.CCELERATED DIS~PJBUTION DEMONS'TION SYSTEM

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9205260156 " DOC.DATE: 92/05/20 NOTARIZED NOFACIL:50-275 Diablo Canyon Nuclear Power Plant, Unit 1, Pacific Ga

AUTH.NAME AUTHOR AFFILIATIONTHIERRY,R.L. Pacific Gas & Electric Co.RUEGER,G.M. Pacific Gas & Electric Co.

RECIP.NAME RECIPIENT AFFILIATION

DOCKET F7

05000275

SUBJECT: LER 92-004-00:on 920425,low vacuum turbine trip &subsequent reactor trip occurred during removal of mainfeedwater pump 1-1 turbine from svc.Caused by programmaticdeficiency. Suction line check valve inspected.W/920520 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR C ENCL 3 SIZE: 7TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.NOTES:

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RECIPIENTID CODE/NAME

PD5 LAROOD,H

INTERNAL: ACNWAEOD/DOAAEOD/ROAB/DS PNRR/DLPQ/LHFB10NRR/DOEA/OEABNRR/DST/SELB SDNRR DS LBSD1

G 02RGN5 FILE 01

EXTERNAL EG&G BRYCE g J ~ HNRC PDRNSIC POORE,W.

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ACRSAEOD/DSP/TPABNRR/,DET/EMEB 7ENRR/DLPQ/LPEB10NRR/DREP/PRPB11NRR/DST/SICBSH3NRR/DST/SRXB SERES/DSIR/EIB

L ST LOBBY WARDNSIC MURPHY,G.ANUDOCS FULL TXT

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Pacific Gas and Electric Company 77 Beale Street

San francisco. CA 94f064 f5/973-4684

Gregory M. Rueger

Senior Vice President and

General ManagerNuctear Power Generation

May 20, 1992

PG&E Letter No. DCL-92-124

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

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

Licensee Event Report 1-92.-004-00Low Vacuum Turbine Trip and Subsequent Reactor Trip Due to aProgrammatic Deficiency

Gentlemen:

Pursuant to 10 CFR- 50.73(a)(2)(iv), PG&E is submitting the enclosedLicensee Event Report concerning a low vacuum turbine trip andsubsequent reactor trip.This event has in no way affected the health and safety of the public.

Sincerely,

Grego y M. Rueger

cc: Ann P. HodgdonJohn B. MartinPhilip J. MorrillHarry RoodCPUCDiablo DistributionINPO

DC1-92-OP-N019

Enclosure

1028S/85K/DPS/2246

9205260156 920520PDR ADOCK 05000275S PDR WE>2.

I]1

LICENSEE EVENT REPORT (LER)

FACIUTYNAMEIll DOCKET NUMBER 2 PACE 3

DIABLO CANYON UNIT 1 0 5 0 0 0 2 7 5 1" 6

TITLE(41 LOW VACUUM TURBINE TRIP AND SUBSEQUENT REACTOR TRIP DUE TO A PROGRAMMATIC DEFICIENCY

EVENT DATE (6lDAYMON

LER NUMBER IelSEOUENTiAL

NUMBERREVISloNNUMBER

REPORT DATE lllDAY YRMON DOCKET NUMBER ISI

0 5 0 0 0

FACIUTYNAMES

OTHER FACILITIES INVOLVED (6)

04 25 92 92 0 0 4 — 0 0 05 20 92 0 5 0 0 0OPERATiNGMODE (9)

THIS REPORT IS SVBHITTED PURSUANT TO THE REOUIREHENTS OF lo CFR: (11)

POWERLEVEL

(10)5 0

X 10 CFR 5D.73 a 2 ivOTHER

(Specify in Abstract below and in text, NRC Form 366A)

UcENsEE coNTAcT FoR THS LDI 1121

RAYMOND L. THIERRY, SENIOR REGULATORY COMPLIANCE ENGINEER

COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN THS REPORT 113l

AREA CODE

805

TELEPHONE NVHB R

545-4004

CAUSE SYSTEH COHPONENT HANUFACTVRER

REPORTABLETo NPRDS

CAUSE SYSTEH COHPONENT HANVFACTURER

REPORTABLETo NPRDS

S H V H 3 6 0 NO

6UPPLEMENTAL REPORT EXPECTED ll41

YES (if yes, complete EXPECTED SUBMISSION DATE) [ X f NO

ABSTRACT (16)

EXPECTEDSUBMISSIONDATE (15)

MONTH DAY YEAR

On April 25, 1992, at 0408 PDT, with Unit 1 in Mode 1 (Power Operation) at50 percent power, Unit 1 experienced a low vacuum turbine trip and subsequentreactor trip. The unit was stabilized in Mode 3 (Hot Standby) in accordancewith plant emergency procedures.

