ML20116P191

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Auxiliary Feedwater System RISK-BASED Inspection Guide for the Maine Yankee Nuclear Power Plant
ML20116P191
Person / Time
Site: Maine Yankee
Issue date: 10/31/1992
From: Bumgardner J, Gore B, Moffitt N, Vo T
Battelle Memorial Institute, PACIFIC NORTHWEST NATION
To:
Office of Nuclear Reactor Regulation
References
CON-FIN-L-1310 NUREG-CR-5826, PNL-7654, NUDOCS 9211240398
Download: ML20116P191 (35)
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NUREG/CR--5826 x

PNL-7654 Auxiliary Feedwater System Risk-Basec Inspection Guide i

for the Maine Yankee Nuclear Power Plant 4

1 1(G re,T. V. Vo, N. E. Moffitt, J. D. Bumgardner Pacific Northwest Laboratory Operated by llattelle Memorial Institute Prepared for

U.S. Nuclear Regulatory Commission PR ADO O

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g AVAILABILITY NOTICE Avai;absinty of Reference Matenais Crted in NRC Pubhcatons Most documents cited in NRC publications wm be avalr',lo from one of the following sources:

1.

The NRC Public Document Room. 2120 L Street, NW, Lower Level, Washington, DC 20555 2.

The Superintendent of Documents, U.S. Government Pririting Office, P O. Box 37082. Washington, DC 20013-7082 3.

The National Technicalinformation Service, Springfield, VA 22161 Although the isting that follows represents the majority of documents cited in NRC publications, it is not intended to be exhaustive.

Referenced documents available for inspection and copyin',

  • a fee from the NRC Public Document Room include NRC correspondence and internal NRC memorartf. jRC bul!etins, circulars, hformation notices, inspection and investigation notices; heensee event reports; vendor rei> orts and corrsspondence: Commis-slon papers; and apphcant and licensee cocumems and correspondence.

The foilowing documents in the NUREG sortes are available for purchase from the GPO Sales Program:

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Neither the United States Govemment nor any agency thereef, or any of their employees, makes any warranty, expresseur impileo, or assumes any legal llab;lity of responsibility for any third party's use, or the results of such use, of any information, apparatus, product or process disclosed in this report, or represents that its use by such third party would not infringe privately owned rights.

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NUREG/CR-5826 PNL-7654 Auxiliary Feedwater System Risk-Based Inspection Guide for the Maine Yankee Nuclear Power Plant Manuscript Corapleted: September 1992 Date Published: October 1992 Prepared by B. F. Gore, T. V. Vo, N. E. Moffitt, J. D. Ilumgardner Pacific Northwest laboratory Richland, WA 99352 Prepared for Division of Radiation Protection and Emergency Preparedness Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555 NRC FIN L1310

L 4

Abstract In a study sponsored by the U.S. Nuclear Regulatory Commission (NRC), Pacific Northwest Laboratory has developed and applied a methodologv for deriving plant-specific risk based inspection guidance for the auxiliary feedwater

. (AFW) system at pressurized water reactors that have not undergone probabilistic risk assessment (PRA).- 31s methodology uses existing PRA results and plant operating experience information. Existing PRA-based inspection guidance information recently developed for the NRC for various plants was used to identify generic component failure modes This information was then combined with plant-specific and industry-wide component information and failure data to identify failure modes and failure mechanisms for the AFW sptem at the selected plants. Maine Yankee was selected as one of a series of plants for study. He product of this effort is a priontized listing of AFW failures which have occurred at the plant and at other PWRs. Ws listing is intended for use by NRC inspectors in the preparation of inspection plans addressing AFW risk-important components at the Maine Yankee plant.

iii -

NUREG/CR-5826

Contents Abstract ill Summary.

17 Acknowledgments.

xi i introduction......

1.1 2 Maine Yankee AFW Splem.

2.1 2.I Sptein Description.

2.I 2.2 Success Criterion 2.1 2.3 System Dependencies.

2.1 2.4 Opcrational Constraints 2.2 3 Inspection Guidance for the Maine Wnkee AFW System..

3.1 3

11 Risk Important AFW Cnmponents and Ibilure Modes..

3.1 3.1.1 Multiple Pump Failures due to Common Cause 3.1 1.1.2 hrhine Driven Pump P-25B Fails to Start or Run...

3.2 3.1.3 Motor Driven Pump P-25A or P-25C Fails to Start or Run.

3.3 1.4 l'urnp P-25A, P.25B,or P 25C Unavailable Due to Maintenance or Surveillance.

3.1.5 Air Operated Isolation and Flow Control Valve Pailure 3.1.6 Mam al Suction or Discharge Wives Fall closed 3.1.7 Leakare of Ilot Feedwater through Check Wlves 3.5 3.2 Risk important AFW Sptem Walkdown Table 3.5 4 Go.cric Risk insights from PRAs 4.1 4.1 Risk Important Accident Sequentes involving AFW Spiem Failure 4.1 4.1.1 less of Power System.

4.1 4.1.2 'Hansient-Caused Reactor or 'lbibine 'Itip.

4.1 4.1.31nss ol Main Feedwater 4.1 4.1.4 Steam Generator hbe Rupture 4.2 4.2 Risk im[ortant Component Failure Mot c.

4.2 5 Failure Modes Determined ftom operating Experience 5.1 5.1 Maine %ntec Experience,

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l 5.1.1 Motor Drive n Pump l2 llu r es.......................................................

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5.1.2 Flow Control %1ve Failures........................

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5.1.3 AIM Chec k %)ve Failu i es..........................................................

5.1 5.2 I n d us t ry Wid e Ex pe r ie n ce..................................................................

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5.2.1 C4mirnon Ca use Fail u r es.............................................................

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!.. t l l u r na n Er r o r s.......................................................................

5.3 5.e.3 Design /Enginecting PtnNems and Errors.............................................

5A 5.2A Co m pone n t Fa il u r es................................................................

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6.1 6 R e fe r en Ct'5..................................................................................

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Figures 2.1 M a i n e Ya n kee A IM sys t e m....................................................................

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'lbbles 3.1 Risk irnjortant AFW system w:tikdown tab!c...................................................,

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Summary 1his document presents a wmpilation of auxiliary feedwater (AFW) system failure information which has been screened for risk tnificance in terms of failure frequerny and degradation of system performance it is a risk-I prioritired listi 4 nll. 'ure events and their asuses that are signifkant enough to warrant consideration in inspection planning at the Mai% Yankee plant. This information is presented to provide inspectors with increased resources for inspection planning at Maine %nkec.

The risk importance of various component failure modes was identified by analysis of the results of probabilistic risk a.ucssments (PRAs) for many pressurized water reactors (PWRs). liowever, the component failure categories identi.

fled in PRAs are rather broad, because the failure data used in the PRAs is an aggregate of many individual failures havinE a variety of root causes. In order to help inspectors focus oli specific aspects of cornponent operation, mainte-nance and design which might cause these failures, an extensive review of component failure information was per-formed to identify ar.d rank the root causes of these comsment failures. Iloth Maine Yankee and industry wide fail.

ute information was analyzed. Pallure causes were sorted on the basis of frequency of occurrence and seriousness of consequence, and categorlied as common cause failures, human errors, design problems, or con,pment failures.

'this information is presented he the tu!y of this document. Section 3.0 provide brief descriptions of these risk impor.

tant failure causes, and Section 5,0 presents more extensive discussions, with specific examples and references, lhe entiles in the two sections are cross referenced.

L An abbreviated system walkdown table is presented in Section 3.2 which includes only components identified as risk important.1his table lists the system lineup for normal, standby system operation.

This information permits an inspector to concentrate on components important to the prevention of core damage, llowever,it is important to note that inspections should not focus exclusively on these componerits, Other compo-nents which perform essential functions, but which are not included because of high reliability or redundancy,inust also be addressed to ensure that degradation does not increase their failure probabilities,and hence their ilsk importance.

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Acknowledgmei.ts We wish to thank the Maine Yankee Atomic Power Company for reviewing and validating this report. Their input to Section 4 provided plant specific EFW/AISV failure mode infortnatiori based on the Maine Yankee PRA, helping to make this report a more useful trapcction tool. 'their co operation is gically appreciated.

