ML20211E073

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Unplanned Operating Event Rept 85-6, Manual Reactor Trip Following MSIV Closure Due to Inadvertent Emergency Feedwater Actuation,851009
ML20211E073
Person / Time
Site: Crystal River, 05000000
Issue date: 09/26/1986
From: Collins M
FLORIDA POWER CORP.
To:
Shared Package
ML19292G087 List:
References
85-6, NUDOCS 8610220344
Download: ML20211E073 (23)
v • d • e


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t TRANSIENT ASSESSMENT PROGRAM REPORT FOR CRYSTAL RIVER UNIT 3 REACTOR TRIP ON OCTOBER 9, 1985 1

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IA4PLAPNED OPERATING EVENT REPORT 95-6

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I MANUAL REACTOR TRIP FOLLOWING

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MetIN STEAM ISOLATION VALVE CLOSURE DUE TO INADVERTENT EMERGENCY FEED 4 DATER ACTUATION i

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i OCTOBER 9,

1985 i

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SUBMITTED f

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I APPROVED t'

ts) KheM

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Nuclear Safety Supervisor Nuclear Safety and Reliability perintendent Nuclear' PlaA#En6lneering and Nu(lev /1npanager Technical Services Manager 1.

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EXECUTIVE

SUMMARY

CRYSTAL RIVER UNIT 3 - OCTOIER 9.1995

SUMMARY

Ee y 8ffb thbbmaN*wMin mE Ycthee ICS Nons were in automatic control mode. The "B" Emergency Nedwater btlation and c

Control EFIO cabinet was doenergized while technicians worked to correct inter 4.ittent trips from the Channel"B" Main Steam Line Isolation Trip Module.

The "B" EFIC cabinet was reenergized at 0936. When the cabinet was reenergized. the "B" Main Steam Isolstion Valves closed. The operator then manually tripped the reactor as required by plant procedures.

Emergency Feedwater EFW) actuation occurred following the reactor tri error, made in response to the actuation, caused EFW to overfill the "B"p. A technician OTSG.

BOOT CAUSE The "B" EFIC cabinet also contains the Channel"B" EFIC Initiate Receiver / Transmitter G/T). When the cabinet was energized, outputs from the cabinet tripped as expected, iracluding the "B" EFIC R/T. Before the technicians ceuld resat the tripped signals, a spurious trip signal was received from the Channel"C" Receiver / Transmitter, prebably due to a f ailed LED transmitter. The Channel"C" signal, coincident with the tripped Channel "B" signal caused the "B" MSIV's to clcse.

The design of the EFIC system does not allow technicians to bypass the trip cutputs of a deenergized EFIC cabinet before re-energizing the cabinet following maintenance. Thus,it j-is not possible to perform maintenance er replace components in an r.FIC cabinet without making the system susceptible to spurious trips due to single component failures.

PERFORM ANCE ANOM ALIES

- EFWinitiated due to momentary low steam generater level Indication which resulted fecm a steam pressure spike folicwing the trip of the main turbine.

- A technician erroneously reset the EFW initiation, resulting in overf til of the "B" OTSG

- Annunciation of EFIC Channel"B" trips was irv?'r tive.

- Operators received no alarm indication of *t-t c4 te turbine driven EFW pump Recall system Loop "B" EFW flow indigc.cns.

e mcorrect.

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EVENT ASSES! MENT A. SElluENCE OF EVENTS The following sequence was obtained from the Post Trip Review Summary, Recall System, and the Annunciator Event Recorder. Times are adjusted te match the Annunciato: Event Recorder as follows.

Ann. Event Rec = Post Trip Review - 2 min.56 sec.

I Ann. Event Rec = Recall System - 4 min.51 see L

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EY.22.1.

Justifieation l~

07100 to Spurious actuations Noted on the EFIC 09:30 of EFIC MSLI Ch."B" status / control Trip Bus #1.

switches in the t

control room.

09:35:24 EFIC

'8' Cabinet Annunciator deenergized.

09:36:24 EFIC *B' Cabinet re-Annunciator energized. All outputs in tripped condition.

J' NSLI Ch. "B' trips Annunciator

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09:36:25

'A' High Level Annunciator alarm clears

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09:36:29 OTSG

'A' High Level Annunciator alarm occurs and I'

then clears l'

09:36:36 Nanual reactor trip Annunciator L.

CRD breakers "A thru "D" open 09:36:37 Turb Remote Trip Annunciator Emergency Feechater initiates L

09:36:38 EFIC Closes EF1J control Annunciator valves ~to prevent overfill of OTSG's l

OTSG "A" High Level alarm occurs

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8 09:34:42 Low RC Pressure alarm Annunciator occurs 09:34:44 Pressurizer Low Level Annunciator alarm received f

09:34:45 to EFW actuation reset Annunciator 09:37:01 by technician working in EFIC cabinet is, 09:37:02 Low RC Press Trip Annunciator to 04 09:37:19 RC PZR Lvl Low-Low Annunciator

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alarm received

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09:38:19 OTSG

'B' high level Annunciator alarm occur's 09:38:26 Notor Driven EFW pump Annunciator Auto-Start signal clears 09:38:27 to Steam Driven EFW pump Annunciator 09:39:08

' Steam Supply Not Ready' alarms and 1

clears four times 09:40:21 Pressurizer Low-l ow Annunciator level clears 09:42:10 Low RC Pressure clears Annunciator and alarms six times in one second t

09:42:22 Low RC pressure Annunciator clears 09:42:37 dTSG *B' High Level Annunciator l

clears l

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09:48:03 Motor driven EFW Annunciator

. pump placed in pull-to-Lock

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9. PLANT PERFORMANCE 4.
1. PRE-TRIP REVIEW

.h,,

Crystal River Unit Three was operating a 94% FP and 833 NWE. Operators had noticed intermittent spurious trip signals on Channel 1 of the Channel (Ch.) "B" Main Steam Line Isolation (MSLI) trip module. The signals occurred at 10 to 20 minute intervals between 0700 and 0930 hrs.

