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ACCESSION NBR:8811220122 DOC.DATE: 88/11/15 NOTARIZED: NO DOCKETFACIL:50-275 Diablo Canyon Nuclear Power Plant, Unit 1, Pacific Ga 05000275

AUTH.NAME AUTHOR AFFILIATIONKELLY,W.J.. Pacific Gas & Electric Co.SHIFFER;J.D. Pacific Gas & Electric Co.

RECIP.NAME RECIPIENT AFFILIATION R

SUBJECT: LER 88-017-00:on 880625,excessive reactor coolant sysleakage due to ECCS check valve.

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This voluntary LER is being submitted for informational purposes only as describedin item 19 of Supplement 1 to NUREG 1022.

On June 26, 1988, at 0955 PDT, TS 3.4.6.2. was entered due to excessive leakagethrough ECCS check valve SI-1-8818C which was discovered during a leak test. At1345 PDT, the Shift Foreman declared an Unusual Event (UE) and commenced an orderlycooldown of the RCS. At 1741 PDT, Unit 1 entered Hode 5, and the UE wasterminated. RHR Train A was removed from service and declared inoperable to effectinspections and repairs on valve SI-1-8818C. The one hour emergency reportrequired by 10CFR50.72 was completed at 1359 PDT.

This event was caused by the manufacturer's improper assembly of the check valvehanger bracket and grinding on the swing arm. New internals were 'installed inValve SI-1-8818C and a satisfactory leak test was conducted.

Applicable maintenance procedures will be prepared or revised to includeinstructions for the inspection of check valve internals for similar conditions.Four check valves in similar installations and the "first-off" ECCS check valvesfor Unit 2 were inspected during the second refueling outa'ge. A similar inspectionwi 11 be performed for Unit 1 at the next refueling outage. Procedures will berevised to ensure a thorough review of applicable industry operating experience.

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approximately 900 psig and RCS temperature 340 F following the second. refueling outage. Final system tests were being conducted in preparation for

transition to Hode 3 (Hot Standby).

r i n f v n

A. Event:

On June 25,. 1988, at 0700 PDT, with Unit 1 in Hode 4 at approximately 900psig and 340'F, Surveillance Test Procedure (STP) V-5A, "ECCS Check ValveLeak Test Post Refueling/Post Haintenance" was initiated to testSI-1-8818 A,B,C,D(BP)(V) and 8956(BQ)(V) A,B,C,D ECCS check valves. Dueto mode limitations/plant operating conditions, the valves were tested:.with an applied differential pressure less than rated across .the disc andseating surface of the valve. The STP indicated valve 8818C to beleaking approximately 8 gpm across its seat. (Subsequent investigationby test engineers who performed this STP showed that up to 6.5 gpm of theobserved leakage was due to test valve leakage, not check valve leakage.A flow test concluded that these test valves were not fully seating asrequired.)

On June 26, 1988, at 0955 PDT, the Unit 1 Shift Foreman- entered TechnicalSpecification (TS) 3.4.6.2. due to the apparent excessive leakage throughSI-1-8818C. At 1345 PDT, in accordance with TS 3.4.6.2, the ShiftForeman declared an Unusual Event and commenced an orderly cooldown ofthe RCS. -The one hour emergency report required by 10 CFR 50.72 wascompleted at 1359 PDT. At 1741 PDT, Unit 1 entered Hode 5, and theUnusual Event was terminated. RHR Train A was removed from service anddeclared inoperable to effect inspections and repairs on valveS I-1-881 BC.

Valve SI-1-8818C is a six inch, ANSI pressure class 1500 psi, swing checkvalve manufactured by Velan Corporation. Refer to Figures 1 and 2 forthe following description. The valve was disassembled. The swing armhad been ground on both the top and bottom surfaces, which createdexcessive movement in the disc to swing arm connection. Conversationswith Velan verified that this grinding had been done by Velan to allowmore valve disc freedom of motion for the purpose of obtaining betterdisc to seating surface alignment and contact.