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xi NUREO/CR 5326 o

1 Intratiuction 3

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  • Ihis document is one of a series providing plant 4pecific The remainder of the document is a discussion of the ir -

inspection guidance for auxiliary Icedwater (AIM) sys-formation used in compiling this inspection guidance, terns at pressurited water fcactors (PWRs). This guld-Section 4.0 providea insights to the risk linportance in-ance is based on information frorr, probabilistic risk formation which has been derived from PR As and its assesstnents (FRAs) for similar PWRs, industry wide f.ourms. As review of that section will show, the failure operating experience with AFW systems, plant 4pecific categories identified in PRAs are rather broad (e.g.,

AFW system descriptions, and plant 4pecific operating pump falls to start or run, valve fails closed). Section 5.0-experience, it is not a detailed in'pection plan, but addresses the specific failure causes which have been rather a compilation of AFW system failure information combined under these categorlet i

which has been screened for risk significance in terms of failure frequency and degradation of system perform.

AIM system operating history was studied to identify ance. 'the result is a risk prioritlico listingof failure the various specific failures which have been aggregated events and their causes that are significant enough to into the PRA failure gnode categories. Section 5.1 warrn,nl consideration in inspecilon planning at the presents a summary 01 Maine Yankec failure informa.

Maine Yankee plant.

tion, and Section 5.2 presents a review ofin lustry wide failure information. The industry. wide information was

'Ihis inspection guidance is presented in Section 3.0, fol-compiled from a variety of NRC sources, including lowing a description of the Mainc Yankee Al'W system AEOD analyses and reports,information notices,In-In Section 2.0, Section 3.0 identifies the risk important spection and enforcement bulletins, and generic letters, system components by Maine Yankee identification and from a variety of INPO reports as well. Some number, followed by brief desc:1ptions of crch of the Licensec Event Reports and NPRDS event descriptions urious failure causes of that component._ These include s cre also resiewed Finally,information was included specific human errors, design deficiencies, and hardware from reports of NRCap(msored studies of the cfIcets o' failures. 'the discussions also identify where common plant aging, which include quantitative analyses of--

cause failures have affected inultiple, redundant compo-reported AFW system failures. 'this industry-wide in-nents. These brief discussions identify specific aspects -

formation was then combined with the plant 4pecific of system or mmponent design, operation, maintenance, f ailure information to identify the various root causes of or testing fr,r inspection by observation, records resiew, the PRA fallare categories, which are identified in training observation, procedures review.or by observa.

Section 3.0.

-tion of the implementation of procedurss. An AFW system walkdown table identifying risk important com-ponents and their lineup for normal, standby system operation is also provided.

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P 2 Maine Yankee AFW Systern

'lhh section presents an ovenlew description of the have had their internal parts removed. Power, control, Maine Yankee Emergeng and Auxiliary I'cedwater and instrumentation associated with each rnotot drivta system, including a simplified schematic system diagram.

pump are independent from one another Steam for the

'Ib be c4msistent with other inspection guides, the turbine driven pump is supplied from the main steam Maine Yankee EISV/AIAV system will be refert:d to e sptem from a point upstream of the main steam non.

Al%Y remgnizing that the plant specific designation is return valves,through MS-P-168. Each AITV pump is technically the EISV spicm. In addition, the system equipped with a recirculation flow sptem, which pre-success criterion, system dependencies, and admMhtra-vents pump deadheading, tive operational constraints are aho preAented Each AITV pump discharge is provided with a check valve and h>eally operated isolation valve Each motor.

2.1 Systen

Description driven ^laV pump supplies feedwater to all three sicam generators. 'lhe turbine-driven pump is connected to The Al4V splem provides feedwater to the steam the motor-driven pumps discharge cross tic line and is pencrators (SG) to allow secondary-side heat tornoval the primary method of short term feedwater supply to from the primary sptem when main feedwater is un-all three steam generators during an Appendh 'R' fire scenario and station blackout.

available. The system is capable of functioning for ex.

tended periods, which allows time to testore main feed-The DWSTis the normalsource of water for the AISV water flow or to proceed with an orderly cooldown of the plant to where the residual heat removal (RilR) sys.

Splem and is required to store sufficient demineralized tem can remove decay heat. A simplified schematic dia-water (l(0/XX) gallons) to maintain the reactor coolant gram of the AISV system b shown in Figure 2.1, system (RCS) at hot standby conditions for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> with steam discharge to atmosphere. All tank connections The system consists of three feedwater pumps that are except those required for instrumentation, emergency arranged in parallel. 'Iko pumps (P 25 A & C) are fec4 water pump suction, chemical analysis, and tank motor driven and are classified as emergency feedwater drainage are located above this minimum level. AFW (EIAV); the third pump (P-25 li) is tuibine-driven and is sm tion may also be switched to the primary water stor-normally called the auxiliary feedwater (AITV) pump age tank using the alternative suction valves, and is used during plant startup and shutdown condi-tions. 3e emergency system is designed to start up and estabihh flow automatically, lloth motor-driven pumps 2.2 Success Criterion start on receipt of a steam generator low level signal if there is no bus 5 or 6 undenultage condition, if an Sptem success requires the operation of at least one undervoltage c(mdition exists, the motor-driven pumps pump supplying rated flow to at least one of the three are started by the loading sequencer thirty seconds after steam generators, the die, sci generator re-energhes the respective bus.

There is no automatic start associated with the turbine-driven pump, however, it can be manually started to feed 2.3 Systent Dependencies the steam generators if needed.

The AITV system depends on AC power for motor-The normal AITV pump suction is from the dem, eral' driven pumps and level control' valves, DC power for m

ited water storage tank (DWST) with the primary water control power to pumps and valves, and an automatic storage tank serving as a backup water source. Each actuation signal. In addition, the turbine-driven pump pump draws from a common header through an isola.

also requires steam availability.

tion valve end a check vahe (EFW-1,43 and 306) that 2.1 NUREO/CR 5826

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Maine Yankte AFW System 2.4 Operational Constraints down to hot standby within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. With two motor-d;iven pumps inoperable, the plant must be shut down to hot standby within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. With all three pumps

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During power operation the Mainc Yankee ikhnical inoperable, corrective action to restore at least one Specifications require that three independent AFW pumps and associated flow paths are operable with each pump to operable status must be initiated as soon as motor-driven pump posered from a separate emergency possible.

bus. If one AFW pump becomes inoperable,it must be ne Mainc Yankee ikhnical Specifications require a restored to operable status within 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> (7 days) or minimum inventory of over HU/XU gallons (.1 hou_t the plant must shut down to hot standby within the next supply) of primary grade water be maintained during sit hours. If the tutbine-driven pump and one rnotor, driven pump arc inoperabic, the plant must be shut plant operation.

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3 Inspection Guidnnce for flic Mnine Yankee AFW System In this section the risk important components of the 3.1.1 Multiple Pump Failures due to Conirnon Maine %nkee A'M system are identified, and the im-Cause portant modes by w hich they are likely to fail are briefly desciibed. 'Ihese h ilure modes include specific human 1hc following listing summarizes the most important errors, design problems, and types of hardware failures multiple-pump failure rmxles identified in Section 5.2.1, which have been observed to occur for these types of Common Cause Failures, and each item below is keyed components, both at Maine %nkee and at PWRs with a 3 digit code to entrics in that section. For exarn-throughout the nuclear industry.1hc discussions also plc, the first item below relates to Common Cause Pail-idernily where nimmon cause failures have affected ute CCl as shown by the 3 digit code following the item.

multiple, redundant components. These brief discus-lb examine Common Cause Failure CCl turn to Sec-slons identify specific aspects of system or component tion 5.2.1 under the CCl entry.

design, operation, maintenance, or testing for observa-tion, records review, training observation, procedures inwrrect operator intervention into automatic sys-teview or by observation of the implementation of tem functioning, including improper manual statt.

Pf"CCd"'CS-ing and securing of pumps, has caused failure of all pumps, including overspeed trip on startup, and ina-Thble 3.1 is an abbresiat(J AIM system walkdown table -

bility to restart prematurely secured purnps. CCl.

which identifies risk important components. This table lists the system lineup for norinal, standby system opct-Inyction Suggntion Observe Abnormal and ation. Inspection of the components identified addres' Emergency Operating Procedure (AOP/EOP) simu-ses essentially all of the risk associated with AIM sp-lator training exercises to verify that the grators tem operation.

comply with proadures during observed es '.tlons.

