ML18036A258

LER 91-004-01:on 910326,reactor Protection Sys Actuation Occurred.Cause Undetermined.Ground Fault in Intermediate Range Monitor Channel C Detector Cable Shield Removed.W/ 910624 Ltr

ML18036A258
Person / Time
Site:	Browns Ferry
Issue date:	06/24/1991
From:	Wetzel S, Zeringue O TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-004-02, LER-91-4-2, NUDOCS 9106270339
Download: ML18036A258 (12)

Text

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9106270339 DOC ~ DATE: 91/06/24 NOTARIZED: NO DOCKET FACZL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 0500026 AUTH. NAME AUTHOR AFFILIATION WETZEL,S.A. Tennessee Valley Authority ZERINGUE,O.J. Tennessee Valley Authority RECIP.NAME RECIPZENT AFFILIATION

SUBJECT:

LER 91-004-01:on 910326,reactor protection sys actuation occured.Cause undetermined. Ground fault in intermediate range monitor channel C detector cable shield removed.W/

910624 ltr.

DISTRIBDTION CODE: IE22T COPIES RECEIVED: LTR TITLE: 50.73/50.9 Licensee Event Report (LER)-,

i ENCL g SIZE:

Incident Rpt, etc.

NOTES:1 Copy each to: S.Black,B.WILSON 05000260 RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ,ID CODE/NAME LTTR ENCL KREBS,M. 1 1 HEBDON,F 1 1

,ROSS,T. 1 1 INTERNAL: ACNW 2 2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DSP 2 2 NRR/DET/ECMB 9H 1 1 NRR/DET/EMEB 7E 1 1 NRR/DLPQ/LHFB10 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB 1 1 NRR/DREP/PRPB11 2 2 NRR/DST/SELB 8D 1 1 NRR/DST/SICB8H3 1 1 NRRyR)S~ LB8D1 1 1 NRR/DST/SRXB 8E 1 1 02 1 1 RES/DSIR/EIB 1 1 RGN2 FILE 01 1 1 EXTERNAL: EG&G BRYCE,J.H 3 3 'L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHY,G.A 1 1 NSIC'OOREPW 1 1' NUDOCS FULL TXT 1 1 NOTES: 5 NOTE TO ALL "RIDS" RECIPIENTS'LEASE HELP US TO REDUCE IVASTE! CONTACT THE DOCUMENT'CONTROL DESK, ROOM P 1-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 38 ENCL 38

iJ Tennessee Valley Authority. Post Office Box 2000. Decatur.'Alabama 35609 O. J. 'Ike Zeringue Vice President, Browns Ferry Operations gUN 24 1991 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

Dear Sir:

TVA BROWNS FERRY NUCLEAR PLANT (BFN) UNIT 2 DOCKET NO. 50-260 FACILITY OPERATING LICENSE DPR-52 REPORTABLE OCCURRENCE REPORT BFRO-50-260/91004, REVISION 1 The enclosed report provides details concerning Unit 2 Reactor Protection System actuation from source range monitor spiking during the performance of time domain reflectometer trace on an intermediate range monitor.

This report is submitted in accordance with 10 CFR 50.73(a)(2)(iv).

Very truly yours, TENNESSEE VALLEY AUTHORITY u~t'i'~(t4(

J ering Enclosure cc: see page 2

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U.S. Nuc'lear Regulatory Commission

""" 24 1991, cc (Enclosure):

INPO,Records Center Sui:te 1500 1100..Circle 75 Parkway Atlanta,,Georgia 30339 NRC Resident Inspector, BFN Regional Administration U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region II 101 Marietta Street, Suite 2900 Atlanta, Georgia 30323 Thierry M. Ross U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland'0852

0 0 Approve HB No. 3150- 0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

FACILITY NAHE (1) (DOCKET NUMBER (2) I B n r TITLE (4) Reactor Protection System Actuation as a Result of Exceeding the Hi-Hi SRH Channel Setpoint During 1

V N ~

0 P T I I I SEQUENTIAL l IREVISIONI I i I FACILITY NAHES )DOCKET NUHBER(S NTH Y AR A N R T DA OPERATING iTHIS REPORT IS SUBHITTED PURSUANT TO THE RE(UIREHENTS OF 10 CFR g:

HODE k r wi l20 402(b) (20.405(c) I~ISO 73(a)(2)(iv)

~ l73 71(b)

~

POWER )20.405(a)( l)(i) (50.36(c)(l) (50.73(a}(2}(v) (73.71(c)

LEVEL [20.405(a)( l)(ii) i50 36(c)(2)

~ (50.73(a)(2)(vii) (OTHER (Specify in

)20.405(a)(l)(iii) I 150.73(a)(2)(i) 150.73(a)(2)(viii)(A) ) Abstract below and in I l20.405(a)( 1)(iv) (50.73(a)(2)(ii) t [50.73(a}(2}(viii}(B}) Text, NRC Form 366A)

.4 v N NT T I AREA CODE I P E N PNNT L 8 0 l I I /REPORTABLE/ ( ) )REPORTABLE)

YT H 1T HA TR T H I l I I. I l

.I I I l I I PP HN P T 14 1 SUBHISSION )

f m T 0 DA N ABSTRACT (Limit to 1400'paces, i.e., approximately fifteen single-space typewritten lines) (16)

On March 26, 1991, at 2024 hours0.0234 days <br />0.562 hours <br />0.00335 weeks <br />7.70132e-4 months <br />, Unit 2 Reactor Protection System actuation occurred'hen the count rate on the .source range monitor (SRM) channel C spiked while a time domain reflectometer (TDR) trace was being performed on the Unit 2 intermediate range monitor (IRM) channel C detector cable shield.

