ML20024J329

LER 94-027-00:on 940903,determined That Channel B Linear Range Nuclear Instrument Inoperable as Result of Connector J6 Being Disconnected from Jack.Connector J6 Reinstalled.W/ 941003 Ltr

ML20024J329
Person / Time
Site:	Millstone
Issue date:	10/03/1994
From:	Lutzi P, Miller D NORTHEAST NUCLEAR ENERGY CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-94-027-01, LER-94-27-1, MP-94-569, NUDOCS 9410130341
Download: ML20024J329 (4)

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Northerst Rope Ferry Rd. (Route 156), Waterford, CT 06385 Nuclear Energy Minstone Nuclear Power Station Northeast Nuclear Energy Company P.O. Box 128 Waterford, C1'06385-0128

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"*-h20u 20 Ci The Northeast Utilities System Donald B. Maler Jr.,

Senior Vice President - Millstone Re: 10CFR50.73(a)(2)(i)

October 3, 1994 MP-94-569 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555

Reference:

Facility Operating Ucense No. DPR-65 Docket No. 50-336 Licensee Event Report 94-027-00 , ,, ,_._

This letter forwards Licensee Event Report 94-027-00 required to be submitted within thirty (30) days pursuant to 10CFR50.73(a)(2)(l).

Very truly yours, NORTHEAST NUCLEAR ENERGY MP NY f

Donald B.- Miller, Jr.

Senior Vice President - Millstone Station DBM/DC:ljs

Attachment:

LER 94-027-00 cc: T. T. Martin, Region I Administrator P. D. Swetland, Senior Resident inspector, Millstone Unit Nos.1, 2, and 3 G. S. Vissing, NRC Project Manager, Millstone Unit No. 2

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Millstone Nuclear Power Station Unit 2 05000336 1 OF 3 TifLE (4)

Channel "B" Unear Range NI Inoperable EVENT DATE (5) LER NUMBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED (8)

MONTH DAY YEAR VEAp SE RE Si MONTH DAY YEAR FACIUTY NAME DOCKET NUMBER g

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TELEPHONE NUMBER (include Area Codei Philip J. Lutzi, Nuclear Licensing (203) 440 -2072 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

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ABSTRACT (umn to 1400 spaces. I e . approomatety 15 smgie-spaced typewrmen sines) (1s)

On September 3,1994, at 0426, with the plant at approximately 5% power, it was determined that the Channel "B" Unear Range Nuclear Instrument was inoperable when the plant changed operating modes from Mode 2 to Mode 1.

f Instrument technicians called in to investigate found High Voltage Connector J6 disconnected from its jack on the back of Channel "B" Drawer. (if J6 is not connected, the High Voltage supply to the ion chambers is interrupted and the drawer output will fail low.)

This event is being reported pursuant to requirements of paragraph 50.73(a)(2)(i), any operation prohibited by the plant's Technical Specifications, because Channel "B" was declared operable prior to entering Mode 1, and then subsequently found to be inoperable.

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1. Descriotion of Event On September 3,1994, at 0426, with the plant in mode 1 at approximately 5% power, it was determined that the Channel *B" Linear Range Nuclear Instrument was inoperable when the plant changed operating modes from Mode 2 to Mode 1. During the previous shift's performance of the Reactor Protection System channel check, Linear Range NI Power Channels A, B, C & D read 1.88%, -0.1%,1.8%, and 1.9%

respectively. These values met the channel check acceptance criteria (deviation between channels less than 5% during Mode 1 or Mode 2 operations), allowing transition to operating mode 1 on backshift.

After shift turnover the power ascension to Mode 1 (> 5% Thermal power) continued. Channel "B" did not track consistently with the other three channels. The plant entered Mode 1 at 0425 on September 3. At j .

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the Plant Process Computer (PP ) in response to the alarm, Indication for Channel B" was -0.11%,

which differed more than 5% from the other channels. Technical Specifications Action Statement 3.3.1.1 was entered, and Channel"B" was declared inoperable. No automatic or manual safety responses occurred.

Instrument technicians called in to investigate found High Voltage Connector J6 disconnected from its jack on the back of Channel "B" Drawer. (if J6 is not connected, the High Voltage supply to the lon chambers is interrupted and the drawer output will fail low.)

