ML20045G866

LER 93-004-00:on 930611,reactor Tripped Due to Turbine Trip Resulting from Inadequate Procedure.Procedure Changes Made to Open Appropriate FW Heater High Level Dump Valves During Plant startup.W/930708 Ltr

ML20045G866
Person / Time
Site:	Calvert Cliffs
Issue date:	07/08/1993
From:	Cruse C, Volkoff J BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-004, LER-93-4, NUDOCS 9307160085
Download: ML20045G866 (6)

Text

B A LTIMORE

. GAS AND ELECTRIC <

l CALVERT CLIFFS NUCLEAR POWER PLANT 1650 CALVERT CLIFFS PARKWAY

• LUSBY, MARYLAND 20657-4702 j CHARLES H CAUSE PLANT GENERAL MANAGER cAtvEntcurrs July 8, 1993 U.S. Nuclear Regulatory Commission Washington, D.C. 20555 ATTENTION: Document Control Desk

SUBJECT:

Calvert Cliffs Nuclear Power Plant Unit No. 1; Docket No. 50-317; License No. DPR 53 Licensee Event Report 93-004 Reactor Trip Due to Turbine Trip Resulting from Inadequate Procedure The attached report is being sent to you as required under 10 CFR 50.73 guidelines. Should you have any questions regarding this report, we will be pleased to discuss them with you.

Very truly yours, ,

, X CHC/JV/bj d Attachment cc: D. A. Brune, Esquire J. E. Silberg, Esquire R. A. Capra, NRC D. G. Mcdonald, Jr. , NRC T. T. Martin, NRC P. R. Wilson, NRC R. I. McLean, DNR J. H. Valter, PSC Director, Office of Management Information and Progra,a Control l

140047 l 9307160085 930708 "'l

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NRC FORM 368 U S. NUCLEAR REGULATORY COMMISSION .

2) ESTEMTED BURDEN PER RESPONSE TO COMPLYWITH THIS INFORMATION i

• CXX. LECT)ON REQUEST. 50.0 HHS. FORWARD COMMENTS RECADDtNG suf 0EN ESTIMATE TO TPE INFORMADoN AND RECOFOS MAtAGEMENT LICENSEE EVENT REPORT (LER) DR/4CH (MND87714). U S. NUCLEAR RECULATORY COMMtSSON.

WASHINGTOR DC 2MHX01. ANoToTHE PAPERWOfM REDUCTION P50)ECT (See reverse for reouired number of rficits/ characters for each blocky 01500104). OFFCE OF MAtAGEMENT AND DVDGET,WASHJNGTCM DC 2@0:L  ;

F ACILIW NAME (1) DOCKET NUMBER (2) PAGE (3) <

Calvert Clif f s, Unit 1 05000 317 1 OF 05  !

TITLE (4) L Reactor Trip Due to Turbine Trip Resulting From inadequate Procedure EVENT DATE (5) LER NUMBER (6) REPORT DATE (7) oTHER F AC:llTIES INVOLVED (B)

S EQUENTIAL REVISION I MONTH DAY YEAR YEAR M ONTH DAY YEAR NUMBER NUMBER >

06 11 93 93 - 004 -

00 07 08 93 05000 OPERATING THIS AEPORT IS SUBurTTED PURSUANT To THE DECUtREMENTS OF 10 CFR MChaci< one or mnre) (11)

MODE (9)

I 20.402 M 20 405.c) l )( 50.73(a)(2)(iv) 73 71(b) ,

, 20 405(a)(1)(i) 50.36(c)(1) 50.73(a)(2)(v) 73.73 gc3 LEVEL 16 20 405(aH1)60 50.36(c)(2) 50.73(a)(2)(vii)

00) 20.405(aH1)6ii) 50.73(a)(2)(0 50.73(a)(2)(viii)(A) - (Srecdy in Abstract below and in Ted NRC Fonn 366A) 20.405(aH1)(iv) 50.73 a)(2)(ii) 50 73(a)(2)(viiO(B) 20.405(a)(1)M J 50.73(a)(2)(iii) 50 73(a)O(x)

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER (include Area Code) j John Volkoff, Compliance Engineer 410-260-3649 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 113) i EMABLE TO ##

CAUSE SYSTEM CO M PONENT CAUSE SYSTEM COMPC NENT TURER NPRDS TURER NPRDS i i l SUPPLEMENTAL REPCRT EXPECTED (14) EXPECTED MONTH t DAY l YEAR 1 SUBMISSION YES X No l af ves comowe EYPECTED SUBMISSION DATE) DATE (15) l >

