ML17348B435

LER 91-007-01:on 911210,4A Sequencer Found in Condition Where Automatic Testing Feature Was Not in Svc Due to Failed Sequencer Auto Test Output Card Relay.Subj Card Replaced & Auto Test Feature disabled.W/920316 Ltr

ML17348B435
Person / Time
Site:	Turkey Point
Issue date:	03/16/1992
From:	Knorr J, Plunkett T FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-92-063, L-92-63, LER-91-007, LER-91-7, NUDOCS 9203240057
Download: ML17348B435 (12)

Text

ACCELERATED ITRJBUTION DEMONS'ATION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

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ACCESSION NBR: 9203240057 DOC. DATE: 92/03'/16 NOTARIZED: NO DOCKET FACIL<50-251 Turkey Point Plant, Unit 4, Florida Power and Light C 05000251 AUTH. NAME AUTHOR AFFILIATION KNORR,J.E. , Florida Power & Light Co.

PLUNKETT,T.F. Florida Power & Light Co.

RECIP.NAME RECIPIENT AFFILIATION 91-007-01:on 911210,4A seguencer f'ound in condition R

SUBJECT:

LER where automatic testing feature was not in svc due to failed sequencer auto test output card relay.Subj,card replaced &

auto test feature di;sabled.W/920316 ltr. D[

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE: S TITLE: 50.73/50.9 Licensee Event R port (LER), Incident Rpt, etc.

NOTES:NRR RAGHAVAN,L 05000251

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A RECIPIENT COPIES RECIPIENT COPIES D ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 LA 1 1 PD2-2 PD 1 1 D AULUCK,R 1 1 INTERNAL: ACNW 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 AEOD/ROAB/DSP 2 2 NRR/DET/EMEB 7E 1 NRR/DLPQ/LHFB1'0 1 1 NRR/DLPQ/LPEB10- 1 NRR/DOEA/OEAB 1 1 NRR/DREP/PRPB11 2'RR/DST/SELB 8D' 1 1 NRR/DST/SICB8H3 ~BR/J)ST SPLB8Dl. 1 1 NRR/DST/SRXB 8E 1 ~REG FILE 02 1 1 RES/DSIR/EIB 1 RGB FILE 01 1 1 EXTERNAL 'EG&G BRYCE g J H 3 3 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHY,G.A 1 1 NSIC PGOREgW. 1 1 NUDOCS FULL TXT 1 1 NOTES:. 1 1 D

'S D

D NOTE TO ALL "RIDS" RECIPIENIS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LKfS FOR DOCUMENTS YOU DON'T NEED!

FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 31 ENCL 31

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P.O. Box 029100, Miami, FL, 33102.9100 QAR 16 1892 L-92-063 10 CFR 50.73 U. S; Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen:

Re: Turkey Point Unit No. 50-251 4'ocket Reportable Event: 91-007-01 Completion of Technical Specification Required Shutdown Due to Failure of 4A 'Load Se uencer Auto Test Out ut Card The attached Supplemental Licensee Event Report 251-91-007-0 is being provided in accordance with 10 CFR 50.73 (a) (2) (i) (A)-

If there are any questions please contact .us.

Very truly yours, T. F. Plunkett Vice President Turkey Point Nuclear TFP/JEK/jk enclosures

, CC: Stewart D. Ebneter, Regional Administrator, Region II, USNRCr Ross C. Butcher, Senior Resident Inspector, USNRC, Turkey Point Plant

'9203240057 'F20316 PDR ADOCK 05000251 S PDR

~EZZ an FPi. Group, company l/i

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LICENSEE EVENT REPORT (LER)

,PACILITY NAHE (1) DOCKET NURSER (2) PACE (S)

TURKEY POINT UNIT 4 05000251 OF Completion of Technical Specification Required Shutdown due to Failure of 4A Load Sequencer Auto Test Output Card.