Observe surveillrice testing on the AIM system to verify it is in strin ompliance with the surveillance 3.1 Risk linportant AFW Components icst procedure, and Failure Modes Wlve mispositioning has caused failure of all Common cause failures of multiple pumps are the most pumps. Pumpsuction steam supply,andinstru-ment isolation valves have been involved. CC2.

risk-important failure modes of AIM system compo-nents.1hese are followed in importance by single pump failures, level control valve failures, and individual check Inspdon Suggetbn Verify that the system valve 4

valve backicakage failures.

alignment, air operated valve control and valve actuating air pressures are correct using 3.1 \\%1k-1he following scetions address each of these failure down Table, the system operating procedurcs, and modes, in decreasing order of importance.1 hey present operator rounds logsheet. Review surveillance pro-the important root causes of these component failure cedures that alter the standby alignment of the modes which have been distilled from historical records.

AIM system. Ensure that an adequate return to normal section exists.

Each item is keyed by a three digit mde to discussions in Section 5.2 which present additional information on his-torical events.

Steam binding has caused failure of multiple pumps.

This resulted from leakage of hot feedwater past i

3.1

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Impection Guidance check valves and a motor-operated valve into a mm.

maintenance and test pmcedures. Examples include mon discharge header. CClo. Multiple-pump if the AIM system has an emergeng source from a steam binding has also resulted frorn improper valve water system with the potential for bio fouling. then lineups, and from running a pump deadheaded.

the system should be periodically treated to prevent CC3.

buildup and routirely tested to assure an adequate flow can be achieved to support operation of all Inspection Sugestion. Verify that the purnp dis.

pumps, or inspected to assure that bio.foulingis not charge temperature is within the limits specified on occurring. Design changes that affect the suction the operator rounds logshect. Assure any instru-flow path should repeat testing that verified an ade-ments used to verify the temperature by the utility quate suction source for simultaneous operation of are of an appropriate range and included in a call-all pumps.

bration program. Verify affected pumps have been vented in accordance with procedures to ensure 3.1.2 Thrbine Driven Pump P.2511 Falls to steam binding has not occurred. Verify that a Start or Run maintenance work request has been written to repair leaking check valves.

improperly.ljusted and inadequately maintained Putnp control circuit deficiencies or design modifi-tur bine governors have caused pump failures, lie 2, Problems include worn or loosene4 nuts, set screws, cation errors have caused failures of snultiple purnps linkages or cabic connections, oll leaks and/or to auto start, spurious pump trips during operation, matamination, and electrical failures of resistors, and failures to restart after pump shutdown, CC4.

transistors, diodes and circuit cards, and erroneous 1

Incorrect setpoints and c4mtrol circuit calibrations grounds and connections. CN.

have also prevented proper operation of multiple purnps. CC5.

Inspection Sugestion. Review PM records to inspection Sugestion Review design change assure the governor oilis being replaced within the implementation documents for the post mainte-designated frequeng. During plant walkdowns carefully inspect the governor and linkages for loose nance testing required prior to returning the equip-ment to service. Assure the testing verifies that all fasteners, leaks, and unsecured or degraded amdult.

potentially impacted functions operate correctly.

and includes repeating any plant r, tart-up or hot Ibrbines with Woodward Model PO.PL governors functional testing that may be affected by the design have tripped on overspeed when restarted shortly change-after shutdown, unless an operator has kically exercised the speed setting knob to drain oil from i

Simultaneous startup of multiple purnps has caused the governor speed setting glinder (per procedure).

Automatic oil dump valves are now available l

oscillations of pump suction pressure causing through'Rrry. DE4.

multiple-pump trips on low suction pressurc, despite the existence of adequate static nel positive suction head (NPSif). CC7. 'this is not a problem Ingction Sugestion Observe the operation of at Mainc Yankee because there are no low suction the turbine driven Aux Fecd pump and assure the pressure trips. At li.!L Robinson, design reviews governor is reset as directed by the merating pro-have identified inadequately sired suction piping cedure. Assure the turbine is not coasting over when in standby which can result in refill of the which could have yielded irnufficient NPSil to suP' speed setting cylinder, port operation of more than one pump. CC8.

C4mdensate slugs in steam lines have caused turbine Inspertion Sugestion - Assure plant mnditions which could result in the bhickage or degradation of overspeed trip on startup. 'Ibsts repeated right after the suction flow path are addressed by system such a trip may fall to indicate the problem due to -

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t Inspection Guidance warming and clearing of the steam lines. Surveil.

breaker. (Control circuit stabs have to make up lance should exercise all steam supply c mnections.

ulxm racking the breaker, control power must be DE2. This is not expected to be a problem at Maine restored, and cell switch damage can occur upon Yankee due to system design.

removal and reinstallation of the breaker.)

Ingertion Sugestion Verify steam traps are Mispositioning of handswhches and procedural valved in on Ihe steam supply line. For steam traps deficiencies have prevented automatic pump start.

that are on a pressuriicd portion of the steam line, llE3.

check the steam trap temperature (if unlagged) to assure it is warmer than ambient (otherwise it may Inqicction Sugestion Confirm switch position us.

be stuck or have a plugged line). If the steam trap ing1hble 3.1 Review administrative procedures discharge is visible, assure there is evidence of liquid concerning documentation of procedural deficien.

discharp cles. Ensure operator training on procedural changes is current.

Vip and throttle valve (MS.T-173) problems which have !alled the turbine driven pump include physi.

Iow lubrication oil picssure resulting from hestup cally bumping it, failure to reset it following testing, due to previous operation has prevented pump and failures to verify c(mtrol toom indication of restart due to failure to satisfy the protective reset. IIE2 Whether either the overspeed trip or interkick. DE5.

TfV trip can be reset without resetting the other, and unambiguity of omtrol room and local indica.

Inyiection Suge tion - Assure the pressure tion of TTV position and overspeed trip linkage switches are in a calibration program, and oil filters reset status affects the likelihood of these errors.

and oil are monitored and changed in acmidance DE3.

with the PM program. Assure controls exist for the use of the correct viscosity oil when adding to or Inqicction Sugestion Carefully inspect the TfV changing the oil.

overspeed trip linkage and assure it is rev't and in gomi physical condition. Assure there is a good 3.1.4 Pump P 25A, P-25ft, or P 25C Unavall-steam isolation to the turbinc, otherwise continued able Due to Maintenance or Surveillance turbine high temperature can result in degradation of the oilin the it.:bine interfering with proper Both scheduled and unscheduled maintenance re-overspeed trip operation.

rnove the system from operability. Surycillance re-quires operation with an altered line-up, although a 3.1.3 Motor Driven Pump P-25A or P 25C pump may not be declared inoperable during test.

l' alls to Start or Run ing. Appropriate scheduling and prompt perform-ance of maintenance and sctveillances minimlic this

  • Control circuits used for automatic and manual unavailability, pump starting are an important cause of motor driven pump failures,as are circuit breaker failures.

Inspection Sugestion Review the time the AFW CF7. Similar failures have also occurred at Maine system and components are Inoperabic. Assure all Yankec.

maintenance is being performed that can be per-formed during a single outage time frame, avoiding Inspection Sugestion - Review corrective mainte-multiple equipment outages.- The maintenance nance records when control circuit problems oaur should be scheduled before the routine surveillance to determine if a trend exists. Every time a breaker test, so credit can be taken for both post mainte-is racked in a PMT should be performed to start the nance testing and surveillance testing, avoiding pump assuring no mntrol circuit problems have excessive testing. Res few surveillance schedule for occuind as a result of the manipulation of the 3.3 NUREO/CR-5826

-I

Inspection Guidance frequency and adequaq to verify system operability 3.1.6 Manual Suction or Discharge Valves Fall requirements per 'Ibchnical Specifications.

Closed 3.1.5 Air Operated Isolntion and Fimy Control TD Pump P 25D: %1ves EIA%2 or AIA%20 Valve }' allure MD Pump P-25A: Wives EIA%'t or EIA%17 MD Pump P-25C: Wlves EIA%307 or EIAV 316 Flow Centr 01 %1ves: FIAvl01.201.301 holatlon W lves: EIAV 338. 339. 340 These manual vahts ate normally locked open. For each pump ch>sure of the first valve listed would block

'These normally open air operated valves (AOW) isolate suction to the pump. Closure of the sec(md valve would and control flow to the steam generators. '! hey fall open bh>ck all pump discharge except recirculation to the -

on loss ofinstrutnent fair.

DWST.

