovered flaw satisfies the criteria for non-code repair as described in GL 90-05 and performing permanent repair in accordance with the ASME Code prior to an extended outage or refueling as permitted by the limiting condition for operation may l not be practical due to the potentist for fit-up problems during repair. The licensee also stated ;

that it prefers to perform the Code repairs under controlled conditions during a scheduled outage longer than allowed by a limiting condition of operation. Further, the licensee has also determined that the dealloying degradation of the piping is a slow process and rapid or catastrophic failure is not a consideration. !n addition, the ECWS is a low pressure system with normal operating pressure of approximately 50 psig and therefore severe failure consequences cssociated with high energy lines are not appleable for the ECWS.

3.6 Licensee's Alternative Proaram

1. Weekly monitoring for qualitative assessment of leakage (quantitative if measurable Icaks are observed). The licensee stated that currently there is no measurable leakage.

2. Continuation of ECWS large bore piping periodic walkdowns. This walkdown is regularly scheduled VT 2 examination. The licensee stated t..at this inspection technique has proven to be an effe:tive means of identifying dealloyed/ cracked components prior to deterioration of structural integrity margins below ASME Section XI requirements.

4.0 STAFF EVALUATION AND CONCLUSIONS 4.1 Ooerability Determination. Root Cause Analysis and Structural Intearity Evalua. ion The licenree determined that the flaw was located in the ECWS which is classified as ASME Code Class 3 system. The flaw includes a dealloying spot on a Unit 2 3-inch flange which is part of the Train "C" screen wash booster pump. The flawed pipe material was identified to be aluminum-bronze which is inherently ductile material (ASME SB 148 CA 954 material). Upon discovery of the flaw, the licensee performed an evaluation of the flaw using the guidance provided in GL 90-05 and found that the flaw satisfies the through-wall criteria prescribed in GL 90-05 and that the flaw meets the criteria for a non-Code repair. The licensee determined that the operability of the system will not be impaired because there was no measurable leakage, and any leakage would be detected before the flaw reaches a limiting size that would affect the operability of the ECWS.

The licensee performed a root cause analycis of the flaw, and determined that the degradation resulted from dealloying. The licensee believes that e preexisting flaw was present tr enable j initiation of the deelloying process. Ultrasonic examination of the Unit 2 3-inch flange found no l

indications of cracking. The small size of the discolored area indicates that the dealloying is relatively minor. The problem of dealloying of t.astings has also been described in previous communications with the NRC.

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4.2 Auamented insoection i The flaw was located in 2-inch flange. The flaw was visually and ultrasonically examined to i assess the flaw. Augmented weekly inspections will be performed and are designed to I enhance the detectiori of even minor changes in the external expression of through-wall dealloying whether it is the quantitative measurement of leakage or the size of the area of discoloration.

4.3 Igmocrarv Noncode Heoair and Monitorina Provisions The licensee is monitoring the flawed area weekly for qualitative assessment of leakage. In I addition, the licensee is continuing its ECWS large bore piping periodic walkdowns. If a j measurable leak was identified, a quantitative assessment of the leak would have been '

performed. in its September 30,1998, letter, the licensee stated that ti.: flaw will be repaired no later than the next Unit 2 refueling outage (scheduled for October 1998). By letter dated November 30,1998, the .icensee stated that a repair that meets ASME Section XI Code requirements was completed on October 5,1998.

4.4 Staff Conclusions The staff has determined that the licensea's flaw evaluation has been consistent with the guidelines and acceptance criteria of GL 00-05. The staff, therefore, finds the licensee's structural integrity and operability assessments to be acceptable. The licensee is monitoring the flawed area weekly for qualitative assessment of leakage. In addition, the licensee is continuing its ECWS large bore piping periodic walkdowns. The licensee's actions constituted an acceptable temporary alternative to the Code requirements. Furthermore, the staff finds that i

performance of an immediate Code repair would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety since the repair may not have been l completed within the time period permitted by the limiting condition for operation and thus an isolation of the affected ECWS piping would have been required. Such an isolation is not in th?

best interest of plant safety, given the magnitude of the flaw and the licensee's alternative program. Further, the licensee has also determined that the leakage can be detected before the flaw reaches a limiting size that would affect the operability of the ECWS (there was no leakage).

l The staff, therefore, concludes that the licensee's proposed alternatives to the Code requirements are authorized pursuant to 10 CFR 50.55a(a)(3)(ii).

Principal Contributor: T. Alexion l Date: December 28, 1998 l

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