Also, one of the anti-rotation buttons was found to be located partiallyunder one side of the swing arm. By rotating the valve disc with alittle difficulty, one of these buttons could pass completely under theswing arm while the other one would not pass under the swing arm due to

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its slightly larger height. If an anti-rotation button were positionedto be centered under the swing arm, the disc could bind and preventproper alignment, thereby allowing leakage. After the lockwire wasremoved from the nut and stud it was found'that the nut which attachesthe disc to the swing arm could be hand tightened approximately 1/8 of aturn. This 1/8 of a turn would not allow the one antirotation button topass under the swing arm.

Also, during reassembly of the valve using the replacement components(disc, disc nut, disc washer, swing arm, and disc nut cotter pin), it was

discovered that there was an interference between the'hanger bracket andthe valve body such that the bracket would not fully sit on its .seatingsurface. A small amount of grinding on one corner of the bracket wasrequired to obtain proper seating. The manufacturer was contacted priorto this work, and his authorization and approval was obtained.

Prior to this event, on April 6, 1988, check valve SI-1-8818A (identical'o SI-1-8818C), which had a bonnet gasket leak requiring valve bonnetremoval, was disassembled and inspected as part of DCPP's normal checkvalve maintenance/inspection program and verified to be in proper workingcondition. The valve internals showed no evidence of wear. Thedisc-to-swing arm clearances were minimal and there appeared to be goodinterference between the anti-rotation butto'ns.

B. Inoperable structures, components, or systems that contributed to theevent:

Six inch Velan swing check valve, SI-1-8818C.

C. Dates and approximate times for major occurrences:

1. June 25, 1988, at 0700 PDT: STP V-5A initiated to test SI-1-8818A,B,C,D and 8956 A,B,C,D ECCS checkvalves.

2. June 26, 1988, at 0955 PDT:

3. June 26, 1988, at 1345 PDT:

4. June 26, 1988, at 1359 PDT:

5. June 26, 1988, at 1741 PDT:

Entered TS 3.4.6.2. due to the apparentexcessive leakage through SI-1-8818C.

Declared an Unusual Event and commencedan orderly cooldown of the RCS.

The one-hour report required by 10 CFR50.72 was completed.

Unit 1 entered Mode 5, and the UnusualEvent was terminated. RHR Train A wasdeclared inoperable to effectinspections -and repairs on valveS I-1-881 8C.

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6. 'duly 01, 1988, at 0016 PDT: Valve SI-1-8818C declared operablefollowing repairs and successfulcompletion of leak test.

Other systems or secondary functions affected:

None

E.

F.

G.

Hethod of Discovery:

During the performance of 'the STP V-5A, the test engineer noted thatcheck valve SI-1-8818C was apparently leaking excessively.

Operator Action:

On Dune 26, 1988, at 0955 PDT, the Unit 1 Shift Foreman entered TS

3.4.6.2. due to the apparent excessive leakage through ECCS check valveSI-1-8818C. At 1345 PDT, in accordance with TS 3.4.6.2, the ShiftForeman declared an Unusual Event and commence'd an orderly cooldown ofthe RCS. At 1741 PDT, Unit 1 entered Hode 5, and the Unusual Event wasterminated. RHR Train A was declared inoperable to effect inspectionsand repairs on SI-1-8818C.

Safety system Responses:

None

v n

A. Immediate cause:

B.

The immediate cause of this event was failure of valve SI-1-8818C tofully seat and leakage past the STP test valves, resulting in apparentexcessive valve SI-1-8818C leakage.

Root Cause:

During the investigation of this event, PGhE conducted an informalrevi ew of industry operating experience which did not initially identifyall relevant information. A subsequent, more formal review identifiedadditional operating experience information pertinent to this event.

PG&E's root cause investigation focused on the following potential areas:

Haterial Degradation'pondisassembly and inspection, no abnormal wear was observed on the

check valve hanger bracket hinge pin or the stud that holds the swing armand disk together. Two marks were observed on top of the valve disc,

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approximately 180 degrees apart, indicating that the disc had not rotatedbut had been contacting the same points in the valve body. No materialdegradation was observed that would cause the valve to not perform itssafety function.

Design

Velan has modified the original design, and replacement valve discs noware forged with a single anti-rotation button welded to the disc.However, many valves at DCPP have the original cast stainless steel valvedisc with two anti-rotational buttons on the backside of the disc.Because the anti-rotation buttons were not easily forged to the disc, onebutton was welded to the disc. This was designed to stop on the side ofthe swing, arm, hence its greater height.

