NRC Generic Letter 1995-03
UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555-0001April 28, 1995NRC GENERIC LETTER 95-03: CIRCUMFERENTIAL CRACKING OF STEAM GENERATOR TUBES
Addressees
All holders of operating licenses or construction permits for pressurizedwater reactors (PWRs).
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this generic letter to(1) notify addressees about the recent steam generator tube inspectionfindings at Maine Yankee Atomic Power Station and the safety significance ofthese findings, (2) request that all addressees implement the actionsdescribed herein, and (3) require that all addressees submit to the NRC awritten response to this generic letter regarding implementation of therequested actions.In addition, this letter alerts addressees to the importance of performingcomprehensive examinations of steam generator tubes using techniques andequipment capable of reliably detecting degradation to which the steamgenerator tubes may be susceptible. The performance of steam generator tubeexaminations is controlled, in part, by Appendix B to Part 50 of Title 10 ofthe Code of Federal Regulations (10 CFR Part 50).BackgroundIn July 1994, the licensee for Maine Yankee shut down the plant as a result ofsteam generator primary-to-secondary leakage. Details of the steam generatortube inspections and investigations are contained in NRC Information Notice94-88, Inservice Inspection Deficiencies Result in Severely Degraded SteamGenerator Tubes," issued on December 23, 1994. As discussed in theinformation notice, inadequate eddy current test procedures since 1990, orearlier, appeared to have been the primary reason the tube degradation wentundiscovered resulting in several of the tubes becoming severely degraded. Infact, with hindsight, most of the indications identified in 1994 could betraced back to at least 1990.After approximately 6 months of operation, the licensee for Maine Yankeecommenced another inspection of the steam generator tubes. The eddy currentprobe (i.e., a three-coil rotating pancake coil probe) and screening criteriaused at the start of the outage were similar to those used during the 1994inspections. These initial inspections resulted in the detection of a numberof circumferential cracks that were larger than anticipated for the amount oftime between the inspections. These results, in part, led the licensee toperform additional inspections with enhanced techniques. These enhanced95042101275 p9 SA4 GL 95-03April 28, 1995 inspections resulted in the identification of many more tubes withcircumferential cracks than had previously been identified. Penetrant testingconfirmed that several indications identified with the enhanced techniqueswere circumferential cracks. Furthermore, the destructive examination ofthree tubes removed from the steam generators (two with marginal responses andone with an intermediate response) confirmed that the tubes hadcircumferential cracks. The preliminary results from the destructiveexamination indicate that the three pulled tubes had maximum crack depths of45 percent, 37 percent, and 57 percent with average depths of 24 percent,23 percent, and 26 percent, respectively. In addition, the preliminaryresults indicate that the circumferential extent of these indications wasunderestimated during the nondestructive examination in the field.Discussion(1) Operating ExperienceBoth NRC and the industry have identified the reliable detection and sizing ofcircumferential cracks in steam generator tubes as a technical issue ofconcern. The detection of circumferentially oriented cracks at variouslocations on the steam generator tubes has resulted in the publication ofseveral NRC information notices (90-49, 92-80, 94-05, and 94-88) and inseveral meetings between the NRC staff and the PWR owners groups, the industry(Electric Power Research Institute), and various licensees. The sizing ofcircumferential cracks has been discussed in meetings between the NRC staffand industry representatives from the Steam Generator Strategic ManagementProgram on January 12 and February 22, 1995.A number of factors affect the detection of circumferential cracking. Thesefactors can be both plant specific and generic. They include, but are notlimited to, the scope of the inspection, the nondestructive examinationmethods used for the inspection (e.g., probes, instruments, and hardware)including the plant specific factors that may affect the sensitivity of thetechniques, the equipment setup for these techniques, the analysis of thenondestructive examination data, the data analyst training and performancedemonstration program, and the methods used to minimize interfering signals.Tubes with circumferential cracks are removed from service by plugging orsleeving on detection. This is due, in part, to (1) the inability to reliablysize these indications, (2) the threshold of detection for circumferentialindications, and (3) the inability to reliably predict crack growth rates. Inaddition, more data, including both laboratory and pulled-tube data, areneeded to support the reliable detection and sizing of these indications.