ML17348B192

LER 91-007-00:on 910925,detector Cables for ex-core Nuclear Instrument intermediate-range Channel N-35 Found Disconnected.Caused by Lifted Leads Between N-35 Drawer & Detector.Maint Policy issued.W/911022 Ltr

ML17348B192
Person / Time
Site:	Turkey Point
Issue date:	10/22/1991
From:	Plunkett T, Dawn Powell FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-91-289, LER-91-007, LER-91-7, NUDOCS 9110300012
Download: ML17348B192 (6)

Text

ACCELERATED STMBUTION DEMON TION SYSTEM REGULATORY INFORMATION DXSTRIBUTION SYSTEM (RIDS)

ACCESSION NBR: 9110300012 DOC. DATE: 91/10/22 NOTARIZED: NO DOCKET g FACIL:50-250 Turkey Point Plant, Unit 3, Florida Power and Light C 05000250 AUTH. NAME AUTHOR AFFILIATXON POWELL,D.R. Florida Power & Light Co.

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

RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 91-007-00:on 910925,detector cables for ex-core nuclear instrument intermediate-range Channel N-35 found disconnected. Caused by lifted leads between N-35 drawer & D detector.Maint policy issued.W/911022 ltr. $

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR J ENCL

.TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

/ SIZE:+

NOTES:

RECIPIENT COPIES RECIPIENT COPIES D XD CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 LA 1 1 PD2-2 PD 1 1 AULUCK,R 1 1 INTERNAL: ACNW 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 NRR/DST/SPLB8Dl 1 1 NRR/DST/SRXB 8E 1 1 RE/A.-

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RES/DSIR/EIB 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 NSIC POOREiW 1 1 NUDOCS FULL TXT 1 1 D

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D NOTE TO ALL "RIDS" RECIPIENTS:

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

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

P.O. Box 029100, Miami, FL, 33102-9100 PtrT,g 289'I 10 CFR 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen:

Re: Turkey Point Units 3 Docket No. 50-250 Reportable Event: 91-007-00 Date of Event: September 25, 1991 Unit 3 Entered Mode 2 With One of Two Intermediate Ran e Nuclear Instrumentation Channels Ino erable The attached Licensee Event Report 250-91-007-00 is being provided in accordance with the requirements of 10 CFR 50.73(a)(2)(i) to provide notification of the subject event.

Very truly yours, T. F. Plunkett Vice President Turkey Point Nuclear TEP/CU"8/clm Attachment cc: Stewart D. Ebneter, Regional Administrator, Region II, USNRC Senior Resident Inspector, USNRC, Turkey Point Plant cr110300012 911022 PDR ADOCK 05000250 PDR

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LICENSEE EVENT REPORT (LER)

FACI).ITY NAME (I) TURKEY POINT UNIT 3 DOCKET NUMBER (2) PACE (3) 05000250 OF TITLE (4) UNIT 3 ENTERED MODE 2 WITH ONE OF TWO INTERMEDIATE RANGE NUCLEAR INSTRUMENTATION CHANNELS INOPERABLE EVENT DATE (5) LER NUMBER(6) RPT DATE (T) OTHER FACILI IES INV. l8)

HON DAY YR YR SEQ 6 HON DAY YR DOCKET ( (S)

FACILITY NAMES 09 25 91 91 007 00 10 22 91 OPERATINC MODE (9) 2 10 CFR 50.73 A 2 i PONER LEVEL (10) 000 LICENSEE CONTACT FOR THIS LER (12)

David R. Powell, Superintendent of Licensing TELEPHONE NUMBER 305-246-6559 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT MANUFACTURER NPRDSI CAUSE SYSTEM COFPONENT HANUFACTURER NPRDS?

SUPPLEMENTAL REPORT EXPECTED (14) NO 8 YES 0 EXPECTED SUBMISSION MONT(( YEAR DATE l1 5)

(lf Yee, cceylete EXPECTED SUBMISSION DATE)

ABSTRACT (16)

At 0851 on September 25, 1991, Unit 3 logged entry into Mode 2. At 0950, the Unit 3 Reactor Control Operator declared Excore Nuclear Instrument Intermediate Range Channel N-35 inoperable, prior to going critical, when it did not respond to increasing neutron counts. The detector cables for the N-35 channel were found disconnected at the back of the drawer. The root cause of the event was personnel error by non-licensed utility personnel, in that inadequate control of the lifted leads between the N-35 drawer and the detector occurred. The cables for all other Unit 3 excore detectors were checked to ensure that no other cables were disconnected. The maintenance procedure has been revised to include lifted lead/connector documentation and independent verification. Outstanding plant work orders involving mode-deferred testing have been reviewed to ensure similar concerns for

~theI systems do not exist. Maintenance personnel have been trained on the significance of the event. A policy letter has been issued requiring the use of Lifted Lead Control procedures for work involving lifted leads, when the leads are not specified and independently verified in a procedure. Turkey Point's lifted lead controls will be reviewed against INPO and industry practices.

LICENSE~NT REPORT (LER) TEX9ONTXNUATION FACILITY NAME DOCKET NOSER LER NUMBER PAGE NO.

TURKEY POINT UNIT 3 05000250 91-007-00 02 OF 04 I. EVENT DESCRIPTION At 0851 on September 25, 1991, Unit 3 logged entry into Mode 2, and began diluting to criticality, following refueling. The shutdown banks were fully withdrawn, and control bank D was at 160 steps. Reactor Coolant System boron concentration was approximately 1212 ppm, The unit was at normal operating temperature and pressure. At 0935, dilution was stopped with the inverse count rate (1/M plot) at approximately 0.1 (reactor subcritical).

