ML18152B357
| ML18152B357 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 10/22/1999 |
| From: | Hartz L VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 99-495, NUDOCS 9910280050 | |
| Download: ML18152B357 (9) | |
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VIRGINIA ELECTRIC AND PowER COMPANY RICHMOND, VIRGINIA 23261 October 22, 1999 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNITS 1 AND 2 ASME SECTION XI RELIEF REQUEST Serial No.99-495 NL&OS/GDM R7 Docket Nos. 50-280, 281 License Nos. DPR-32, 37 TEMPORARY NON-CODE REPAIR TO A CLASS 3 COMPONENT Surry Power Station Units 1 and 2 are presently in the third ten year inservice inspection interval, and examinations are conducted to the requirements of the 1989 Edition of ASME Section XI. Pursuant to 10 CFR 50.55a(g)(6)(i), relief is requested from certain ASME Section XI Code requirements associated with a temporary repair of an ASME Class 3 pipe. Specifically, a through wall leak was discovered on a 30 inch component cooling heat exchanger (CCHX) discharge pipe associated with the service water system common to Surry Units 1 and 2. *
- Both units are currently operating at 100% power.
Performing a permanent Code weld repair at this time is considered impractical because: 1) the affected piping cannot be isolated from the common service water discharge header, 2) the Unit 1 service water discharge tunnel would have to be de-watered to conduct repairs, 3) a plant modification is required to install a temporary se.rvice water discharge jumper and 4) Unit 1 would have to be shut down resulting in an unnecessary transient.
Therefore, a relief request from the requirements of ASME Section XI is attached for your approval to allow a temporary non-Code repair on this moderate energy system in accordance with Generic Letter 90-05 until the next scheduled refueling outage. An engineering evaluation was performed and concluded that the present pipe condition does not affect the operability of the service water system or the capability of the pipe to perform its design function. An augmented inspection plan was performed for service water piping in similar applications and did not reveal additional concerns. A temporary non-Code repair is acceptable until a permanent repair can be performed in accordance with ASME Code requirements. The attached relief request for Surry Units 1 and 2 has been reviewed and approved by the Station Nuclear Safety and Operating Committee.
In addition, it is our intent to submit a subsequent relief request within the next 30 days to permit the continued use of a temporary non-Code repair for the subject CCHX SW discharge line until the Surry Unit 1 Fall 2001 refueling outage. This would permit the
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use of a temporary non-Code repair for one operating cycle past the next Unit 1 refueling outage in Spring 2000. The extension is necessary to facilitate the significant planning and implementation of a permanent Code repair of the SW line as the Unit 1 discharge tunnel must be de-watered and a temporary SW pipe jumper must be installed from the CCHXs' SW discharge lines to the Unit 2 discharge tunnel to effect the repair. This effort requires extensive planning which is already underway for the Fall 2001 Unit 1 refueling outage in support of other planned SW system maintenance efforts. To provide additional assurance that the temporary non-Code pipe repair will be adequate for one additional operating cycle, a more substantial temporary non-Code repair will be implemented prior to the Surry Unit 1 Spring 2000 refueling outage.
Details of the more substantial temporary non-Code repair to be used will be provided in the future relief request.
If you have any additional questions concerning this request, please contact us.
Very truly yours, Leslie N. Hartz Vice President - Nuclear Engineering and Services Attachment Commitments contained in this letter:
- 1. A subsequent relief request will be submitted within the next 30 days to permit the use of a more substantial temporary non-Code repair for the subject CCHX SW discharge line until the Surry Unit 1 Fall 2001 refueling outage.
- 2. A more substantial temporary non-Code repair will be implemented prior to the Surry Unit 1 Spring 2000 refueling outage.
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U.S. Nuclear Regulatory Commission Region II Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303 Mr. R. A. Musser NRC Senior Resident Inspector Surry Power Station Mr. R. Smith Authorized Nuclear Inspector Surry Power Station
ATTACHMENT ASME SECTION XI RELIEF REQUEST RELIEF REQUEST FOR TEMPORARY REPAIR ON "D" COMPONENT COOLING HEAT EXCHANGER SERVICE WATER DISCHARGE PIPING SURRY POWER STATION UNITS 1 AND 2
Surry Power Station Units 1 and 2 Third Ten Year Interval Relief Request for Temporary Repair on "D" Component Cooling Heat Exchanger Service Water Discharge Piping 1.0 Background/Basis of Relief Surry Units 1 and 2 are currently operating at 100% rated power. A through wall leak exists on the 30 inch component cooling heat exchanger (CCHX) service water discharge pipe, 30"-WS-41-10. The leak is downstream of the "D" CCHX (1-CC-E-1 D) discharge isolation valve 1-SW-27 on pipe that ties into the common 42-inch discharge header.
