ML14309A186
| ML14309A186 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 11/01/2014 |
| From: | Stephanie Pyle Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML14309A181 | List: |
| References | |
| 2CAN111401 | |
| Download: ML14309A186 (9) | |
Text
En eg- Entergy Operations, Inc.R~a-En trW 1448 S.R. 333Russellville, AR 72802Tel 479-858-4704Stephenie L. PyleManager, Regulatory AssuranceArkansas Nuclear One2CAN 111401November 1, 2014U.S. Nuclear Regulatory CommissionAttn: Document Control DeskWashington, DC 20555-0001
Subject:
Supplement to Relief Request ANO2-ISI-017, "Emergency Request Alternative toUtilize the Flaw Evaluation Methodology of ASME Code Case N-513-4,"Evaluation Criteria for Temporary Acceptance of Flaws in Moderate EnergyClass 2 or 3 Piping Section Xl, Division 1"Arkansas Nuclear One -Unit 2Docket No. 50-368License No. NPF-6
Reference:
Entergy letter dated October 31, 2014, "Emergency Request Alternative to UtilizeASME Code Case N-513-4, "Evaluation Criteria for Temporary Acceptance ofFlaws in Moderate Energy Class 2 or 3 Piping Section Xl, Division 1", ReliefRequest ANO2-ISI-01 7
Dear Sir or Madam:
By letter dated October 31, 2014, Entergy Operations, Inc. (Entergy) requested emergencyNRC approval of a proposed alternative to the American Society of Mechanical Engineers(ASME) Boiler and Pressure Vessel Code, Section Xl for Arkansas Nuclear One, Unit 2(ANO-2), in accordance with 10 CFR 50.55a(a)(3)(ii). The alternative is for the current fourth10-year inservice inspection interval. This interval began on March 26, 2010.As a result of a teleconference held between ANO and NRC staff at 1900 on October 31, 2014,the NRC determined changes to the Entergy request were required in order to fully meet NRCacceptance criteria. This letter therefore supersedes the reference letter and includes theadditional information required.Specifically, Entergy is requesting relief to apply the flaw evaluation methodology of N-513-4, tostructurally evaluate Class 2 and 3 moderate energy piping including elbows, bent pipe,reducers, expanders, and branch tees. Although the flaw evaluation methodology of N-513-4 isrequested, ANO-2 will continue to apply all other requirements contained within CodeCase N-513-3, "Evaluation Criteria for Temporary Acceptance of Flaws in Moderate EnergyClass 2 or 3 Piping Section Xl, Division 1", as associated with the subject flaw.Acw7 2CAN 111401Page 2 of 3This methodology is to be used to evaluate a through-wall flaw that was identified in a 6-inchbranch connection from the Service Water (SW) supply header to the suction of the"B" Emergency Feedwater Pump. This line was determined to be inoperable and the unitentered a Technical Specification 72-hour allowable outage time (AOT) in accordance withLimited Condition of Operation (LCO) 3.7.3.1 on October 30, 2014, at 2118. Immediate repairor replacement of the pipe is not feasible during this LCO. Without approval of this relief,ANO-2 will be required to shutdown following expiration of the AOT and result in a hardship or,unusual difficulty without a compensating increase in the level of quality and safety.It has been determined that the root cause of the flaw is microbiological induced corrosion(MIC). The majority of leaks in ANO-2 SW piping in the past have been MIC-induced. Theassociated piping system continues to be capable of performing its required safety function andis not susceptible to sudden or catastrophic failure.The attached request maintains the quality and safety considerations of structures, systems,and components required for safe operation of ANO-2.Entergy requests the use of the Code Case N-513-4 flaw evaluation methodology until aSection Xl compliant repair / replacement can be completed prior to startup from the nextrefueling outage (fall of 2015) or exceeding the temporary acceptance criteria of CodeCase N-513-3 and this relief request, whichever comes first.Attachment 1 contains the request for alternative. The stress analysis is provided inAttachment 2 with the NDE Data Sheet provided in Attachment 3.Entergy requests approval of this relief prior to the expiration of the LCO AOT which will end at2018 on November 2, 2014.This letter contains new commitments included in Attachment 4.Should you have any questions regarding this submittal, please contact