ML20045B641
| ML20045B641 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 06/15/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20045B638 | List: |
| References | |
| GL-90-05, GL-90-5, NUDOCS 9306180207 | |
| Download: ML20045B641 (3) | |
Text
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Enclosure
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UNITED STATES i
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RE0 VEST FOR RELIEF FROM ASME CODE REPAIR REQUIREMENTS FOR ASME CODE CLASS 3 PIPING t
NORTHEAST NUCLEAR ENERGY COMPANY MILLSTONE NUCLEAR POWER STATION. UNIT 3 DOCKET N0, 50-423 i
1.0 INTRODUCTION
By letter dated March 25, 1993, Northeast Nuclear Energy Company, the licensee, requested relief from ASME Boiler and Pressure Vessel Code (hereafter called the Code) repair requirements for a leak in a moderate energy Class 3 pipe at Millstone Nuclear Power Station, Unit 3.
The leak was detected in a 3-inch service water lina. The operating temperature ranges from 33 to 75 degrees; the design pressure is 100 psig. The pipe is made of a copper nickel alloy.
The leak is a through-wall pit caused by erosion corrosion from high velocity flow in this area. The diameter of the pit is 3/32". The adjacent nominal wall thickness is.219".
The licensee requested relief from doing the repair on the basis of impracticality. The repair cannot be completed in the 72-hour limiting condition for operation (LCO). The licensee plans to instc11 a soft rubber patch as a temporary repair until the next refueling outage scr.eduled for July 31, 1993.
2.0 DISCUSSION The Code of Federal Regulations at 10 CFR 50.55a(g) requires nuclear power facility piping and components to meet the applicable requirements of Section XI of 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 nf the operational mode of the plant when the flaw is detected. Those repairs not in compliance with Section XI of the Code r
i are non-Code repairs. However, the required Code repair may be impractical for a flaw detected during plant operation unless the facility is shut down.
Pursuant to 10 CFR 50.55a(g)(6)(1), the Commission will evaluate y
determinations of impracticality, and may grant relief and may impose alternative requirements. Generic Letter (GL) 90-05, entitled " Guidance for i
Performing Temporary Non-Code Repair of ASME Code Class 1, 2, and 3 Piping,"
i 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 Commission may grant relief based on a staff evaluation i
considering the guidance in GL 90-05.
9306180207 930615 PDR ADDCK 05000423 P
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Articles IWA-4000 and IWD-4000 of Section XI of the Code describes the Code repair requirements. A Code repair requires removal of the flaw and i
subsequent weld repair. This repair weld is also subject to post-repair nondestructive examination and pressure testing.
The licensee requested relief from performing a Code repair for the flaw which 1
was detected during plant operation in Code Class 3 piping, on the basis that Code repair requirements are impractical unless the facility is shut down.
4 The licensee proposed to use the guidance in GL 90-05 to perform a temporary non-Code repair.
3.0 EVALVATION i
The licensee's submittal shows that the temporary repair is in conformance with GL 90-05 as follows:
1.
The system is a Class 3 moderate energy piping system within the scope of GL 90-05.
2.
The licensee detected the flaw during operation and determined a Code repair to be impractical within the LCO allowable outage time.
3.
The licensee assessed the operability.
It determined that the service.
. water system had adequate flow margin and no components or equipment would be affected by spraying water or flooding.
If a failure occurs, the area can be
. i isolated.
4.
The licensee determined the most likely cause of the leak was erosion l
corrosicq.
5.
The licensee evaluated the flaw according to Draft Code Case N513.
This Code Case is consistent with the staff guidance in GL 90-05. An evaluation of design loading conditions found all Code stress equations were met.
6.
The licensee performed an augmented inspection of five susceptible areas in small bore piping. These five inspections identified three more areas of thinned walls, but these were determined to be acceptable.
7.
The licensee proposed to monitor the temporary repair by performing a walkdowr. inspection at least once per shift and follow up nondestructive i
testing at least every 3 months.
If further degradation occurs, the '11censee will reevaluate the temporary repair and determine whether further corrective actions are needed.
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4.0 CONCLUSION
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~The staff has' determined that Code repair requirements in this case are i
impractical as defined in GL 90-05. Repairing the pipe in conformance with Code requirements would require a plant shutdown.
Furthermore, the licensee has committed to the guidance provided in GL 90-05 which will reasonably assure structural integrity and protect public health and~ safety.
Accordingly, the staff concludes that granting relief where Code requirements are impractical and imposing alternative requirements are authorized by law and will not endanger life or property or the common defense and security and are otherwise in' the public interest, given due consideration to the burden upon the licensee and facility that could result if the Code requirements were imposed on the facility.
Pursuant to 10 CFR 50.55a(g)(6)(i), and consistent with the guidance in GL 90-05, relief is granted until the next scheduled outage exceeding 30 days, but no later than the next scheduled refueling outage. The flawed pipe must then be repaired or replaced in accordance with the Code.
Principal Contributor:
M. Banic Date:
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