ML20138J521

Safety Evaluation Accepting Temporary Request for Relief from ASME Code Repair Requirements for ASME Code Class 3 Valve

ML20138J521
Person / Time
Site:	Hatch
Issue date:	02/05/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20138J517	List: ML20138J513 ML20138J521
References
NUDOCS 9702070323
Download: ML20138J521 (5)

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p reg y i UNITED STATES g j NUCLEAR REGULATORY COMMISSION o $ WASHINGTON, D.C. 20666-0001 1

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULAllqN RE0 VEST FOR RELIEF FROM ASME CODE REPAIR REOUIREMENTS l FOR ASME CODE CLASS 3 VALVE l GEORGIA POWER COMPANY EDWIN 1. HATCH NUCLEAR PLANT. UNIT 2 4 I RQfKET NO. 50-366 l.0 INTRODUCTION i

Title 10 of the Code of federal Regulations (10 CFR) Section 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 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.

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 tn 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 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 Commission will evaluate determinations of impracticality and may grant relief and may impose alternative requirements as it determines are authorized by law and will not endanger life or property or the common defense and security and are otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.

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2.0 BACKGROUND

On September 25, 1996, at the Edwin I. Hatch Nuclear Plant, Unit 2 (Hatch-2),

members of the Georgia Power Company (hereafter referred as the licensee) staff discovered rust stains on the valve body of Plant Service Water (PSW) i' System air release valve 2P41-F3320. Investigation by the licensee determined that the stains were caused by moisture on the valve body from a suspected 4

small leak. Subsequently, a thickness check by ultrasonic test (UT) and radiographic test (RT) were performed. The UT indicated no wall thinning at or near the suspected leak area. All thickness measurements were consistent with the valve body design thickness of 1/2-inch. The RT showed an indication consistent with " casting shrinkage" that is branched and irregular in shape, but contained within an area approximately 1-inch in diameter. The indication is stable and thus the structural integrity of the valve is maintained. The air release valve body is cast steel ASTM A216, Grade WCB material. The valve is 8-inch diameter located on 8-inch diameter branch line that is attached to the PSW pump discharge piping.

The PSW system contains four pumps and four air release valves, at the plant intake structure. One air release valve is attached to system piping near the discharge of each pump. The PSW system is a low pressure and temperature system. Piping (and valve) design pretsure is 180 psig and the design temperature is 125'F with normal operating conditions of 140 psig and 95'F.

The function of PSW system air release valve 2P41-F332D is to provide an automatic vent for the FSW system during startup. During operation, the valve is normally closed. Because of the nature of the flaw, operation of the valve will not be affected during system startup.

By letters dated October 4 and 30, 1996, the licensee requested relief from the ASME Code,Section XI replacement requirements. The licensee based its request for relief on the results of a 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 RE00EST 3.1 Components for Which Relief is Reauested Rust stains were found on air release valve 2P41-F332D located on ASME Code Class 3 plant service water system. Subsequent examinations of the valve have established that the present condition of the valve is caused by a casting defect that does not meet the ASME Code requirements.

3.2 Section XI Edition for Edwin I. Hatch. Unit 2 1980 Edition of the ASME Code,Section XI, through and including 1981 Addenda.

4 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 the rules found in Articles IWA-4000 or IWA-7000, respectively. The intent of these rules serve to e provide an acceptable means of restoring the structural integrity of a 1

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 air release valve 2P41-F332D located on the plant service water system in accordance with the requirements of Article IWA-4000 or IWA-7000, respectively. Relief is being sought until the next maintenance outage of sufficient duration, but no later then the next refueling outage scheduled to begin in March 1997.

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 flaw in accordance with the guidance provided in Generic Letter 90-05.

Based upon the evaluation, and on the results of the UT and RT examinations, the flaw is a stable casting flaw. It would e inappropriate to repair the flaw during operation because a division of the PSW will have to be taken out of service.

3.6 Licensee's Alternative Proaram Because the valve flaw is a stable casting flaw that most likely has been almost through-wall since the valve was installed, only a small amount of wall reduction because of corrosion was required to cause the rust stains. A significant amount of time was needed to build up to the point that it broke through the paint on the valve external surface. As a compensatory measure, the valve will be added to the daily operations surveillance rounds for visual inspection to ensure that the leakage does not change significantly. The valve is not expected to fail in the present condition. An operability evaluation of air release valve 2P41-F332D has been completed by the licensee and the results indicated that the valve is operable.

4.0 STAFF EVALUATION 4.1 Operability Determination. Root Cause Analysis and Structural Intearity Evaluation The licensee determined that a flaw exists in the casting body of air release valve 2P41-F332D, which is located on the PSW system. The flaw does not meet the ASME Code design requirements. Upon discovery of the flaw, the licensee performed an operability determination of the valve and found that the valve is operable in "as found" condition. Based upon the results of ultrasonic and I

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radiographic examination that was performed on the valve, the licensee determined that the flaw is a casting defect that most likely was present in the valve since the valve was installed in service. The valve is not leaking and there would be no adverse affect on any other safety-related equipment in the surrounding area.

Based on the UT and RT data, the location of the flaw was determined to be i localized and caused by casting shrinkage. The UT indicated no wall thinning at or near the suspected leak. All thickness nwisurements were consistent with the valve body design thickness of 1/2-inch. The licensee also performed an operability assessment of valve 2P41-F332D in accordance with the guidance i provided in GL 91-18. The results indicated that the valve is fully capable of performing its intended function during normal operation, transients, and design basis accidents.

4.2 Auamented Insnection The licensee identified rust stains on air release valve 2P41-F332D.

Subsequent UT and RT examinations revealed casting shrinkage in the body of the valve. The UT examination also revealed no wall thinning at or near the suspected leak. As a compensatory measure, the licensee has added the valve to the daily operations surveillance rounds for visual inspection to ensure the leakage does not change significantly.

4.3 Proposed Temocrary Non-Code Repair and Monitorina Provisions Because the valve flaw is a stable casting flaw and the valve is not leaking, no immediate temporary repairs are planned. The licensee has added the valve to the daily operations surveillance rounds for visual inspection to ensure the leakage does not change significantly. These surveillance rounds will continue until the permanent Code repair is completed. Furthermore, an operability evaluation of the valve has been completed and the evaluation results indicated that the valve is operable.

5.0 STAFF CONCLUSIONS The staff has determined that the licensee's flaw evalbation has been consistent with the gu Melines and acceptance criteria of GL 90-05. The staff therefore finds the licensee's structural integrity and operability assessments to be acceptable. The licensee is monitoring the valve by performing daily operation surveillance rounds for visual inspection to ensure the leakage does not change significantly. The licensee's actions constitute an acceptable temporary alternative program to the Code requirements.

Furthermore, the staff finds that performance of an immediate Code repair would constitute an undue burden (or hardship) upon the licensee since it would require an isolation of the affected plant service water piping. Such an isolation is not in the best interest of plant safety, given the magnitude of the flaw and reasonable assurance of valve integrity is provided by the licensee's alternative program. Therefore, the staff concludes that the

1 licensee's compliance with the requirements of ASME Code,Section XI, Article IWA-4000 or IWA-7000, would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Accordingly, as requested and pursuant to 10 CFR 50.55a(a)(3)(ii), the proposed alternatives to the requirements of the ASME Code are authorized until the next maintenance outage of sufficient duration, but no later than the next refueling outage i scheduled to begin in March 1997. At that time a Code repair will be performed.

Principal Contributor: George Georgiev '

late: February 5, 1997