ABSTRAC T (urmt to 1400 spaces. Le . apprommately15 single-space typewntten knes) (16)

On June 11, 1993, Unit 1 tripped due to an automatic wtuation of the Reactor Protection System (RPS). An RPS loss of load si pal was generated when the turbine tripped due to a low pressure feedwater heater (F'a) high level turbine trip signal. The signal was generaced because the Fa high level dump -l (HLD) valve handswitch was left Closed during startup. The unit was au <

16 percent power. ,

A Cause of the event was that opening the WH HLD valves for plant startup was not adequately proceduralited. One Contributing factor was that one operating i crew questioned the valves position but did not effectively follow-up on the j question or pass it along to the next Crew who did not detect the improper handswitCh positions. Procedure Changes were made to open the appropriate F'a HLD valves during plant startup. The design of the WH high and high-high l l

level alarm Circuits was reviewed. Reactor trip and normal shutdown j procedures and valve lineups will be reviewed for similar valve position j i problems. Troubleshooting of the Fa water level alarm Circuits will be l performed.

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l NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 315o 0104 l

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> EXPIRES 5/31/95 l CSTtMATED BURoEN PER RESPONSE To COMPLY WffN THIS INFoRMATCN CoLLEcTON REoVEST; 50 0 HRS. FoRW ARo l LICENSEE EVENT REPORT (LER) couuENTs eccARoiNo euRoEN EsT: MATE to THE iuFoRuATCN ANo RE0oPoS MANAoEMENT BRANCH lMNB8 7714), U.S NUCLEAR TEXT CONTINUATION RoutATcRv couuissCN. wAsHacToN. oc rosas.ooot. Ano To THE PAPERWORK REoVCTCN PROJECT (3150 o104), oFFCE oF 'l MANAGEMENT ANo BUoGET, WASHWGToN. oc 20503 F ACIUTY MAME (1) DOCKET NUMBER (2) LER NUMSER (3) PAGE (4)

Calvert Cliffs, Unit 1 05000 3 1 7 93 -

004 - 00 02 0F 05 TEXT or . .u. w.a = .amo= c . or NRc F.mi sesAi (173 I. DESCRIPTION OF EVENT ,

1 At 12:59 p.m. on June 11, 1993, the Unit 1 reactor tripped due to an automatic actuation of the Reactor Protection System (RPS). An RPS loss of load signal -

was generated when the Unit 1 Turbine tripped due to a 12C low pressure i feedwater heater (SH) high level turbine trip signal. The signal was generated  ;

because the 12C FkH high level dump (HLD) valve handswitch was left closed during a Unit 1 startup, allowing a high water level in the FAM. At the time, l Unit 1 was at 16 percent power (MODE 1). ,

l Feedwater heaters use steam extracted from various stages of low and high I pressure turbines to preheat feedwater. Unit 1 has six FkH stages, 11 - 16. i Stage 12 has three parallel F4Hs located inside the condenser, 12A, 12B and 12C. l During normal power operation, the condensed extraction steam that collects in j the F'JHs is drained in a controlled manner to prevent the FbHs from completely I flooding or draining. DHs 12A, 123 and 12C each a have a HLD valve and contain two float switches, high and high-high level. The high level float ';

switch has two contacts, one that initiates a high level alarm on the Control Room (CR) feedwater panel and opens the 53 HLD valves, the othe? is the first ,

i of two contacts for a turbine trip signal. The high-high level float switch also has two contacts , one that initiates a plant computer high-high level alarm, the other is the second of the two contacts for a turbine trip signal. 1 The turbine trip is to protect the turbine from an overspeed condition, klien '

both turbine trip contacts are closed, a turbine trip signal is generated. The circuit has a 1.5 second time delay to prevent float chattering from causing a turbine trip.

k~ hen the plant is at a low power level, WM pressures fluctuate with steam flow changes. As FbH pressure changes, liquid flashes to steam in the FbH and causes i the float level to chatter. To preclude an inadvertent turbine trip signal generated by pressure surges from flashing liquid, the DH HLD valves are lef t l open during plant startup. The FbH HLD valves are controlled by handswitches from the feedwater panel in the CR.

