ML20117K412

Requests Temporary Relief from Requirements of ASME Section XI,1989 Edition,Per Requirements of 10CFR50.55a(a)(3)

ML20117K412
Person / Time
Site:	Wolf Creek
Issue date:	09/03/1996
From:	Muench R WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20117K415	List: ML20117K412 ML20117K417
References
ET-96-0065, ET-96-65, NUDOCS 9609110264
Download: ML20117K412 (4)

Text

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NUCLEAR OPERATING CORPORATION Richard A. Muench Vice President Engineering September 3, 1996 ET 96-0065 U.

S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station Pl-137 Washington, D.

C.

20555

]

Subject:

Docket No.

50-482:

Request for Temporary Relief From ASME Section XI Requirements Gentlemen:

Pursuant to the requirements of 10 CFR

50. 55a (a) (3), Wolf Creek Nuclear Operating Corporation (WCNOC) requests temporary relief from the requirements of ASME Section XI, 1989 Edition. ASME Section XI, IWA-4000 and IWA-7000 require repair or replacement of through wall pressure boundary leaks.

Consistent with the intent of Generic Letter 90-05, " Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1,

2, and 3 Piping," temporary relief is requested from performing the IWA-4000 and IWA-7000 repair or replacement for a pinhole leak in the Emergency Diesel Generator Intercooler drain line. This relief request would allow for additional monitoring and examination until a Section XI repair or replacement is completed in January 1997.

The Attachment contains the relief request and the Enclosures provide supporting documentation.

This relief request was discussed with Mr. Jim Stonc, and other members of the NRC Staff, during a telephone conversation on August 5, 1996.

If you have any questions concerning this matter, please contact me at (316) 364-8831, extension 4034, or Mr. Terry S.

Morrill, at extension 8707.

Very truly yours, 9609110264 960903 PDR ADOCK 05000482 p

PDR Richa A. Muench RAM /jad Attachment Enclosures A

cc:

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Callan (NRC), w/a/e

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W. D. Johnson (NRC), w/a/e j

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F. Ringwald (NRC), w/a/e J. C.

Stone sNRC), w/a/e P.O. Box 411/ Burbngton, KS 66839 / Phone: (316) 364-8831 090037 x come, ogge,,mm.,, c,. ev., u e sc~<1 1

Attachment to ET 95-0065 Page 1 of 3 8

I RELIEF REQUEST FROM IMMEDIATE CODE REPAIR OF EMERGENCY DIESEL GENERATOR B TRAIN INTERCOOLER HEAT EXCHANGER Backaround During plant operation on August 2,

1996, a six drop per minute leak was discovered upstream of valve KJ-V786B in the B Emergency Diesel Generator (EDG) ' Intercooler Heat Exchanger drain line, just below-the seal weld where the 3/4" line connects 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. depicts the piping and heat exchanger.

Enclosures 1 and 3 depict the location of the leak.

The affected intercooler heat exchanger is an ASME Code Class 3 heat exchanger which forms part of the closed cycle EDG cooling water system.

Thia heat exchanger provides cooling water to the EDG and rejects heat from the diesel engine to the Essential Service Water (ESW) system. The heat exchanger is of the horizontal shell and tube type, with ESW being supplied to the tube side.

The leaking drain line is on the ESW side of the heat exchanger-.

Performing an immediate Code repair or replacement 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 this time is not commensurate with the safety significance of this flaw.

The assessments described below have demonstrated that this flaw is not detrimental to the pipe's structural integrity.

Additional monitoring and examinations planned until a scheduled Code repair or replacement is performed in January 1997, also described below, will ensure that any significant degradation of the flaw will be detected during this time.

In accordance with the provisions of Generic Letter (GL) 90-05 " Guidance For Performing Temporary Non-Code Repair of ASME Code Class 1,

2, and 3 Piping,"

relief is being requested from immediate Code repair'or replacement of the B EDG Intercooler Heat Exchanger drain line.

The bases for requesting relief, in accordance with the GL 90-05 guidance, include assessments that have been performed of the structural integrity of the flawed piping and the overall degradation of the system.

The results of these assessments are described below.

Flaw Evaluation and Characterization The leak consists of a localized corrosion pit measuring approximately 3/8" maximum diameter at the pipe inside diameter (ID) surface.