At 0950, the Unit 3 Reactor Control Operator declared Excore Nuclear Instrument Intermediate Range (IG) Channel N-35 inoperable when respond to increasing neutron counts. The operating crew commenced 3-ONOP-it did not 059.7, Intermediate Range Nuclear Instrumentation Malfunction, and discovered that the signal, compensating, and power cables (IG)(CBL3) from the N-35 cabinet drawer (IG) (CAB) to the detector (IG) (DET) were disconnect-ed at the back of the drawer, The cables were reconnected, and N-35 operability was verified using procedure 3-OSP-059.2, Intermediate Range Nuclear Instrumentation Analog Channel Operational Test. The Plant Supervisor Nuclear then ordered that the control rods be inserted, and that an evaluation of the N-35 failure be performed prior to recommencing staztup. An Event Response Team (ERT) was formed to evaluate the failure.

This event is being reported as a failure to meet Technical Specification 3.0.4, in that Unit 3 entered Mode 2 with less than the minimum number of intermediate range channels operable. Although the action statement was met by returning the channel to operable status prior to increasing thermal power above 10% of rated thermal power (Action 3 of Table 3.3-1), TS 3.0.4 does not allow entry into Mode 2 with only one intermediate range channel operable.

ZZ; EVENT CAUSE An analysis of N-35 maintenance history was performed. The ERT .constructed an event time line, interviewed the personnel involved, and reviewed the Plant Work Orders (PWOs) and procedures that were used in the maintenance of N-35 'roblems specific to this event include the following:

Procedure MP 12707.1, Excore Nuclear Instrumentation Pre-Installation and Post-Installation Inspections and Tests of Detectors, does not

equize the documenting or independent verification of 1ifting/restoring leads.

PWO 8810/63 identified the wrong entry step into MP 12707.1. The section should have been 9.3.2, Post-Installation Electrical Tests; Intermediate Range, which repeats the pre-installation tests, but includes steps to remove the channel from service, and to restore all connections after the test.

PWO 8810/63 indicates that the N-35 cables were left disconnected, and supervisory post-review of the PWO did not confirm reconnection of the cables. The PWO also indicates that MP 12707.1 was completed through step 9.3.2 on September 11, 1991. Substep 9,3.2.4 states, "On completion of tests, restore all connections and install instrument power fuses."

LICENSE~NT REPORT (LER) TEXTONTINUATION FACILITY NAME DOCKET NUMBER LER NVMBER PAGE NO.

TURKEY POINT UNIT 3 05000250 91-007-00 03 OF 04 Verbal communication errors occurred between the I&C day shift and peak shift on September 12, 1991.

Multiple PWOs were in progress on N-35 with no cross-reference between the PWOs.

Post-maintenance testing cannot verify channel functionality. Full circuit verification requires an increase in neutron count rate.

Review of these problems indicates that the immediate cause of the event was failure to reconnect the cables at the back of the N-35 drawer, leaving the Intermediate Range channel inoperable.

The root cause of the event was personnel error by non-licensed utility personnel, resulting in inadequate control of lifted leads.

III . EVENT SAFETY ANALYSIS During a reactor startup, when either of the two intermediate range channels detects greater than 1 E 10 " amps, permissive P-6 is enabled, allowing the operator to block the source range high flux reactor trip. Since failure to do so results in a preventable reactor trip, operators are particularly attentive to the overlap between source and intermediate range indications.

As a result, the operators immediately recognized the failure of N-35 to indicate an on-scale reading at the same time as N-36 (the second channel of intermediate range instrumentation); ultimately this resulted in the conservative termination of the startup, prior to criticality.

The intermediate range high flux reactor trip requires only one of the two channels to cause the trip. Since N-36 was operable, the intended reactor protection function was continuously available. Therefore the health and safety of the public was not affected.

IV. CORRECTIVE ACTIONS I&C Maintenance has revised MP 12707.1 to include independent verifica-tion of lifted leads/connectors.

The cables for the othez intermediate range channel, and for all other Unit 3 excoze detectors were checked to en. uze that no other cables were disconnected.

3. Outstanding PWOs have been reviewed for mode-deferred testing to verify that similar concerns do not exist.

4. A Maintenance policy letter has been issued to require that Attachment 4 of 0-GMI-102.1, Troubleshooting and Repair Guidelines, be included in all I&C PWOs where lifting of leads is concerned, and the leads are not specified and independently verified in a procedure. Attachment 4 documents lifting, landing, and independent verification of leads, cables, or connectors.

LICENSE~NT REPORT (LER) TEXTONTINUATION FACILITY NAME DOCKET NUMBER LER NUMBER PAGE NO.

TURKEY POINT UNIT 3 05000250 91-007-00 04 OF 04

5. The above Maintenance letter also requires that Attachment 3 of 0-GHE-102.1, Troubleshooting and Repair Guidelines, be included in all Electrical PWOs (with the same qualifier as in the I&C PWOs).

Attachment 3 documents lifting, landing, and independent verification of leads, cables, or connectors, for electrical work.

6. The Technical Department will review INPO's good practices on lifted leads, and the lifted lead programs of other power plants, and compare them to our existing lifted lead controls to evaluate the adequacy of our program. The review will be completed by October 31, 1991.

7. The Maintenance Department has trained personnel on (1) the importance and overall responsibility of a complete and thorough PWO pre- and post-review, (2) the importance of proper communication during shift turnovers, and (3) ensuring interrelated PWOs are cross referenced.

V. ADDITIONAL INFORMATION LER 251-89-003, Rev. 01, described a reactor trip due in part to inadequate control of lifted leads. In that event the work was controlled by the Construction Group's Administrative procedures. LER 250-90-010 reported Unit 3 entering Mode 3 with insufficient instrumen-tation to satisfy technical specifications.