Operating Procedure (OP)-2, " Plant Startup from Hot Standby to Minimum Load," l Attachment (2), Checklist (Reactor Trip Recovery), requires checking initial l conditions for turbine startup per Operating Instruction (01)-43A, " Main Turbine and Generator / Exciter Operation Unit 1." One of the initial conditions for 01-43A is that FbH vents and drains are aligned per OI-8B. "Feedwater Heater Vents and Drains." OI-8B Attachment (1), a valve lineup for the Feedwater ,

Heater Vents and Drains, sho1s the difference between ene startup (OPEN) and 1 l

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's4 NRC FORM 366A . U.S. NUCLEAR REGULATORY COMMISSION AFPROVED BY OMB NO. 315o-0104 ,

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• EXPtRES 5/31/95 .,

EsTuATEo BURDEN PER RESPONSE To COMP (Y WTH TH,9 )

McAuATION CoLLECTCN REQUEST: 50 0 MFG FoRWAAo l

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l F AcruTv NAuf m ooexET uuusEn ca (En muuaEn <st Pace tai Calvert Cliffs, Unit 1 05000 3 1 7 93 -- 004 - 00 03 0F 05 TEXT Of mom space e requewa. use addet:onal copes of NPC Form 366A) (17) normal operating (SHUT) positions for the AT HLD valves, but OI-43A does not specifically refer to Attachment (1) of 01-83.

On the morning of June 11, 1993, preparations were being made for a Unit 1 startup af ter tripping the day before (see LERs 317/93-03 and 318/93-03). The Unit 1 Reactor Operator (RO) was_ tasked with completing OP-2 Attachment (2) for Unit 1. The Control Room Operator (CRO) coordinated various activities related to Unit 1. A Senior Reactor Operator (SRO) was dedicated to Unit 1 startup.

The SRO reported to the R0 that SH vents and drains were arranged per OI-8B '

after he checked the initial conditions, in 01-8B,Section II, Startup (Normal).

The RO signed off step 5 of the OP-2 checklist. Indicating that the initial conditions of OI-43A were met, including the 01-8B conditions.

Later during startup preparations, the SRO noted that the SH HLD valve handswitches on the feedwater panel in the CR were in the shut position. He questioned this condition, knew they should be OPEN during the startup and  ;

discussed with the RO whether the valves should be opened. The SRO reviewed procedure steps he had completed, found no step placing the WH HLD valve handswitches in the OPEN position, and thought a later step in the startup '

procedures would OPEN the WH HLD valves prior to increasing power.

Independently, the CR0 cycled the n'H HLD valves per OP-2 step C.5 open and then shut. The OP-2 step does not specify valve position only to cycle the valves.

The CR0 thought that SH relief valve work going on required the valves to '

remain shut after cycling.

The operators on the shift brought the reactor critical just prior to the '

June 11 shift turnover. The next shift did not detect that the WH HLD valves were shut and should be open. Unit 1 reached 16 percent power at 12:53.

Approximately one minute before the trip, the plant computer received four 12B '

WH high-high level alarms, each lasting approximately 2-2.5 seconds and resetting prior to tripping the turbine. The signals were_ listed on the plant computer alarm list. The plant computer alarm list is not routinely monitored '

because it is the secondary source of alarms for the operators. These were four i of 63 plant computer alarms listed during the minute at 12:58. No high level alarms were observed on the feedwater control panel in the CR.

At 12:59, a 12C RH high-high level signal lasted for 2.4 seconds, meeting conditions for initiating a turbine trip and the subsequent RPS trip.

Appropriate actions were taken for the plant trip. ,

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9 NRC FORM 366A . U.S. NUCLEAR REGULATORY COMMISSION . APPROVED BY OMB NO. 3150-0104

5.sa - EXPfRES 5/31/95 l EST MATED BURDEN PER RESPONSE To COMPLY WITH THIS INFORMAT1oN COLLECT 1oN REQUEST

50 0 NFG. FoRWARo LICENSEE EVENT REPORT (LER) ceMuENTs RecARoma suRcEN EsnMATE To THE MoRMATloN AND PECoRDS MANAGEMENT BRANCH (MNBS 7714). U.S. NUCLEAR TEXT CONTINUATION REauuTORY CoMMISSloN. WASHfNGToN. oC 20555-0001. ANo TO THE PAPERWoR4 REDUCTION PROJECT p1So-0104L OFFICE OF MANAGEMENT ANo BUDGET, WASHINGTON, DC 20503.

