ML18153A384
| ML18153A384 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 12/03/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML18153A383 | List: |
| References | |
| GL-90-05, GL-90-5, NUDOCS 9712150308 | |
| Download: ML18153A384 (5) | |
Text
e UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR APPROVAL TO REPAIR FLAWS IN ACCORDANCE WITH GENERIC LETTER 90-05 FOR ASME CODE CLASS 3 SERVICE WATER PIPING VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION. UNIT 1 DOCKET NO. 50-280
1.0 INTRODUCTION
10 CFR 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 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.
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 an acceptable level of quality and safety in lieu of the Code requirements [10 CFR 50.55a(a)(3)(i)J. 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)J.
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)J. Pursuant to 10 CFR 50.55a(g)(6)(i). the Commission will evaluate determinations of impracticality and may grant relief and may impose alternative requirements as it determines is authorized by law.
Generic Letter (GU 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.
Enclosure 9712150308--97i203-PDR ADOCK 05000280 G
2
2.0 BACKGROUND
On February 25. 1997. at the Surry Power Station. Unit 1. members of the Virginia Electric and Power Company (hereafter referred to as the licensee) discovered one location with evidence of possible previous leakage on a 3" vent line connected to a 24" service water discharge line from a recirculation spray heat exchanger. A temporary non-Code repair was made. and a structural analysis was performed in accordance with the provisions of GL 90-05 for the vent line. Seven associated vent lines (four inlets and three outlets) were ultrasonically examined for evidence of leakage.
No additional lines were identified with potential leakage.
However. all lines had experienced reduced wall thickness as determined by the ultrasonic thickness measurements.
Replacement of all of the above-mentioned piping was accomplished during the March 7. 1997. outage.
By letter dated May 20. 1997. the licensee requested.
pursuant to 10 CFR 50.55a(g)(6). a relief from the ASME Code.Section XI replacement requirements for the period of February 25. 1997. until the next scheduled refueling outage that commenced March 7. 1997.
The licensee based its request for relief on the results of a "through-wall 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 REQUEST 3.1 Component for Which Relief is Requested Line No.
3"-WS-36-10 Drawing No.
11448-CBM-071A-3. Sheet 3 Class 3
The above line is a vent line from a 24" service water discharge line from recirculation spray heat exchanger 1-RS-E-lD.
The piping is ASTM A53 Grade A extra strong (.300"), maximum temperature is 100°F. and maximum pressure is 20 psig.
The piping is considered to be a moderate energy system as discussed in GL 90-05.
3.2 Section XI Edition for Surry 1 The 1989 Edition of the ASME Code.Section XI.
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 serve to provide an acceptable means of restoring the structural integrity of a degraded Code Class system back to the original design requirements.
3 3.4 Content of the Relief Request Relief is sought from performing a repair or replacement of the service water piping per the requirements of Article IWA-4000 or IWA-7000. respectively.
Relief is being sought for the period of February 25. 1997. through March 7.
1997. because performing a Code repair during that period was determined to be impractical. The licensee has accomplished Permanent Code repair during the outage that was scheduled to begin on March 7. 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 NRC staff reviewed the proposed alternatives for compliance with the provisions of 10 CFR 50.55a(a)(3)(ii). The licensee has evaluated the flaw in accordance with the guidance provided in GL 90-05.
Based upon the evaluation.- it was established that the discovered flaw satisfies the criteria for non-Code repair as described in GL 90-05.
Performing permanent repair in accordance with the ASME Code during the period of February 25. 1997. through March 7. 1997. would have constituted an undue burden (create undue hardship) upon the licensee since the repair would have necessitated the unnecessary isolation of portions of the service water system (SWS) that are structurally sound and thus reduce the margins of safety of the SWS.
In addition. the unit was scheduled for shutdown on March 7. 1997. and the licensee's structural analysis indicated that the piping is acceptable for non-Code repair as permitted by GL 90-05.
3.6 Licensee's Alternative Program During the period of February 25. 1997. through March 7. 1997. the line in the SWS with the identified possible through-wall flaws was temporarily repaired by applying a soft patch held in place by hose clamps.
Seven associated vent lines (four inlets and three outlets) were ultrasonically examined for evidence of leakage.
No additional lines were identified with potential leakage.
However. all lines had experienced reduced wall thickness as determined by the ultrasonic thickness measurements.
Replacement of all of the above-mentioned piping was accomplished during the March 7. 1997. outage.
4.0 STAFF EVALUATION AND CONCLUSIONS 4.1 Operability Determination. Root Cause Analysis and Structural Integrity Evaluation The licensee determined that one location on the SWS had a "through-wall flaw" and the flaw was analyzed in accordance with the position stated in GL 90-05.
The licensee evaluated the structural integrity of the flawed piping and found that the flaw can be temporarily repaired as permitted by GL 90-05.
The licensee repaired the line by applying a soft patch over the flawed area held in place by hose clamps.
In addition. seven associated vent lines (four inlets and three outlets) were ultrasonically examined for evidence of leakage.
No additional lines were identified with potential leakage.
.e 4
However. all lines had experienced reduced wall thickness as determined by the ultrasonic thickness measurements.
Replacement of all of the above-mentioned piping was accomplished during the March 7. 1997. outage.
4.2 Augmented Inspection To assess the overall degradation of the SWS. augmented ultrasonic examinations were performed on seven additional locations on lines having the same function.
No additional lines were identified with potential leakage.
However. all lines had experienced reduced wall thickness as determined by the ultrasonic thickness measurements.
4.3 Proposed Temporary Non-code Repair and Monitoring Provisions During the period February 25. 1997. through March 7. 1997. the licensee repaired the flawed line by applying a soft patch over the flawed area held in place by hose clamps.
Evaluation of structural integrity of the flawed piping was performed and the evaluation indicated that the piping is acceptable for temporary repair as permitted by GL 90-05.
No monitoring of the flawed areas was performed because the unit remained on line only for a few days after the wall thickness measurements were taken.
4.4 Staff Conclusions The staff has determined that the licensee's flaw evaluation has been consistent with the guidelines and acceptance criteria of GL 90-05.
The staff. therefore. finds the licensee's structural integrity and operability assessments to be acceptable.
The licensee has repaired all flaws during the scheduled outage of March 7. 1997.
Furthermore. the staff finds that performance of an immediate Code repair during the period February 25. 1997. through March 7. 1997. would have constituted an undue burden (create undue hardship) upon the licensee since the reppir would have necessitated the isolation of structurally sound portions of the SWS.
Isolating portions of the SWS to perform a Code repair is not in the best interest of plant safety, given the magnitude of the flaw and the licensee's alternative program.
The staff. therefore. concludes that the licensee's alternative program is acceptable.
Principal Reviewer:
G. Georgiev
~-
Memorandum Dated December 3, 1997 (4,
cfilook-etE:t::le_