ML20133E736
| ML20133E736 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 12/31/1996 |
| From: | Tulon T COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20133E738 | List: |
| References | |
| GL-90-05, GL-90-5, NUDOCS 9701130135 | |
| Download: ML20133E736 (13) | |
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Commonwealth F4livin Company liraidwood Generating Station Route *ol. Ik)x Rs Hraceville, IL 60407%19 Tcl 815-15&2801 l
December 31,1996 U.S. Nuclear Regulatory Commission Washington D.C. 20555 Attention: Document Control Desk l
Subject:
Braidwood Station Unit 1 Service Water System Operational Leakage NRC Docket No. 50-456
Reference:
Conference Call Between Comed and USNRC Conducted on December 31,1996 The Reference teleconference was conducted in order to discuss the circumstances surrounding the identification and proposed disposition of a small leak on the drain line for the strainer associated with the Unit I, "A" Train Essential Service Water Pump at Braidwood Station. The affected piping is ASME Class 3, moderate energy piping.
Pursuant to the provisions of GL 90-05, ASME Class 3 moderate energy piping experiencing operational leakage can be considered operable if acceptable structural integrity is demonstrated and stafT review and approval is sought. This provision is intended to prevent the undesi tble shutdown of an operating unit in those cases where
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a fracture mechanics evaluauon clearly demonstrates suflicient structural integnty exists.
The purpose of this letter is to provide for the staffs review and acceptance of the basis for which the affected system has beer. determined to be capable of performing its intended function. Included as Attachment A is the description of the affected piping, the service conditions to which it is exposed, and the characterization of the 4
observed degraded condition. Attachment B provides our determination that the piping continues to be capable of performing its design function, while Attachment C j
provides the linear fracture mechanics evaluation applicable to throughwall flaws as referenced in GL 90-05.
Augmented inspections in accordance with GL 90-05 will be performed within 15 days p
from the date ofinitial discovery. A root cause determination of the failure mechanism h' 9701130135 961231 PDR ADOCK 05000456' P
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m.~m aa A linicom Company
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, U.S. Nuclear Regulatory Commission December 31,1996 2
for the affected piping will be undertaken when the Code repair is accomplished. This repair is currently anticipated to be completed the week ofJanuary 6,1997.
This letter and its attachments have been reviewed and approved by the Station Plant Operations Review Committee.
Please direct any questions to: T. Simpkin, Regulatory Assurance Supervisor, at (815) 458-2801, extension 2980.
i Sincerely,
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N T. othy J. Tulon station Manager Braidwood Nuclear Station TJT/fb/-ou Attachments cc: A.B Beach, Regional Administrator - Region III R.R. Assa, Project Manager - NRR C.J. Phillips, Senior Resident Inspector - Braidwood Oflice of Nuclear Facility Safety - IDNS
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j ATTACHMENT A i
Description of the Affected Piping Configuration of Essential Service Water Strainer Backwash Pinina 1
The area of concern is located in the backwash line downstream from the Braidwood Unit l A essential service water strainer. This section of the line is not isolable from the strainer. The configuration of this pipe run shown in Figure 1.and is described as
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follows. A short 3 inch line extends vertically from the bottom of the strainer to a flanged connection. Beyond this flanged connection is another short three inch pipe section welded to a 3'k 6" reducer. This reducer is welded to a 6 inch, 90 degree elbow which connects to the 6'k 8" reducer, where the flaw is located. This reducer is welded to a horizontal 8 inch pipe which attaches to a valve by a flanged connection.
The direction of flow through the line is from the strainer, through the 3 inch pipe,~ to the 8 inch valve. The line is normally stagnant _ at system pressure except during strainer backwash approximately 5 minutes per 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> shift.
Visual and Ultrasonic Examination Results t
i Visual and ultrasonic examinations were performed to identify the physical characteristics of the flaw and the extent of degradation.
Visual inspection j
characterized the flaw as a through-wall hole with a diameter of approximately 1/8 i
inches in the basemetal of the 6"x 8" reducer. The reducer is oriented horizontally i
l and is connected to an elbow on the small end and piping on the large end. The hole is located on the bottom side of the reducer in the transition area. The water stream j
from the hole is directed toward the floor. Axially, the hole is located closer to the large end of the reducer.
Ultrasonic thickness measurements were made in areas surrounding the flaw to 4
determine the extent of degradation on the inner diameter and in the through-wall direction of the reducer and its attachments. These measurements were performed by a Comed NDE Level III Examiner using two different ultrasonic transducers.