Wlve mispositioning has resulted in failures of Control problems have been a primary cause of fall-utes, both at Maine %nkee and elsewhere. CI9.

multiple trains of AIAV. CC2. It has also been the

%lve failures have resulted from blown fuses, fall-dominant cause of problems identified during oper-ute of control components (such as current /pneu-ational readiness inspections.1IE1. Events have j

matic mnvertors), broken and dirty contacts, mis-occurred most often during maintenance,calibra-aligned or I roken limit switches, mntrol power loss, tion, or system modifications. Important causes of and calibration problems. Degraded operation has mispositioning include:

also resulted from improper air pressure due to air Failure to provide complete, clear, and specific regulator failure or leaking air lines. Mechanical wear and slippage of mechanical adjustments have procedures for tasks and system restoration caused flow control valve f ailures at Maine Wnket Pailure to promptly revise and validate pro-Inspection Sugestion Check for control air system cedures, training, and diagrams following system alignment and air leaks during plant walkdowns.

modifications (Regulators may have a small amount of external Failure to complete all steps in a procedure biced to maintain downstream pressure.) Check for cleanliness and physical condition of visibic circuit I allure to adequately review uncompleted pro-elements. Review valve stroke time surveillance for adverse trends, especially those valves on reduced cedural steps after task completion testing frequency. Review air sptem suncillances Failure in verify support functions after moisture content of air is within established limits.

restomion Out-of. adjustment electrical flow controllers have caused improper valve operation, affecting multiple Failure to adhere scrupulously to administrative trains of AFW. CC12 procedures regarding tagging, control and track-ing of valve operations Inspation Sumestion - Review PM frequency and records if a trend of valve controller failure occurs.

Failure to log the manipulation of scaled valves l

NUREG/CR-5826 3)

Inspection Guidance 4

Ibilure to follow good practices of written task Slow leakage past the final check nive of a series assignment and feedback of task completion may not force upstream check *;4lves closed, allow-information ing leakage past each of them in turn. Piping orien-tation and valve design are important factors in Failure to provide easily read system drawings, achieving true series protection. CFl.

legible valve labels corresp(mding to drawings and procedurcs, and labeled indications of kical inspection Suggestion Covered by 3.1.1 bullet 3.

valte position Inspection Suggestion Review the adtninistrative 3.2 RiskImportant AFW System controls that relate to valve positioning and scaling, Walkdown "lhble system restoration following maintenance, valve labeling, system drawing updating, and procedure revision, for proper implementation.

'Pable 3.1 presents an AFW system walkdown table in-cluding only components identified as risk important.

3.1.7 leakage ofIlot Feedwater through Wsinf rmati nall wsinspect rs t c ncentrate their Check Valves efforts on components important to prevention of core damage. However,it is essential to note that inspections should not focus exclusively on these com-At MFW cimnectiont %Ives EIM-1R 2% 304 ponents. Other components which perform essential At Pump Discharres: Wlves EFW ls.18. 314 functions, but which are absent from this table because of high reliability or redundang, should also be lxakage of hot feedwater through several check addressed to ensure that their risk importances are not valves in series has caused steam binding of multiple inercased. Examples include the (open) steam lead iso-pumps. leakage through a closed level control lation valves upstream of MS-T 173, an adequate water valve in series with check valves has also occurred, level in the DWST, and the (closed) valves cross con-as would be required for leakage to reach the motor necting the sections of the motor-driven pumps to the driven pumps P25A and P25C. CC10.

primary water storage tank and the discharges of the ins;wetion Suggestion Covered by 3.1.1 bullet 3.

- 3.5 NUREG/CR-5826

?

Inspection Guidance hble 3.1 Risk Important AITV system wulkdown table Component 1(equired Actual Number Component Name location Position Position Jilectrical P-25 A Motor Driven Pump Racked in/

Open Charging Springs Charged P-25 C Motor Driven Pump Racked in/

Open Charging Springs Charged

%Ive ERV1 DWST Discharge %!ve Open with internals -

removed /

hand-whcci removed /

placard in place EFW 2 TDP P25D Suction Wlve 12)cked Open EIAV 3 MDP P25A Suction Wlve Locked Open ERV 43 MDP P25A Suction Check Wlve Internals Removed ERV 17 MDP P25A Discharge Whc l>>cked Open EIAV 306 MDP P25C Suetion Check Wlve Internals Rernoved -

ERY 307 MDP P25C Suction W1ve locked Open Al%V 20 TDP P25B Discharge Wlve locked Open

(

ERV 316 MDP P25C Discharge Whe _

Locked Open NUREC/CR 5826 3.6

=.

Inspection Guidance Table 3.1 (Continued)

Component Required Actual Number Compcment Name location Position Position Wlve EIAV 338 Emergency Feedwater isolation Valve Open*

to SG 13 ETAV 339 Emergeng Feedwater Isolation Wlve Open' to SO l 2 EISV 340 Emergency Feedwater Isolation Wlve Open' to SO l 1 EFW 301 Emergencyliedwater Control Wlvc Open to SO l-3 EFW 201 Emergency Feedwater Control wive Open to SG 12 EFW 1 ~ '

Emergency Feedwater Control Wlve Open to SO 1 1 EFW 42,

MDP P25A Supply Wlve from PWST Closed EFW 4 TDP P23B Supply %1ve from PWST Closed EFW 315 MDP P25C Supply Wlve from PWST Closed MS P-168 TDP Steam Supply Press ire Closed Control Wlve MS-T 173 TDP' Rip and Throttle Wlve Open Governor Wlve Not Closed EFW 21 MDP P25A Recirculation isolation Open Wlve i.

AFW 26 TDP P25B Recirculation isolation Open

- Wlve

' Flats on valve shaft parallelwith pipe.

1 3.7 NUREO/CR 5826

-=-

Inspection _Guldance

'thble 3.1 (Continued)

Component Required Actual Numter Component Name location Position l'osition

.Yit}E EFW 312 MDP P25C Recirculation isolation Open

%lve ERV 11 MDP P25A Oil Cooler Isolation Open W!ve ERY 308 MDP P25C Oil Cooler Isolation Open Wlve ERV304 Piping Upstream of Check Wlve Cool' ERV 204 Piping Upstream of Check Whe Cool' ERV 104 Piping Upstream of Check Wlve Cool' ERV 15 Piping Upstream of Check Wlve Cool' AFW 18 Piping Upstream 01 Check Wlve

- Cool' EFW 314 Piping Upstream of Check Wlve Cool'

  • VVithin 10 F orambient,use, a hand held instrument that is in a calibration program.

t b

l NUREO/CRI5826 3.8

.-.=,. _.. -.. _ _. _ _. _ _,.. _., _ _ _ _ _. _.. _.

b 1

4 Generic Risk lusights frorn PilAs Imu of 4160v AC llus 6 causes a lon of power to PRAs for 12 PWRs were analy7cd to identify risk-important accident sequences involving kns of Alv, P 25A. Thh h followed by failure of the remainder and to identify and risk prioriti/c the comp < ment failure of the EIN/Al'W system. [ Note: At Maine rnodes involved. He results of thb analysis are Yankee, kiss of AC llus 6 causes loss of scamdary described in thh section. They are consistent with component cooling and,if backup cooling is riot i

results reported by INEL and llNL (Gregg et al 1988, credited, instrument air.) His results in loss of and hvis et al,1988).

main feedwater resulting in core damage.

A Station lilatkout is followed by failure of the Maine Yankee Atomic Power Company aho provided input to the laws of Power System section based on the turbine-driven AIM pump,1csulting in core Maine Yankee PRA. Events down to 8E-04 were ex-damage.

amined for risk significant sequences involving AIN/

Station Illackout, operators re4uver one train of EIM Most of theimportant sequeners with AIM /

EIM unavailable involve some type of loss of power.

power; however, EIM/AFW falls, resulting in core With all power / support availabic, Main Feedwater is damage.

available. Therefore, AIM /EIN is less important in Imss of DC3 causes loss of train Il power (P 25A these sequences. At Maine Yankee,instrumen; air and scumdary comp (ment cooling water are dependent on power supply). %ls is followed by fallute of the train 11 and loss of these systems results in a loss of inain remainder of the EIM/ AIM system, resulting in i

feed-water; loss of unin il power tends to be more im-core damage. [Noic: DC3 powers train 11 fast trans.

portant than loss of train A power.

fer, train 11 dicsci start and sequence and train 11 breaker nmtrol.]

