Information Notice 1988-72, Inadequacies in The Design Of DC Motor-Operated Valves

Inadequacies in The Design Of DC Motor-Operated Valves

ML031150133
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, Three Mile Island, 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, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	09/02/1988
Revision:	0
From:	Rossi C E Office of Nuclear Reactor Regulation
To:
References
IN-88-072, NUDOCS 8808300018
Download: ML031150133 (9)

UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555September 2, 1988NRC INFORMATION NOTICE NO. 88-72: INADEQUACIES IN THE DESIGN OF DC MOTOR-OPERATED VALVES

Addressees

All holders of operating licenses or construction permits for nuclear powerreactors.

Purpose

This information notice is being provided to alert addressees to potentialproblems in the design specifications of dc motor-operated valves, especiallyfor conditions that may involve reduced or degraded dc voltage and/or elevatedtemperatures. It is expected that recipients will review the information forapplicability to their facilities and consider actions, as appropriate, toavoid similar problems. However, suggestions contained in this informationnotice do not constitute NRC requirements; therefore, no specific action orwritten response is required.

Description of Circumstances

On July 1, 1988, a high pressure coolant injection (HPCI) steam admission valvefailed to open during a post-maintenance test at the Brunswick nuclear powerplant, Unit 1. The same valve had failed in December 1987 and on May 28, 1988.The licensee, Carolina Power and Light Company, established a team to investi-gate the cause of failure, and the team identified the most probable cause asa dc motor failure due to a shunt-winding to series-winding short circuit. Theteam believed that this condition was precipitated by thermal binding of thevalve internals. The previous failure in May was also diagnosed as having beencaused by thermal binding. As a result of these failures, the licensee reviewedthe design of the dc motor-operated valves for both the HPCI and the reactorcore isolation cooling (RCIC) systems. This review identified a number ofsignificant design deficiencies going well beyond the problems with thermalbinding. The deficiencies constitute a potential common cause failure mechanismfor safety-system valves. Unit 1 was shut down on July 14, 1988 to replace thefailed HPCI valve motor and to implement design modifications to other motor-operated valves.Discussion:Pressure locking and thermal binding of gate valves were identified as poten-tially important valve failure mechanisms within the nuclear industry several880830018tA"Py-

.IIN 88-72September 2, 1988 years ago. Pressure locking occurs when a gate valve is closed under fullsystem pressure and fluid is trapped in either the bonnet cavity or betweenthe disks of a double disk valve. When the valve is subsequently heated, thetrapped fluid expands or flashes to steam and causes pressure to increase inthe valve bonnet area and between the wedges of the valve disk. The pressureincrease inhibits opening of the valve by causing the wedges to press tightlyagainst the valve seats, resulting In binding of the valve. This phenomenoncontributed to the May 1988 HPCI valve failure. To prevent recurrence-of thisfailure, the licensee drilled a small drain hole in the upstream disk to providea pressure relief path. This remedy was only partially successful because thevalve also underwent thermal binding, which was not recognized at that time.Thermal binding occurs when a valve is seated in a hot condition and, duringsubsequent temperature changes, the valve body contracts a proportionallygreater amount than the valve internals because of the different expansionand contraction characteristics of the valve body and the disk. This isparticularly true for valves with internals which have reduced clearancesdue to improper maintenance or alterations. Several potential remedies havebeen suggested to alleviate this situation, including slightly opening andreclosing a valve during cooldown, limiting valve actuator closing forces,and using compensating spring packs to reduce valve inertial closing forces.In general, neither ac nor dc valve motor operator sizing analyses accountfor the extra torque needed to unseat a valve when it is thermally bound.It should be noted that certain valves may become functionally inoperablewhen conditions induce thermal binding.The dc motor operator design problems discovered at Brunswick as a result ofthe review following the July 1 HPCI valve failure were attributed by thelicensee to a lack of design coordination and inadequate consideration ofthe valves' functional operability requirements by the architect engineeringfirm, United Engineers and Constructors. The licensee found that inadequatetorque was available to open the valves, particularly under reduced dc busvoltage conditions, and when MOVs were installed in locations that are-normallyat elevated ambient temperatures. Reduced or degraded dc bus voltage conditionscould occur during accidents in which battery charging capability is lost (forexample, during a station blackout or failure of the chargers). Four designflaws were identified in the licensee's review.(1) The specified motor operator torque was found to be deficient. Also,the design temperatures-used for sizing the motors were found to bebelow the actual ambient temperature in which some valves were oper-ating. Thus, the motors were unable to develop the torque requiredto unseat (open) the valves under reduced dc voltage conditions. Ad-ditionally, the operability of some of the valves during accidentconditions, such as high-energy line breaks, was questionabl IN 88-72September 2, 1988 (2) The presence of starting resistors and their impact on startingtorque were not considered in motor sizing. The resistors wereinstalled to limit the dc current until the motor starts and ac-celerates toward rated speed. However, they were found to reducethe "hammer blow" effect needed to ensure valve opening. They alsoincreased the potential for motor stalling against a seated valve.(3) Cable resistance contributed to reduced motor terminal voltage andstarting current. As a result, actual torque supplied by the motorwas further reduced.(4) High-voltage transients were induced in the dc motor's shunt windingswhenever the motor's power supply circuit breaker was opened. (Insome cases, high voltage transients may also result when motor startercontacts are opened in installations in which the shunt field is setup for intermittent service; i.e. energized only when the armature isenergized.) This process led to degradation of the insulation on theshunt and field windings.These dc motor-related design flaws were not uncovered during routine surveil-lance testing nor during post-maintenance testing. In part, this was becausedc voltage was normally maintained at or above nominal values by battery chargersoperating "in float" with the batteries when the tests were conducted. Thus,design flaws related to reduced dc voltage performance would not be readilydetected.Additionally, Motor Actuator Characterizer (MAC) traces were made from valvetests performed during certain maintenance testing activities. These-MACtraces indicated anomalies in valve performance. However, the deviationsfrom expected performance were subtle. Careful engineering review was neces-sary to properly interpret these traces.The corrective actions taken by the licensee included removal of starting re-sistors, replacement of certain motors and cable, and the addition of metaloxide varistors to dissipate induced voltage transients during power supplyinterruptions. (Discussions with Limitorque have revealed that, for the pastfive years, the company has recognized the need to control voltage transientsin their motor operators. Therefore, they have included depictions of voltagesurge suppression devices in their electrical drawings for their motor-operatedvalves.)It is important to note that the removal of dc motor operator starting resistorsmay cause a significant increase in the 1-minute load on the station's batteries.A battery performance assessment was conducted by the Brunswick licensee toensure that the dc power system continued to meet plant safety analysis require-ments following removal of the resistor IN 88-72September 2, 1988 No specific action or written response is required by this information notice.If you have any questions about this matter, please contact one of the technicalcontacts listed below or the Regional Administrator of the appropriate regionaloffice.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts: P. W. Baranowsky, NRR(301) 492-1157E. N. Fields, NRR(301) 492-1173