Installation

4.

5.

A review of installation records indicate that no valve modifications=including the valve modification which allowed the valve disc morefreedom of motion had been performed by PG&E.

Hanufacturing/Assembly

It was determined that the manufacturer failed to properly seat thehanger bracket to the hanger bracket seat. This resulted inmisalignment, which was corrected by grinding on the swing arm to producesufficient looseness to allow proper seating of the disc. Thismodification by the manufacturer was determined to be the root cause forthe leaking valve.

Preventive Haintenance

A review of maintenance history for these valves indicated no similarproblems at DCPP.

In addition to routine and preventive maintenance, prior to this eventseveral Velan swing check valves had been disassembled and inspected inresponse to Information Notice 81-30, "Velan Check Valves". No'problemssimilar to those identified in the Information Notice were found.

Haintenance records, procedures, and operational histories were reviewedseveral times in response to IE Bulletin 79-04, "Incorrect Heights forSwing Check Valves Hanufactured by Velan Engineering Corporation", and IEInformation Notice 80-41, "Failure of Swing Check Valve in the Decay HeatRemoval System at Davis Besse Unit No. 1".

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Again, no problems similar to those identified i'n the Bulletin and Noticewere found.

INPO SOER 86-3, "Check Valve Failures or Degradations" contained tworecceeendations to improve check valve performance. PG&E is currentlyimplementing the SOER recommendations. Engineering is evaluating allsafety-related and significant m in steam and feed water system checkvalves at DCPP based on the Electric Power Research Institute (EPRI)"Guidelines for Applicatio'n and Use of Check Valves in Nuclear PowerPlants". This effort will enhance the selection process for check valveinspections based on physical orientation in piping systems and valveswhose flow rates are marginal to ensure full opening under all serviceconditions. The data collection effort is approximately 80 percentcomplete. PG&E-initiated full implementation of the inspectionguidelines during the Unit 2 second refueling outage which began inSeptember 1988.

INPO SER 20-83, "Velan Swing Check Valves" and its supplement discussedbinding probl.ems observed in Velan swing check valves models C58 and89-3114B-13HS. In response to this SER, PG&E ins'pected two Velan checkvalves in Unit 1 but did not observe any of the problems identified inthe SER.

In summary, although PG&E implemented an inspection program in responseto numerous industry operating experience documents, this program was notadequate to identify the improper assembly of the check valve internals.

6. Testing

There are eight six-inch Velan swing check valves installed in the ECCS

train per unit, for a total of sixteen valves at DCPP. These valves aretested for backleakage whenever their respective unit is brought out ofcold'hutdown, and have been tested a total of 82 times since initialUnit 1 criticality in 1984. Of those tests, the only failure is the oneinvolving SI-8818C which initiated this report. Since backleakage canonly occur when the system is depressurized, this testing is deemed

adequate to detect such leak problems.

On Dune 30, 1988, PG&E initiated an Action Plan to investigate thepotential for commn mode failure of Velan swing check valves. A reviewof the operational history of these valves indicates these valves havenever required flushing or an increase in Reactor Coolant System pressureto facilitate seating.

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A complete maintenance history review was conducted of Velan swing checkvalves of other sizes 1nstalled 1n DCPP units 1 and 2. This reviewidentified 37 valves in Unit 1, and 29 valves in Unit 2 which areinstalled in various systems such as Auxiliary Feedwater, Chemistry andVolume Control, Main Steam, and the Reactor Coolant System. 'he reviewconcluded that none of these Velan swing check valves in other systemshave experienced a s1milar failure to that reported for SI-1-8818C.

The manufacturer was contacted to determine 1f these valves were designedto seal against a low differential pressure in the range of 200 psi andunder. The'manufacturer explained that a valve with th1s high of apressure rating (1500 psi) would not normally be placed in such a lowpressure application, however the valve would be capable of sealing insuch low pressures with finely polished seating surfaces. Such sealingcapabil1ties would deteriorate with normal wear.

Hhen asked about the as-found condition of the valve swing arm, the .

manufacturer stated that some valves have required machining'of the swingarm to obtain proper fit and alignment, and that this was a rareoccurrence. Records were not available from the manufacturer to identifywhich valves had required this type of maphining.