RPT DATE (I) OTHER FACILITIES INV. (6)

EVENT DATE (5) LER NUMBER (6)

DAY SEQ 6 NON DAY DOCKET 6 (S)

MON YR NAME 12 10 91 91 007 01 3 16 92 OPERATINO NODE (2) 10 CFR 50.73 a 2 tOkER LEVEL (10) 100 (Spoof fy In Abstract belov and in text)

LICENSEE CONTACT FOR THIS LER (12)

James E. Knorr, Regulation and Compliance Specialist TELEPHONE NURSER 305-246-6757 COHPLETE ONE LINE FOR EACH COFZONENT FAIIURE DESCRIBED IN THIS REPORT (IS)

SYSTEH NPRDS CAUSE SYSTEH NPRDS CAUSE EK '1 60

'XPECTED SUPPLEMENTAL REPORT EXPECTED (16) SUBHISS ION DATE (1$ )

MONTH DAY YEAR (If yea, coraplete EXPECTED SUBHISSION DATE)

ABSTRACT (16)

On December 10, 1991, with Unit 4 at 100% power, during a routine system walkdown by the system engineer, the 4A sequencer was found in a condition where the automatic testing feature was not in service.

Since the functionality of. the sequencer could not be verified, the sequencer was declared inoperable at 1345 on that date. No Technical Specification specifically covers the load sequencer. However some safety related systems rely on the sequencer under various analyzed conditions of the plant. Technical Specifications that cover safety-related systems that involve the sequencer have specific Action statements. The most, conservative applicable Action statement required a reactor shut down to hot standby (Mode 3) within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

The plant was taken to Mode 3 at 1937 that same day.

An investigation revealed the root cause of the out-of-s( rvice auto test feature to be a failed sequencer auto test output card relay because of current inrush during each auto test sequence. The card has been replaced and the auto test feature disabled.

This item is reportable in accordance with 10 CFR 50.73(a) (2) (i) (A) .

LICENSEE ENT REPORT (LER) TEXIQONTINURTION FACILITY NAME DOCKET NUMBER LER NUMBER PAGE NO.

TURKEY POINT UNIT 4 05000251 91-007-01 -02 oF 04 Z. EVENT DESCRIPTION On December 10, 1991, a routine system walkdown of the load sequencers was being conducted by the responsible system engineer.

As part of the walkdown the engineer noticed that the 4A sequencer (EIIS-EK) (IEEE-34) was no longer in the auto test mode even though the auto test switch was in the auto test position. The system engineer unsuccessfully attempted to verify the status of the auto test function in the sequencer. Operations personnel were contacted for a restart of the auto test function and a manual test attempt.

These attempts were also unsuccessful. No abnormal alarms, other than the auto test light out, were indicated on either the sequencer alarm modules or in the control room. Since normal operation of the sequencer could not be verified, the sequencer was declared inoperable at 1345 on December 10, 1991.

Technical Specification Table 3.3-2, "Engineered Safety Features Actuation System Instrumentation," defines minimum channels operable and Action statements if these minimums can not be met. The most restrictive of- these Action statements invoked Technical Specification 3.0.3. This specification required the plant to be in hot standby within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, hot shutdown within the following 6 and cold shut down within the subsequent 24.

Turkey Point declared an Unusual Event in accordance with its Emergency Plan at 1737 due to the start of a Unit 4 shutdown required by Technical Specifications. Unit 4 reached hot standby (Mode 3) at 1937 on December 10, 1991 and hot shutdown .(Mode 4) at 0142 on December ll, 1991.

Repair efforts identified and cleared an invalid indication of undervoltage on the 4C load center. During the troubleshooting effort, plant personnel found a faulty auto test output contact card on the 4A sequencer,programmable logic controller .(PLC) (IEEE-DCC) .

Following review and assessment of the corrected fault the sequencer was returned to service and declared operable at 2115 December 1991.

ll, The Unusual Event was terminated at 2115 December 11, 1991.

Notifications of declaration and termination of the Unusual Event were made in accordance with the Turkey Point Emergency Plan Implementing Procedures.

Unit 4 returned to service on December 17, 1991.

II. EVENT CAUSE

a. Immediate Cause The immediate cause of the Unit 4 shutdown was a condition found in the 4A sequencer which had an unknown effect on the operability of the sequencer. Technical Specification Table 3.3-2 action statement 23 required the shutdown of Unit 4 within ( hours.

