ML20198F424

Safety Evaluation Granting Relief Request for Approval to Repair ASME Code Class 3 Service Water Piping Flaws in Accordance with GL 90-05 for VC Summer Nuclear Station

ML20198F424
Person / Time
Site:	Summer
Issue date:	12/18/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20198F422	List: ML20198F418 ML20198F424
References
GL-90-05, GL-90-5, NUDOCS 9812280122
Download: ML20198F424 (5)

Text

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arc p4 4 UNITED STATES j

i g NUCLEAR REGULATORY COMMISSION l o t WASHINGTON, D.C. 2066M001

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION j RELIEF REQUEST FOR APPROVAL TO REPAIR ASME CODE CLASS 3 SERVICE WATER PIPING FLAWS IN ACCORDANCE WITH GENERIC LETTER 90-05 FOR ,

I SOUTH CAROLINA ELECTRIC AND GAS COMPANY  ;

I VIRGIL C. SUMMER NUCLEAR STATION DOCKET NUMBER 50-395

1.0 INTRODUCTION

The Code of Federal Regulations,10 CFR 50.55a(g), requires nuclear power facility piping and i components to meet the applicable requirements of Section XI of the American Society of '

Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (hereafter referred to 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 cf the Code are non-Code repairs. However, implementing required Code (weld) repairs to ASME Code Class 1,2 or 3 systems is often impractical, since the repairs normally require isolating the system to be repaired, and often shutting down the nuclear power plant.

Licensees may u.ae alternatives to Code requirements when the U. S. Nuclear Regulatory Commission (NRC) authorizes this. The NRC may authorize this if the proposed alternatives to the requirements 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 requirements would l

result in hartjship or unusual difficulty without a compensating increase in the level of quality and safety [10 CFR 50.55a(a)(3)(ii)].

Licensees may also subinit requests for relief from certain Code requirements when they determine that conforming 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.

Generic Letter (GL) 90-05," Guidance for Performing Temporay Non-Code Repair of ASME i Code Class 1,2 and 3 Piping," dated June 15,1990, provides guidance for the staff in evaluating licensee relief requests for temporary non-Code repairs of Code Class 3 piping. For

. the purpose of the GL, impracticality is defined to exist if the flaw detected during plant j 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 (LCO) of the affected

9812290122 981218 ADOCK 05000395 PDR j P PM i

l system as specified in the plant Technical Specifications (TS), and performance of Code repair necessitates a plant shutdown.

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2.0 BACKGROUND

Licensee personnel found a through-wall defect in a 4-inch carbon steel, moderate energy, service water (SW) system pipe. South Carolina Electric & Gas Company (SCE&G) estimated the leakage to be about five drops per minute. The affected pipe is a branch connection which functions as a nuclear safety-related emergency make-up source from the SW system "A" Train to the component cooling water system surge tank. The leak exists in the heat-affected zone of  ;

the butt weld which connects the 4-inch pipe to the weld-o-let on the adjacent 20-inch SW system piping. SCE&G installed a lightweight, temporary patch constructed of hose clamps and rubber gasket material over the defect to impede any leakage which might occur. SCE&G performed a structural analysis, and ultrasonically examined additional piping locations, as GL 90-05 requires. These measurements showed slight wall thinning, but none of the locations had a measured wall thickness that violated the calculated, minimum-allowable wall thickness.

SCE&G's May 13,1998, letter submitted a relief request in accordance with 10CFR50.55a(a)(3)(i) and GL 90-05, seeking NRC approval to delay repairing the ASME Code Class 3 piping through-wall defect. SCE&G determined that the time needed to complete the Class 3 Code repair would exceed the 72-hour TS LCO 3.7.4 action statement allowance. They estimated that the repair activity would take 88 hours0.00102 days <br />0.0244 hours <br />1.455026e-4 weeks <br />3.3484e-5 months <br /> to complete, and could not be performed without shutting down the "A" train SW system. Exceeding the SW system 72-hour LCO action l statement requires a plant shutdown.

3.0 LICENSEE'S RELIEF REQUEST SCE&G requested relief from repairing the SW piping through-wall defect in accordance with the requirements of ASME Code,Section XI, Article IWA-4000. SCE&G determined that performing the Code repair within the 72-hour SW systern LCO 3.7.4 Action Statement was impractical. SCE&G will make an ASME Code-approved repair by replacement during the next scheduled outage exceeding 30 days, or Refueling Outage (RFO) 11, which is currently scheduled for the Spring of 1999.