In the case of valve 8818C, it should be noted that if the sw1ng arm tohanger bracket assembly had been properly fitted by the manufacturer, themachining to produce looseness would not have been required to allow thevalve to seat properly. After replacement of the valve intervals, thevalve seated properly without excessive looseness.

The Nuclear Plant Reliability Data System (NPRDS) was searched to obtaina maintenance history of similar valves at other nuclear power plants.For the six-inch Velan swing check valves there were fifty-two failurereports in the data base. Of the 52 failure reports, 20 were ResidualHeat Removal/Low Pressure Safety In)ection, 19 were High Pressure SafetyIn)ection, and 13 were from secondary systems such as feedwater or mainsteam. The failure reports cite 1nstances of body to bonnet leakage,disc to seat leakage, and bending or breakage of the hanger bracketassembly, all attributable to normal wear and tear. There were 2 casesof a failure of the check valves to seat. In both cases, the check .

valves were stuck open due to interference between the valve body anddisk nut lock wire. As a corrective action for both, the manufacturer .

had been contacted and a cotter pin 1nstalled 1n place of the lock wire,and the valves returned to service. No failure reports cited checkvalves stuck open as a result of the rotation button sliding under theswing arm. In addition, there were no failure reports concerningexcessive seat leakage for reasons other'than normal wear of the valveseating surfaces.

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Based on this investigation, PG&E concluded that the valve modificationby,the manufacturer to allow more freedom of disc movement createdexcessive clearance which allowed the anti-rotat1on button to rotatebeyond its normal position to a position under the disc swing arm andprevent proper disc alignment, thus allowing leakage. The modificationto allow more freedom had been necessary because the swing arm to hangerbracket fit was improperly estab'.ished by the manufacturer. If thecomponents had been properly assembled, these modifications would nothave been required'.

IV. nl 1 f vn

The NSSS vendor, Westinghouse,. was contacted to provide guidance on the roleof check valves 1n the accident analyses performed for DCPP.

Westinghouse applies single failure criteria when performing accident analyseswhich rely on safety related mitigation systems. The intent of a singlefailure analysis is to identify whether a fluid or electrical system hassufficient redundancy of components to accomoodate a single failure (inaddition to the initiating event) and still perform the system's safetyfunction.

Check valves are not subject to active fa11ures from an accident analysispoint of view because they are not powered components. In addition,- thefailure of a safety-related check valve to open when required is notconsidered credible by Westinghouse. And, in the case of the ECCS injectionlines, the failure to reseat is protected against by the two check valves inseries.

An accident was postulated in which the RCS would depressurize below the RHR

injection setpoint and then repressurize above the RHR design pressure. If inthis event the check valves did not reseat, the RHR system would beoverpressurized resulting in a possible LOCA outside containment. In responseto this scenario, a rev1ew of FSAR Chapter 15 Accident Analyses shows that nosuch accident could result. In addition, two large (approximately 600 gpm)relief valves are provided to protect the RHR from overpressurization.

.The following Chapter 15 transients have a potent1al of actuating e1ther thehigh head, intermediate head, accumulators, or RHR systems.

Rod EjectionSmall and Large Break LOCA

Steam Line BreakAccidental Depressurization of the RCS

Spurious Operation of Safety InjectionExcessive Heat Removal due to Feedwater System MalfunctionSudden Feedwater Temperature ReductionExcessive Load IncreaseRod DropSteam Generator Tube RuptureAccidental Steam System Depressurization

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Of these, accidents, only the large break LOCA requires actuation of the RHR

system. Thus, this is the only accident for which failure of check valveSI-l-8818C to reseat following an actuation is an issue. In the case of a

large Break LOCA, the RCS rap1dly depressur1zes to containment pressure and

the RHR system would begin delivery of water into the RCS at 187 psig.

Because of-the large opening in the RCS, there is no credible scenario whichwould result 1n repressurization of the RCS. Since the RCS will always be thesystem low pressure point, RCS water cannot flow back 1nto the RHR'ystem. Inaddition, the safety in)ection flow cannot divert to the RHR system since itwould always flow to the lower pressure RCS. Further, even 1f thisrepressurization of the RCS occurred, the presence of an additional checkvalve in series with SI-1-8818C along with RHR pressure relief capabilitywould prevent overpressurization of the RHR system.