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l first transducer was a 5.0 MHz, O degree, pulse-echo transducer. The second was a 5.0 MHz, O degree, pitch-catch transducer. A Panometrics Epoch 11 flaw detector j
was used to record the UT data. Thickness measurements were made in the general l
area of the flaw in both circumferential and axial directions. The measurements made j
in the axial directions extend beyond the reducer welds.
Circumferentially, 1
measurements extend 90 degrees on each side of the flaw.
Results of the UT measurements are shown in Figures 2 and 3. Wall thicknesses in area surrounding the flaw ranged from 0.335 inches to 0.422 inches.
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Thickness measurements were also performed on the top side of the reducer and t
connecting pipe and elbow. The results of these measurements are consistent with i
those made in the area of the flaw. They range from 0.315 to 0.400 inches with the lowest reading in the large end of the reducer. Nominal wall thicknesses of six and eight inch schedule 40 pipe per piping design tables are 0.280 and 0.322 inches respectively.
A shear wave examination was also performed on all four sides of the flaw (approximately 1/2 inches) using a 5.0 MHz,45 degree ultrasonic transducer. No indications of cracks propagating from the hole were detected during this examination.
A preliminary conclusion, based on the results of the visual and ultrasonic examination, is that the degradation of the reducer is due to localized corrosion.
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STRAINER
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FLANGE CONNECTION 8" PIPE
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REDUCER LEAK LOCATION DETAIL VALVE
FIG.
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UT READINGS teAn
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SX R:EDUCER AK LOCATION
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WELD WELD
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SECTION "_B-B" S:+'y l.jjp S:38,t:
i (TOP) 0;g9 0;3l l;4 0.401" 9.422" 0.345"-0.35F 9
2" 0
0.353" 9.402".
0.350*-0.38 7 (14)
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1 (15)
(12) (11)(10)(9)(8) (7)(6)(5 (3)
(2) (1)
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Y ME (19)
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SECTION "A-A" WELD (BOT.)
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ATTACIIMENT B Operability Assessment l
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BwAP 330-10 Revision 2 Information Use ATTACHMENT B CONCERN SCREENING FORM PIF # 456201362952 1.0 ISSUE TDENTIFICATION:
(See St.ep F.13 ) Date 12 H1/96 i
1.1 Description of operability Istue ER #
Preparer Dan Leg A 1/8* throuch wall hole was disc 2Yered on the 1A SX strainer UNIT 1 backwash ninina 1SX93AA.
The hqlt is located on the bottom System SX section of a 6*x8* reducer.
Leagrace throuch the hole is EPN(s)
ISX93AA accroximatelv 2 anm.
Attachment C Expected Due Date 1/28/97 1.2 How and by whom was this condition identified?
The condition was discover.ad by the oneratina cersonnel durino a walk-down of the A train SX oume ragm.
2.0 CONCEFll SC RE EM IHG :
M QQ 2.1 Does the issue involve a condition of a SSc where there has been a loss of quality or functional capability?
8 0-2.2 Does the issue involve a failure to conform to applicable cod (s or
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i standards specified in the USPAR?
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2.3 Does the issue involve equipment NOT meeting USFAR design requirements?
O B
2.4 Does the issue involve operating experience information or engineering reviews that demonstrate a design inadequacy?
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2.5 Does previous guidance require an operability determination?
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2.6 Does the issue involve an existing but unanalyzed condition or accident?
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If any of the above questions 2.1 - 2.6 = YES, continue with section 3.0 below.
If all of the above questions 2.1 - 2.6 = No, attach a justification, sign 4.3 below, exit talt procedure and continue with IRp process.
3.0 INITIAL OPERABILITY ASSES 3MEHT:
M HQ 3.1 Is a valid prior evaluation of this condition available? If YES, attach copy to this form, sign 4.3 below, exit this procedure and continue with the IRP process.
If NO, continue below.
O B
3.2 Does previous operability policy exist in the Appendices?
If YES, record applicable section and take O
E the required action.
3.3 Is it reasonable to expect that operability will be assured as result of a more detailed evaluation? Briefly explain basis:
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Jee attached writeun If 3.3 = No, NOTIFY the Shift Engineer to IMMEDIATELY declare the equipment inoperable.
IF 3.3 a YES, initiate Attachment C in a timely manner commensurate with the safety significance.
