REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR: 8711020399 DOC. DATE: 87/10/2V NOTARIZED: NOFACIL: 50-323 Diablo Cangon Nuclear Power Planti Unit 2I Pacific Ga

AUTH. NAME *UTHQR AFFILIATIONSISKI D. P. Pacif ic Gas 8c Electric Co.SHlFFERI J. D. Pacific Gas 5 Electric Co.

RECIP. NAME RECIPIENT *FFILIATION

DOCKET 505000323

SUBJECT: LER 87-Q05-01: on 870410I RHR flow interrupted when bothtrains became inoperable due to airbound RHR pumps. Caused bginadequate communications. Procedures OP A-2: II re drainingof RCS 8. OP AP-16 re RHR f low loss revised. W/871029 ltr.

DISTRIBUTION CODE: IEEED COPIES RECEIVED: LTR t ENCL SIZE: 9TITLE: 50. 73 Licensee Event Report (LER)I Incident Rpti etc.

NOTES:

RECIPIENTID CODE/M*ME

PD5 LATRAMMELLIC

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UCENSEE EVENT REPORT tLER)

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INTERRUPTION OF RHR FLOW DURING RCS MIDLOOP OPERATION

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On April 10, 1987, at 2123 PDT, with the unit in Mode 5 (Cold Shutdown) during arefueling outage, residual heat removal (RHR) flow was interrupted when both RHRtrains became inoperable due to airbound RHR pumps. The 4-hour nonemergency eventreport required by 10 CFR 50.72 was made at 2230 PDT; April 10, 1987.

The reactor coolant system (RCS) had been drained to midloop level to'facilitateremoval of steam generator (SG) primary manways for nozzle dam installation. Inaddition, preparations were in progress for local leak rate testing of a seal waterreturn line (including draining of the penetration). Due to a leaking valve usedas a clearance point in the piping to the penetration being drained, RCS inventorywas lost to the reactor coolant drain tank. This loss of inventory caused adecrease in RCS water level, vortexing in the pumps'uction line, and airentrainment in the RHR pumps.

At 2251 PDT, after verification that the SG manways were still installed and afterventing of the RHR pumps, the RCS was flooded from the refueling water storage tankand an RHR pump started. RHR flow was interrupted for approximately 1 hour and28 minutes. This resulted in some localized boiling but no damage to the core orsignificant radiological release. The unit was stable at 0130 PDT, April ll, 1987.and was returned to normal Mode 5 midloop operation.

8711020399 871029PDR ADOCK 0500032S8 PDR

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NRC Folrrr 3SSA(9%3 l

LICENSEE EVENT REPORT {LER) TEXT CONTINUATIONU.S. NUCLEAR REGULATORY COMMISSION

APPROVEO OM8 NO. 3150WI04EXPIRES: 8/31/88

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iil niiUnit 2 was in Hode 5 (Cold Shutdown) with the reactor coolant system (RCS)vented to the atmosphere and a reactor coolant average temperature ofapproximately 90 degrees Fahrenheit.

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A. Event:

On April 10, 1987, at 2123 PDT, with the unit in Mode 5 (Cold Shutdown)during a refueling outage, residual heat removal (RHR) flow wasinterrupted. Operators had observed amperage fluctuations on RHR pump2-2 (BP)(P) and shut it down. RHR pump 2-1 (BP)(P) was started. Within60 seconds, indications of vortexing were observed on this pump also, andit was shut down. This resulted in both RHR trai ns (BP) beinginoperable. The 4-hour nonemergency event report required by 10 CFR50.72 was made at 2230 PDT, April 10, 1987.

The reactor coolant system (RCS)(AB) had been drained to midloop level tofacilitate removal of steam generator (SG) primary manways for nozzle daminstallation. In addition, preparations were in progress for a leak ratetest on a seal water return line (including draining of thepenetration). Due to a leaking valve used as an isolation point in thepiping to the penetration being drained, RCS inventory was lost to thereactor coolant drain tank (RCDT). This loss of inventory caused adecrease in RCS water level, vortexing in the pumps'uction line, andair entrainment in the RHR pumps.

