ML20116B147
| ML20116B147 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 07/19/1996 |
| From: | Link B WISCONSIN ELECTRIC POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20116B150 | List: |
| References | |
| GL-90-05, GL-90-5, VPNPD-96-047, VPNPD-96-47, NUDOCS 9607290118 | |
| Download: ML20116B147 (4) | |
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Wisconsin Electnc POWER COMPANY l
231 w M,cnioon. PO Box 2046. Mdwoukee. Wi 53201-2046 (414)221-2345 l
VPNPD-96-047 July 19,1996 10CFR50.55a Document Control Desk US NUCLEAR REGULATORY COMMISSION Mail Station PI-137 Washington,DC 20555 Gentlemen:
DOCKETS 50 266 AND 50-301 REOUEST FOR RELIEF TEMPORARY NON-CODE REPAIR ASME CODE CLASS 3 SERVICE WATER SYSTEM PIPING POINT BEACH NUCLEAR PLANT. UNITS 1 AND 2 Wisconsin Electric Power Company, licensee for the Point Beach Nuclear Plant, Units 1 and 2, licenses DPR-24 and DPR-27 respectively, hereby requests relief from the requirements of 10CFR50.55a. Reliefis requested to allow operation with a temporary repair effected to control leakage from a through wall flaw in the Senice Water System. Senice Water System piping is designated ASME Code Class 3. Permanent, Code acceptable repairs will be performed during the next scheduled unit outage, presently scheduled to commence on October 5,1996 l
l On July 16,1996, a four gallon per ndnute leak was discovered in a branch section of piping ofTthe west senice water header at Point Beach Nuclear Plant. The leak is in a section of senice water piping that is unisolable from the west header. Because the leak is unisolable, cirecting a Code repair of the piping would require a dual unit shutdown.
We have performed a temporary repair, conducted inspections and evaluations, and implemented compensatory measures as outlined in Generic Letter 90-05, " Guidance For Perforndng Temperaty Non-Code Repair of ASME Code Class 1,2, and 3 Piping." Attached is the information discussed in Generic Letter 90-05 required to support the NRCs resiew of this relief request.
If you have any questions or requirc additional information, please contact us.
Sincerely, B
ink Vice Presi nt Nuclear Power TWH cc:
NRCRegional Administrator NRC Resident Inspector 9607290118 960719 PDR ADOCK 05000266 P
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Relief Request Re;ief Temporary Non-Code Repair ASME Code Class 3 Service Water Piping I. Description
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On July 16,1996, a 4 gpm leak was discovered in a branch connection off the west service water header at the Point Beach Nuclear Plant. The leak is in the 6 inch piping supplying service water to the decontamination area.
The leak is located approximately 18 inche.
~.he west header on an elbow. The leaking piping is not isolable from the west header. There is normally no flow in this line. The west service water header is a moderate energy Class 3 system (maximum operating pressure ofless than 90 psig and a maximum operating temperature of 75*
i F). The west header supplies the spent fuel heat exchangers, two containment accident fan coolers in each unit, and the Residual Heat Removal area room cooler, i
A condition report was initiated, and operability of the system verified. The leakage was diverted to floor drains I
as repair options were evaluated. A rubber and Teflon patch was attached to the pipe with clamps as a stopgap j
measure. An evaluation was initiated to demonstrate the adequacy of this repair until the next refueling oWage.
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Code replacement of the leaking elbow is not practical during plant operation. The leak can not be isolated from the west service water header, and there is not sufficient room for a freeze seal on the 6"line. Even if there was sufficient room for a freeze seal, it is not possible to establish a freeze seal with flow through the 14" west header i
because the 6"line taps off of the top half of the header. Isolation of the enti.e west service water header would j
require a dual unit shutdown in accordance with PBNP Technical Specification 15.3.3.B since more than one accident fan cooler in each unit would be rendered inoperable in violation of Technical Specification require-3 l
ments. Isolation of the leak could be accomplished during a Unit 2 outage utilizing a freeze seal on the 14" west header since only the supply to the unit 2 A & C accident fan coolers is downstream of the decontamination area i
supply.
