NRC Generic Letter 1994-02

NRC Generic Letter 1994-002: Long-Item Solutions and Upgrade of Interim Operating Recommendations for Thermal Hydraulic Instabilities in Boiling Water Reactors

ML031070189
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Washington Public Power Supply System, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Clinch River, Crane
Issue date:	07/11/1994
From:	Zimmerman R P Office of Nuclear Reactor Regulation
To:
References
GL-94-002, NUDOCS 9407010241
Download: ML031070189 (10)

UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON D.C. 20555July 11, 1994NRC GENERIC LETTER 94-02: LONG-TERM SOLUTIONS AND UPGRADE OF INTERIMOPERATING RECOMMENDATIONS FOR THERMAL-HYDRAULIC INSTABILITIES IN BOILING WATER REACTORS

Addressees

All holders of operating licenses for boiling water reactor except Big RockPoint.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this generic letter torequest that each addressee (1) take the appropriate actions to augment itsrespective procedures and training for preventing or responding to thermal-hydraulic instabilities in its reactors and (2) submit to the NRC a plandescribing the long-term stability solution option it has selected and theimplementation schedule it proposes for the modification of plant protectionsystems to ensure compliance with General Design Criteria (GDC) 10 and 12 inAppendix A to Part 50 of Title 10 of the Code of Federal Regulations(10 CFR Part 50).BackgroundThe possibility of power oscillations due to thermal-hydraulic instabilitiesin boiling water reactors (BWRs) and the consequences of such events have beenof concern for many years. The staff evaluated thermal-hydraulic stability asGeneric Issue B-19 and recommended closure actions for resolution of thatissue in Generic Letter 86-02, "Long-Term Solutions to Thermal-HydraulicInstabilities in Boiling Water Reactors," which requested BWR licensees toexamine each core reload and to impose operating limitations, as appropriate,to ensure compliance with GDC 10 and 12. GDC 10 requires that the reactorcore be designed with appropriate margin to assure that specified acceptablefuel design limits will not be exceeded during any condition of normaloperation, including the effects of anticipated operational occurrences.GDC 12 requires assurance that power oscillations which can result inconditions exceeding specified acceptable fuel design limits are either notpossible or can be reliably and readily detected and suppressed.On March 9, 1988, LaSalle Unit 2 experienced an instability event. The workby both the staff and industry organizations following the event has providedadditional insight into thermal-hydraulic instabilities in BWR cores. TheLaSalle event is described in NRC Information Notice 88-39, "LaSalle Unit 2Loss of Recirculation Pumps With Power Oscillation Event," dated June 15,1988. NRC Bulletin 88-07, also dated June 15, 1988, highlighted the genericconcerns identified in light of the LaSalle event and requested all BWR9407010241 PD0 AbocK oS0ooo0) P CI(O 91