(2) Safety AssessmentOn the basis of previous NRC studies (e.g., NUREG-0844, "Voltage-Based InterimPlugging Criteria for Steam Generator Tubes"), a safety concern which wouldwarrant immediately shutting down plants does not exist based on probability GL 95-03April 28, 1995 and risk considerations; however, since tube ruptures represent a failure ofone of the principal fission product boundaries and present a pathway forprimary system activity release to the environment bypassing containment, allreasonable precautions should be taken to prevent such an occurrence.Inspection practices should furnish assurance that steam generator tubedegradation will be reliably detected so that the potential for the rupturingof a tube is maintained at an acceptably low level. If licensees concludethat unexpected levels of tube degradation may exist in their steamgenerators, they should implement compensatory measures to minimize the chancethat tube integrity is compromised and to ensure that the plant can safelyrespond to a tube failure. Such measures should have the objective ofmaintaining a safe operating posture through a defense-in-depth philosophy of(1) prevention of uncontrolled tube degradation, (2) early detection of tubedegradation, and (3) mitigation of the consequences of failed tubes.To verify compliance with regulatory requirements (10 CFR Part 50 Appendix B;technical specifications) and to maintain an appropriate degree ofdefense-in-depth measures, the NRC has concluded that it is appropriate forPWR licensees to take the measures enumerated in this generic letter.Requested ActionsAll addressees are requested to(1) Evaluate recent operating experience with respect to the detection andsizing of circumferential indications to determine the applicability totheir plant.(2) On the basis of the evaluation in Item (a) above, past inspection scopeand results, susceptibility to circumferential cracking, threshold ofdetection, expected or inferred crack growth rates, and other relevantfactors, develop a safety assessment justifying continued operationuntil the next scheduled steam generator tube inspections are performed.(3) Develop plans for the next steam generator tube inspections as theypertain to the detection of circumferential cracking. The inspectionplans should address, but not be limited to, scope (including sampleexpansion criteria, if applicable), methods, equipment, and criteria(including personnel training and qualification).Licensees are encouraged to work closely with industry groups on coordinationof inspections, evaluations, and repair options for all forms of steamgenerator tube degradation. In the interest of optimizing the use ofresources, licensees are encouraged to develop generic safety assessments andinspection plans as described above for logical groupings of plants, wherepossible. Plant-specific factors that may affect the applicability of thegeneric assessment to a plant should be addressed (e.g., gross chemistryexcursions).
GL 95-03April 28, 1995 Requested InformationAll addressees are requested to submit(1) a safety assessment justifying continued operation that is based on theevaluations performed in accordance with Requested Actions (1) and (2)above.(2) a summary of the inspection plans developed in accordance with RequestedAction (3) above and a schedule for the next planned inspection.The NRC is aware that generic industry guidance with respect to performingsteam generator tube inspections has been developed and is continually beingupdated. If the addressee intends to follow the guidance developed for thisissue by the industry, reference to these and other relevant generic documentsis acceptable, and encouraged, as part of the response, as long as thereferenced documents have been officially submitted to the NRC. However, asdescribed previously, additional plant-specific information may be appropriateto establish justification for continued operation.Reauired ResDonsePursuant to Section 182a of the Atomic Energy Act of 1954, as amended, and10 CFR 50.54(f), each holder of an operating license for a PWR shall submit,under oath or affirmation, the following written response to this genericletter:(1) Within 60 days from the date of this generic letter, all addressees arerequired to submit a written response* with the requested information if the addressee has implementedthe actions requested above.* If an addressee has not completed or chooses not to implement therequested actions, submit a description of any proposedalternative course of action, the schedule for completing thealternative course of action (if applicable), and the safety basisfor determining the acceptability of the planned alternativecourse of action.The NRC will review the responses to this generic letter, and if concerns areidentified during the review, those licensees will be notified of the NRCstaff concerns.The NRC recognizes that addressees may have already conducted inspectionsand/or performed safety assessments. However, as the inspection scope anddetails of the methods used should reflect cumulative experience to date, asappropriate, this required response applies to all PWRs.