The location of the leak is immediately (approximately 2 inches) above the turbine building concrete floor, which the 30-inch line penetrates. Performing a permanent Code weld repair at this time is considered impractical because: 1) the affected piping cannot be isolated from the common service water discharge header, 2) the Unit 1 service water discharge tunnel would have to be de-watered to conduct repairs, 3) a plant modification is required to install a temporary service water discharge jumper, and 4) Unit 1 would have to be shut down resulting in an unnecessary plant transient. With the temporary non-Code repair in place, the present condition of the pipe does not affect the operability of the service water system, and the discharge pipe continues to perform its design function.
Consequently, the proposed temporary non-Code repair is considered the only practical alternative.
2.0 Evaluation 2.1 Component Identification/Description The line in question, 30"-WS-41-10, is designated ASME Class 3 in the ASME Section XI Program. The leak is located downstream of valve 1-SW-27, which is the service water discharge of the 1-CC-E-1 D component cooling heat exchanger. The service water system is a moderate energy system with a maximum operating temperature of 110 degrees Fahrenheit and a maximum operating pressure of 20 psig.
The pipe material is carbon steel, welded construction with a nominal thickness of 0.5 inches. The inside of the pipe is coated with coal tar epoxy, and an anti-sweating coating called Erote is applied on the outside of *the pipe.
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- 2.2 Code Requirements
(
Articles IWA-4000 and IWD-4000, of ASME Section XI, 1989 Edition, describe Code repair requirements.
The Code requires a weld repair to correct the through wall leak. As discuss.ed above, performing a permanent weld repair is considered impractical because the section of pipe to be repaired cannot be isolated from the common service water discharge header without de-watering the Unit 1 service water discharge tunnel, implementing a plant design change to install a temporary service water discharge flow path to the Unit 2 discharge tunnel, and shutting down one unit. Any replacement in accordance with IWA-7000 and IWD-7000 would be precluded for the same reasons.
2.3 Relief Request In accordance with 10 CFR 50.55a(g)(6)(i) and the provisions of Generic Letter 90-05, relief is requested from the stated Code requirements.
A temporary non-Code repair using soft patch material has been installed. A temporary repair, either the soft patch or a more substantial temporary non-Code repair, will remain in place until a permanent Code repair is performed. A separate relief request will be submitted for the installation of a more substantial temporary non-Code repair.
2.4 Temporary Repair 2.4.1 Repair Design Considerations The temporary repair is comprised of a rubber gasket material with a 1/8 inch steel backing plate, 4 inches in width and 8 inches in length (circumferential direction). _Two steel bands approximately 1/2 inch in width and 1/32 inch thick, similar to hose clamps, were used to hold the patch in place. The band and patch arrangement has negligible contribution to the load on the pipe. The temporary repair is designed to minimize leakage from the hole in the pipe.
Engineering has analyzed the patch and determined that it will remain in place and prevent excessive leakage during all normal modes of operation and during a Design Basis Earthquake event.
2.4.2 Piping Design and Flaw Analysis The actual flaw was analyzed based on the through wall flaw approach in accordance with the guidance provided in Generic Letter 90-05. The flaw measured 3 inches in circumferential length and 1.25 inches in the axial direction.
Based on ultrasonic
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thickness readings in the are*a, a representative wall thickness of 0.106 inches around the flaw was used in the analysis.
Actual available average wall thickness is greater than 0.106 inches. The flaw was evaluated by three different analyses:
- 1) The Limit Load Analysis showed adequate margin against net section plasticity; therefore, a ductile rupture would not occur.
- 2) The Fracture Mechanics Analysis proved a failure by brittle fracture was highly unlikely.
- 3) The Area Reinforcement Analysis showed adequate base metal exists around the flaw to prevent possible failure due to ductile tearing.
The evaluation concluded that with respect to these three failure modes the flaw would riot preclude the service water pipe from
- performing its intended function and structural integrity would be maintained.