me.Sincerely,SLP/rwcAttachments:1. Relief Request ANO2-ISI-01 72. Structural Integrity Associates Calculation 1401289.3013. UT Thickness Examination -Report 2-BOP-UT-14-0404. List of Regulatory Commitments 2CAN 111401Page 3 of 3cc: Mr. Marc L. DapasRegional AdministratorU. S. Nuclear Regulatory Commission, Region IV1600 East Lamar BoulevardArlington, TX 76011-4511NRC Senior Resident InspectorArkansas Nuclear OneP. 0. Box 310London, AR 72847U. S. Nuclear Regulatory CommissionAttn: Ms. Andrea E. GeorgeMS O-8B1One White Flint North11555 Rockville PikeRockville, MD 20852 ATTACHMENT I TO2CAN111401RELIEF REQUEST ANO2-ISI-017 to2CAN111401Page 1 of 5RELIEF REQUESTANO2-ISI-017Component / Number: 2HCC-2003 (elbow) and 2HBC-33 (sweep-o-let)Code Class: American Society of Mechanical Engineers (ASME Section III)Class 3
References:
ASME Code, Section Xl, 2001 Edition with the 2003 AddendaCode Case N-513-4Description: Service Water (SW) to 2P-7B, Emergency Feed Water (EFW)Pump SuctionUnit / Inspection Interval Arkansas Nuclear One, Unit 2 (ANO-2) / Fourth (4th) 10-yearApplicability: interval, 2R24 Refueling OutageCODE REQUIREMENTSThe applicable ASME Section XI Code Edition and Addenda for ANO-2 is the ASMECode,Section XI, 2001 Edition with the 2003 Addenda. Articles IWD-3120 andIWD-3130 require that flaws exceeding the defined acceptance criteria be corrected byrepair / replacement activities or be evaluated and accepted by analytical evaluation.ASME Code,Section XI, IWD-3120(b) requires that components exceeding theacceptance standards of IWD-3400 be subject to supplemental examination, or to arepair / replacement activity:I1. PROPOSED ALTERNATIVEBackgroundOn October 20, 2014, as documented in condition report CR-ANO-2-2014-02970,Operations personnel identified leakage in a dissimilar metal weld between an 18" stdwall x 6" schedule 40 carbon steel sweepolet, and a 6" schedule 40 stainless steel 450elbow on the SW piping to the suction of the "B" EFW pump. This leak is located in theArkansas Nuclear One, Unit 2 (ANO-2) Auxiliary Building. The insulation around thesubject line was wet; however, the leak rate at the time of discovery was 1 to 2 drops perhour. According to Operations, the current leak rate is 32 drops per hour. The piping inquestion forms a branch connection, via a sweepolet, with the main SW header.NDE Report 2-BOP-UT-14-040 (Attachment 3) provides a detailed UT mapping of thearea immediately around the leak. The UT data characterized the flaw at the leaklocation and verified that the flaw could be treated as a single flaw with respect to theproximity of other thinned regions. The UT report noted that the flaw could becharacterized as a nonplanar flaw. The report states that the flaw is located in the toe ofthe weld on the sweepolet (carbon steel) side of the weld. The size of the pinhole is toosmall to measure (32 drops per hour). Based on the results of the report, the remaining to2CAN1 11401Page 2 of 5piping beyond the flaw is sufficient to maintain a pressure-retaining boundary andpostulated leakage does not exceed operability margins. The nonplanar indication is theresult of microbiological induced corrosion (MIC). Such corrosion indications arehistorically limited to localized areas on ANO-2 SW piping and piping components anddo not manifest in general thinning, cracking, or other prompt structural failureprecursors. This isolated corrosion area can be reliably monitored to ensure flow andstructural integrity are maintained.The weld material is ER309/E309. ER309 yield strength is 57 ksi with an ultimate tensilestrength of 86 ksi.ASME Code Case N-513-3 is conditionally acceptable to the NRC (per RegulatoryGuide 1.147, "Inservice Inspection Code Case Acceptability, ASME Section Xl,Division 1," Revision 17). However, N-513-3 does not allow evaluation of flaws locatedaway from attaching circumferential piping welds that are in elbows, bent pipe, reducers,expanders, and branch tees. ASME Code Case N-513-4 provides guidance forevaluation of flaws in these locations. This code case was recently endorsed by ASMEon May 7, 2014. This code case has not been generically approved by the NRC.SW System DescriptionBriefly, the SW system for ANO-2 consists of two independent full capacity 100 percentredundant loops. Each SW loop is capable of supplying cooling water to the