At 2251 PDT, after verification that the SG manways were still installedand after venting of the RHR pumps, the RCS was flooded from therefueling water storage tank (RWST) and 'an RHR pump started. RHR flowhad been interrupted for approximately 1 hour and 28 minutes. Thisresulted in some localized boiling but no damage to the core orsignificant radiological release. The unit was stable at 0130 PDT, April11, 1987, and was returned to normal Mode 5 midloop operation.

During this event, small amounts of reactor coolant were lost tocontainment via steam through the reactor head vent and via leakage ofthe SG manways when the RCS was flooded from the RWST. Releases ofradioactive material to the atmosphere via open containment hatches andvalves were well within that allowed by the Code of Federal Regulations.

1727S/0052K

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NRC Fons 388A(0431

LICENSEE EVENT REPORT (LERI TEXT CONTINUATIONUS. NUCLEAR REOULATORY COMMISSION

APPROVEO OMS NO, 3150&1(HEXPIRES: 8/31/88

FACILITYNAME I'l OOCKET NUMSER (2) LER NUMBER 181

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

l. Valve 8976 (common safety injection pump suction from the RHST) wascleared electrically (could be opened manually).

2. All core exit thermocouples had been determinated in preparation forreactor vessel head removal.

3. Postaccident monitoring panels 1 and 2 were out of service formodifications.

4. All four accumulators had been cleared and drained.

5. The charging system flow meter was inoperable.

6. The equipment hatch and personnel hatches and three manual ventvalves outside of containment were open.

C. Dates and approximate times for ma)or occurrences:

l. April 10, 1987, at 2043 PDT: An engineer opens valve to drainreactor coolant pump seal returnpenetration in preparation for localleak rate test. Shift foreman was notnotified that draining had started.

2. April 10, 1987, at 2051 PDT: Control room operator noticed volumecontrol tank (VCT) level trendingdown, therefore increased RCS letdownto VCT to increase level.

3. April 10, 1987, at 2123 PDT: Event date — RHR pump 2-2 was stoppeddue to indication of vortexing andpump 2-1 was started. RHR pump 2-1was stopped 60 seconds later whenindication of vortexing was observed.

4. April 10, 1987, at 2138 PDT: Operators closed valve to stopinventory loss from the VCT. Leveldecrease in VCT stopped.

5. April 10, 1987, at 2230 PDT: Health Physics on 140-foot levelnoticed increase in airborne activity.

6. April 10, 1987, at 2230 PDT: Four-hour nonemergency event reportmade in accordance with 10 CFR 50.72.

1727S/0052K

NRC For~ 3eeA(QCI3 I LICENSEE EVENT REPORT (LER) TEXT CONTINUATION

U.S. NUCLEAR REOULATORY COMMISSION

APPROVEO OM8 NO. 3150M( OC

EXPIRES: 8/31/88

FACILITYNAME (II

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7. April 10, 1987, at 2251 PDT: RCS level increased from RHST. RHR

pump started.

8. April ll, 1987, at 0130 PDT: Unit stable in Mode 5, returning tonormal midloop operation.

9. April ll, 1987, at 0320 PDT: Reactor vessel water level abovemidloop 108 feet 4 inches. SG manwayleakage stopped.

D. Other systems or secondary functions affected:

None

E. Method of discovery:

Control room operators observed pump amperage fluctuations.

F. Operator actions:

After securing the second RHR pump, an auxiliary operator was dispatchedto vent the RHR pumps in preparation for restarting. Another auxiliaryoperator was sent to check the status of the SG manway removal prior torefloodi ng the reactor coolant system and to verify RCS level from avisual standpipe. Hhen manway covers were verified to be in place, thereactor coolant system was flooded by gravity feed from the RHST, and oneRHR pump was restarted to establish flow through the core.