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At 0935 I&C technicians deenergized the

'B' Emergency Feedwater i

Initiation and Control (EFIC) cabinet to replace the OTSC "B' NSLI trip

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module. The module tvas thought to be the cause of the intermittent trip signals. It was later learned that the signals were caused by the j-Ch.

'C' Initiate Logic module. The EFIC cabinets are located in a room

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directly below the control room. Operators maintained two-way communications with the technicians while work in the cabinet was under way.

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2. INITIATING EVENT

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The EFIC Channel

'A",

"B",

'C',

and "D' Initiate Logics all feed the

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Ch."B" NSLI trip module. The module uses one-out-of-two-twice loc!c to produce a trip. The NSLI module produces one half-trip from the Ch.'A' QR Ch.*C" trip module inputs, and one half-trip from the Ch."B' OR j

Ch."0" trip module inputs. When the

'B' EFIC cabinet was energized, all

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outputs from the cabinet were tripped, as expected, including the Ch.'B' Initiate Logic. A spuriou's trip signal from the

'C' Initiate Logic appeared before the

'B' cabinet outputs could be reset. The' tripped Ch."B" Initiate signal, coincident with the spurious Ch."C" signal satisfied the one-out-of-two-twice condition and resulted.in closure of the

'B' OTSG Main Steam Isolation Valves.

I When the MSIV's closed the operator manually tripp'ed the reactor.

Nanual trip is required by plant procedure OP-204, " Power Operat i on."

i At this point the control room operator interrupted communication wi th

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the technicians in the EFIC equipment room.

3. POST-TRIP RESP (NSE Closure of the turbine throttle and governor valves resulted in a pressure surge in the DTSG's. Due to the nature of the OTSG 1evel instruments, the pressure surge caused a momentary indication of low l

steam generator level. This phenomenon has been obsrrved at other B&W designed plants with similar instrumentation. The low level indication l

l caused Emergency Feedwater (EFW) actuation. EFIC began to throttle EFW i

control valves (EFV-11,14, 31, and 33) to control EFW flow. The normal standby position for these valves is full open.

l The technicians noticed the EFW actuation and attempted to stop EFW flow t

by resetting the low level trip. When the trip was reset, the EFW control valves returned to the normal standby position while the EFW pumps were still running. Plant procedures require that EFW control valves be in manual control and fully shut before resetting EFW actuations. The technicians reset the trips out of sequence due to lost communication with the control room.

i The

'B' OTSG filled to 100% on the operate range. The

'A' OTSG, which was still steaming, filled to 90%. During the resulting overcooling, pressurizer level dropped from 200 inches to eight inches in r s approximately one minute. Operators started an additional makeup pump to help restore pressurizer level.

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y, During pressurizer level recovery the operators manually closed the EFW ys control valves.

4. OPERATOR ACTI(N AND PROCEDUIML ADEQUACY Operator actions were proper and timely in response to the transient.

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Plant procedures provided adequate instructions for the operators.

Procedures would have prevented the overcooling if the technician had not improperly reset the low level EFW actuation. Guidance did not exist for technicians reguarding expected or allowed actions to be performed when unplanned automatic safejy system actuations occur during b

maintenance activities.

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C. SAFETY CONSIDERATIONS v

1. REACTIVITY CONTROL The reactor was shutdown with all control rods fully inserted following manual trip by the operator.

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2. THERMAL CONTROL Adequate subcooling margin was maintained throughout the transient.

Pressurizer level decreased rapidly during the overcooling, but was

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restored quickly by the operators.

The PORV and RCS code safety relief valves were not challenged.

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3. RADIOACTIVITY INVENTORY CONTROL The radioactive dose as measured from the main steam resin column was less than.01% of all cumulative release permits.

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4. SAFETY EQUIPMENT AVAILABILITY No safety equipment was damaged or otherwise made inoperable during this event.

I D. ASSESSMENT CONCLUSIONS The design of the EFIC system does not provide for bypassing the trip l

outputs of a deenergized EFIC cabinet before re-energizing the cabinet j

following maintenance. Therefore, it is not possible to perform on-line t

maintenance or replace components in an EFIC cabinet without making the system susceptible to spurious actuations due to s;ngle component failures.

Nain Steam Isolation Valves closed automatically due to a spurious EFIC l

Channel

'B' trip module. The operator then manually tripped the Channel

'C' trip signal coincident with a tripped output from the l

4 reactor, as required by plant procedures.

' i Emergency Feedwater initiated despite adequate steam generator levels.

Initiation occurred due to the OTSG 1evel instrumentation response to a pressure surge following turbine trip.

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The ensuing overfeed would have been avoided had the technician conmunicated with the control coorn.before resetting-the EFW actuation.

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18/89/85 09:48 08 FLORIDA POWER CORP. GROUP 8

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