requiredcomponents during normal and emergency conditions. This redundancy allowscontinued plant operation when a single component failure occurs. System crosstievalves provide additional redundancy by allowing one of the three SW pumps to beremoved from service for maintenance. The remaining two pumps provide total systemflow for both SW loops.In the event of an emergency, the SW system can be the supply source for the EFWsystem (ANO-2 Technical Specification (TS) 3.7.1.3).The design pressure for the ANO-2 SW system is 150 psig and the design temperatureis 130 *F.ANO-2 TS 3.7.3 requires that two SW loops shall be operable and powered fromindependent essential buses to provide redundant and independent flow paths inModes 1, 2, 3, and 4. ANO-2 TS 3.7.4 requires the Emergency Cooling Pond (ECP) tobe operable in Modes 1, 2, 3, and 4. Two EFW pumps and associated flow paths are toremain operable in Modes 1, 2, and 3 (ANO-2 TS 3.7.1.2).On October 30, 2014, at 2118, Loop 1 of SW and EFW pump 2P-7B were declaredinoperable and the appropriate TS actions entered. Immediate repair or replacement ofthe pipe is not feasible during this LCO. The inoperable loop is required to be restoredwithin 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or the unit must 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 /> and ColdShutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> per ANO-2 TS 3.7.3. Based on theinsignificance of the flaw, it appears inappropriate to challenge the operation of the plant. to2CAN1 11401Page 3 of 5Due to the fact that the original flaw is MIC-induced, and ANO-2 has extensiveexperience with similar flaws in this system and it is well understood by ANO-2 staff,consideration of flaw growth is not a significant concern. Therefore, it has beenconcluded that the overall condition and the continued operation of the associated SWloop until the next ANO-2 refueling outage is acceptable.Proposed AlternativeThe NRC issued Generic Letter 90-05, "Guidance for Performing Temporary Non-CodeRepair of ASME Code Class 1, 2, and 3 Piping (Generic Letter 90-05)," to address theacceptability of limited degradation in moderate energy piping. The generic letterdefines conditions that would be acceptable to utilize temporary non-code repairs withNRC approval. The ASME recognized that relatively small flaws could remain in servicewithout risk to the structural integrity of a piping system and developed CodeCase N-513. NRC approval of Code Case N-513 versions in Regulatory Guide 1.147,"Inservice Inspection Code Case Acceptability, ASME Section Xl, Division 1," allowsacceptance of partial through-wall or through-wall leaks for an operating cycle providedall conditions of the Code Case and NRC conditions are met. The Code Case alsorequires the Owner to demonstrate system operability due to leakage and any implied Ipotential spray.ASME recognized that Code Case N-513-3 did not include flaw evaluation for pipingcomponents such as elbows, bent pipe, reducers, expanders, and branch tees. CodeCase N-513-4 was recently approved by the ASME to expand the flaw evaluationmethodology for use on these locations and to revise several other areas of the CodeCase. It should be noted that Code Case N-513-4 is not listed in the latest revision ofRegulatory Guide 1.147 (Revision 17, August 2014). Thus, there is no approved currentmethodology for ANO to evaluate the through-wall flaw.ANO-2 will invoke all the requirements commensurate with Code Case N-513-3associated with the identified condition, with the exception that ANO-2 will use themethodology from Code Case N-513-4 for flaw evaluations of piping components suchas elbows, bent pipe, reducers, expanders, and branch tees.Ill. BASIS FOR ALTERNATIVEFlaw Evaluation (N-513-4)A structural evaluation using the methodology presented in Code Case N-513-4 wasperformed for the affected piping components. The evaluation used conservativeallowable stress values based upon carbon steel materials with the highest momentsapplied. The basis for the evaluation includes Structural Integrity Associates (SIA)calculation number 1401289.301 (ANO calculation CALC-14-E-0200-01, Attachment 2).The evaluation provides an allowable flaw size which assures a safety factor, comparedto the critical crack size, in accordance with ASME Section Xl, Appendix C.