A review of Velan swing check valves in other applications has 1ndicated thatdue to- extensive testing and monitoring programs, any problems with thesevalves would be promptly identified and appropriate maintenance activitieswould be conducted. A review of maintenance history records for these valvesindicates that no similar problems have been identified.

rr iv A i n

Valve SI-1-8818C had new internals installed and a satisfactory leak test was

conducted.I

Four check valves in similar 1nstallations were inspected during the Unit 2

refueling outage. The "first-off" ECCS check valves (manufactured byAnchor-Darling) were inspected during the Unit 2 'refueling outage. The fourcheck valves used the "first-off" ECCS check valves for Unit l will be

inspected during the next fuel outage.

Applicable PGhE maintenance procedures will be prepared or revised as

appropriate to be consistent with the EPRI guidelines concerning check valveperformance, and will contain specific items to check for and address when

conducting check valve inspections.

To 1mprove the review and implementation of relevant industry operatingexperience, Nuclear Plant Administrative Procedure C-12, "Ident1fication and

Resolution of Problems and Nonconformances" will be revised to require a

rev1ew of applicable industry operating experience for all nonconformancereports. This rev1ew will include, but not be limited to, a review of theNuclear Plant Reliability Data System (NPRDS), NRC IE information notices,bulletins, and gener1c letters, and INPO SOERS and SERs.

i inl Infrm inA. Failed Component

Component: 6 1nch, 1500 psi, swing check valve, SI-l-8818C

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Hanufacturer: Vel an Val ve Company

NPRDS Code: V085

-B. Previous LERs on similar events

None

C. Additional Information

Indirectly related to the event reported in the LER was the occurance ofa waterhammer in the RHR system.

Initial attempts to seat the check valve by accumulator pressurizationfailed. The Shift Foreman directed the start of 1-2 Residual HeatRemoval (RHR) pump in an attempt to flush the seat and.subsequently sealthe valve by passing water through the valve in the forward direction viathe safety in)ection test system . An audible waterhammer occurred whenRHR Pump 1-2 was started, which was noticed by operators in both theAuxiliary Building and the Control Room. Operators monitored RHR and RCS

system pressures to ensure system integrity and were di spatched toinspect system piping. (A later engineering'valuation determined that avoid had been created in the highest point of the RHR piping insidecontainment during the performance of STP V-5A'and that the suddencollapse of this void upon starting the 1-2 pump caused the waterhammer.This evaluation concluded that no damage was sustained by thewaterhammer.)

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Fi.gure 1

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HANGER BRACKET BUSHING

HANGER BRACKET'BLOCK)

.0

INTERFERENCE

HANGER

0

SECTION A—AHANGER BRACKET

ANTI-ROTATION BUTTON

HOLE I.D.LARGEST DIA.—1.290"SMALLEST DIA.— 1.261"

0.852"

I II II II II I

0.808"

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Figure 2

DISC

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. Pacific Gas and Electric company 77 Beate Street

San Francisco, CA 94106

4i5/972 7000TV/X910 372 6587

James 0. Shifter

Vice President

Nuclear Pointer Generation

November 15, 1988

PGhE Letter No. DCL-88-275

U.S. Nuclear Regulatory CommissionAttn: Document Control DeskHashington, D.C. 20555

Re: Docket No. 50-275, OL-DPR-80Diablo Canyon Unit 1

Licensee Event Report 1-88-017-00 (Voluntary)Excessive Reactor Coolant System Leakage Due to a Leaking ECCS

Check Valve

Gentlemen:

Pursuant to item 19 of Supplement 1 to NUREG 1022, PGtmE issubmitting the enclosed Licensee Event Report (LER) regardingexcessive reactor coolant system leakage due to a leaking ECCS checkvalve.

This event has in no way affected the public's health and safety.

Kindly acknowledge receipt of this material on the enclosed copy ofthis letter and return it in the enclosed addressed envelope.

Sincerely,

/.hi

Enclosur .

cc: 3. B. HartinH. M. MendoncaP. P. NarbutB. NortonB. H. VoglerCPUCINPO

DCl-88-HH-N073

2372S/0064K/DY/2107