The pit has a general conical shape which tapers down to a pinhole size opening on the pipe outside diameter (OD) surface.

The size and shape of the pit was determined by a combination of ultrasonic (UT) and radiographic (RT) examination.

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Attachment to ET 96-0065 Page 2 of 3 WCNOC Calculation KJ-C-005, "KJ System Drain Line Flaw Evaluation," (Enclosure

2) has been performed to evaluate the effect of the flaw. on the structural integrity of the intercooler heat exchanger drain piping.

This calculation uses the "through-wall flaw" approach provided by GL 90-05, and considers deadweight, pressure, thermal expansion, and seismic loads.

The calculation determined that the critical stress intensity factor is 3.955 ksi(in) , which is less than the 35 ksi(in)' allowable value for ferritic steel. Based on this calculation, it was concluded that the structural integrity of the piping with the flaw is acceptable.

j To further validate the results obtained using the through-wall flaw approach, a " leak before break" evaluation was performed using the Linear Elastic Fracture Mechanics (LEFM) method and Limit Load Analysis.

This evaluation indicates a maximum stress from pressure, deadweight, and seismic loads in the faulted condition of 6.35 ksi.

This value compares favorably to an allowable 1

stress of 14.84 ksi, and therefore validates the previously mentioned through-wall flaw results.

This additional evaluation supports the previous conclusion that the structural integrity of the piping with the flaw is

.5 acceptable.

Auamented Insoection Augmented inspection was performed within 15 days of the detection of the flaw 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 4

train A and B intercooler, jacket water, and lube oil cooler heat exchangere, providing a total of' 12 inspection locations.

The UT/RT examinations j

indicated that the most severe case of wall thinning is on the A train lube I

oil cooler. outlet drain line, where an area approximately 1/2" x 1/8" exhibits a minimum wall reading of

.097".

Although this value is much less than the 4

j 0.154" nominal pipe wall thickness, it is still above the ASME Code required j

minimum thickness, calculated to be.065" considering all loading conditions, as indicated in Enclosure 2.

Periodic Assessment of Flaw and Schedule for Code Repair or Roolacement An additional UT (and if needed RT) examination will be performed during the j

4th quarter 1996 on the flawed piping to monitor its structural integrity.

A Code repair or replacement will be completed in January 1997 when the B train EDG is scheduled to be taken out of service for maintenance - and testing.

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.

This periodic examination will continue until the corrosion has stabilized or until appropriate corrective action has been taken.

Leakace Monitorina The previously described leak is being monitored by plant operators each shift to detect any further degradation which may occur.

If the leak becomes a continuous stream, an engineering evaluation will be performed to assess the extent of the degradation to determine what additional corrective actions are required.

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i Attachment to ET 96-0065 Page 3 of 3 l

System Interactions The consequences of flooding, spraying water on equipment, loss of flow, loss J

of ultimate heat sink (UHS) inventory, and ef fects. on ESW pump and system l

performance because of the intercooler heat exchanger drain line leak, have i

been considered and are summarized below.

i j

The six drop per minute leak has no potential to initiate an internal flood

.because of its insignificant flow rate.

The leak is located very close to the bottom dead center of the heat exchanger,- and the water is dripping onto the floor directly beneath the elbow.

Leaking at a rate of six drops per minute j

at ESW pressure, there is no spray on nearby equipment and no other equipment j

is affected.

l The UHS is sized to accommodate a 140 gpm leak for 30 days.

Currently there

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is approximately 32 gpm of identified leakage from the ESW system, which leaves

a. margin of 108 gpm.

Six drops per minute is an insignificant leak ~

compared to the margin available. The UHS will not be affected by this leak.

j J

The ESW B train is required to provide a flowrate of 11,426 gpm during normal 3

j plant operation and up to 14,821 gpm during post-LOCA operation..The pump has

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a flow rating of 15,000 gpm.

The six drop per minute leak will have no effect j

on pump operation.

Six drops per minute is an insignificant leak compared to j

the system margin.

j Based on'the above considerations, the ESW B train is capable of performing i

its safety related design function with the EDG intercooler heat exchanger drain line leak.

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Enclosures:

(1)

WCNOC Piping and Instrumentation Drawing M-12KJ04 (2)

WCNOC Calculation KJ-C-005 (3)

WCNOC Drawing 10466-M-018-0196-02 3

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