The root cause of this event could not be determined. The scram was the result of an unexpected hi-hi trip generated during the performance of TDR tracing on an located in the proximity of the SRM channel C cable. However, the cause of IRM'able the hi-hi trip signal could not be determined or repeated.

The ground fault in the IRM channel C detector cable shield was removed. In addition, the neutron monitoring system, including the interaction between channels, was evaluated. From the information gathered during this evaluation; TVA developed and implemented corrective actions directed to both the neutron monitoring hardware and to the maintenance procedures-NRC Forrri 366(6-89)

IO l

t 0rm Approve ONB No. 3150- 0104 (6-89) Expires 4/30/92 lICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NANE (1) )OOCKET NUMBER (2)

I I I 'tSEQUENTIAL 1 IREVISIONJ f ) I f .

I I I I I

rw 'F TEXT (If more space is required, use additiona1 NRC Form 366A's) (17)

On Narch 26, 1991, at 2024 hours0.0234 days <br />0.562 hours <br />0.00335 weeks <br />7.70132e-4 months <br />, Unit 2 Reactor Protection System (RPS) [JC1 actuation occurred when the count rate on source range monitor (SRM) [IG]

channel C spiked high. The high count rate resulted in the receipt of a hi-hi trip signal by the RPS logic which was in the non-coincident scram mode.

At the time of this event, Unit 2 IRM channel C detector cable shield had been identified to be shorted to ground, and a time domain reflectometer (TDR) trace was being performed on the IRM detector cable shield to determine the location of the ground. During the performance of the TDR trace, SRM channel C count rate suddenly increased (spiked) causing a full reactor scram. The TDR was immediately turned off following the scram. The spiked SRM was cleared and the scram reset at 2026 hours0.0234 days <br />0.563 hours <br />0.00335 weeks <br />7.70893e-4 months <br />.

Units 1 and 3 were defueled. Unit 2 was in cold shutdown with all control rods fully inserted. All systems functioned as expected under the above plant condition. This event is reportable in accordance with 10 CFR 50;73(a)(2)(iv).

A hi-hi tr'ip signal on an SRN channel with the neutron monitoring system in the non-coincident mode will generate a full .reactor scram whenever the count rate exceeds a preset limit. Since the SRM scram circuitry functioned according 'to design, this event had no adverse impact on nuclear safety.

The root cause of this event could not be determined. The scram was the result of an unexpected hi-hi trip signal genera'ted during the performance of TDR tracing on an IRM cable located in the proximity of"'the SRM channel C cable.

However, the cause of the hi-hi trip signal could not be determined or repeated.

The ground fault in the IRM channel C detector cable shield was removed by reworking the detector cable connector at the drywell penetration.

The interaction between channels was,evaluated to determine if the source of the hi-hi trip signal on the SRM channel could be located. This evaluation was unable to repeat the incident and was also unable to identify the source of this phenomenon.

NRC Form 366(6-89)

Ik (6-89) oPAl R LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION I

l Approved ONB No. 3150-0104 Expires 4/30/92 FACILITY MANE (1) lOOCKET NUNSER (2) 1 J SEQUENTIAL ) ) REVISION) )

I I I I TEXT (If more space is required, use additional NRC Form 366A's) (17)

In addition, a team of TVA and vendor personnel has evaluated the entire Unit 2 neutron monitoring system, including the IRMs, SRMs, local power range monitors, rod block monitors and traversing incore probes. This evaluation involved diagnostic testing such as: cable leakage currents, signal loss, electromagnetic interference (EMI), pre-amplifier gain and proper detector response.

From the information gathered during this evaluation, TVA developed corrective actions directed to both the neutron monitoring hardware and to the maintenance procedures. Hardware repairs or replacement included items such as: cleaning or replacing connectors with high leakage, using ferrite beads on SRM and IRM detector cables to reduce EMI problems, replacement of pre-amplifiers in two IRM channels to eliminate intermittent noise and oscillations, replacement of capacitors in the IRM high voltage power supplies to reduce noise output, and replacement of zener diodes in the IRM modules to alleviate temperature induced voltage drift.

The evaluation of neutron monitoring procedures involved review of both plant maintenance procedures and surveillance instructions (SIs). Although no deficiencies were identified, the vendor provided its specific procedures for implementation at BFN. TVA is in the process of upgrading BFN maintenance procedures for the neutron monitoring system to incorporate the vendor information.

None TVA will revise BFN's maintenance procedures for the neutron monitoring system to incorporate the vendor information. These actions will be completed prior to startup following the Unit 2, cycle 6, refueling outage.

Energy Industry Identification System (EIIS) codes are identified in the text as fxx] .

NRC Form 366(6-89)

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