The turbine trip occurred during the removal of the Hain Feedwater Pump (HFP)l-l turbine from service to allow troubleshooting and repair of the turbine tripoil system. Problems that occurred during HFP turbine isolation causeddegrading condenser vacuum. The root cause for this event is programmaticdeficiency. Inadequate instructions were available for the task. In addition,the condenser vacuum pump suction line check valve leaked excessively.

The operating procedure for removing an MFP from service was revised to addprecautions about removing the pump from service when the condenser may havedegraded air removal capacity. In addition, the condenser vacuum pump suctionline check valve for each unit shall be inspected and repaired as necessarybefore the end of the next refueling outage for each unit.

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LICENSE ENT REPORT (LER) TEXT CO NUATION

FACiLITY NAME (I) IOCKET NUMBER (2) LER NUMBER 6 PAGE 3

DIABLO'CANYON UNIT 1

TEXT (17)05 0 0 0 2 7 5 92 004- 0 0 2 " 6

Plant Conditions

Unit 1 was in Hode 1 (Power Operation) at 50 percent power.

Descri tion of" Event

A. Description of Event:

A planned unit curtailment was in progress 'to clean the main circulatingwater conduits (NN)(CND) associated with Circulating Water Pump (CWP)l-l (NN)(P) and the west half of the condenser (SG)(COND). The easthalf of the condenser was in service. Plant licensed and non-licensedoperators were removing Hain Feedwater Pump (HFP) l-l (SJ)(P) fromservice to allow troubleshooting of the trip oil (SJ) system.

At 2342 PDT, HFP l-l was secured for maintenance. At 0342 PDT, whileisolating the HFP l-l turbine from the condenser in accordance withoperating procedures, condenser vacuum began to degrade. 'The partialloss of vacuum (increase in condenser back pressure) was observed afterthe exhaust vent valve (SJ)(V), Hain Steam (HS) 1-738, was cracked opento vent the turbine casing (SJ)(TRB). Closing HS-1-738 stabilized theback pressure at approximately 2.5 inches of mercury.

At 0345 PDT, an attempt to reseat HS-1-738 resulted in a furtherincrease in condenser back pressure (to approximately 4.5 inches ofmercury).

At 0352 PDT, a second secondary air ejector (SH)(EJR) was placed inservice, but had no immediate effect on condenser back pressure.

At 0359 PDT, the Unit 1 Shift Foreman was alerted to the condenserproblems. He directed the operators to back out of the job andre-establish sealing steam to the HFP l-l turbine.

Sealing steam was re-established, and the HFP l-l turbine casing was,vented to the main condenser. Since the turbine casing was full of air,this injected another volume of air into the condenser, causingcondenser back pressure to increase to approximately 6 inches ofmercury. The condenser back pressure turbine trip setpoint is a backpressure of approximately 8 inches of mercury.

At 0400 PDT, the control room operators entered Abnormal OperatingProcedure AP-7, "Loss of Condenser Vacuum." In accordance with thisprocedure, a turbine load decrease was initiated. This load decreasehad no significant effect on indicated condenser vacuum.

At 0405 PDT, in accordance with AP-7, non-licensed operators in theturbine building (NH) were directed by telephone to place the condenservacuum pump (SH)(P) in service. A second operator was dispatched to

-help. The vacuum pump was started from the control room. The operators

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LICENSE ENT REPORT (LER) TEXT CO UATION

FACILITY NAME (I) ~ DOCKET NVM8ER (2) LER NUM8ER 6

DIABLO CANYON UNIT 1

TEXT (17)0 5 0 0 0 2 7 5 92 004 0 0 3 0F 6

B.

did not have time to review the place in service procedure for thevacuum pump because of the sense of urgency placed on this task. Thesecond operator stated that the instruments did not look right. Thefirst operator stated that the seal water pump (SH)(P) had been verifiedto be running, that the seal water sump level had been checked, and thatthe control room had noted that getting the vacuum pump on-line wasurgent to save the plant. Investigation revealed that the vacuum pumpseal water isolation valve (SH)(V) had not been opened since the lasttime the vacuum pump was operated.

At 0407 PDT, the vacuum pump suction valve (SH)(V) from the Unit 1 westcondenser half was opened. Condenser back pressure increased rapidly.The pump suction valve was closed as soon as it was noted that thisoperation worsened condenser conditions. However, the rapid increase incondenser back pressure exceeded the turbine trip setpoint, and at0408 PDT Unit 1 experienced a low vacuum turbine trip and subsequentreactor trip. The unit was stabilized in Node 3 (Hot Standby) inaccordance with plant emergency procedures.

Inoperable Structures, Components, or Systems that Contributed to theEvent:

C.

Condenser Vacuum Pump Suction Line'Check Valve CND-1-747 (SH)(V) wasobserved to leak excessively when the condenser vacuum pump suction

.valve was opened.

Dates and Approximate Times for Hajor Occurrences:

l. April 25, 1992, at 0342 PDT: HFP turbine 1-1 was isolated fromcondenser, vacuum transient starts.