4.0 ADDITIONAL REOUIRED ACTIONS:
4.1 Notify SED /SEC for evaluation support, if required: Person Notified 4.3 verifier _W1.~^I IW -
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Preparer A
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/t / 3/ / 'YP 4.3 Shift EngineTr Approval operability Determination Log # --
4.5 shift Engineer forward copy of completed form and all attachments to Regulatory Assuran:e.
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j Attachment B Operability Justification - PlF # 456201962952 Description of problem:
During a walkdown of the A train Essential Service Water (SX) pump room, it was discovered that a through-wall hole had developed on the 1A SX strainer back-wash piping 1SX93AA-8". The hoe is approximately 1/8"in diameter and is located on the bottom of the transition area of a 6" x 8" reducer. SX water leakage through this hole is approximately 2 gpm. A UT inspection of the area of the hole suggested that the hole is caused by localized corrosion. This operability screening is being generated to evaluate the effect on the SX system operability of the current condition.
J Justification for' Operability:
Line 1SX93AA-8" is ASME class 3 piping with a design temperature
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of 125* F and design pressure of 125 PSIG and is therefore classified as moderate energy piping. For operational leakage from a Class 1,2, or 3 component pressure j
boundary, Generic Letter (GL) 91-18 provides guidance for evaluating operability.
The following areas are evaluated 1) flooding,2) water spray on equipment, i
- 3) loss of flow, and 4) structuralintegrity of the fiawed piping. Each of these areas is discussed below.
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- 1) Floodina,
p Line 1SX93AA-8" is inside the A train SX pump room. The leak rate from the through wal! flaw is estimated to be 2 gpm. The existing flooding analysis for the SX 2
pump room is based on a 0.00166 ft crack on the 4" chemical feed piping with a resulting leak rate of 99.2 gpm (ref. Calc 3C8-0685-002, Rev 3). This calculation i
indicates that the flood level resulting from a 99.2 gpm leak is less than 2"in 30 minutes. In comparison, a flood level of 12"in the SX pump room would not disable the SX pumps. Based on the above discussion, a 2 gpm addition to the 99.2 gpm leak rate would not result in a flooding concern for the SX pump room.
- 2) Sprayino water on e'auipment The location of the hole is on the bottom of the reducer, resulting in the water t
spraying toward the floor. Currently the leakage is contained by a catch basin which drains to the floor drain sump. No safety equipment is adversely affected by the leakage from the strainer drain line hole.
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- 3) Loss of flow :
.The leak rate from the hole is estimated to be about 2 gpm. Using a typical SX pump discharge flow of 15,000 gpm during winter, the leakage amounts to 0.01%
4 of the total SX flow. This leak rate does not reduce the SX system flow below the required flow.
- 4) Structural intearity evaluation :
For class 3 components, GL 91-18 indicates that the structuralintegrity of the piping should be evaluated in accordance with the methodology provided in GL 90-05. A "through-wall flaw" evaluation has been performed in accordance with the methodology provided in GL 90-05. The result of the evaluation, as documented in attached calculation BRW-96-951-M, demonstrates that the stress intensity factor "K" resulting from the flaw is within the acceptance criteria specified in GL 90-05, and therefore, it is reasonably assured that the structural integrity of the piping is maintained.
in addition, based on a UT inspection, the pipe wall thickness in the area surrounding the 1/8" through wall hole was determined to be greater than the required piping minimal wall thickness of 0.036" In fact, the actual measured thicknesses were greater than 0.322" which is the nominal wall thickness of the attached 8" sch. 40 piping, i
Based on the above evaluations, the SX system is determined to be operable.
Corrective Action The following contingencies are in place to monitor any change in the size of the hole and to further ensure the operability of the SX system.
Continaencies:
Monitoring of the following alarms and indications:
SX pump room leak detection sump high level SX pump room sump level high high SX pump room sump run indication lights Operator rounds / observations have been increased on the affected piping:
Leak checked approximately every 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> by operators Preparing system isolation contingencies An out-cf-service is pmared for immediate use to isolate the 1 A pump and strainer, if necessary.
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Additional actions will include the following which will be further discussed in the Attachment C of this operability assessment.
a) Replacement of the flawed section of the pipe in accordance with ASME code requirement.
b) A root cause determination of the failure mechanism (s) upon pipe replacement.
c) Implement augmented inspections as addressed in GL 90-05.
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ATTACIIMENT C Fracture Mechanics Evaluation