ML20147C156
| ML20147C156 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 01/31/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20147C154 | List: |
| References | |
| GL-90-05, GL-90-5, NUDOCS 9702050376 | |
| Download: ML20147C156 (5) | |
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! # 0" 4 UNITED STATES
- ,, NUCLEAR REGULATORY COMMISSION l o t WASHINGTON, D.C. 20666 4 001
% *****/SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RE0 VEST FOR RELIEF FROM ASME CODE REPAIR RE0VIREMENTS l
FOR ASME CODE CLASS 3 PIPING WOLF CREEK NUCLEAR OPERATING CORPORATION l WOLF CREEK GENERATING STATION i DOCKET NO 50-482 l.0 INTRODUCTION Section 50.55a(g) of Title 10 of the Code of Federal Regulations 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 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 i 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 l
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)(i), the Commission will evaluate determinations of impracticality and may grant relief and may impose alternative requirements as it determines is authorized 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 that could result if the requirements were imposed on the facility.
Generic Letter (GL) 90-05, entitled " Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2 and 3 Piping," dated June 15, 1990, provides guidance for the staff in evaluating relief requests submitted by 9702050376 970131 PDR ADOCK 05000482 P PDR t
J licensees for temporary non-Code repairs of Code Class 3 piping. For purposes of this generic letter, impracticality is defined to exist if the flaw detected during plant operation is in a section of Class 3 piping that cannot be isolated for completing a code repair within the time period permitted by the limiting condition for operation of the affected system as specified in the plant technical specifications (TSs) and performance of a code repair necessitates a plant shutdown. For this case, the leak can be isolated and, with proper planning, repairs made within the TSs allowed outage time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. However, the leakage is only six drops per minute and the licensee proposes to delay repairs until January 1997 when the diesel generator with the leaking heat exchanger drain line is scheduled for preventative maintenance.
2.0 BACKGROUND
On August 2,1996, at the Wolf Creek Generating Station (WCGS), members of the Wolf Creek Nuclear Operating Corporation (WCNOC) (hereafter referred as the licensee) discovered a six drop per minute leak upstream of valve KJ-V7868 in the emergency diesel generator (EDG) intercooler heat exchanger drain line.
The location of the leak is just below the seal weld where the 3/4 inch line connect to the heat exchanger outlet end bell. The cause of the leak is a corrosion pit on the inside surface of the pipe, which extends through the pipe wall. The affected heat exchanger is an ASME Code Class 3 heat exchanger which forms part of the closed cycle EDG cooling water system. This heat exchanger provides cooling water to the EDG and rejects heat from the diesel generator engine to the essential service water (ESW) system. The heat exchanger is of the horizontal shell and tube type, with DW being supplied to the tube side. The leaking drain is on the ESW side of the heat exchanger.
By letter dated September 3, 1996, the licensee requested relief from the ASME Code,Section XI repair and replacement requirements. The licensee based its request for relief (i.e., to delay making the repair) on the results of a flaw evaluation that was performed by the licensee in accordance with the guidelines and acceptance criteria contained in the NRC Generic letter 90-05 (GL 90-05).
3.0 LICENSEE'S REllEF RE0 VEST 3.1 Components for Which Relief is Reauested Temporary relief is being requested from Code repair or replacement of the B EDG intercooler heat exchanger drain line using the flaw evaluation methodology of GL 90-05. The drain line is constructed from 3/4 inch diameter, schedule 80 carbon steel SA 106, Grade B pipe material. The design pressure of the pipe is 200 psi and the design temperature is 150*F.
3.2 Section XI Edition for WCGS 1980 edition of the ASME Code,Section XI through and including 1981 addenda.
J 3.3 ASME Section XI Code Reouirement 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. l 3.4 Content of the Relief Reaunt :
Temporary relJef is sought from performing a repair or replacemerit of the B EDG intercooler drain line per the requirements of Article IWA-4000 or IWA-7000, respectively. Temporary relief is being sought until the ASME Code,Section XI repair or replacement is completed in January 1997. ;
3.5 Basis for Relief Request for temporary relief has been submitted by the licensee under the provision of 10 CFR 50.55a(a)(3)(1) that the proposed alternative to the Code requirements would provide an acceptable level of quality and safety. 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 flaw satisfies the criteria for non-code repair as described in GL 90-05. To perform a Code qualified repair during power operation would require removing the B train EDG from service. Loss of availability of one of the two EDG trains to perform a Code repair or replacement at the time of discovery was not commensurate with the safety significance of the flaw. Based on the results of the visual inspection which confirmed that the drain line is leaking only six drops per minute, it would be appropriate to delay repairs until January 1997, when the B train EDG is scheduled to be taken out-of-service for maintenance and testing.