Based on Engineering's visual inspection of the patch, the seismic evaluation of the patch and the flaw evaluation, the service water pipe will continue to perform its intended design function even if subjected to design loading conditions.
2.5 Root Cause Upon initial investigation, extensive exterior pipe corrosion was noted on the "D" CCHX service water discharge pipe. Due to the exterior corrosion, a power wire brush was used to prepare the surface for UT readings.
A cursory visual inspection of the other three discharge pipes found exterior surface corrosion to a lesser degree than the "D" CCHX discharge piping.
As discussed during *a September 3, 1999 conference call with the NRG, the preliminary conclusion at that time was that the failure mechanism was localized pitting caused by internal coating failure of the coal tar epoxy in conjunction with general wall thinning due to exterior pipe corrosion.
Upon further investigation of the exterior pipe condition and an examination of the inside of the pipe through the flaw, it has been concluded that the through wall flaw originated from the inner diameter and proceeded to the outer diameter. The failure mechanism for the flaw was general corrosion caused by failure of the internal coal tar epoxy coating. Although exterior corrosion is occurring due to moisture being trapped behind the Erote coating, the exterior corrosion was not a major contributor to the through wall failure. The general wall thinning/corrosion seen on the "D" CCHX discharge Page 3 of 5
piping is believed to have resulted from failure of the coal tar epoxy. The coal tar epoxy coating in these discharge lines is the original coating application.
2.6 System Interactions Upon discovery of the leak, the pipe was declared inoperable, the "D" CCHX was removed from service, and a flood watch was -established in the immediate vicinity.
Once the structural integrity of the pipe had been evaluated, and a temporary patch that was qualified for a Design Basis Earthquake Event had been installed, no immediate concern existed for surrounding equipment, piping and components.
The flood watch was suspended.
Weekly visual inspections are being performed, and quarterly UT pipe wall thickness readings at the flaw area to detect potential further degradation will be performed. Flow through the "D" CCHX may be restricted, if necessary, by throttling the inlet and outlet valves 1-SW-25 and 1-SW-27, respectively.
2.7 Augmented Inspections To assess the overall condition of the service water system in similar applications, the discharge piping on the remaining three component cooling heat exchangers, the inlet piping on the "C" and "D" CCHXs, and* the discharge piping of emergency service water pumps "B" and "C" were analyzed by UT thickness readings.
The following minimum thickness readings were measured:
"A" CCHX Discharge piping, 30-WS-17-10 "B" CCHX Discharge piping, 30-WS-18-10 "C" CCHX Discharge piping, 30-WS-19-10 "C" CCHX Inlet piping, 30-WS-16-10 "D" CCHX Inlet piping, 30-WS-40-10 1-SW-P-1 B Discharge piping, 24-WS-39-10 1-SW-P-1C Discharge piping, 24-WS-52-10 0.500 in.
0.418in.
0.439 in.
0.326 in.
0.524 in.
0.287 in.
0.281 in.
The nominal wall thickness of the above piping is 0.5 inches. The minimum allowable wall thickness was determined for each pipeline considering stresses in all loading conditions, including seismic.
This value was determined to be 0.1 inches for all lines inspected.
Thus, the lines will remain within the allowable Code limits provided the wall thickness remains greater than 0.1 inches.
Furthermore, the identified wall thickness reductions were localized as opposed to a general wall-thinning phenomenon, as observed on the "D" CCHX discharge piping.
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3.0, 6perational Considerations Per the Technical Specifications, one of the four CCHXs may be declared inoperable with Units 1 and 2 remaining on line. Two CCHXs are required for one unit operation.
The "D" CCHX was declared inoperable when the flaw was discovered.
A temporary patch was installed, and the heat exchanger was returned to service in accordance with Generic Letters 90-05, 91-18 and NRG Part 9900: Technical Guidance "Resolution of Degraded and Nonconforming Conditions".
4.0 Conclusion The proposed temporary non-Code repair has been evaluated and determined to provide adequate pressure boundary integrity for the "D" CCHX service water discharge pipe. The temporary repair is being visually inspected on a weekly basis and ultrasonically examined on a quarterly basis to ensure that it continues to perform its function adequately. Because the present condition of the pipe does not affect the operability of the service water system and a permanent Code repair is not practical at this time, a temporary repair is acceptable.
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