3.1 Licensee's Component identification The defective piping is 4-inch carbon steel, moderate energy (design conditions are 65 psig and 95*F), ASME Code Class 3 SW system pipe.

3.2 ASME Code,Section XI RequirementsSection XI,1989 edition, Subarticle IWA-4310 requires the following:

Defects shall be removed or reduced in size in accordance witn this Article. The component shall be acceptable for continued service if the resultant section thickness created by the cavity is equal to or greater than the minimum design thickness. If the resulting section thickness is reduced below the minimum des.gn thickness, the component shall be repaired in accordance with this Article. Alternatively, the component may be evaluated and accepted in accordance with the design rules of i

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either the Cont'ruction Code, or Section Ill, when the Construction Code was not Section Ill. The repair program and the associated evaluation analyses shall be subject to review in accordance with IWA-4130(c).

3.3 Licensee's Proposed Alternatives Based on GL 90-05 SCE&G installed a lightweight, temporary patch constructed of hose clamps and rubber gasket material over the defect to impede any leakage which might occur. SCE&G performed an augmented inspection of five additanal piping locations, in accordance with GL 90-05. The licensee selected these locations because they are subjected to flow conditions similar to those at the defect. SCE&G used ASME Code methods to calculate the minimum allowable wall thickness for each location. SCE&G then took ultrasonic testing (UT) measurements at each l location in a band around the pipe circumference. These measurements showed slight wall l thinning, but none of the locations had a measured wall thickness that violated the calculated minimum allowable wall thickness. SCE&G halted the augmented inspection at the initial five locations since they did not identify any more flaws.

SCE&G Quality Services will qualitatively assess the patch at least once per week for any degradation in the patch or base piping. They will visually note any changes in the amount of leakage from the patch. SCE&G will perform an engineering evaluation when they note any changes. At least once every 3 months, SCE&G will remove the patch and evaluate the affected pipe for structuralintegrity. This will be accomplished by making UT measurements of the pipe wallin the affected area. SCE&G will perform an engineering evaluation of the results l to estimate the degradation, and prescribe remedial actions,if necessary. These activities will continue until the plant reaches Mode 5 as part of a scheduled 30-day outage. SCE&G will document these evaluations, and will place them into the plant records. SCE&G will promptly initiate a Code repair if structuralintegrity of the pipe cannot be assured.

3.4 Licensee's Basis for Relief The licensee's basis for relief is as follows:

1) An evaluation for the performance of a code repair resulted in a determination that the required time to complete the repair would be in excess of the time allowance of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> under the action statement for the Limiting Condition for Operation (LCO-3.7.4). The repair activity is estimated to take 88 hours0.00102 days <br />0.0244 hours <br />1.455026e-4 weeks <br />3.3484e-5 months <br /> to complete and cannot be performed without shutting down the "A" train SW System. This would resun :n "A"

, train ECCS [ emergency core cooling system) equipment inoperability in excess of l the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> action statement of LCO 3.5.2.

i l 2) A "Through wall Flaw" Evaluation of flaw stability as outlined in GL 90-05 showed the

flaw to be acceptable for continued operation with a stability parameter of 29 ksi*in"5 l versus the acceptance criteria of 35 ksi+in"5 i

a 3) An augmented inspection of five additionallocations was performed as required by

] GL 90-05. All five inspections measured acceptable wall thickness with respect to

calculated minimum allowable wall thickness.

l j_ 4) The following is an evaluation based on failure of the pipe:

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4 a) The current leakage, estimated at 5 drops per minute, is minor and does not impact system flow requirements. The worst case leakage would occur if a postulated crack-break developed at the defect location. The size of this crack would be equivalent to a 5/8 inch hole and would conservatively result in a 95 gpm [ gallon per minute] leak. The SW system flow margin is approximately 2,000 gpm during norrnal operation and approximately 2,800 gpm during post accident operation. The postulated 95 gpm leak is well within these margins and its acceptability is further supported by an evaluation of the pump curve which shows an insignificant effect on total developed head at an additional 95 gpm of flow, b) There are no essential to safe shutdown components or equipment within the immediate area which would be affected by spraying water.

c) The pipe is not an anti-falldown concern because it is approximately 6 feet above the floor and would fall to the floor without impacting any essential to safe shutdown equipment.

d) Flooding is not a concern because the volume of the Tendon Jacking and Tcndon Access Gallery areas is the limiting factor in the design flood level of elevation 412'-8". When this area becomes full, the water levelin the Intermediate Building general area will begin to rise. A conservative leakage estimate from this 4 inch pipe assuming a catastrophic failure would be 3,000 gpm. Assuming Operator action to stop the leak within 30 minutes, the total volume of water would be 90,000 3allons which is less than the Tendon Jacking and Tendon Access Gallery volume of 168,000 gallons.