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LZCENSEE ENT REPORT (LER) TEX1ONTZNUATZON FACILITY NAME DOCKET NUMBER, LER NUMBER PAGE NO.

TURKEY PGINT UNIT 4 05000251 91-007-01 03 oF 04

b. Root Cause The cause of the Unit 4 shutdown was the failure of an output relay on the auto test output contact card on the 4A sequencer PLC.

Detailed inspection of the contact card revealed a sticking contact on a small output relay. The sticking contact provided an input signal to the sequencer that appeared to the sequencer to be a valid input signal of undervoltage on the 4C load center. The sequencer does not allow either auto test or manual test to function input signal is present. This fault resulted in the auto test if a valid function being stopped while the sequencer waited for a safety injection signal. Without the safety injection signal the sequencer would not have actuated. The vendor of the failed output card concluded, after testing, that the output relay failed closed due to high in-rush current exceeding the contact rating of the relay. The vendor theorized that the high in-rush current was due to the effect of direct current switching capacitance created by long field cables.

X-ray examination of the failed relay contacts revealed'hat the failure was due to a material transfer from the fixed contact to the moving arm contact.

III. EVENT SAFETY ANALYSIS The 4A sequencer receives an input from the load center 4C undervoltage relays in a two out of two logic configuration external to the sequencer. Receipt of this signal either from the output relays from this logic or from a test signal which lasts longer than

.2 seconds from the test circuit will take the sequencer out of the auto test mode. An undervoltage signal in conjunction with safety injection and the emergency diesel generator breaker open initiates sequencer operation (i.e., bus stripping if this condition is present for longer than 10 seconds) . Since the safety injection signal was not present, bus stripping and loading did not occur.

The sequencer design allows the performance of a continuous automatic test of all logic inputs and to abort the auto test in response to a valid input. The sequencer can not differentiate between an excessively long test signal and a valid field signal. The sequencer performed- as designed when what it it terminated the auto test in response to sensed as a valid input signal. In this case the signal had not come from the field but from a failed high output module.

Therefore the process logic for a valid undervoltage on the 4C load center was enabled.

Testing has been successful in recreating the intermittent failure of the test output module. Further an intermittent failure was left in place on an identical sequencer used for training. This training sequencer was then tested with a safety injection signal. The test was successful when the sequencer performed and completed its stripping and loading function upon the receipt of the safety injection signal. Had a safety injection signal occurred with a false load center undervoltage signal present the 4A sequencer would have performed its design function for loss of off-site power and safety injection.

'i~ 0 LICENSEE.ENT REPORT (LER) TEEONTINUATION FACILlTY NAME DOCKET NUMBER LER NUMBER PAGE NO.

TURKEY 'POINT UNIT 4 05000251 91-007-01 04 oF 04 If a safety injection signal had occurred without a loss of off-site power the sequencer would have actuated and stripped the 4A 4Kv bus from off-site power, started the emergency diesel generator and sequenced on each of.-the safeguards loads onto the 4A bus. The 4B 4Kv bus would have remained powered from off-site power. During the time of this event the redundant 4B 4Kv bus, the 4B sequencer and the 4B EDG and their associated equipment were operable and capable of performing their intended functions.

IV. CORRECTIVE ACTIONS AD Immediate Corrective Actions

1. Unit 4 was shut down on December 10, 1991.

2. The faulty auto test output contact card on the 4A sequencer programmable logic controller (PLC) was replaced. The auto test output card was also replaced on the 4B sequencer.

3. Verification of operation of the auto test circuit was required to be verified each 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.

B. Corrective Actions to Prevent Recurrence

1. Turkey Point will administratively control the auto test switch in the off position to prevent any other spurious test circuit caused signals on Unit 3 and Unit 4 sequencers.

2. Each eight hours a visual inspection will be made of appropriate status lights on the exterior door of the Unit 3 and Unit 4 sequencers.

3. Every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> the sequencer doors will be opened to verify appropriate status lights on the inside of the cabinet.

4. A manual test of the sequencer is scheduled to be performed according to procedure once each 30 days.

V. ADDITIONAL INFORMATION A. Similar Events None.

B. Failed Parts Manufacturer: Allen Bradley Model Number: Output Module 1771-OW Vendor: United Controls Inc.

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