4.' Risk liniun-innt Accitlent Sequences 4.1.21ransient Caused Reactor or1brbine 1HP involving AFW System Failure A transient causul trigiis followed by a kss of PCS 4.1.1 IAss of Power Systern and AIM Ferd-and bleed cooling fails either duc to failure of the operator to initiate it,or due to nualloss of Vital iluses causes auto-isolation of all hardware faHures, resulting in mre damage.

I feedwater (spurious SI AS and low steam generator pressure initiate Main Steam Line Break Protec-4.1.3 Loss of Main Feedwater tion). His is followed by operator failure to recover (bypass signal), resulting in core darnage-A fenlwater line break drains the common water source for MIM and AfM The operators fall to loss of Swit< agear Room Ventilation causes a loss of power to the EIM pumps (P-25 A and P-25C).

provide feedwater from other sources, and fall to -

initiate feed-and bleed cooling, resulting in core Dis is followed by (1) a failure of the AIM pump

damage, (P-258), or (2) failure of the EFCV air system, y hich supplies TL25, resat*ing in eventual loss of A loss ot' main feedwater trips the plant, and AfM air required to keep the P., Orl steam admission fails due to operator error and hardware failures.

valves open, or (3) failure of the power supply to the The operators fall to initiate feed-and-bleed cooling, 1

EFCV air system (Appendis R diesel generator).

resulting in core damage.

4.1 NUREG/CR 5826

__.......-_m._

Generic Rhk l

4.1.4 Steam Generator %I>e Rupture now mntrolvalves A SGTR is followed by failure of AITV. Q>olant is pump discharge valves lost from the primary until the RWSTis depleted.

IlPl falh since recirculation cannot be established pump suction valves frorn the empty sump, and core damage results.

valves in testing or maintenance.

4.2 Risk Insportant Component Failure 5-S"pplysuction sources ohs Dcminerallied Water Storage 1hnk The generic component failure modes identified from Prfrnary Water Storagc1hnk PRA analyses as irnportant to AFW system failure are listed below in decreasing order of risk irnportance.

O ndensaic System 1.

~1brbine-Driven Pump Failure to start or Run.

In addition to individual hardware, circuit, or instru-merit Dilures, cach of these failure modes may result 2.

Motor. Driven Pump Failure to Start or Run.

frorn mmmon causes and human errors, Common cau.c failures of AFW pumps are particularly risk 3.

TDP or MDP Unavailable due to Tbst or important. Valve fatturm are somewhat less important Maintenance.

due to the multiplicity of steam generators and c4mnection paths. Iluman errors of greatest risk 4.

AIAV System Valve Failures importance involve: failures to initiate or control system operation when required; failure to restore proper steam admhslon valves splein lineup af ter maintenance or testing; and failure to switch to alternate sources when required.

trip and throttle valve NUREG/CR 5826 4.2

5 / allure Modes Deterinined from Operating Experience His section describes the primary root causes of wm.

from normal wear of valve internals allowing e.wessive ponent failures of the AISV system,as determined from leakage, and slippage of mechanleal adjustments in the a review of operating histories at Maine Yankee and at valve operators.

Other PWR5 throughout the nuclear industry. Sec-tion 5.1 describes experience at Maine Yankee between 5.1.3 AFW Check Valve Failures 1974 and 19'At Section 5.2 summartws information compiled from a variety of NRC sources, including Since 1974 there have been seven events involving AIAV AEOD analyses and repor ts, information notices, in-check valve fallutes resulting in excessive leakage. He spection and enforcement bulletins, and generic letters, failure causes have been wear of valve internals and and from a variety of INPO reports as well. Some defective seal joints.

Liecnsec Event Reports (LERs) and NPRDS event des-criptions were also teviewed. Finally,information was included from reports of NRC sponsored studies of the 5.2 Industry Wide Experience eflects of plant aging, which include quantitative analy-ses of AIAV system failure reports. His information lluman errors, design /enginecting pro 51 cms and errors, was used to identify the various root causes expected for and component failures are the primary root causes of the broad PRA-based failure categories identified in AITV Sptem failures identified in a review of industry Section 4.0, resulting in the inspection guidelines wide system operating history. Common cause failures, presented in Section 3.0.

which disable more than one train of this operationally redundant system, are highly risk significant, and can 5.1 Maine Yankee Experience His section identifies important common cause failure The AFW system at Maine Yankee has experienced ap-modes, and then provides a broader discussion of the proximately 20 significant equipment failures since single failure effects of human enors, design / engineer.

1974. These include failures of the AIAV pumps, the ing problems and errors, and component failures. Para-pump discharge level control valves to steam generators, graphs presenting details of these failure modes are and system check valves, liiiture modes include electri-coded (e.g., CCl) and cross-referenced by inspection cal, instrumentation, and hardware failures.

Items in Section 3.

5.1.1 Motor Driven Pump Failures 5.2.1 Conunon Cause Failures Here have been five failures of the ATTV pumps to start ne dominant cause of AIAV system multiple-train fall-and/or run experienced since 1974. These have resulted ures has been human error. Design / engineering errors from failures of circuit breakers, flow transmitters or and mmponent failures have been less frequent, but other pump related failures. He failure causes are nevertheless significant, causes of multiple train failures.

mechanical wear, corrosion, or inadequate test pro-cedures. Tbilure of the motor-driven pump to achieve CCl. Iluman error in the form of incorrect operator rated speed or discharge pressure has resulted from a intervention into automatic AIAV system functioning worn impdler on the pump.

during transients resulted in the temporary loss of all safety grade AIAV pumps during events at Davis Besse 5.1.2 Flow Control Valve Failures (NUREG-1154,1985) andojan (AEODfr416,1983).

In the Dans Ilesse event, improper manual initiation of There have been three failures of the pump discharge the steam and feedwater rupture control system kvel control valves since 1974. These have resulted 5.1 NUREG/CR-5826 l

Ibilure Modes (SIT (CS) led to overspeed tripping of both turbine-main feedwater. At 71on 2, restart of toth motor driven driven AFW pumps, probably due to the introduction of pumps was bk>cked by circuit failure to deenergize when 4

condensate into the AIM turbines from the long, un.

the pumps had been tripped with an automatic start sig.

heated steam t upply lines. (The splem had noer been nal present (IN 82-01,1982). In addition, AMV control tested with the abnormal, cross <onnected steam supply circuit design reviews at Salern and Indian Point have lineup whkh resulted ) In the 'nojan ornt the operator identified designs where failures of a single component Incorrectly stopped both AIAV pumps due to misin.

muld have failed all or multiple pumps (IN 87 34, j

tetptelation of MISV pump speed indication. The 1987).

j diesel driven pump would not restart due to a protective i

feature requiring complete shutdown, and the turbine-CC5. Incorrect setpoints and control circuit settings

)

Wh:n pump tripped on overspeed, requiring k>eal reset resulting from analpis errors and failures to update pro-of the trip and throttle valve, In cases where manual cedures have also prnented pamp start and caused

.{

intervention is required during the early stages of a pumps to trip spuriously, Eriors of this type may transient, training should emphasite that actions should remain undetected despite surycillance testing, unless i

be performed methodically and deliberately to guard surveillance tests model all types cf sptem initiation against such errors, and operating conditions. A greer fraction ofinstru-mentation and control circuit problems has been Identi.

CC2. Vahe mispositioning has accounted for a signifi, fied during actual system operation (as opposed to sur-cant fraction of the human errors failing multiple trains veillance testing) than for other types of failures.

of AIM. ;~his includes closure of normally open suction valves or steam supply valves, and ofisolation valves to CC6. On two occasions at a foreigri plant, failure of a sensors having control functions, incorrect handswitch balance-of. plant inverter caused failure of two AIM positioning and inadequate temporary wiring changes pumps. In addition to loas of the motor driven pump have also presented autornatic starts of multiple pumps.

whose auxiliary start relay was powerM by the invertor, Factors identified in studies of mispositioning errors the turbine driven pu np tripped on overspeed because include failure to add newly installed valves to valve the governor valve opened, allowing full steam flow to checklists, weak administrative controlof tagging, the turbine. This illustrates the importance of assessing restoration, independent verification, and locked valve the effects of failures of balance of plant equipment logging, and inadequate adherence to procedures. llleg-which supports the operation of critical components.

ible or confusing hscal valve labeling, and insufficient The instrument air splem is another example of such a training in the determination of valve position may sptem.

cause or mask mispositioning, and surveillance which does not excreise complete system functioning may not 007. Multiple AIM pump trips have occurred at rewat mispositionings.