\-> VGL 94-02July 11, 1994 licensees, regardless of BWR type or analytical core stability margin, toreview the adequacy of procedures and instrumentation to respond to poweroscillations, and requested review of operator training programs with regardto power oscillations. In response to these concerns, the BWR Owners' Group(BWROG) initiated a project to investigate actions that should be taken toresolve the BWR stability issue.On October 28, 1988, the General Electric Company (GE) notified the NRC under10 CFR Part 21 that thermal margins might not be sufficient to preventviolation of the minimum critical power ratio safety limit for some BWR plantsif a 10-percent average power range monitor (APRM) oscillation was used as aprocedural action point for manual scram of the plant. Based on thispossibility, GE recommended stability "interim corrective actions" in aNovember 1988 letter to BWR utilities. On December 30, 1988, the NRC issuedBulletin 88-07, Supplement 1, approving the proposed BWROG/GE interimoperating recommendations and stating additional conditions. One of theseconditions addressed the applicability of the experience-based stabilityexclusion boundaries defined in the interim operating recommendations, andnoted the need to reevaluate and justify these boundaries for cores thatinclude new fuel designs. This bulletin also discussed long-term correctiveactions. Such corrective actions might include hardware modifications oradditions to facilitate manual or automatic protective response to avoidneutron flux oscillations or to suppress oscillations should they occur.Since it is possible for some oscillations to grow to levels exceeding NRCsafety limits in the order of a minute, automatic protection action isgenerally indicated. The detailed design specifications for the automaticprotection are being defined by an expanded post-LaSalle BWROG study todevelop a generic resolution to the stability issue.In June 1991, the BWROG issued NEDO-31960 (Ref. 1) which documented proposedlong-term solutions to the stability issue as well as methodologies that havebeen developed to support the design of these long-term solutions. Supple'ment 1 to NEDO-31960 (Ref. 2) was issued in March 1992 and contained finalmethodology details and additional information requested by the NRC. By aJuly 1993 letter from A. C. Thadani (NRC) to L. A. England (BWROG), the NRCtransmitted its safety evaluation report (Ref. 3) on NEDO-31960 and itsSupplement 1 to the BWROG. Reference 3 describes the results of the staffreview of the proposed solution concepts and their associated methodologies.This generic letter requests information about licensee plans for implementa-tion of the approved solution concepts and actions taken in response to laterBWROG guidance and stability experience until the long-term solution is imple-mented. This resolution assumes the protection system will function whenrequired and does not consider the combination of instability and anticipatedtransients without scram (ATWS). That subject is being addressed by other NRCand BWROG activities.Need for Enhancement of Interim Ogerating RecommendationsIn early 1992, the BWROG, citing its continuing studies, provided its membersadditional guidance on implementation of the interim recommendations forstability actions attached to NRC Bulletin 88-07, Supplement 1. In the 1992 GL 94-02July 11, 1994 guidance, the BWROG emphasized the need for caution when operating near theexclusion regions and recommended reexamination of procedures and training toensure that uncertainties in the definition of exclusion region boundarieswere appropriately reflected. The NRC staff considered this guidance inconjunction with an Augmented Inspection Team (AIT) review of a WashingtonNuclear Power Unit 2 (WNP-2) 1992 instability event. The AIT report (Ref. 4)discusses that review and the BWROG guidance.On August 15, 1992, Washington Nuclear Power Unit 2 (WNP-2) experienced poweroscillations during startup. The WNP-2 operators recognized the oscillationsand responded promptly, consistent with their procedures and training, toinitiate a manual scram. The NRC evaluated this event, concluding thatthe primary cause of the oscillations was very skewed radial and bottom peakedaxial power distributions due to insufficient procedural control of controlrod removal patterns during power ascension. It was concluded fromdiscussions with other licensees that similar procedural practices were notunusual for some other BWRs. The skewed power distributions make the coretend towards the "harder to detect" out-of-phase oscillation mode. TheWNP-2 power distribution was inconsistent with the more normal operatingconditions that have been associated with the experience-based stabilityexclusion boundaries, and was also inconsistent with the power distributionassumptions employed in the methodology for development of long-term solutionexclusion region boundaries based only on power and flow parameters. TheWNP-2 core design, consisting of a mixture of 9x9 and 8x8 fuel types whichcaused unbalanced flow and pressure drop characteristics, was also acontributor to uncertainty in its stability exclusion boundary. The WNP-2event is described in NRC Information Notice 92-74, "Power Oscillations atWashington Nuclear Power Unit 2," dated November 10, 1992.Most of the BWROG long-term solutions proposed in NEDO-31960 (Ref. 1) involvesubstantial modifications to the plant protection system hardware; thesemodifications are not expected to be ready for implementation until 1995-1996.The staff review of analytical studies in support of these solutions, theadditional guidance provided by the BWROG, and the circumstances leading tothe WNP-2 event, have identified the following items which are appropriate toenhance the effectiveness of the interim procedures and training, implementedin response to Bulletin 88-07, Supplement 1, until implementation of the long-term solutions can be accomplished:(1)Bulletin 88-07, Supplement 1, requested licensees of BWRs to takeactions including a procedural requirement for a manual scram under allcircumstances in which there are no recirculation pumps operating withthe reactor in the RUN mode. This action was not applicable to plantswith effective automatic scram protection against out-of-phase regionaloscillations.Bulletin 88-07, Supplement 1 indicated that a flow-biasedAPRM scram circuit without a simulated thermal power monitor (filteredAPRM signals) would provide such protection. However, more recentanalyses by the BWROG show that the flow-biased APRM scram does notprovide sufficient protection for the out-of-phase mode of instability,which can produce very large asymmetric oscillations before exceedingthe average power scram setpoint. The need for protection against GL 94-02July 11, 1994 out-of-phase oscillations remains under review for a few small coreplants with small inlet orifices. Likewise, NRC plant-specific reviewsare incomplete for the BWR2 plants, Oyster Creek and Nine Mile Point 1,to ensure the effectiveness of the quadrant based APRM scram protectionprovided for these plants. Therefore, prior to completion of reviews ofthe long-term solutions for individual plants, all plants are assumed tohave ineffective scram protection against out-of-phase oscillations andshould comply with the Bulletin 88-07, Supplement 1 requested proceduralrequirement for manual scram.