II. Root Cause Determination and Flaw Characterization The flaw was inspected utilizing UT and RT, and it was determined that there is no other significant degradation in the elbow. The through-wall flaw is a localized pit. Sketches in the attached stress calculation indicate dimensions of the flaw.
l A root cause evaluation of the flaw determined that the most probable cause is Microbiologically Influenced Corrosion (MIC). Typically MIC manifests itself by producing deep localized corrosion sites while the surrounding metal shows little or no wall loss. RT indicates silting in the elbow and a spherical pit morphology which are also indicative of MIC.
Ill Flaw Evaluation An evaluation of the flaw was conducted using the "through-wall flaw" approach described in enclosure 1 of Generic Letter 90-05. The attached calculation (# 96-0149) documents this evaluation. The flawed piping satisfies the criteria of the "through-wall flaw" approach, therefore, a temporary non-code rcpair of the piping may be proposed. The temporary non-code repair is applicable until the next scheduled refueling outage, or until structural integrity is no longer demonstrated.
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d IV. Description of the Temporary Renair he temporary repair was completed using an elastomer patch ( 1/8 inch block rubber) with a plastic backing plate (1/8 inch Teflon) held onto the piping by 3/4 inch wide stainless steel ' band-it' straps. The temporary repair was reviewed for design loading conditions and material compatibility. It was concluded that the temporary repair is acceptable until a permanent repair can be performed.
V. Specific Considerations The temporary patch effectively stops the leakage. There are no concerns due to flooding or spraying water on adjacent equipment even if the pa*ch begins to leak. Ifleakage occurs, the situation will be monitored to ensure no equipment is impacted. If the patch were to fail completely, the 4 gpm can easily be diverted to floor drains.
There is no effect on system operability. He magnitude of the original leak is such that there is negligible effect on design flow of the senice water system. A leak rate up to the capacity of one of the two auxiliary building sump pumps ( 75 gpm ) is alsojudged not to have any negative impact on flow in the system. Contingencies for increased leakage will be included in the work plan used to perform the permanent repair. Containment integrity is not affected since the leak is located outside of the containment boundary formed by the accident fan cooler supply manual valves.
The integrity of the piping will be assessed every three months until a permanent repair can be completed.
Radiographs will be taken of the flaw and structural integrity of the pipe will be re-evaluated. Additionally, a qualitative assessment ofleakage through the patch will be performed weekly to detemtine any degradation of structural integrity. Operators will be able to identify any significant leakage during normal rounds.
VI. Aucmented Inspections Five additional locations in the senice water system were selected for inspection in order to assess degradation of the sys:cm. The locations were determined to be the most susceptible (and accessible) locations based on the root cause determination. These inspections are in progress and will be completed within fifteen days of discovery of the leak. Any flaws discovered during the augmented inspection program will be evaluated against the code required minimum wall thickness. If required, the augmented inspection plan will be expanded per Generic Letter 90-05.
Two of the five sugmented inspection locations and inspections of additional locations on the affected line have been completed. Only minimal wall thinning has been detected with no location below the minimum required wall thickness.
Vll. Future Plans and Conclusions Code repair options are currently under evaluation. Present plans call for a modification to the system in which a 1" capped branch connection is welded to the pipe. This would leave the flaw in the pipe and relocate the prere boundary of the system. Annual inspections of the flaw will be performed to ensure that the defect is not growing. This modification will be completed prior to the end of the next unit 2 refueling outage, presently scheduled to begin October 5,1996, and is intended to return the system to compliance with the code.
4 Replacement of the elbow will be performed when plant conditions allow isolation of the west senice water header. Methods to isolate the west header are currently under investigation. We are also considering the addition ofisolation values in the system.
The temporary patch currently on the pipe is considered adequate until a code repair can be performed. The flaw and patch will be evaluated every three months to ensure continued structural integrity.