II. Cause oLEvent I When the Channel "B" Linear Range NI drawer was opened by I&C personnel, technicians found connector J6 disconnected from its jack. The J6 connector for each Model NP-6 Dual Linear Power Drawer energizes two B-10 lon chambers which then indicate neutron flux in the Linear (Power) Range. If J6 is not properly connected, the High Voltage supply to the lon chambers is interrupted and drawer output will fait low. The suspected Root Cause of this event is a combination of personnel error and equipment configuration, in that HV Connector J6 on the Linear Range NI Power Drawer may not have been properly reconnected following maintenances, and subsequent repeated opening and closing of the drawer apparently caused the connector to loosen.

The J6 connector for each drawer is removed and reinstalled twice in each of two separate l&C test procedures. The last time either of these procedures was performed prior to the event was July 21,1994.

l&C personnel reinstalling the connector after maintenance or testing cannot confirm visually that the connection is correctly made up. After monthly testing in Mode 1, I&C technicians confirm proper system restoration by comparing Linear Range NI Power Drawer indication with other channels before testing on a second drawer is started. Below Mode 1, this comparison is not meaningful because neutron flux levels are off-scale low for the Unear Range Nis. The Unit experienced no deviation alarms on channel "B" between July 21 and July 27, when the unit came off line for upgrade of the Reactor Coolant Pump (RCP)

Oil Collection System. Because no deviation alarms were received, it can be assumed that the J6 connector did not come loose until during the shutdown.

The J6 connector is subject to bending stresses from the position of the connector relative to the cable bundle for the drawer. If not properly reconnected after being removed for testing, the stresses from repeated opening and closing the Ni drawer could cause J6 to work loose. Five procedures require Linaar Range Ni Power Orswers to be opened for access to test potentiometers. Three of these procedures were performed during the August shutdown. Two of them were performed during the week prior to the J6 connector being found disconnected. Neutron flux levels were off-scale low for the Linear Range Nis, which would preclude discovery of a loose J6 connector by either channel deviation alarms or comparison with other channels. While shutdown, technicians also removed and reinstalled the J6 connector on the "B" Linear Range NI Drawer while conducting ground loop isolation for Channel "B" ion chamber cabling.

Again, neutron flux levels were off-scale low, prohibiting comparison with other channels

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94 - 027 - 00 03 OF 03 TEXT (n mas space e regwed, use addmonal copes of NRC Form 366A) (17) til. Analysis of Event This event is being reported pursuant to requirements of paragraph 50.73(a)(2)(i)(b), any operation prohibited by the plant's Technical Specifications.

Channel "B" was declared operable prior to entering Mode 1 and then subsequently found to be Inoperable because the J6 High Voltage connector was disconnected from the Unear Range NI Drawer.

The safety consequences of this event have been determined to be negligible. The ability of the Reactor Protection System to provide a trip signal from two of the three channels of unear Range Nls (the minimum called for by the plant Technical Specifications) was unaffected.

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IV. Cor75ctive ActioD The J6 Connector was reinstalled. When the "B" drawer was reenergized, NI power indication on all four channels matched closely at approximately 7% power. The l&C Technician who had performed the most recent work related to connector J6 was counseled on the need to ensure that this, and similar connectors, ere properly and securely made up.

The next time connector J6 was removed and replaced for testing, the following cautionary note to technicians was added to the work package:

" Ensure that connector J6 is documented with lifted lead form (WC-10 attachment 3). Ensure connector is M Cur 3.*

Action to Prevent Recurrence All N1 drawer connectors will be verified properly terminated to their respective jacks during the current refueling outage, which started October 1,1994.

An automated work order has been written to add cable restraining harnesses to the Unear Range HV cables in the RCOSA/B/C/D cabinets to relieve tension on the cables and their electrical connections in the rear of the drawers.

This event was also discussed in detail during an l&C Department meeting.

V. Additional information The drawer is Gulf General Atomics Model NP-6 Dual Unear Range Drawer, ELJ 179-00005L, serial number W61149-5.

No similar LERs found in a database search.

Ells Codes PR-SAF-B JC-B/P-G063

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