GL 95-03April 28, 1995 Address the required written reports to the U.S. Nuclear RegulatoryCommission, ATTN: Document Control Desk, Washington, D.C. 20555-0001, underoath or affirmation under the provisions of Section 182a, Atomic Energy Act of1954, as amended, and 10 CFR 50.54(f).This generic letter requires submittal of information that will enable the NRCto verify that the licensee is in compliance with existing regulatoryrequirements (10 CFR Part 50 Appendix B; technical specifications).Accordingly, an evaluation justifying this information request is notnecessary under 10 CFR 50.54(f).Related Generic CommunicationsNRC Information Notice 94-88, "Inservice Inspection Deficiencies Result inSeverely Degraded Steam Generator Tubes," December 23, 1994NRC Information Notice 94-62, "Operational Experience on Steam Generator TubeLeaks and Tube Ruptures," August 30, 1994NRC Information Notice 94-43, "Determination of Primary-to-Secondary SteamGenerator Leak Rate," June 10, 1994NRC Information Notice 94-05, "Potential Failure of Steam Generator TubesSleeved With Kinetically Welded Sleeves," January 19, 1994NRC Information Notice 93-56, "Weaknesses in Emergency Operating ProceduresFound as a Result of Steam Generator Tube Rupture," July 22, 1993NRC Information Notice 93-52, "Draft NUREG-1477, 'Voltage-Based InterimPlugging Criteria for Steam Generator Tubes,'" July 14, 1993NRC Information Notice 92-80, "Operation With Steam Generator Tubes SeriouslyDegraded," December 7, 1992NRC Information Notice 91-67, "Problems With the Reliable Detection ofIntergranular Attack (IGA) of Steam Generator Tubing," October 21, 1991NRC Information Notice 91-43, "Recent Incidents Involving Rapid Increases inPrimary-to-Secondary Leak Rate," July 5, 1991NRC Information Notice 90-49, "Stress Corrosion Cracking in PWR SteamGenerator Tubes," August 6, 1990NRC Information Notice 88-99, "Detection and Monitoring of Sudden and/orRapidly Increasing Primary-to-Secondary Leakage," December 20, 1988NRC Bulletin 88-02, "Rapidly Propagating Cracks in Steam Generator Tubes,"February 5, 1988 GL 95-03April 28, 1995
Federal Register Notification
A notice of opportunity for public comment was not published in the FederalRegister because NRC needs licensees to submit the information requested bythe generic letter in a timely manner. However, comments on the actionsrequested and the technical issue addressed by this generic letter may be sentto the U.S. Nuclear Regulatory Commission, ATTN: Document Control Desk,Washington, D.C. 20555-0001.
Paperwork Reduction Act Statement
The information collections contained in this request are covered by theOffice of Management and Budget clearance number 3150-0011, which expiresJuly 31, 1997. The public reporting burden for this collection of informationis estimated to average 350 hours0.00405 days <br />0.0972 hours <br />5.787037e-4 weeks <br />1.33175e-4 months <br /> per response, including the time forreviewing instructions, searching existing data sources, gathering andmaintaining the data needs, and completing and reviewing the collection ofinformation. Send comments regarding this burden estimate or any other aspectof this collection of information, including suggestions for reducing thisburden, to the Information and Records Management Branch, (T-6 F33), U.S.Nuclear Regulatory Commission, Washington, D.C., 20555-0001, and to the DeskOfficer, Office of Information and Regulatory Affairs, NEOB-10202,(3150-0011), Office of Management and Budget, Washington, D.C. 20503.Compliance with the following request for information is voluntary. Theinformation would assist the NRC in evaluating the cost of complying with thisgeneric letter.