(2)Bulletin 88-07, Supplement 1, endorsed the experience-based power/flowboundaries of the interim corrective actions based on the assumptionthat other factors important to the core stability characteristics(e.g., radial and axial peaking, feedwater temperature, and thermal-hydraulic compatibility of mixed fuel types) were consistent withprevious experience and the bounding values expected during normaloperation. The BWROG studies and the precautions recommended in theearly 1992 letter to its members indicated that uncertainties existed inthe definition of these boundaries (Ref. 4). The WNP-2 instabilityevent and subsequent NRC evaluation determined that some licensees mayhave given inadequate attention to the impact on core stability of thereload core design and operating procedures for changing reactor power.The WNP-2 experience also highlighted the value of using on-linestability monitors as an operational aid to avoid unstable operation;the capability for on-line stability monitoring does not exist currentlyfor most BWRs.Reauested Actions1. All licensees of BWRs, except for Big Rock Point which does not have thecapability for operation under variable flow conditions, are requestedto review their current procedures and training programs and modify themas appropriate to strengthen the administrative provisions intended toavoid power oscillations or to detect and suppress them if they occurprior to implementation of the long-term solutions. The experiencegained at WNP-2 should be a primary guide in this review. In doingthis, each licensee of a BWR (except for Big Rock Point) should:a. Ensure that procedural requirements exist for initiation of a manualscram under all operating conditions when all recirculation pumpstrip (or there are no pumps operating) with the reactor in the RUNmode, and ensure that operators are aware of the potential for verylarge power oscillations and the potential for exceeding corethermal safety limits before automatic protection systems functionfollowing the trip of all recirculation pumps (the procedural manualscram is not necessary after long-term solutions are approved andimplemented for individual plants); andb. Ensure that factors important to core stability characteristics(e.g., radial and axial peaking, feedwater temperature, and thermalhydraulic compatibility of mixed fuel types) are controlled withinappropriate limits consistent with the core design, power/flow GL 94-02July 11, 1994 exclusion boundaries, and core monitoring capabilities of thereactor in question, and that these factors are controlled throughprocedures governing changes in reactor power, including startup andshutdown, particularly at low-flow operating conditions. Eachlicensee should review its procedures and determine if instabilitycan be avoided by these procedures and if the procedures can becarried out using existing instrument information. If it isconcluded that a near-term upgrade of core monitoring capability iscalled for to ease the burden on operators, determine the need toincorporate on-line stability monitoring or monitors for stabilitysensitive parameters and inform the NRC of the schedule andtechnical evaluation for such upgrades found to be necessary.(These procedural operation controls will no longer be necessary forlicensees which implement fully automatic long-term solutions, suchas Options III or 111a of Reference 2. Licensees should propose forplant-specific review the administrative controls to be retained inconjunction with other long-term solutions.)2. All licensees of BWRs, except for Big Rock Point, are requested todevelop and submit to the NRC a plan for long-term stability correctiveactions, including design specifications for any hardware modificationsor additions to facilitate manual or automatic protective responseneeded to ensure that the plant is in compliance with General DesignCriteria 10 and 12. An acceptable plan could provide for implementingone of the long-term stability solution options proposed by the BWROGand approved by the NRC in Reference 3 or in subsequent documentation.The plan should include a description of the action proposed and aschedule of any submittal requiring plant-specific design review andapproval by the NRC and an installation schedule (if applicable). Theplan should also address the need for near-term and long-term technicalspecification modifications. Generic BWROG documents or plannedsubmittal may be referenced in the plan.Reporting RequirementsPursuant 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 BWR, except for BigRock Point, shall:1. Within sixty (60) days of the date of this letter:a. Inform the NRC, in writing and under oath or affirmation, of thelicensee's plans and status with respect to the actions requested inthis letter; andb. If the licensee does not plan to take an action requested in thisletter, the reasons for not taking the action, a description of thenature of any substitute action, and a schedule for completing orimplementing the substitute action;2. If the licensee plans to take an action requested, or a substituteaction, within thirty (30) days of the completion of the action, inform vJ-2 GL 94-02July 11, 1994 the NRC, in writing and under oath or affirmation, of the action takenand verify its completion or implementation.Each submittal shall be addressed to the U.S. Nuclear Regulatory Commission,ATTN: Document Control Desk, Washington, DC 20555. A copy shall also besubmitted to the appropriate Regional Administrator.This generic letter requires submittal of information that will enable the NRCto verify that the licensee is complying with its current licensing basisregarding GDC 10 and 12. Accordingly, an evaluation justifying thisinformation request is not necessary under 10 CFR 50.54(f).References1. NEDO-31960, "BWR Owners' Group Long-Term Stability Solutions LicensingMethodology," June 1991.2. NEDO-31960, Supplement 1, "BWR Owners' Group Long-Term StabilitySolutions Licensing Methodology," March 1992.3. Letter from A. Thadani, NRC, to L. A. England, Chairman, BWR Owners'Group, Acceptance for Referencing of Topical Reports NEDO-31960 andNEDO-31960, Supplement 1, "BWR Owners' Group Long-Term StabilitySolutions Licensing Methodology," dated July 1993.4. Letter from J. B. Martin, NRC, to A. L. Oxsen, Washington Public PowerSupply System, "NRC Augmented Inspection of Washington Nuclear Project,Unit 2", September 29, 1992.