G. Safety system responses:

None

1727S/0052K

NRC form 3SSA(943)

LICENSEE EVENT REPORT ILER) TEXT CONTINUATION

DOCKET NUMSER I?l

U*. NUCLEAR REOULATORY COMMISSION

APPROVEO OMS NO. 3150-0)04EXPIRES: 8/31/89

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A. Iaeediate cause:

PG&E concluded that actual vortexing began at the conclusion of thedrain-down to midloop which was accomplished earlier during the day shifton April 10, 1987. During the drain-down, RCS water level was loweredseveral inches below the midloop point of 107 foot. The RHR flow of3,000 gallons per minute and the low RCS water level resulted in theformation of a vortex that continued until the RHR pump was removed fromservice. An analysis of the reactor vessel refueling level indicationsystem (RVRLIS) indications during this period concluded that RCS waterlevel was not raised high enough to stop the vortex.

Since the charging system flow meter was inoperable, the operator had touse RCS level and VCT level to balance charging and letdown flows. Dueto the VCT's smaller surface area, flow imbalances were noted in the VCTlevel considerably faster than in the RCS level; thus operators reliedheavily on the VCT level to balance letdown and charging flow.

The RCS inventory loss that resulted from the leaking isolation valvelowered the VCT level. Believing an imbalance had developed betweenletdown flow and charging flow, operators increased letdown flow and thusreduced RCS water level, increasing the vortex effect in such a way thatair entrainment resulted in pump motor amperage fluctuations. Theoperator decided to secure the pumps to prevent possible damage to them.

B. Root cause:

1. Vortex conditions were not thoroughly understood by operatingpersonnel.

2. Personnel other than operators were operating valves to drain andvent a system (engineer conducting leakrate test) inside theclearance boundary.

3. Inadequate communications:

a. The engineer performing the leak rate test did not inform theoperator.

b. Inadequate communication caused delays in identification andclosure of the leak, in reporting the status of SG manways, andin direct visual verification of RCS water level via the tygontube.

1727S/0052K

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NRC Form 3SSA19B3)

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION

DOCKET NUMBER 13)

U.S. NUCLEAR REOULATORY COMMISSION

APPROVED OMS NO. 3IEOWI04EXPIRES: 8/31/88

DIABLO CANYON UNIT 2

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Analysis shows that in the absence of recovery actions, no core damage wouldhave occurred for about 47 hours after the initial loss of RHR. Analysesperformed by Westinghouse show that the rapid heatup and cooldown associatedwith this event did not reduce the integrity of the reactor vessel. Inaddition, the amounts of reactor coolant lost to containment via steam fromthe head vent and via the steam generator manway were small, and releases tothe atmosphere were well within that allowed by the Code of FederalRegulations. Thus the health and safety of the public were not affected bythis event.

V. rr iv A i n

1. The procedure for draining the reactor coolant system, OP A-2:II, hasbeen revised to (1) strengthen the requirements for maintaining thecontainment building in a condition such that pathways to the envi ronmentduring midloop operations are capable of being closed in a timely manner;(2) require that the narrow range RVRLIS be in service prior to enteringmidloop operations; (3) provide precautions relating RHR flow to RCSlevel to preclude significant air entrainment due to vortex formation;and (4) provide checklists and walkdowns to ensure proper alignment ofthe reactor head and RVRLIS vent systems. PG&E is evaluating a change toOP A-2:II to provide guidance on RHR flow reduction to a value (to bedetermined with Westinghouse) consistent with adequate decay heat removaland other considerations.

