ML20206M197

SER Accepting Request for Approval to Repair Flaws in ASME Code Class 3 Salt Svc Water Piping at Plant

ML20206M197
Person / Time
Site:	Pilgrim
Issue date:	05/11/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20206M192	List: ML20206M189 ML20206M197
References
NUDOCS 9905140215
Download: ML20206M197 (5)

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., 1 UNITED STATE 8

! J,.i ,j . NUCLEAR REGULATORY COMMISSION i *, ,

WASHINGTON, D.C. 20066-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l

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REQUEST FOR APPROVAL TO REPAIR FLAWS IN

' ASME CODE CLASS 3 SALT SERVICE WATER PIPING BOSTON EDISON COMPANY PILGRIM NUCLEAR POWER STATION J l

DOCKET NO 50-293 l

1.0 INTRODUCTION

Title 10 of the Code of Federal Reaulations (10 CFR) Part 50.55a(g) requires nuclear power facility piping and components to meet the applicable requirements of Section XI of the i American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (the j 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 l the structuralintegrity 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 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 licensees when authorized by the Commission 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)(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 it has I 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 attemative requirements as it determines is authorized by law. .

l 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. The staff uses the guidance in GL 90-05 as its criteria for making its safety evaluation of relief requests for temporary non Code repairs of Code Class 3 piping.

9905140215 99051123 DR ADOCK 0 Enclosure

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2.0 BACKGROUND

I in a letter dated August 26,1998, Boston Edison Company (the licensee) reported to the NRC 1 that through-wall leaks have been identified on piping in the salt service water (SSW) system l to the reactor building closed cooling water system (RBCCW) at the Pilgrim Nuclear Power )

Station (Filgrim). There are two discrete through-wall pits. The leak location is in an elbow downstream of the RBCCW heat exchanger. The SSW system is a moderate energy system

- and provides the ultimate heat sink for containment heat removal. The licensee requested under the provisions of 10 CFR 50.55a(g)(6)(i) relief from the ASME Code,Section XI requirements to perform Code repair or replace the degraded piping. The relief was sought until the next refueling outage which is scheduled to take place in May 1999. At that time, the licensee is planning to make a permanent ASME code repair. 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 Component for Which Relief is Requested The piping in the SSW system to the RBCCW heat exchanger has through-wall leaks due to localized delamination of the rubber lining and subsequent erosion and corrosion of the carbon steel pipe. The leak location is in an elbow downstream of the RBCCW heat exchanger, There are two discrete through-wall pits. The 18-inch elbow is 300 series stainless steel having nominal thickness of 0.375 inches. The line is designed to take 100 psi pressure.

However, the line is open-ended; and, there is usually a small vacuum in the pipe at this location depending on the changing tides.

3.2 ' Section Xi Edition for the Pilgrim Plant The applicable Edition of Section XI of the ASME Code for Pilgrim is the 1980 Edition including the Winter 1980 Addenda.

-3.3 ASME Section XI Code Requirement 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 serves to provide an acceptable means of restoring the structuralintegrity of a degraded Code Class system back to the original design requirements.

3.4 Content of the Relief Request Relief is sought from performing a Code repair or replacement of the SSW system piping per the requirements of Article IWA-4000 or IWA-7000, respectively. Relief is being sought until the next refueling outage which is scheduled to take place in May of 1999. The relief is being sought because performing a Code repair during plant operation was determined to be impracticable.- The licensee will perform a Permanent Code repair for the affected piping during the next scheduled refueling outage (RF012).

e 3.5 Basis for Relief Request for relief has been submitted and attematives to the Code requirements have been proposed by the licensee. The licensee has evaluated the piping in accordance with the guidance provided in GL 90-05. Based upon the evaluation, it was established that the piping is degraded, but it is operable. The piping also satisfies the criteria for non-code repair as

' described in GL 90-05 and performing permanent repairs in accordance with the ASME Code l during plant operation would constitute an undue burden (create undue hardship) upon the licensee since the repairs would have necessitated a plant shutdown.  ;

3.6 Licensee's Alternative Program

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. The licensee has proposed a temporary Code repair to maintain the structural integrity of the i

. piping until the piping is replaced during an outage of sufficient duration. The temporary repair will consist of stainless steel cover plates that encapsulate the 18-inch elbow. The plates (elbow pieces) will be welded to the pipe at the leak location. The welding procedures and the welders will be qualified using the guidance provided in ASME Code Case N-562. Although ASME Code Case N-562 was written as guidance for the weld overlay repair method, it will be used as a technical guide to attach the cover plate. The cover plate method was selected as ,

the preferred temporary repair instead of the overlay method for the following reasons:

. The cover plate repair method will stop the leak with less risk of enlarging the pitting than the overlay method. All other guidance of N 562 will be followed as applicable, j For example, the cover plate will be UT examined periodically for erosion until the pipe  !

is replaced in RF012.

