2CAN079802, Requests Temporary Relief to Allow non-code Repair of Piping as Required by GL 90-05.Attachment Provides Justification for Temporary Repair of Piping

Requests Temporary Relief to Allow non-code Repair of Piping as Required by GL 90-05.Attachment Provides Justification for Temporary Repair of Piping

ML20236Q235
Person / Time
Site:	Arkansas Nuclear
Issue date:	07/13/1998
From:	James D ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
2CAN079802, 2CAN79802, GL-90-05, GL-90-5, NUDOCS 9807200088
Download: ML20236Q235 (7)

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c Entergy operations,Inc.

1448 S.R. 333 RusscMio. AR 72801 Tel501858 5000 July 13,1998 2CAN079802 U. S. Nuclear Regulatory Commission Documer.t Control Desk Mail Station OPI-17 Washington, DC 20555

Subject:

Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6 Non-Code Piping Repair per Generic Letter 90-05 Gentlemen:

During routine operator rounds on June 12,1998, a 5 drop per minute leak in a 1" drain line from the spent fuel pool heat exchanger (2E-27) connecting to the Arkansas Nuclear One, Unit 2 (ANO-2) loop 2 service water (SW) header was observed. Based on visual inspection, it was determined that the source of the leak was a through-wall defect in the drain line just above a weld between the pipe and an elbow. The operability of the SW system in the "as found" condition was assessed and determined to be operable. The purpose of this letter is to request temporary relief to allow a non-code repair of the piping as required by Generic Letter 90-05, " Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2, and 3 Piping."

The attachment providesjustification for a temporary repair of this piping in accordance with the guidance provided in Generic Letter 90-05. Using this guidance, the flaw and flaw area -

were evaluated to verify the structural integrity of the pipe. The evaluation concluded that the flawed piping satis 6ed the "through-wall-flaw" stability criteria of the generic letter.

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Additionally, other system interactions were considered such as flooding, water spraying on l

plant equipment as a result of the leak, and loss of flow to service water-supplied components.

The leakage is insignificant and does not present a flooding concern, nor are there any

,1 components in the vicinity of the leak that would be affected by spray from this leak should gV the leak worsen. The reduction in flow to the associated loop 2 components due to this pinhole leak is insignificant and will not cause the service water loop, nor individual system components, to be degraded. Also, the leakage provides another drain path from the emergency cooling pond; however, the small amount ofleakage is well within the allowable system leak rate of the emergency cooling pond.

9807200088 900713 ~

PDR ADOCK 05000368 P

PDRa

' U. S. NRC July 13,1998 2CAN079802

'Since the flaw satisfies the criteria for a non-code repair as described in Generic letter 90-05, and permanent repairs in accordance with the American Society of Mechanical Engineers (ASME) Code are impractical during plant operation, Entergy Operations requests relief permitting a temporary non-code repair of the affected service water piping as an alternative to the repair methods of the ASME Boiler and Pressure Vessel Code,Section XI. The permanent code repair is scheduled to be performed during the next Unit 2 refueling outage (2R13) which is currently scheduled to begin January 8,1999.

The leakage is currently being contained by a catch basin since the leak is small and not impacting any equipment in the area; however, should the leak worsen, a temporary clamp device would be installed over the defect area as a "stop gap" measure to limit leakage for housekeeping purposes. Any installed clamp would not alter the structural integrity of the piping and would be evaluated prior to installation. If a clamp is installed, it is planned to maintain this clamp as the temporary repair.

In accordance with Generic Letter 90-05 guidance, the integrity of the non-code repair will be assessed on a quarterly basis utilizing an ultrasonic testing examination method. Furthermore, a qualitative visual assessment ofleakage through the temporary non-code repair and the affected piping will be performed on a weekly basis to determine any degradation of structural integrity. These inspections will continue until the code repair is completed. Should you have any questions, please contact me.

Very truly yours, 1<

ale James Acti Director, Nuclear Safety DEJ/nbm Attachment

' U. S. NRC July 13,1998 2CAN079802

'ec:

Mr. Ellis W. Merschoff Regional Administrator U. S. Nuclear Regulatory Commission RegionIV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 NRC Senior Resident Inspector

' Arkansas Nuclear One P.O. Box 310 London, AR72847 Mr. William D. Reckley NRR Project Manager Region IV/ANO-1 & 2 U. S. Nuclear Regulatory Commission NRR Mail Stop 13-H-3 One White Flint North 11555 Rockville Pike Rockville, MD 20852

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2CAN079802 I.