3.6 Licensee's Alternative Proaram Because the pipe leak is small, no immediate temporary repairs are planned.
However, if the leak becomes a continuous stream, an engineering evaluation will be performed by the licensee to assess the extent of the degradation and to determine what corrective actions would be required. In accordance with GL 90-05 guidance, the integrity of the piping will be assessed during the fourth quarter of 1996 utilizing an ultrasonic testing (UT) examination method and if needed radiographic testing (RT) examination. Additionally, UT/RT examination will be periodically performed on the inlet and outlet drain lines of all six EDG A and B train heat exchangers. Furthermore, the leak is monitored by plant operators each shift to detect any further degradation which may occur.
4.0 STAFF EVALVATION AND CONCLUSIONS 4.1 Operability Determination. Root Cause Analysis and Structural Intearity Evaluation The licensee discovered six drops per minute leak located on the B train of
1 the EDG intercooler heat exchanger drain line. This system was constructed ir accordance with the ASME Code, Class 3 requirements. Augmented inspection was performed within 15 days of detection of the leak to assess the overall degradation of the system. The inspection consisted of UT and RT examination of inlet and outlet drain piping locations on the EDG train A and B intercooler, Jacket water, and lube oil cooler heat exchangers providing a total of 12 inspection locations. The inspection results indicated that all 12 locations had wall thicknesses higher than the minimum ASME Code required ;
design thickness. The licensee also determined that the system is operable as is and because the leak is small there would be no adverse affect on any other safety-related equipment in the surrounding area.
Based on the inspection data, the cause of the leak was determined to be localized corrosion pit on the inside surface of the pipe, which extends through the pipe wall. The licensee also evaluated the structural integrity of the piping using the guidance of GL 90-05. Based upon the evaluation it !
was determined that the integrity of the piping would be maintained. '
4 4.2 Auamented Insoection The licensee has examined 12 additional areas on inlet and outlet drain lines of EDG A and B train heat exchangers. These locations will be periodically UT/RT examined until the corrosion has been stabilized or until appropriate corrective actions are taken by the licensee.
4.3 Proposed Temocrary Non-Code Repair and Monitorina Provisions Because the pipe leak is small (six drops per minute), no immediate temporary repairs are planned. However, if the leak becomes a continuous stream, an engineering evaluation will be performed by the licensee to assess the extent )
of degradation and determine what corrective actions will be required. In ;
accordance with GL 90-05 guidance, the integrity of the piping will be j assessed on a quhrterly basis utilizing an ultrasonic examination method and ;
radiographic examination if needed. Additionally, UT/RT examination will be l periodically performed on the inlet and outlet drain lines of all six EDG A 1 and B trair heat exchangers. Furthermore, the leak is monitored by plant operators each shift to detect any further degradation which may occur.
These inspections will continue until the permanent Code repair is completed in January of 1997.
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 is monitoring the leak every shift and ultrasonic examination is being performed quarterly on 12 locations of the inlet and outlet drain lines of all six EDG A and B train heat exchangers to determine any degradation of structural integrity. The licensee's actions constitute an acceptable temporary alternative to the Code requirements and will ensure that any degradation will be promptly identified.
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Furthermore, the staff finds that performance of a Code repair can be delayed l based en the magnitude of the leak (six drops per minute), the structural (
analysis and monitoring program implemented by the licensee. The staff therefore concludes that the licensee's proposed alternative provides an acceptable level of quality and safety. Pursuant to 10 CFR 50.55(a)(3)(i), i
- the alternative is authorized until the next scheduled plant outage exceeding '
30 days, out no later than January 31, 1997. At that time a Code repair will be performed.
- Principal Contributor: G. Georgiev Date: January 31, 1997
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