2. The abnormal procedure for loss of RHR flow, OP AP-16, has been revisedto (1) include requirements for not starting the second RHR pump if thefirst pump cavi tates unti 1 adequate reactor vessel level is restored (OPA-2:II also provides guidance on this topic); (2) provide a table wherebythe operator may determine the amount of time until the RCS will reach200 degrees Fahrenheit without forced flow; (3) include recovery actionsto be taken in the event that RCS level or flow decreases belowacceptable values; (4) require that major pathways to the environment beclosed if RHR flow is interrupted; and (5) provide contingencies for RCSfeed and bleed if forced RHR flow cannot be reestablished.

1727S/0052K

NRC Form 388A(9B3)

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION

OOCKET NUMSER Ill

U.S. NUCLEAR REOULATORY COMMISSION

APPROVEO OMS NO. 3150WIOOEXPIRES: 8/31ISS

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VI.

3. Emergency Procedure EP G-l, "Accident Classification and Emergency PlanActivation," has been revised to require operators to declare an unusualevent if RHR flow is not restored within 10 minutes . In addition, analert will be declared if RCS temperature exceeds 200 degrees Fahrenheit(measured or projected). In addition, an alert will be declared if RHRflow is not restored within one hour.

4. A narrow range level transmitter was installed on Unit 2 beforeresumption of midloop operations after the April 10, 1987, interruptionof RHR flow event, to sense the loop 3 hot leg level, referenced to thereactor vessel head. This provided indication in the control roomthrough an accumulator level indicator with high and low alarmcapabilities. Also, wide range indication sensing of the loop 2crossover leg level, referenced to the pressurizer vapor space, has beenadded to Unit 2 and will be added to Unit 1. This is indicated in thecontrol room through an accumulator level indicator with high and lowalarm capabilities.

5. Additional training has been given to operating crews with respect tomidloop operations as described in OPs A-2:II and AP-16. The trainingalso covered RCS venting and RHR system venting (pumps and piping).Training for the midloop mode of operation will be included in the formaloperator training program.

6. All outage activities were reviewed to identify any work item that mighthave provided a drain path from the RCS or opened a vent path betweencontainment atmosphere and the environment. Hork on these items wasdeferred until midloop operations were complete.

7. A knowledgeable engineer or manager was put on shift for midloopoperations during this outage.

frm inA. Failed components:

Valves

1. CVCS-2-8396A

Type: DiaphragmManufacturer: GrinnellModel No.: 2466-10-H

1727S/0052K

NRC form 3SSP.1943 I

LICENSEE EVENT REPORT (LER1 TEXT CONTINUATIONUA. NUCLEAR REOULATORY COMMISSION

APPROVEO OMB NO. 3150WI04EXPIRES: 8/31l88

PACILITYNAME 11) OOCKET NUMBER I31 LER NUMBER IBI

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2. CVCS-2-8380

Type: DiaphragmHanufacturer: GrinnellModel No.: 2466-10-M

B. Previous LERs on similar events:

None

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4

PA.CXF IC CvA.B A.ND ZLZC TR,ZC COMPA NT&W~K ~ 77 BEALE STREET SAN FRANCISCO, CALIFORNIA94106 ~ (415)781.4211 ~ TWX 910.372 6587

October 29, 1987

PGhE Letter No.: DCL-87-256

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

Re: Docket No. 50-323, OL-DPR-82Diablo Canyon Unit 2Licensee Event Report 2-87-005-01Interruption of RHR Flow During RCS Hidloop Operation

Gentlemen:

Pursuant to 10 CFR 50.73(a)(2)(v), PGhE is submitting the enclosed revision toLicensee Event Report 2-87-005 concerning the interruption of residual heatremoval (RHR) flow during reactor coolant system (RCS) midloop operation.This revi sion is bei ng submi tted to provide additional information on theevent, its cause, and corrective actions taken to preclude recurrence. Thisevent did not affect the public's health and safety.

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

Sincerely,

J. D. Shiffer

Enclosure

cc: 3. B. HartinH. H. HendoncaP. P. NarbutB. NortonB. H. VoglerCPUCDiablo DistributionINPO

1727S/0052K/RHH/1538DC2-87-OP-N040

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