Page I cf 4 Technical Justification for a Temporary Repair

In Accordance with Generic Letter 90-05 1.0 Maw Detection and System Description On June 12,1998 at 2300 hours0.0266 days <br />0.639 hours <br />0.0038 weeks <br />8.7515e-4 months <br /> during operator rounds in the ANO-2 auxiliary building, water was discovered on the floor. Further inaa-* ion found that the 1" drain line just upstream of valve 2SW-1151 had water dripping off ofit onto the floor. Based on visual inspection, it was determined that the source of the leak was a through-wall defect in the drain linejust above a weld between the pipe and an elbow. The leak was very small and was initially estimated to be approximately 5 drops per minute or approximately 0.0001 SPm.

The specific location of the pinhole leak is approximately 7" upstream of drain valve 2SW-1151 on the 1" pipe that connects the drain valve to the SW loop 2 return header 2HBC-81-12" from the spent fuel pool (SFP) heat exchanger 2E-27. This portion of the drain line is downstream of the last isolation vs.lve (2SW-44B) and is not isolable from the loop 2 SW return piping; therefore, it is pressurized at the normal return header pressure (approximately 34 psig) and is normally

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The SFP heat exchanger can be supplied by either loop of SW and can return this flow through either of two return loops.

Both of the SW loop return lines normally have flow through them since loop separation is maintained by check valves. The drain line that the leak is on is pressurized but is normally isolated and stagnant since this portion of the SW system is rarely removed from service. The Unit 2 SW system was constructed in accordance with ASME Section III 4

Cir.ss 3. This drain line piping is a 1" carbon steel, schedule 80 (nominal wall thickness of l

0.179"), class HBC " moderate energy" pipe.

In the event that an entire loop of SW is declared inoperable, cascading technical l

specifications cause the associated emergency diesel generator, high pressure injection, low pressure injection, reactor building spray, and reactor building cooling to be inoperable. As a result, a condition that would cause one loop of SW to be inoperable for more than.72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> requires that the plant be placed in hot shutdown within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> per ANO-2 Technical Specification 3.7.3.1.

2.0

. Operability Assessment k

The operability of the SW system in the "as-found" condition was assessed. Based on this

=s==nant, the SW piping, system, and associated equipment remain operable and available. The issues considered were structural integrity, flooding concerns, effect of leakage spray on area components, reduction in flow to SW supplied components, and emergency cooling pond (ECP) inventory concerns.

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' Attachment to 2CAN079802 Page 2 of 4 Structuralintenrity The through-wall defect is in a vertical run of a 1" carbon steel drain line, located just upstream of valve 2SW-1151. In order to evaluate the piping in the region of the leak, ultrasonic (UT) thickness mae=rements were taken on a 360* band around the circumference of the pipe. A more detailed UT thickness mapping was conducted immediately around the _ leak.

This thickness mapping provided the means of characterizing the flaw at the leak location and verification that the flaw could be treated as a single flaw with respect to the proximity of other flaws.

The data revealed that the through wall flaw originated from corrosion pitting on the interior surface of the pipe and included localized wall thinning in the immediate area. The pipe contained pits of varying degrees around the circumference of the drain line; however, the average overall pipe wall thickness was determined to be greater than 0.16".

The thinnest recorded wall thickness, except at the leak location, was 0.063".

Using the guidance of Generic Letter 90-05, the flaw and flaw area were evaluated to verify the structural integrity of the pipe which is documented by Desisa Engineering.

Calculation 98-E-0040-01, Revision 0. The evaluation concluded that the. flawed piping satisfied the "through-wall flaw" stability criteria of the generic letter. 'Ihe qualifying stress calculation (94-D-6035-02, Revision 0) was reviewed to determine the maximum pipe stress levels in the area immediately upstream of valve 2SW-ll51. The existing ASME Section III Class 3 code allowable pipe stress levels were determined to be under

12% excluding pipe wall thinning. With the pipe wall thickness conservatively assumed as 0.060" for the full circumference, the maximum pipe stress was assessed to be approximately 26% of the code allowable stress levels. Therefore, even with the entire i

pipe wall circumference conservatively es na=A to be thinned to 0.06", the pipe would be l

within code allowable strength requirements. The through-wall flaw has been shown to be "l

stable for expected plant loading conditions, provided that the wall thicknew of the pipe does not drop below 0.06" in an area greater than that which would be enclosed by a 0.5" diameter circle.

Floodina concerns The leakage at present (approximately 0.0001 gpm) is insigni6 cant and does not present a flooding concern. A floor drain is located approximately six feet from the leak and is sized to remove normal leakage from this area of the plant. Any significant unobserved increase in leak rate would be identified by an increase in the auxiliary building sump level.