(1) the licensee staff time and costs to perform requested record reviewsand develop plans for inspections(2) the licensee staff time and costs to prepare the requested reports anddocumentation(3) the additional short-term costs incurred as a result of the inspectionfindings such as the cost of the corrective actions or the costs of downtime(4) an estimate of the additional long-term costs that will be incurred as aresult of implementing commitments such as the estimated costs ofconducting future inspections and repairs GL 95-03April 28, 1995 If you have any questions about this matter, please contact one of thetechnical contacts listed below or the appropriate Office of Nuclear ReactorRegulation project manager.Z 44an, at irector for ProjectsOffice of Nuclear Reactor RegulationTechnical contacts:Kenneth J. Karwoski(301) 415-2754Joseph E. Donoghue(301) 415-1131Lead project manager:Daniel G. McDonald(301) 415-1408Attachment:List of Recently Issued NRC Generic LettersWAC544/o/64/Qk AttachmentGL 95-03April 28, 1995 LIST OF RECENTLY ISSUED GENERIC LETTERSGenericI ^++E WDate ofT ecasn.eMCeh;atfTccevit TnLvt: t sv1 ;PUU.IvL t 1:a.lx aus -95-0289-04,SUPP. 195-0194-04USE OF NUMARC/EPRI REPORTTR-102348, "GUIDELINE ONLICENSING DIGITAL UPGRADES,"IN DETERMINING THE ACCEPT-ABILITY OF PERFORMINGANALOG-TO-DIGITAL REPLACE-MENTS UNDER 10 CFR 50.59GUIDANCE ON DEVELOPINGACCEPTABLE INSERVICETESTING PROGRAMSNRC STAFF TECHNICAL POSI-TION ON FIRE PROTECTIONFOR FUEL CYCLE FACILITIESVOLUNTARY REPORTING OFADDITIONAL OCCUPATIONALRADIATION EXPOSURE DATAINTERGRANULAR STRESSCORROSION CRACKING OF CORESHROUDS IN BOILING WATERLONG-TERM SOLUTIONS ANDUPGRADE OF INTERIMOPERATING RECOMMENDATIONSFOR THERMAL-HYDRAULICINSTABILITIES IN BOILINGWATER REACTORS04/26/9504/04/9501/26/9509/02/9407/22/9407/11/94ALL HOLDERS OF OLs ORCPs FOR NUCLEAR POWERREACTORS.ALL HOLDERS OF OLs ORCPs FOR NUCLEAR POWERREACTORS.ALL CURRENT LICENSEES& APPLICANTS FOR URANIUMCONVERSION & FUELFABRICATION FACILITIES.ALL HOLDERS OF OLs OR CPsFOR NPRs, RADIOGRAPHYLICENSEES, FUEL PROCES-SING LICENSEES, FABRICA-TING & REPROCESSINGLICENSEES, MANUFACTURERS& DISTRIBUTORS OF BY-PRODUCT MAT'L, INDEPEND-DENT SPENT FUEL STORAGEINSTALLATIONS, FACILITIESFOR LAND DISPOSAL OF LOW-LEVEL WASTE, & GEOLOGICREPOSITORIES FOR HIGH-LEVEL WASTE.ALL HOLDERS OF OLs OR CPsFOR BOILING WATERREACTORS EXCEPT FOR BIGROCK POINT, WHICH DOESNOT HAVE A CORE SHROUD.ALL HOLDERS OF OLs FORBOILING WATER REACTORSEXCEPT BIG ROCK POINT94-0394-02L -CP -NPR -OPLKRAIIN LICNLECONSTRUCTION PERMITNUCLEAR POWER REACTORS
GL 95-03April 28, 1995 GL 95-03April 26, 1995
- s S *The Commissioners-2-warrant immediately shutting down plants does not exist based on probabilityand risk considerations. However, prompt actions are necessary to ensure thatlicensees evaluate the recent operating experience and take appropriateactions.A notice of opportunity for public comment on the proposed generic letter wasnot published in the Federal Register because of the urgent nature of theinformation requested by the generic-communication. The generic letter willbe published in the Federal Register when it is issued.The proposed generic letter has not been formally reviewed and endorsed by theCommittee To Review Generic Requirements (CRGR) because of its immediatelyeffective nature. However, the proposed generic letter was discussed withCRGR during its meeting on April 11, 1995. The staff has incorporated thecomments provided by CRGR at that meeting. The generic communication, as wellas the appropriateness of treating it as an immediately effective genericletter, will be discussed with CRGR at its next regularly scheduled meeting.The Office of the General Counsel reviewed this generic letter and has nolegal objections.The staff intends to issue this generic letter approximately three workingdays after the date of this information paper. OtWGdWJames M. TaylordameSLM1hoamnExecutive Director Lfor OperationsAttachment: Proposed Generic Letter*SEE PREVIOUS CONCURRENCEDOCUMENT NAME: G:\KARWOSKI\COMM.MEMTo receive a copy of this document, indicate in the box: "(attachment/enclosure 'E" = ConY with attachment/enclosureCn = Copy withoutIN" = No conYOffice i*EMCB l iE *EMCB:BC I C *DE:DD lI*DE:D l *DSSA:D lName l KKarwoski JStrosnider GLainas BSheron GHolahanDate 4/13/95 4/13/95 14/14/95 4/14/95 4/14/95Office *OECB 7 *DOPS: *OGC E *NRR:ADPR *NRR:ADTName l RKeissel BGrimes JGoldberg RZimmerman AThadaniDate l 4/14/95 4/14/95 4/14/95 4/18/95 4/17/95Office NRR:DD l *NRR:7 *TECHED lName l FMiraglia WRussell MMejac JMTaylorDate I 4/ /95 4/18/95 4/11/95 4 /b/95 _OFFICIAL RECORD COPY