Paperwork Reduction Act Statement

The information collections contained in this request are covered by theOffice of Management and Budget clearance number 3150-0011, which expiresSeptember 30, 1994. The public reporting burden for this collection ofinformation is estimated to average 300 hours0.00347 days <br />0.0833 hours <br />4.960317e-4 weeks <br />1.1415e-4 months <br /> per response, including the timefor reviewing instructions, searching existing data sources, gathering andmaintaining the data needed, 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, 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 procedurereviews and implementation of changes;

V v'-' GL 94-02July 11, 1994 (2) the licensee staff time and costs to prepare the requested reports anddocumentation;(3) the additional short-term costs incurred to address the changes, such asthe costs of the corrective actions or the costs of down time; and(4) an estimate of the additional long-term costs that will be incurred as aresult of implementation commitments.

Backfit Discussion

This generic letter defines the requested actions and reporting requirementsfor all holders of operating licenses for BWRs, except for Big Rock Point, inorder to enhance the current interim operating recommendations and to providea long-term solution to the issue of thermal-hydraulic instabilities in BWRs.The staff has concluded that these requested actions are a backfit that isnecessary to ensure compliance with GDC 10 and 12. The basis for thedetermination is stated in the preceding discussion of the generic letter(Background section). Accordingly, pursuant to 10 CFR 50.109(a)(4)(i), abackfit analysis is not required.If you have any questions about this matter, please contact the technicalcontact listed below or the appropriate NRR project manager.AddPa in#mancie irector for ProjectsOffice o Nuclear Reactor RegulationTechnical contact: Larry Phillips, NRR(301) 504-3232Attachment:List of Recently Issued NRC Generic Letters I-> K> AttachmentGL 94-02July 11, 1994 LIST OF RECENTLY ISSUED GENERIC LETTERSGenericDate ofTc--nTceitaA TnLetter Subject Ibbucilvs .aJ2M WV94-0186-10,SUPP. 1REMOVAL OF ACCELERATEDTESTING AND SPECIAL RE-PORTING REQUIREMENTS FOREMERGENCY DIESEL GENERATORSFIRE ENDURANCE TESTACCEPTANCE CRITERIA FORFIRE BARRIER SYSTEMS USEDTO SEPARATE REDUNDANTSAFE SHUTDOWN TRAINS WITHINTHE SAME FIRE AREA (SUPP. 1 TOGL 86-10, "IMPLEMENTATION OFFIRE PROTECTION REQUIREMENTS")05/31/9403/25/94ALL HOLDERSNPRsALL HOLDERSFOR NPRsOF OLs FOROF OLs OR CPs89-10,SUPP. 693-0893-0793-06INFORMATION ON SCHEDULEAND GROUPING, AND STAFFRESPONSES TO ADDITIONALPUBLIC QUESTIONSRELOCATION OF TECHNICALSPECIFICATION TABLES OFOF INSTRUMENT RESPONSETIME LIMITSMODIFICATION OF THE TECH-NICAL SPECIFICATION ADMINI-STRATIVE CONTROL REQUIRE-MENTS FOR EMERGENCY ANDSECURITY PLANSRESEARCH RESULTS ONON GENERIC SAFETY ISSUE 106,"PIPING AND THE USE OFHIGHLY COMBUSTIBLE GASES INVITAL AREAS"03/08/9412/29/9312/28/9310/25/93ALL LICENSEES OFOPERATING NUCLEARPOWER PLANTS AND HOLDERSOF CONSTRUCTION PERMITSFOR NPRsALL HOLDERS OF OLs FORNPRsALL HOLDERS OF OLs ORCPs FOR NPRsALL HOLDERS OF OLs ORCPs FOR NPRsOLCPNPR=OPERATING LICENSECONSTRUCTION PERMITNUCLEAR POWER REACTORS