However, based on the structural assessment and engineering experience with respect to flaw growth, no significant leak rate ' crease is expected to occur.

m Effect ofleakane sorav on area components A survey of the immediate area determined that there are no components which would be adversely affected by spray from this pinhole leak. The leak is located on the northeast

Awkment to 2CAN079802 Page 3 of 4 side of the piping and is approximately seven feet from the east wall and six feet from the

' floor. There are two air operated valves in the vicinity of the leak that could potentially be affected by spray from the leak. The valves (2CV-5638-2 and 2CV-5637-1) are used for i

purification of the refueling water tank through the SFP purification system (safety position of these valves is closed). These valves are four feet south and east, and three feet below the leak. They would not be directly impacted by significant spray from the leak area. The valves and associated components (solenoid valves and limit switches) would not be adversely affected from any spray since all are resistant to water intrusion that could occur from any indirect spray that might reach the valves. Additionally, actions would be taken to contain and stop any excessive leakage or spray in a short period of time that would prevent any adverse long term impacts to the valves. The local floor drain would also accommodate the leakage.

Reduction in flow to SW supplied comoonents Based on the most recent refueling outage (2R12) as-left SW flow test, the total loop 2 SW flow was 9950 gpm, with the system in an engineered safeguards alignment.'

Adequate flow margin was available to all components. The reduction in flow to the i

associated loop 2 components due to this pinhole leak is insignificant and would not cause the SW loop nor individual system components to be degraded.

Emergency coolina cond inventory concerns This pinhole leakage provides an additional drain path from the ECP. The overall leakage from the ECP is routinely accounted for by totaling the sluice gate and system boundary valve leakage from both ANO-1 and ANO-2 since the ECP is a shared emergency source of SW. The 2R12 as-left sluice gate and system boundary valve leakage tests determined that the total leakage from ANO-2 was 5.97 gpm compared to an allowable ANO-2 Safety Analysis Report Section 9.2.5.3 value of 75 gpm which indicates a margin of 69.03 gpm.

The current pinhole leak rate of 0.0001 gpm is bounded by the allowable system leak rate of 69.03 gpm.

3.0 Root Cause Determination i

Based on the UT data, the flaw was characterized as a highly localized through-wall pit typical of corrosion degradation in SW piping. Previous evaluations of the large bore SW pipe condition, as part of ANO's Service Water Integrity Program, has determined that l

l similar pitted areas are most likely due to microbiologically induced corrosion (MIC) in the form of anaerobic sulfate reducing bacteria under deposits or tuberculation.

A tubercle can form a protective barrier for these organisms which makes chemical treatment effectiveness vary from pipe location to pipe location. The drain pipe in which the leak is located is attached to a line with flow that allows the water in the drain pipe to be semi-stagnant which is an excellent environment for MIC to occur.

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2CAN079802 Page 4 cf4 4.0 Augmented Inspection Five additional locations, representative of the environment seen by the defect, were selected for the augmented inspection via UT. These locations included one location on a drain line for tb loop 2 SW supply for SFP cooling, one location on the drain piping just downstream of the existing leak, one location on each drain line for the SW loop 1 supply i

and return lines to the containment coolers, and one location on a drain line for the SW loop 2 return from the containment coolers. The piping ' spected as a result of this event m

indicated that the actual leak location was the only location that exceeded the minimum required wall thickness for pressure with the remaining surrounding area having sufficient thickness based on measured system corrosion rates.

Based on the fact that the original flaw is already through-wall and previous ANO experience of similar flaws, flaw growth is not a significant concern This is because the projected wall thinning is approximately 0.008" per year based on ANO wall thinning rates at pit locations; therefore, the overall condition of the system is acceptable.

5.0 Impracticality of Repair Determination Conducting a code-qualified repair during power operation is not feasible since loop 2 of J

SW would have to be removed from service. This loop of SW is necessary to support operation of one entire train of engirmed safeguards features sycems (e.g., emergency diesel generator, high pressure safety injection, and low pressure safety injection). Based l

on the insignificance of the leak, it would be inappropriate to challenge the operation of i

the plant in this high risk configuration for the repair.

The leakage is currently being contained by a catch basin since the leak is small and not impacting any equipment in the area; however, should the leak worsen, a temporary clamp device would be installed over the defect area as a "stop gap" measure to limit leakage for p

housekeeping purposes. Any installed clamp would not alter the structural integrity of the l

piping and would be evaluated prior to installation. If a clamp is installed, it is planned to maintain this clany as the temporary repair. Should this temporary repair fail, there is no equipment in close proximity to the leak location that would be adversely affected by water spray, and the leak rate would be so small that local floor dr6s would mitigate any potential for flooding. The loss of system flow through the leak would not reduce the ability to provide cooling water to critical equipment since the leak rate would be insignificant compared to the over all capacity margin of the SW system. Because failure of the temporary repair would have no adverse safety impact, the structural condition of the clamp would not require a rignrous structural analysis. No credit would De taken for i

the additional structural strergth contribution from the clamp.

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