5) A least once per week the patch and its surrounding area will be visually inspected for degradation and leakage. At least once every three months the patch will be removed and UT measurements of the pipe wall in the affected area will be obtained and evaluated for degradation.

4.0 STAFF EVALUATION AND CONCLUSIONS 4.1 Root Cause Analysis. Structural Inteority Evaluation. and Operability Determination The licensee determined that one location on a 4-inch ASME Code Class 3 SW system line had a through-wall defect. The leak exists in the heat-affected zone of the butt weld connecting the 4-inch pipe to the weld-o-let on the adjacent 20-inch SW system piping. SCE&G believed that microbiologically induced corrosion caused the defect.

SCE&G evaluated the structural integrity of the flaweo piping in accordance with GL 90-05, and found that the flaw satisfies the GL 90-05 through-v.all criteria for non-Code repair. A visual inspection of the pipe indicated that the leak resulted from localized corrosion, and was not a crack. UT measurements around the defect indicated that the affected area was less than 3/16 inch in diameter. SCE&G's through-wall flaw evaluation, prepared using GL 90-05 guidance, showed the flaw to be acceptable for continued operation with a stability parameter of 29 ksi*in" versus the acceptance criteria of 35 ksiain" Wall thickness measurements on the affected 90-degree elbow revealed only the expected general wall thinning and the presence of i

corrosion pits. All measured wall thickness was above the 0.093 inch calculated minimum, except for the defect itself. SCE&G calculated the minimum allowable wall thickness using ASME Code methodology. This methodology included a stress intensification factor that accounted for the existing through-wall defect to conservatively ensure pipe integrity.

SCE&G determined the system operability was not impaired because the leakage wa.s minor, and did not impact system flow requirements. SCE&G estimated that worst-case leakage at the defect location would be about 95 gpm. The postulated 95 grm leak is well within system flow requirements. SCE&G also concluded that there is no essentw. to-safe-shutdown I components or equipment within the immediate area which spraying water would affect, and flooding was not a concern.

4.2 Auamented Inspection SCE&G ultrasonically examined five additional piping locations for evidence of leakage. These measurements showed slight wall thinning, but none of the locations had a measJred Wall thickness which violated the calculated, minimum-allowable wall thickness.

4.3 Proposed Temocrary Non-Code Repair end Monitorina Provisions SCE&G applied a soft patch, held in place by hose clamps, over the flawed area to temporarily repair the flawed line. SCE&G's structuralintegrity evaluation of the flawed piping indicated l that the piping is acceptable for temporary repair, as GL 90-05 permits. SCE&G will visually inspect the flawed area at least once per week for degradation and leakage, and will take and I evaluate UT measurements of the pipe wallin the affected area at least once every 3 months. )

4.4 Staff Conclusions The staff has determined that the licensee's flaw evaluation is consistent with GL 90-05 guidelines and acceptance criteria. The staff, therefore, finds the licensee's structural integrity and operability assessments to be acceptable. Furthermore, the staff finds that making an immediate Code repair is impractical for the V. C. Summer Nuclear Station, since the Class 3 l Code repair would require isolating the SW system for longer than the 72-hour TS LCO 3.7.4 action statement allowance. Exceeding the SW system 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> LCO action statement requires a plant shutdown. SCE&G indicated that they will perform a Code replacement of the defective piping during the next scheduled outage exceeding 30 days, or during RFO 11, currently scheduled for the Spring of 1999. Therefore, in accordance with 10 CFR 50.55a(g)(6)(i), the staff finds that the Code requirements are impractical, grants the requested relief, and imposes the alternatives, until the next refueling outage (RFO 11) is complete. The relief granted is authorized by law and will not endanger life or property or the common defense and security and is,otherwise in public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.

Principal Contributor: M. Padovan Date: December 18, 1998 l-l

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