F ACIUTY NAME (1) DOCKET NUMBER (2) LER NUMBER (3) PAGE H) t Calvert Cliffs, Unit 1 05000 3 1 7 93 - 004 - 00 04 0F 05 f TEXT [N more scace is required, use addibonal copies of NRC Form 366A) tt 7)

II. CAUSE OF EVENT l t

A cause of the event was that opening the F.H HLD valves for plant startup was not adequately proceduralized. Operators were aware that the FaH HLD valves needed to be open for startup, but thought the procedures would open them at the appropriate time. OI-43A did not direct the operators to verify the feedwater '

va.ve lineup, Attachment (1) in 01-8B, and no other procedural steps opened the FH HLD valves for unit startup.

4 A contributing factor was that on-shift personnel preparing the unit for startup  !

questioned why the AH HLD handswitches were not open but did not pursue where in the procedure the valves should be opened.. They assumed the valves would be opened later in the procedure and therefore did not convey this question to the oncoming shift. Additionally, the oncoming crew did not detect the handswitches were out of position during shift turnover or. subsequent activities.

If the FJH high level alarms on the feedwater panel in the CR had alarmed before the trip, they might have alerted the operators to the fact that .the AH HLD valve handswitches were in the SHUT position in time to prevent th'e trip.

However, during Unit startup, when flashing in the P.Hs is more likely to cause spurious alarms than during normal operations, such trips are prevented'by opening the SH HLD valves as a routine part of the startup.

III. ANALYSIS OF EVENT The event is reportable under 10 CFR 50.73(a)(2)(iv), as a condition that <

resulted in an automatic RPS actuation. The reactor tripped as designed for a loss of load trip. All protective systems performed as expected and operators performed their tasks correctly and interpreted indications properly. The turbine trip signal from the 12C F H was probably generated by liquid flashing to steam in the F.3 during startup. The 123 F.H high-high level alarms may have occurred due to localized steam flashing causing the high-high level float to close its contacts, while the high level float did not experience simultaneous  ;

flashing, resulting in no plant trip. It is unclear why no high level alarm was observed for 12C FwH and the turbine trip signal was still generated. The-turbine trip signal protects the turbine, not the reactor. The loss of load reactor trip performed properly. There were no significant safety consequences as a result of this event.

IV. CORRECTIVE ACTIONS Appropriate actions were taken for the plant trip.

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1 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 31So-oto4 I NRC FORM 366A .*

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EXPIRES 5/31/95 ESTNATED BURoEN PER RESPONSE To COMPLY Wf7H THis INFoRMATON CoLLECTON REcuEST: So.0 HRS. FoRWARo LICENSEE EVENT REPORT (LER) CoMuENTs REGARo.NG euRoEN EsruATE To twE woRMATON ANo RECoRoS MANAGEMENT BRANCH (MNDO 77ial, U $. NUCLEAR TEXT CONTINUATION REOULAToRY CoMMISSON. WASHINGTON, DC 20$55{C01, ANo To THE PAPERWORK REoUCTON PRCUECT pt50-0104h OFFICE CF MANAGEMENT AND BUoGET, WASHINGTON, oC 20503.

F ACluTY NAME (1) DOCKET NUMBER (a LER NUMBER (3) PAGE (4)

Calvert Cliffs, Unit 1 05000 3 1 7 93 -

004 -

00 05 0F.05 ]

TEXT g , . ,. . o. .amooco. .f NRC F.,. seaAi it7) i Procedure changes were made to open the appropriate F%H HLD valves during plant startup.

We understand that procedures are not the only barrier to ensure event free  ;

operation. We expect operators to pay careful attention to detail while i performing tasks. The General Supervisor-Nuclear Plant operations has recently reemphasi::ed these expectations via his daily Notes and Instructions to the crews.

Reactoe trip and normal shutdown procedures and valve lineups will be reviewed for tr: p-sensitive valves lef t in a post-trip or shutdown position different  ;

from the required startup position. .

We evaluated the design of the 12 F%H high and high-high level alarm circuits i and found them to be appropriate for their intended function. This evaluation identified no explanation why the high level alarm was not observed for the 12C  !

F%H high level condition.

Troubleshootingofthe12FWHhighandh2gh-highlevelalarmcircuitswillbe performed to try to determine why the turbine trip occurred without receiving ,

F.H high level alarms. l l

V. ADDITIONAL INFORMATION ,

A. Affected Component Identification EIIS EIIS f Component Funct Code System Code FWH HLD valve LSV SJ

3. Previous Similar Events There have been three previous events involving plant trips related to the P.H HLD valves, but the previous causes were unrelated to  ;

this event. They were documented in Unit 1 LERs85-011, 85-012. and 88-005.

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