GL 94-02July 11, 1994 (2) the licensee staff time and costs to prepare the requested reports anddocumentation;(3) the additional short-term costs incurred to address the changes, such asthe costs of the corrective actions or the costs of down time; and(4) an estimate of the additional long-term costs that will be incurred as aresult of implementation commitments.

Backfit Discussion

This generic letter defines the requested actions and reporting requirementsfor all holders of operating licenses for BWRs, except for Big Rock Point, inorder to enhance the current interim operating recommendations and to providea long-term solution to the issue of thermal-hydraulic instabilities in BWRs.The staff has concluded that these requested actions are a backfit that isnecessary to ensure compliance with GDC 10 and 12. The basis for thedetermination is stated in the preceding discussion of the generic letter(Background section). Accordingly, pursuant to 10 CFR 50.109(a)(4)(i), abackfit analysis is not required.If you have any questions about this matter, pleasecontact listed below or the appropriate NRR projectcontact the technicalmanager.Otrnal signed byRoy P. ZimmermanAssociate Director for ProjectsOffice of Nuclear Reactor RegulationTechnical contact: Larry Phillips, NRR(301) 504-3232Attachment:List of Recently Issued NRC Generic LettersAlso See SECY 94-171 1)OGCB/DORSNRR AC/4CBHi ORS:NRRPWen W> N R i RDennig07/-7/94 'ft' ' 07/1/94DO NRRes17/i /94* a fillADPR gP~.RPZim Jrman07/ J /94 The Commissioners-3 -The staff intends to issue this generic letter approximately 10 working daysafter the date of this information paper.oXilin*1 stnned by"lS^:tnt%: r. TOWTJames M. TaylorExecutive Directorfor Operations-I:Atjk SL& < .LI) X 4 JA'Enclosure:Proposed Generic Letter Titled RLong-Term Solutions and Upgrade of InterimOperating Recommendations for Thermal-Hydraulic Instabilities in Boiling WaterReactors"*err WrVTniic rnmriivvrwrr-acr fIl eMAL rrsc E wuv wvI-OFFICE OGCB/DORS* SRXB/DSSA* SC:SRXB/DSSA* PM:PDII* TECH ED* AC:SRXB/DSSA*NAME PCWen HRichings LPhillips PO'Connor RSanders TCollinsDATE 05/16/94 05/16/94 05/16/94 05/17/94 05/17/94 05/19/94I A IAnnf.nlCCA* I Anl.nlVA*nc.r*ACr¶ fl(q nRS*I n -t6RSZ_/I ADTAAU~i ./AADPR/NRRRJones MVirgilio SLewis RJKiessel j_ L7III AT0 5 fn 0P' L 0/94e6 405/20/94 05/21/94 J 5259 05/31/94 f 4__0& 9 06,'7 /94 j--I1D:EMDQj~06/7j/94 ==-DOCUMENT NAME: PWINSIB.LUMIi~,CUKNFEOT UAME Po1Z THE QT-XEZJ~C, LErrkZ- pwwhsTe -6