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. The cover plates are acceptable for up to 100 psi, although the pressure at the leak's location ranges from a slight vacuum to a slight positive pressure, it is dependent on 1 tide level because the line discharges to the sea. The line's 100 psi design j specification was selected at Pilgrim's construction to make it uniform with other parts j of the system that are subjected to higher pressures; therefore,100 psiis a conservative value for this application.

. The cover plate method has less potential impact on the existing rubber lining of the pipe because it exposes the pipe to less heat from the welding process. Existing procedures for welding the cover plate to a water-backed pipe are qualified.

• The cover plate method will not affect plant operations I

4.0 STAFF EVALUATION AND CONCLUSIONS  !

4.1 Operability Determination, Root Cause Analysis and StructuralIntegrity Evaluation l

The piping elbow condition was analyzed by the licensee and found to be within the allowable stress limit of 35 ksi. The licensee performed an operability determination of the SSW system in the "as found" condition and the system was determined to be operable. The l

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4 system was constructed in accordance with the requirements of ASME Code, Class 3.

The root cause of the piping degradation was attributed to delamination of aging rubber pipe lining. Rubber lined piping flaws experience accelerated erosion and corrosion where the rubber lining has delaminated. Where the lining remains intact, the pipe remains at its nominal full-wall thickness. Hence, the wall erosion is local to the areas where lining has delaminated.

This conclusion'was also confirmed by the results of the u:trasonic examination of nine additional pipe locations which identified no other type of operationally caused defects. The licensee evaluated the structuralintegrity of the piping using the guidance of GL 90-05. Based upon the evaluation it was determined that the two through wall pits are within the stress criteria allowable pit size and the integrity of the piping will be maintained and that the degraded piping satisfied the criteria of GL 90-05.

4.2 Augmented inspection To assess the overall degradation of the SSW system, augmented ultrasonic examinations were performed on nine additionallocations as described in the August 26,1998 letter. The ,

l locations that were examined are similar locations to the SSW system piping location where the leaks occurred. All augmented inspection results at these locations found values greater than the manufacturer's minimum pipe-wall thickness.

4.3 Proposed Temporary Non-code Repair and Monitoring Provisions The licensee has proposed a temporary Code repair to maintain the structural integrity of the piping until the piping is replaced during an outage of sufficient duration. The licensee will install stainless steel cover plates to the pipe at the degraded locations as a temporary repair.

After completion of the repair, the cover plate will be ultrasonically examined periodically until the pipe is replaced in the next refueling outage. This is acceptable because the pressure at the repair location is low. It ranges from a slight vacuum to a slight positive pressure. In addition, plant operators will visually monitor any changes to the pipe once per shift during operator tours until permanent ASME Code repair is completed. Further, bi-weekly monitoring (ultrasonic testing) of the carbon steel material adjacent to the cover plate, and quarterly monitoring of the stainless cover plate material, will continue until test results show the test frequencies can be changed.

4.4 Staff Evaluation No safety-related components are within the proximity of the piping pitting location that would be directly affected by this leakage. The leakage is accommodated by the design of the auxiliary bay Airin-leakage has a negligible effect on the flow rate through the heat exchangers. . The staff has determined that the licensee's flaw evaluation is consistent with the guidelines and acceptance criteria of GL 90-05. Therefore, based on the preceding, the staff finds the licensee's structuralintegrity and operability assessments to be acceptable.

The licensee will weld stainless steel plates to encapsulate the degraded piping elbow as a temporary repair. During the period of plant operation and until a permanent Code repair is accomplished, the repair area will be monitored by plant personnel. The licensee has evaluated the temporary repair and determined that the SSW is operable.

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5.0 CONCLUSION

The staff finds that performance of an immediate Code repair during plant operation would have constituted an undue burden (create undue hardship) upon the licensee since the repair would have necessitated a plant shutdown. Shutting the plant down is not in the best interest of plant safety, given the magnitude of the flaw and the licensee's altemative program. The staff, therefore, grants the licensee's request for relief from performing the Code repair, pursuant to 10 CFR 50.55a(g)(6)(i), and finds .that implementation of the licensee's attemative progrism is authonzod 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 and facility that could have resulted if the Code requirements were imposed on the facility. The attemative program is authorized.

PrincipalContributor: A. Wang Date: May 11, 1999 1

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