Millstone-3, Cook-1,'nojan and Zion-2 (IN 87 53, 1987) caused by brief, low pressure oscillations of sue-CC3, At ANO-2, both AIM pumps hist suction due to tion pressure during pump startup. These oscillations steam binding when they weic lined up to both the CST occurred despite the availability of adequate stafic and the hot startup/ blowdown demineralizer effluent NPSil, Correcthc actions taken include: extendhsg the (AEOD/C441,1984). At Zion 1 steam created by run-time delay associated with the low pressure trip, remov-ning the turbine-drisen pump deadheaded for one ing the trip, and replacing the trip with an alarm and minute caused trip of a motor-driven pump sharing the operator action.

l same inlet header, as well as damage to the turbine-driven pump (Region 3 Morning Report,1/17NO). Both CG Design errors dhcovered during AIM spiem re-ewnts were caused by procedural inadequacies.

. i slysis at the Robinson plant (IN 89 30,1989) and at Millstone-1 resulted in the supply header from the CST -

CC4. Design / engineering errors hava acco'mted for a being too small to provide adequate NPSII to the smaller, but significant fraction of common cause fail-pumps if more than one of in,. threc pumps were o

ures. Problems with control circuit design modifications operating at rated Dow conditions. This could lead to -

at Farley defeated AIM pump auto. start on loss of multiple pump failure due to cavitation. Subsequent

' NUREG/CR 5826 5.2 a.

l Failure Modes i

reviews at Robinson id:ntified a loss of feedwater on the high torque required to unscat a closed valve, tramient in which inadequate NPSli and flows less than Previous problems with these valves had been addicued design values had occurred, but which were not by increasing the torque switch trip setpoint a fix which remgnited at the time. Event analpis and equipment failed during the event due to the higher torque required trending, as well as surveillance testing which duplicates due to high differential pressure across the valve.

service conditions as much as is practical, can help Similar common mode failures of MOW have also identify such design errors.

owurred in other systems, resulting in luuance of i

Generic letter 89-10,

  • Safety Related Motor-operated l

i CC9. Asiatic clams caused failure of two AFW flow

%1vell: sting and Surveillanu (Partlow,1989)? 1his cxmtrol valves at Catawba 2 when low suction pressure generic lettcr requires lleensecs to develop and caused by starting of a motor-driven pump caused suc-implement a program to provide for the testing, tion source realignment to the Nuclear Service Water inspection and maintenance of all safety related MOW system. Pipes had not been routinely treated to inhibit to provide assurance that they will function when clam growth, not regularly rnonitored to detcet their subjected to design basis conditions.

presence, and no strainers were installed. The r.ced for surveillanec which exercises alternative system oper-CCl2. Other component failures have also resulted in ational modes, as well as complete system functioning, is AFW multi. train failures. These include out.cf. adjust.

emphasi/ed by this event. Spurious suction switchover ment electrical flow controllers resulting in improper has also occurred at Callaway and at McGuire, although discharge valve operation, and a failure of oil cooler no failures :esulted.

cooling water supply valves to open due to sitt cumulation.

CC10. Common cause failures have also been caused by component failures (AEOD/C4N,1984) At Surry 2, 5.2.2 Iluman Errors toth the turbine driven pump and one motor driven pump were declared inoperable due to steam binding 11FJ. The overwhelmingly dominant cause of tiroblems caused by backleakage of hot water through multiple identified during a series of operational readiness check valves. At Robinson-2 Imth motor driven pumps evaluations of AFW systems was human performance, were found to be hot, and both motor and steam driven The majority of these human performance problems pumps were found to be inoperable at different times.

resulted from incomplete and incorrect procedures, llackicakage at Robins (m.2 passed through closed particularly with respect to valve lineup information. A motor-operated isolation valves in addition to multiple study of valve mispositioning events involving human check valves. At Parley, both motor and turbine driven error identified failures in administrative control of tag-pump casings were found hot, although the pumps were ging and logging, procedural mmp.'iance and mmple-not declared inoperable. In addition to multi. train fall-tion of steps, verification of support systems, and inade-ures, numerom b Als of top train failures have quate procedures as important. Another study found occurred,i o ' k the dcQuuen of" Steam 131nding that valve mispositioning events occurred most often oi Amilim A w Pump / as Generic Issue 93.

during maintenana, calibration, or modification activi-This gerv.

resolved by Generic letter 88-03 tics. Insufficient trainingin determining valve position, (Miraglia, m 3, - Ah required licensees to monitor and in administrative requirements for controlling valve AFW piping tem; eratures cach shift, and to maintain positioning were important causes, as was oral task procedures for recogniting steam binding and for restor-assignment without task completion feedback, ing system operability, llE2. %rbine driven pump failures have been caused try CCI1. Common cause failures have also failed motor human errors in calibrating or adjusting governor speed operated valves. Duri9g @

x1lossof feedwater control, poor governor maintenance, incorrect adjust-topen AFW isolation ment of governor valve and overspeed trip linkages, and event at Davis 13csse.17. - :

valves failed to open N vre inadvertently errors associated with the trip and throttic valve.1TV-closed. The failure was t'c s.mproper setting of the associated errors include physically bumping it, failure torque switch bypass sWith which prevents motor trip

'l 5.3 NUREG/CR 5826

~

Pa!!ure Modes to restore it to the correct pmition after testing, and DE4. Startup of turbines with W(xxlward Model PG-failures to verify control room Indication of'!TV posi-PI governors within 30 minutes of shutdown has tion folkswing actuation.

resulted in overspeed trips when the speed $ctting knob was not exerched locally to drain oil from ihe speed set-JJQ. Motor driven pumps have been failed by human ting cylinder, Speed mntrol is based on startup with an errors in mispositionir$ andswitches,and by proadure empty cylinder. Problems have involved turbine -

h deficiencies.

rotation due to both procedure violations and leaking -

steam. Tbtry has marketed two types of dump valves for 5.2.3 Design / Engineering Problerns and automatically draining the oil after shutdown Errors (AEOD/C602,1986).

DM. As noted above, the majority of AIM subsystem At Calvert Cliffs, a 1987 kiss of offsite power event failures, and the greatest relative system degradation, required a quick, mid startup that resulted in turbine has been found to result from turbine-driven pump fall.

trip due to PG PL governor stability problems. He short term corrective action was Installation of r tilfer utes. Overspeed trips of1brry turbines controlled by Woodward governors have lun a significant source of buffer springs (IN 88-09,1988). Surveillance had always these failures (AEOD/C602,1986). In many cases these been preceded by turbine warmup, which illustrates the overspeed trips have been caused by slow response of a importance of testing which duplicates service condi-Wo(xlward Model EO governor on startup,at plants tions as much as is practical.

where full steam flow is alknved immediately. His over-QFh. Reduced viscosity of gear box oil heated by prior F

sensitivity has been removed by installing a startup steam bypass valve which opens first, allowing a control-operation caused failure of a motor driven pump to start led turbine acceleration and buildup of oil pressure to due to insufficient lube oil pressure. Lowering the pres.

control the governor valve when full steam flow is sure switch setpoint solved the problem, which had not

admitted, been detected during testing.

pH. Overspeed trips ofibtry turbines have been DEtj. Waterhammer at Palisades resulted in AIM line caused by condensate in the steam supply lines.

and hanger damage at both steam generators. The AIN Condensate skiws down the turbine, causing the spargers are kicated at the normal steam generator level, governor vah'e to open farther, and ovenpced results and are frequently covered and uncovered during level before the governor valve can respond, after the water fluctuations. Waterhammerin top-feed ringsteam' slug clears. His was determined to be the cause of the generators resuhed in main feedline rupture at Maine loss-of all AIM cvent at Davis Desse (AEOD/602, Yankee and feedwater pipe cracking at Indian Point 2 1986), with condensation enhanced due to the long (M32,1984).

