NRC Generic Letter 1986-07
UNITED STATESNUCLEAR REGULATORY COMMISSIONWASHINGTON, D. C. 20555A March 20, 1986TO ALL REACTOR LICENSEES AND APPLICANTSGentlemen:SUBJECT: TRANSMITTAL OF NUREG-1190 REGARDING THE SAN ONOFRE UNIT 1LOSS OF POWER AND WATER HAMMER EVENT (GENERIC LETTER 86-07)On November 21, 1985, while operating at 60% power, Southern California EdisonCompany's San Onofre Unit 1 Nuclear Power Plant experienced a loss of acelectrical power followed by a severe water hammer in the secondary system whichcaused a steam leak and damaged plant equipment. Shortly after the event, theNRC Executive Director for Operations directed that an NRC Team be sent to SanOnofre, in conformance with the recently established Incident InvestigationProgram, to investigate the circumstances of this event. The NRC Team has nowcompleted its investigation and has documented the factual information and theirfindings and conclusions associated with the event (see enclosed NUREG-1190,entitled "Loss of Power and Water Hammer Event at San Onofre Unit 1, on,November 21, 1985").In this report, the team has concluded that the event was significant because(a) all inplant ac power was lost for 4 minutes; (b) all steam generator feedwaterwas lost for 3 minutes; (c) a severe water hammer caused by check valve failureswas experienced in the feedwater system which caused a leak, damaged plantequipment and challenged the integrity of the auxiliary feedwater system;(d) all indicated steam generator water levels dropped below scale; and (e)the reactor coolant system experienced an acceptable but unnecessary cooldowntransient. In the team's view the most significant aspect of the event wasthat five safety-related feedwater system check valves degraded to the pointof inoperability during a period of less than a year, without detection, andthat their failure jeopardized the integrity of safety-related feedwater piping.The cause of the feedwater system check valve failures has been preliminarilyidentified by SCE as partial or complete separation of the check valve discassemblies due to fluid flow conditions. Information submitted to the staffon this subject is currently under review.You should review the information in the enclosed report for applicability toyour facility. In addition, you should ensure that the information in NUREG-1190is made available to your plant staff as part of your training program in connectionwith the Feedback of Operating Experience to Plant Staff (TMI Action Plan Item I.C.5).8@<)ijvf0 Wh&7/t?P>A~c >OSDOOOoOf March 20, 1986-2-On February 4, 1986, the Executive Director for Operations (EDO) identifiedand assigned responsibility for generic and plant-specific actions resultingfrom the investigation of the San Onofre event. Some of the generic actionsmay be applicable to your facility. A copy of the EDO memorandum is includedfor your information.This generic letter is provided for information only, and does not involve anyreporting requirements. Therefore, no clearance from the Office of Managementand Budget is required. The enclosed report is currently under NRC review.Any generic requirements stemming from the report will be transmitted at alater date following completion of the appropriate procedural steps.Sincerely,Harold R. Denton, Director-Offic of Nuclear Reactor RegulationEnclosures:e>l6,O> ( ) A1. NUREG-11902. EDO Memorandum of February 4, 19863. List of Generic Letters STAFF ACTIONS RESULTING FROM THE INVESTIGATIONOF THE NOVEMBER 21 SONGS-1 EVENT(Reference: NUREG-1190)1. Item: Adequacy of feedwater check valves to perform safety function.