Attachment:

List ofRecently Issued NRC Information Notices AttachmentIN 88-72September 2, 1988 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to88-7188-7088-69Possible EnvironmentalEffect of the Reentryof COSMOS 1900 andRequest for Collectionof Licensee RadioactivityMeasurements Attributedto That EventCheck Valve InserviceTesting ProgramDeficienciesMovable Contact FingerBinding in HFA RelaysManufactured by GeneralElectric (GE)9/1/888/29/888/19/88All holders of OLsor CPs for nuclearpower reactors, fuelcycle licensees, andPriority 1 materiallicensees. -All holders of OLsor CPs for nuclearpower reactors.All holders of OLsor CPs for nuclearpower reactors.88-48,Supplement 1Licensee Report of DefectiveRefurbished Valves8/24/88All holders of OLsor CPs for nuclearpower reactors.88-6888-6788-66Setpolnt Testing of Pres-surizer Safety Valves withFilled Loop Seals UsingHydraulic Assist DevicesPWR Auxiliary Feedwater PumpTurbine Overspeed TripFailureIndustrial RadiographyInspection and EnforcementInadvertent Drainages ofSpent Fuel PoolsReporting Fires in NuclearProcess Systems at NuclearPower Plants8/22/888/22/888/22/888/18/888/18/88All holders of OLsor CPs for nuclearpower reactors. -All holders of OLsor CPs for nuclearpower reactors.All NRC industrialradiography licensees.All holders of OLsor CPs for nuclearpower reactors andfuel storage facilities.All holders of OLsor CPs for nuclearpower reactors.88-6588-64OL = Operating LicenseCP = Construction Permit IN 88-72September 2, 988No specific action or written response is required by this information notice.If you have any questions about this matter, please contact one of the technicalcontacts listed below or the Regional Administrator of the appropriate regionaloffice.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:P. W. Baranowsky, NRR(301) 492-1157E. N.(301)Fields, NRR492-1173

Attachment:

List of Recently Issued NRC Information Notices* see previous concurrence*OEAB:NRR *OEAB:NRR *RPB:ARMPBaranowsky NFields TechEd8/12/88 8/12/88 8/04/88*C:OEAB:NRRWLanning8/12/88*D:DEST:NRRLShao8/17/88*C: OGCB: NRR&!~VCCHBerlinger CERossi8/25/88 8/3//88 IN 88-August , 1988 ( some cases, high voltage transients may also result when motorsta er contacts are opened in installations in which the shuntfield is set up for intermittent service, i.e. energized only whenthe arm ture is energized.) This process led to degradation of theinsulati on the shunt and field windings.These dc motor-relate design flaws were not uncovered during routinesurveillance testing no0during post-maintenance testing. In part this wasbecause dc voltage was no ally maintained at or above nominal values bybattery chargers operating 'in float" with the batteries when the tests wereconducted. Thus, design fla related to reduced dc voltage performance wouldnot be readily detected.Additionally, Motor Actuator Cha terizer (MAC) traces were made from valvetests performed during certain main enance testing activities. These MACtraces indicated anomalies in valve rformance. However, the deviations fromexpected performance were subtle. Car ful engineering review was necessary toproperly interpret these traces.The corrective actions taken by the licens included removal of startingresistors, replacement of certain motors and able, and the addition of metaloxide varistors to dissipate induced voltage t ansients during power supplyinterruptions. (Discussions with Limitorque ha revealed that, for the pastfive years, the company has recognized the need t control voltage transients intheir motor operators. Therefore they have include depictions of voltagesurge suppression devices in their electrical drawin for their motoroperated valves.It is important to note that the removal of dc motor oper tor starting resistorsmay cause a significant increase in the 1-minute load on t station'sbatteries. A battery performance assessment was conducted t ensure that thedc power system continued to meet plant safety analysis requi ments followingremoval of the resistors.No specific action or written response is required by this informa ion notice.If you have any questions about this matter, please contact the tech icalcontact listed below or the Regional Administrator of the appropriate egionaloffice.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor Regulation