1 length of the cross-connected sicamlines. Repeated tests folk) wing a cold start trip may be successful due to DE7. Mnually reversing the direction of motion of an system heat up.

operating valve has resulted in MOV failures where such loading was not mnsidered in the design (AEOD/

pn3. wrbine trip and throitic valve (ITV) problems C6tu,1986). control circuit design may prevent this, re-aEa significant cause of turbine driven pump failures quiring stroke completion before reversal.

j

- (IN 844). In some cases lack ofITV position indica-tion in the control room prevented recognition of a DE8. At cach of e units of the South 1bxas Project, tripped 1TV. In other cases it was possible to reset space heaters provided by the vendor for use in pre-cither the overspeed trip or the 1TV without resetting installation storage of MOVs were found to be wired in

{

the other. This problem is compounded by the fact that parallel to e Class 1E 125 V DC motors for several the position of the overspeed trip linkage can be mis-AFW valves (IR 50-489/8911; 50-499/N9-11,1989). De leading, and the mechanhm may lack labels indicating valves had been environmentally qualified, but not with.

when it i< in the tripped position (AEOD/C602,1986).

the non safety related heaters energized.

NUREO/CR-5826 5.4 r

m-

,n s

, - ~ w e em rvw

,s m-r,

--r---

-,-m

~

-e-w-~

mm.-

w.

-r

-n.

- w -

i i

f Failure Males i

5.2.4 Cornptment Fnllures suction piping. At a fort n PWR st resulted in a severe waterhammer event. At palo Verde-2 the MFW suction i

Generic issue ll.!!.6.1,'in Situ 'Rsting Of Wlves" was piping was overpressurlied by check valve leakage from -

divided into four sub.luucs (lleckjord,1989), three of the AITV system (Al!OD/C4GI,1984). Gross check which relate directly to prevention of AITV system com.

valve leakage through idle pumps represents a potential i

ponent failure. At the request of the NRC,in-situ test.

diversion of AISV pump flow.

ing of check valves was addressed by the nuclear indus-try, resulting in the El'RI report,' Application Guide.

E$ Roughly one third of AISV system failures have lines for check Wives in Nuclear power plants (11:ooks, twen due to valve operator failures, with about equal i

1988)? This extettsive report provides information on failures for MOW and AOW. Almost half of the MOV check valve applications, limitations, and inspection failures were due to motor or switch failures (Casada, i

. techniques. In4itu testing of MOW was addressed by 1989). An extensive study of MOV events (AEOD/

Generie letter 89-10,

  • Safety Related Motor-Operated CND 1986) indicates continuing inoperability problems i

Wive 'Ihting and Surveillanec" (Partlow,1989) which caused by: torque switth/limil switch settings, adjust-requires licensees to develop and implement a program ments,or failures; motor burnout; improper sizing or for testing, inspection and maintenance of all safety.

use of thermal overload devices; premature degradation l

related MOW. ' Thermal Overload Protection for E!ce.

related to inadequate use of protective devices; damage tric Motors on Safety Related Motor-Operated Wlves.

due to inisuse (valve throttling, valve operator hammer.

Generic issue 11.1M1 (Rothberg,1988)* concludes that ing); mechanical problems (h>osened parts, improper valve motors shot id be thermally protected,yet in a way assembly); or the torque switch bypass cireuh improper-y which emphasizes system f unction over protection of the ly installed or adjusted. The study concluded that cut.

operamr.

tent methods and procedures at many plants are not adequate to assure that MOW will operate when Gl. The common.cause steam binding ef fects of check needed under credible accident amditionsc Specifically, valve leakage were identified in Section 5.2.1, entry a surveillance test which the valve passed might result in CCl3 Numerous single. train esents provide additional undetected valve inoperability due to component failure insights into this problem. In some cases leakage of hot (motor burnout, operator parts failure, stem disc r,cpa.

MITV past multiple check valves in series has occurred ration) or improper positioning of protective devices because adequate valve. seating picaure was limited to (therrnal overload, torque switch, limit switch). Ocnerie the valves closest to the steam generators (AEOD/C404, Lrtter 8910 (partlow,1989) has subsequently required 1984). At Robinson, the pump shutdown procedure was licensees to implement a program casuring that MOV changed to delay closing the MOW until af ter the check switch settings are maintained so that the valves will valves were seated. At Farley, check valves were operate under design basis nmditions for the life of the changed from swing type to lift type. Check vahe plant.

rework has twen done at a number of plants. Different valve designs and manufacturers are f rivolved in this CF5. Comp < ment problems have caused a significant problem, and recurring leakage has been experienced, number of turbine driven pump trips (AEOD/C602,

~

even after repair and replacement.

1986). One group of events involved worn tappet nut faces, loose cable amnections, h>osened set screws, M At Robinson, heating of motor operated valves by improperly latched 'ITW,and improper assembly, Ans check valve leakage has caused thermal binding and fail.

Other involved oilleaks due to component or seat fail-ute of AITV discharge valves to open on demand. At utes, and oli contamination due to poor maintenance Dasis flesse, high differential pressure heross AISV in.

activities. Governor oil may not be shared with turbine jection valves resulting from check valve leakage has lubrication oll, resulting in the need for separate oil

+

prevented MOV operation (AEOD/CNB,1986).

changes. Electrical component failures included transis-tot or resistor failures due to anoisture intrusion, _

CF3. Gross check valve leakage at McGuire and erroneous grounds and connections, diode failures, and -

Robinson causeo overpressuriyation of the A14W a faulty circuit card, 5.5 NUREG/CR.5826 L-

i

\\

b I;ailure Modes 1

i CF6. Electrohydraulic-operated discharge valves have required for MOVs manufactured since 1975. MOV performed very poorly, and three of the five units using refurbishrnent programs may yield other changeovers to j

them have removed them due to recurrent failures.

EP-0 greasc.

+

Failures included oil leaks, contaminated oil, and hydraulic purnp failures.

[Ey Ihr AFW 5ptems using air operated valves, almost half of the system degradation has resulted from C17. Control circuit failures were the dominant source failurcs of the valve amtroller circuit and its instrument of motor driven AFW pump failures (Casada,1989).

inputs (Casada,1989). P,illures occurred predominantly TMs includes the controls used for automatic and at a few units using automatic electronic controllers for manual starting of the pumps, as opposed to the instru-the flow amtrol valves, with the majority of failures due mentation inputs. Most of the remaining problems were to electrical hardware. At Tbrkey Ibint 3, controller due to circuit breaker failures.

malfunction resulted fiam waterin the Instrument Air i

sptem due to maintenance inoperab'llty of the air QT. *1lydraulic lockup

dryers, packs has preventco proper spring mmpresslor to actuate the MOV torque swi'ch, due to grease trapped CF10. For sptems using dicsci driven pumps, most of in the spring pack. During,

.veillance at 'Dojan, fail-the failures were due to start control and governor speed ute of the torque switch to trip thc1TV motor resulted control circuitry lialf of these occurred on demand -

in tripping of the thermal overload device, leaving the opposed to during testing (Casada,1989).

turbine driven purnp inoperable for 40 days until the next surveilboce (AEOD/E702,1987). Problems result CFil. For sptems using AOVs, operabl;ity requires the from grease,. anges to EXXON NEBULA EP-0 grease, availability of instrurnent Alt, backup alt, or backup one of only two greases considered environmentally nitrogen.1lowever, NRC Maintenance ' Ram Inspec-qualified by I a nitorque. Due to lower viscosity,it slow-tions have identified inadequate testing of check valves ly migrates from the gear case into the spring pack isolating the safety related portion of the I A sptem at Grease changeover at Vermont Yankee affected 40 of several utilities (letter, Roc to Richardson). Generic the older MOVs of which 32 were safety related. Grease letter 88-14 (Miraglia,1938), requires licensecs to relief kits are needed for MOV operators manufactured verify by test that air-operated safety related compo-before 1975. At Limerick, additional grease relief was nents will perform as expected in accordanx with all design basis events, including a k>ss of normal IA.

1 NUREG/CR 5826 5.6

~n

i I

l J References J

lleckjord, E. S. June ) 0,1989. Closcout of Gt ric /ssee AEOI) Regerte ll.E.hl, 'in Situ lhting ofl'ahrs.* lxtter to V.

cllo, Jr., U.S. Nuclear Regulatory Commission, h ngton, AEOD/C441. W. D. lanning. July 1984. Steam Binding DC ofAuriliaryFredwater}%mps. U.S. Nuclear Regulatory Commission, Washington, DC l

iltooks, B. P.1988. Application Guidelines for Check lahrs in Nuclearlbwer flants. NP 5479, Electtic AEOD/CM2. C lisu. August 19% Operational i

Power R~scarch Institutc, Palo Alto, CA.

Erperience Invoh'ing 71 tbtne Oirnpred 7)ips. U.S.