(References: Commission briefing, Sections 6.2.4, 6.4, 6.7, and PrincipalFinding)ActionResponsible OfficeCategoryImplement and coordinatethe staff and industry actionsnecessary to assure the reliabilityof safety-related check valves.Other offices to assist asrequested. Areas to beevaluated include:IEPlant-specificGeneric-licensee's engineeringreport on root causeanalysis and proposedcorrective actions-adequacy of check valvedesign for this applica-tion-adequacy of InserviceTesting (IST) Program andprocedures to detectdegraded and failed valves-adequacy of check valves(and related testingprograms) in other systemssuch as RHR system2. Item: Completeness of resolved USI A-1,(References: Finding numbers 1, 2, 3, 8Action ResponsiblfAssess the need to re- NRIevaluate USI A-1 tospecifically address thepotential for and preventionof condensation-induced waterhammers in feedwater piping(assume the issue concerningcheck valve integrity will beresolved in item 1)."Water Hammer".and 9)* Office CategoryGeneric
-2 -3. Item: Adequacy of San Onofre(Commission briefing, FindingActionImplemert and coordinatethe staff's actions tore-evaluate the followingSan Onofre design features:Unit 1 design.numbers 11 and 13)Responsible OfficeNRRCategoryPlant-specificmanual loading of thediesel generators follow-ing a loss of power eventmanual actuation of steamline isolation valves andassurance of steam generatoravailability to remove decayheatlack of steam generatorblowdown status in controlroomadequacy of the licensee'sdesign change to eliminatespurious SI indication onloss of ower4. Item: Ade'cy of post-trip review.(References: Sections 6.6 and 7.2.2.4 and Findingnumber 17)Category-ActionResponsible Officea. Evaluate NRC require-ments for ensuring thatsufficient event dataare retrievable toaccurately reconstructthe event following aloss of offsite power.NRRGenericb. Evaluate the licensee'sprocess for post-tripreview and evaluation,including the thoroughnessof review and oversightprovided by the onsite andoffsite nuclear safety reviewgroups.Region VPlant-specific
_ 3 -5. Item: Adequacy of licensee's recordkeeping practices.(References: Section 6.5 and Finding number 20)ActionEvaluate the adequacy ofthe licensee's maintenancerecords.Responsible OfficeRegion VCategoryPlant-s pecific6. Item: Adequacy of operator training and/or procedures.(References: Section 7 and Finding numbers 14, 15 and 16)ActionResponsible OfficeCategoryReview the implementationof the training programregarding operator under-standing and actions in thearea of electrical systems, andinvoking technical specificationaction statements.Region VPlant-specificresponse.Category7. Item: Adequacy of emergency notifications and NRC(References: Section 7.3 and Finding number 22)ActionResponsible Officea. Verify the adequacy ofthe licensee's proceduresand training for reportingof events to NRC OperationsCenter.b. Evaluate the need forchanges in NRC policy orguidance regarding: theuse of the ENS line; theuse of NRC personnel asENS communicators; andpossible approaches toimprove the ability todetermine the overallplant status.Region VPlant-specificIEGeneric
-4 -8. Item: Significance of backlog of license amendments.(Reference: Commission briefing)ActionResponsible OfficeEvaluate whether a backlogof license amendments andtechnical specificationchanges contributed to delaysin approving the licensee's.IST program.Ca tegotyPlant-specificNRR
List of Recently Issued Generic LettersGenericLetter No.SubjectDate of IssueIssued To86-06To be IssuedTo be Issued86-0586-0486-0386-0286-0185-22Policy Statement onEngineering Expertiseon ShiftApplications for LicenseAmendmentsTechnical Resolution ofGeneric Issue B-19 -Thermal Hydraulic StabilitySafety Concerns Associatedwith Pipe Breaks in theBWR Scram SystemPotential for Loss of Post -LOCA Recirculation CapabilityDue to Insulation DebrisBlockage02/13/8602/10/8601/23/8601/03/8612/03/85All Power ReactorLicensees andApplicants for PowerReactor LicensesAll Power ReactorLicensees and OLApplicantsAll Licensees ofOperating BWRsAll BWR Applicantsand LicenseesAll Licensees ofOperating Reactors,Applicants for OLsand Holders of CPs85-21Not Issued85-20Resolution of Generic Issue69: High Pressure Injection/Make-up Nozzle Cracking inBabcock and Wilcox Plants10/30/85All Licensees withBabcock and WilcoxOperating Reactors