Attachment I to2CAN 111401Page 4 of 5Flooding / Spray Concerns (N-513-3)The results of these evaluations are presented below.Flooding / Spray ConcernsThe leakage at present is insignificant and does not present a flooding concern. Noequipment susceptible to water damage is under or adjacent to the leakage site. Themagnitude of the water loss can easily be accommodated by the room drainage systemand does not pose a flooding concern. The leak is located in a well-lighted area (ANO-2Auxiliary Building) that is frequented by Operations personnel on rounds. Thus if theleak rate experienced a rapid increase it would be quickly identified and addressed. Afloor drain is located approximately 3 feet from the leak and is sized to remove normalleakage from this area of the plant. However, based on the structural assessment andengineering experience with respect to flaw growth, no significant leak rate increase isexpected to occur.Reduction in Flow to SW Supplied Components (N-513-3)Due to the small leak magnitude there is no appreciable impact on flow to othercomponents in the ANO-2 SW System. The flow margin above that required for theminimum margin component is bounded, assuming all leakage in this condition weretaken from that component, per the latest SW flow test.ECP Inventory Concerns (N-513-3)The current leak is essentially imperceptible relative to ECP inventory and thus has noimpact on ECP inventory.Periodic Inspections (N-513-3)Frequent periodic inspections of intervals of no more than 30 days. In addition, dailywalkdowns shall be used to confirm analysis conditions remain valid.Extent of Condition (N-513-3)Augmented volumetric examinations will be performed at five of the most susceptibleand accessible locations based upon similar geometry and similar material properties.Additional inspections will be in accordance with the requirements of N-513-3. to2CAN111401Page 5 of 5IV. DURATION OF PROPOSED ALTERNATIVEThe proposed alternative is for use of Code Case N-513-4 in the evaluation of the flawidentified in ANO-2 SW piping components. A Section XI compliant repair / replacementmust be completed prior to startup from the next refueling outage (fall of 2015) or prior toexceeding the structural limits identified by the evaluation as approved by this reliefrequest, or prior to a leak rate greater than 5 gpm, whichever comes first.V. PRECEDENTBy letter dated March 5, 2014 (ML14073A059), as supplemented by letter datedMarch 25, 2014 (ML14091A407), Entergy Nuclear Operations, requested authorizationof a proposed alternative to certain requirements of the ASME Code, Section X1,Article IWD-3000 for the Pilgrim Station. Specifically, it was proposed to use alternateanalytical evaluation criteria for acceptance of through-wall flaws. The alternateanalytical evaluation criteria were based on the draft Code Case N-513-4. The NRCgranted verbal authorization of the proposed alternative on March 26, 2014. The safetyevaluation associated with the authorization was provided via letter dated September 30,2014 (ML14240A603).