Technical Contact:

P.W. Baranowsky(301) 492-1157E.N. Fields(301) 492-1173 p

Attachment:

List of Recently Issued NRC Information Notices* see previous concurrence M145*OEAB:NRR *OEAB:NRR *RPB:ARM C:OEAB:NRR D:DEST:NRR C:OGCB:NRR D:DOEA:NRRPBaranowsky NFields TechEd WLanning LShao CHBerlinger CERossi/ /88 / /88 / /88 / /88 / /88 J'/,S88 / /88 IN 88-August , 1988 (In me cases, high voltage transients may also result when motorstarte contacts are opened in installations in which the shuntfield i set up for intermittent service, i.e. energized only whenthe armat e is energized.) This process led to degradation of theinsulation the shunt and field windings.These dc motor-related d ign flaws were not uncovered during routinesurveillance testing nor ing post-maintenance testing. In part this wasbecause dc voltage was norma ly maintained at or above nominal values bybattery chargers operating in oat with the batteries when the tests wereconducted. Thus, design flaws elated to reduced dc voltage performance wouldnot be readily detected.Additionally, Motor actuator charac rizer (MAC) traces were made from valvetests performed during certain mainte nce testing activities. These MACtraces indicated anomalies in valve pe ormance. However, the deviations fromexpected performance were subtle. Caref 1 engineering review was necessary toproperly detect and interpret these trace The corrective actions taken bythe licensee included removal of starting r sistors, replacement of certainmotors and cable, and the addition of metal ide varistors to dissipateinduced voltage transients during power supply interruptions. (Discussionswith Limitorque have revealed that for the past five years the company hasrecognized the need to control voltage transients in their MOVs. Thereforethey have included depictions of voltage surge sup ression devices in theirelectrical drawings for their MOVs.)It is important to note that the removal of dc motor o erator starting resistorsmay cause a significant increase in the 1-minute load batteries. A batteryperformance assessment was required to ensure that the d power systemcontinued to meet plant safety analysis requirements folbo ing removal of theresistors.No specific action or written response is required by this inf mation notice.If you have any questions about this matter, please contact the echnicalcontact listed below or the Regional Administrator of the appropr ate regionaloffice.Charles E. Rossi, DirectorDivision of Operational Events Assessm tOffice of Nuclear Reactor Regulation

Technical Contact:

P.W. Baranowsky(301) 492-1157E.N. Fields(301) 492-1173

Attachment:

List of Recently Issued NRC Information Notices*See previous concurrence*OEAB:NRR *RPB:ARM C:; P NRR D:D W R C:OGCB:NRR D:DOEA:NRRIB ranowsky NFields Tech.Ed. WLanning I, o CHBerlinger CERossiM 17/88 g.//i8/ /8/ 8 //(V 88 /17/88 / /88 / /88

+ W4 YOU IN 88-<AX August , 1988 Motor act tor characterizer (MAC) traces were made f om valve tests performedduring certa maintenance testing activities. These traces indicated anomaliesin valve perfo ance. However, the deviations from expected performance weresubtle. Careful gineering review was necessary to properly detect andinterpret these tra s. The corrective actions taken by the licensee includedremoval of starting re istors, replacement of certain motors and cable, and theaddition of metal oxides ristors to dissipate induced voltage transients duringpower supply interruptions IIt is important to note that t removal of dc motor operator starting resistorsmay cause a significant increase n the 1-minute load on batteries. A batteryperformance assessment was require to ensure that the dc power systemcontinued to meet plant safety analy s requirements following removal of theresistors.No specific action or written response is equired by this information notice.If you have any questions about this matter please contact the technicalcontact listed below or the regional/dminist tor of the appropriate regionaloffice.

Technical Contact:

P.W. Baranowsky(301) 492-1157Charles E. Rossi, rectorDivision of Operatio _ EventOffice of Nuclear Reac r Re(LtA MAJ 1o fNorhcStE.N. Fields(301) 492-1173A1"^,o+: *u5+- , 9t .CAOY TES&*0EAB:NRR 10EAB:NRR TV)OEs C:4EAB:NRRPBaranowsky 8 Fields Wianning/o5/88 £/of/88 'i/O9I/88 / /88D:DEST:NRRLShao/ /88C:OGCB:NRRCHBerlinger/ /88D:DOEA:NRRCERossi/ /88