2 ~ April 25, 1992, at 0408 PDT: Event date / Discovery date - Alarmsand other indications in the controlroom announced the reactor trip.

3. April 25, 1992, at 0510 PDT: Four-hour, non-emergency report made toNRC in accordance with 10 CFR 50.72.

D. Other Systems or Secondary Functions Affected:

None.

E. Method of Discovery:

Alarms and other indications in the control room provided immediatenotification to the control room operators that the event had occurred.

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LICENSE ENT REPORT (LER) TEXT CO NUATION

FACILITY NAME (1) DOCKET NVMBER (3) LER NVMBER

SIOVENTkLNUMSOl

RWISONNVMBOI

PAGE 3

DIABLO CANYON UNIT 1

TEXT (17)0500027592 004 0 0 4 '

F. Operator Actions:

Plant operators stabilized the plant in Mode 3 (Hot Standby) inaccordance with Emergency Operating Procedures E-O, "Reactor Trip orSafety Injection," and E-0. 1, "Reactor Trip Recovery."

G. Safety System Responses:

l. The main turbine. tripped.

2. The reactor trip breakers opened and all control and shutdown rodsfell into the core.

3. The auxiliary feedwater pumps started.

III. Cause of the Event

A. Immediate Cause:

The turbine tripped on low condenser vacuum (high condenser backpressure). The reactor tripped due 'to the turbine trip with reactorpower greater than P-9.

B. Root Cause:

l. Programmatic Deficiency

The root cause of this event is programmatic deficiency, in thatinadequate instructions were available for the task. Since theoperators were instructed to place the vacuum pump in servicewithout an opportunity to review or obtain operating procedures, theseal water isolation valve was not opened as required.

2. Component Failure

The condenser vacuum pump suction check valve, CND-1-747, appears tobe suffering severe leakage since, if it worked properly the vacuumshould not have been lost through the unsealed vacuum pump.

C. Contributory Cause:

A contributory cause to this event is that the instructions for removingan MFP from service at power did not provide for precautions forclearing the pump in a condition where the main condenser could nothandle increased air in-leakage.

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LICENSE~ENT REPORT (LER) TEXT COINUATION

FACiLITY NAHE (1) DOCKEt NIIHBER (2)YEAR

LER NUHBER PAGE 3

DIABLO CANYON UNIT 1

TEXT, (17)0 5 0 0 0 2 7 5 92 004 005 "6

IV. Anal sis of the Event

V..

A reactor trip due to a turbine trip is a previously analyzed ConditionII'ventdescribed in the Final Safety Analysis Report (FSAR) Update Section-

15.2.7, "Loss of External Electrical Load and/or Turbine Trip." The FSARUpdate shows that following a turbine trip/reactor trip, the automaticsteam dump system (SB) accommodates the excess steam generation. Reactorcoolant (AB) temperatures and pressure do not significantly increase if thesteam dump system and pressurizer pressure control system (AB)(PZR) arefunctioning properly. Since the 10 percent steam dump and pressurizercontrol system functioned as designed, the health and safety of the publicwere not adversely affected, and there were no adverse consequences orsafety implications resulting from this event.

Corrective Actions

A. Immediate Corrective Actions:

Plant operators stabilized the plant in accordance with EmergencyOperating Procedures E-0 and E-0. 1.

B. Corrective Actions to Prevent Recurrence:

1. The condenser vacuum pump suction line check valve will be inspectedand -repaired in each unit before the end of the next refuelingoutage, currently scheduled for, September 1992 for Unit 1 andHarch 1993 for Unit 2.

2. An Operations Incident Summary was prepared and distributeddescribing this event. This summary was prepared to sensitizeoperations personnel to this type of personnel error.

3. A review will be conducted of all Emergency and Abnormal Operatingprocedures to identify situations where operators might bedispatched to perform equipment operations without normal procedureissuance (prompt actions necessary).

Local instructions/procedure postings will be added as determined bythis review.

4. Operating Procedure C-8: III, "Shutdown and Clearing of a HainFeedwater Pump," was revised to add precautions and limitations forpossible vacuum transients when removing the pump from service. Inaddition steps were added to configure the plant to handle increasedair in-leakage.

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LICENSE ENT REPORT (LER) TEXT CO UATION

FACILITY NAHE (I) DOCKET NJMBER (2) LER NVHBER 6SBNWTNL

PAGE 3

DIABLO CANYON UNIT 1

TEXT (17)05 0 0 0 2 7 5 92 004 0 0 6 " 6

VI. Additional Information

A. Failed Components:

CND-1-747, the check valve in the condenser vacuum pump suction linefrom Unit 1 condenser appears to be leaking excessively.

Hanufacturer: Hission Drilling ProductsHodel Number: 155HF-83Type: C0244

B. Previous LERs on Similar Problems:

None.

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