Nuclear Regulatory Commission, %hshington, DC Casad:s, D. A.1989. nuxiliary Fredwater System Aging Dudy. V <lume 1. Operating Esperience and Current ABODIC603. E. J. lltown. December 19% A Rcriew

\\fonitonny Practices. NUREGICR-b404. U.S. Nuclcar of Alotor.Opcrated l'ah c Performance. U.S, Nuclcar Regulatory Commission, %hshington, DC Regulatory Commission, Washington, DC Gregg, R. E, and R. E. Wright.1988. Appendir Review AEOD/E702. E.J. Brown. March 19,1987. Afol' forIkominant Generic Contributors. BLB.3188. Idaho failure Due to Hylraulie Lockup l>vm Encessive Grease National Engineering 121mratory, Idaho Falls, Idaho.

in SpringPack. U.S. Nuclear Regulatory Commission.

Washington, DC Miraglia, E J. February 17,1988. Resolution ofGeneric Safety issue 93, ' Steam Binding ofAuxiliary Ferdwa'er AEODfl'416. January 22,1983. Exss ofESFAntiliary 1%mps* (Generic Letter 88 03). U.S. Nuclear Regulatory Fredwater 1%mp Capability at 7Fejan on January 22, Commission, Washington, DC 1981 U.S. NucJear Regulatory Commission, Washington, DC.

Miraglia, E J. August 8,1988. Instrument Air Supply System l>oblems Affecting Safety-Related Equipment information Notiers (Generic Letter 88-14). U.S. Nucleat Regulatory Commission, Washington, DC IN 82-01. January 22,1982. Auriliary Feedwater ihmp Lockout Resultingfrom 1l'estinghouse IV 2 Switch Circuit Partlow, J. O. June 28,1989 Safety-Related Afotor.

Afwhfication. U.S. Nuclear Regulatory Commission, Operated l'ah'e Testing and Sunrillance (Generic Letter Washington, DC 3910). U.S. Nuclear Regulatory Commission, Washington, DC IN 84-32. E. L Jordan. April 18,1984. Aurillary FredwaterSpargwandPipe HangarDamage. U.S.

Rothberg, O. June 1988. ThermalOverleedIYotection Nuclear Regulatory Commission, Washington, DC.

for Electric Afotors on Safety-Related Alotor-Operated Undetected Unavailabilityof Iahrs Genericissuell.E.6.1. NURBG 1296. U.S.

IN 844i. August 17,1984.

Nuclear Regulatory Commission, Washington, DC the 7hrhine.Ikiven Auriliary Fredwater 7Fein. U.S.

- Nuclear Regulatory Commission, Washington, DC

'Itavis, R. and J. Thylor.1989. Development of t,

. Guidancefor Generic, Functionalf Oriented PRA. Based iN 87 34. C E. Rossi. July 24,1987. Single Failuresin f

Team inspections for BlVR Plants. identification of Risk-Autiliary Feedwater Systems. U.S. Nuclcar Regulatory important Systems, Compments and fluman Actions.

Commission, Washington, DC TLR-A-3874.T6A, Brookhaven National laboratory, Upton, New York.

t 6.1 NUREGICR 5826 -

- =

. - - -.. =. =

Rcferences IN 87 53. C E. Rossi. October 20,1987. Antillary losgiection Reguirt 1;redwatcr 1%mp Trips Resultingfrotu. vw Suction LYessure. U.S. Nuclear Regulatory Commission, IR 50-489/8911;!0499/8911. May 26,1989. South Whington, DC liaas kject inspection Report. U.S, Nuclear Regulatory Cornmission, Washington, DC, IN 8849. C E. Rossi. March 18,1988. Reduced Reliability of Stram Driven Ausiliary Feedwatcr 1%mps NUREG Htguert Caused byInstabilityof ffinodwardPG.PL Type Governors. U.S. Nuclear Regulatory Commission, NUREO 1154.1985. Loss ofMain andAurillary Washington, DC Feedwater Event at the ihnis Besse Plant on June 9,1985.

U.S. Nuc! car Regulatory Commission, Washington, DC i

IN 8940. R. A. Azua. August 16,1989. Robinson Unli

.? Inadequate NPSil ofAurillary [k edwater 1%mps. Also,

}

Event Notification 16375, August 22,1989. U.S.

Nuclear Regulatory Commission Washington, DC i

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NUREG/CR 5326 PNL 7654 Distribution l

l No. of No. of cootes Ogg OT M rrE 4

Maine Yankee Resident Ininector Omec U.S. Nuclear Reculatory Commiulon J. II.1bylor Dmokhaven National laboratory l

B. K. Orlines Bldg.130 OWIH 9 A2 Upton, NY 11973 E Contel R. 'Itavis OWFN 10 E4 Drookhaven National lateratory Didg.130 i

A. C. Thadani Upton, NY 11973 OWTH SE2 R. Gregy i

G. D.1lolahan EG&O idaho, Inc.

OWTH BE2 P. O, ihn 1625

'I Idaho Falls,ID 83415 S. M. Long OWFN 10 A2 Dr. D. R. Edwards Profcuor of Nuclear Engineering E. it. 'nottier University of Missouri OWFN 14DI Rolla Rolla, MO 65401 K. Campe ONStrE OWFN 1 A2 22 Mfic Northwest Laboraton 10 J. Chung OWlH 10 A2 J. D. Bumgardner L R. Dodo B. E Gore (10) 2 B. homas OWFN 12 H26 N. E. Mof0tt B. D. Shipp U.S. Nuclear ucculatorv Commission -

E A. Simanen Begion_1 T V.Vo-Publishing Coordination C. W. Hehl Tbchnical Report File (5)

W. E Kane l

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UDE BIBLIOGRAPHIC DATA SHEET is - w,,

NUREG/CR-5826 PNL 7654

& t ANs suoma Amiliary Feedwater System Risk-Based Inspection Guide for t* Maine Yankee Nuclear Power Plant

""' 5[,' D D

October 1992

4. flN Om Ga ANT NvMata L1310
6. TYPr QS REPORT
b. AvlHORiki nical BF Gore TV Vo

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NE Moffitt JD Bumgardr.er 4/91 - 9/92

$. PERFORMlfdG OHGAN12 AT ION - N AME AND ADDMEss se, sw.c.e.=

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. on.,.

.i.1 Pacific Northwest Laboratory P.O. Box 999 Richland, WA 99352 Ogago ANizATioN. N Au t *No Acoa oss m..c.

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. u.x N c,

s Division of Radiation Protection snd Emergency Preparedness Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555

10. svPf" EMENT ARY NOTES

' 11. ABSTkACT noo es., mes In a study sponsor.,

by the U.S. Nuclear Regulatory Commission (NRC), Pacific Northwest Laboratory has developed and app'ied a methodology for deriving plant-specific risk-based inspecti" -"idance for the auxiliary feedwater ( AFW) system at pressurized water reactors ut M e not undergone probabilistic risk assessment (PRA). This methodology uses r; etirq PRA results and plant operating experience i nf ormati or..

Existing PRA-basca intpection guidance information recently developed for the NRC for various plants was used to identify generic component failure modes.

This informati..; was then combined Jith plant-specific and industry-wide component informatien and failure data to identify feilure modes and failure mechanisms for the AFW system at the selected plar's. Maine Yankee was sziected as one of a series of plants fer study. The product of this effort is a prioritized listiag of AFW failures wL;ch have occurred at the plant and at other PWRs. This listing i intended for use by NRC inspectors in the preparation of insnection plans addressing AFW rid-important components at the *aine Yankee plan' pt...,#..o r, s i. r am a

u. iar. ;aossotsca:.r ans a.

Unlimited Ihspec'4 a, Risk PRA, Maine Yank.e, Auxiliary Feedwater (AFW)

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Unclassified a..

Unclassified th. NUMBER OF PAGLs 16.PRiC1 I

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Printed on recycled paper i

Federal Recycling Program

NUREG/CR-5826 AUXILIARY FEEDWATER SYSTEM RISK. BASED INSPECTION GUIDE OCTOBER 1992.-

FOR TIIE MAINE VANKEE NUCLEAR POWER PLANT '

UNITED STATES FIRST CLASS MAIL NUCLEAR REGULATORY COMMISSION POSTAGE AND FEES PAID WASHINGTON, D.C. 20555-0001 ussac -

PERMIT NO. G-67 OFFICIAL BUSINESS PENALTY FOR PRIVATE l'SE. $300 L

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