05000400/LER-1987-001, :on 870111,alarm Received Indicating That Data B Inputs Failed on Rod Withdrawn from Core.Caused by Mfg Deficiency Leading to Unreliable Rod Position Info.Reactor Trip Breakers Opened

:on 870111,alarm Received Indicating That Data B Inputs Failed on Rod Withdrawn from Core.Caused by Mfg Deficiency Leading to Unreliable Rod Position Info.Reactor Trip Breakers Opened

ML20210T503
Person / Time
Site:	Harris
Issue date:	02/06/1987
From:	Hudson O, Watson R CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
HO-870348-(O), LER-87-001, LER-87-1, NUDOCS 8702180202
Download: ML20210T503 (4)

LER-1987-001, on 870111,alarm Received Indicating That Data B Inputs Failed on Rod Withdrawn from Core.Caused by Mfg Deficiency Leading to Unreliable Rod Position Info.Reactor Trip Breakers Opened

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)
4001987001R00 - NRC Website

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Abstract While the plant was in mode 3, with shutdown banks C & D withdrawn, Digital Rod Position Indication (DRPI) Data A inputs were out of service to repair loose connector pins. At 0232 on January 11, 1987, an alarm was received indicating Data B inputs had failed on a rod withdrawn from the core.

Technical Specification 3.1.3.3 requires DRPI to be capable of determining control rod position with i 12 steps for rods not fully inserted. The action required for loss of this indication is to immediately open the Reactor Trip Breakers. Therefore, upon receipt of the alarm on Data B inputs, the Reactor Trip Breakers were opened.

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Description

The event resulted due to a failure in the Digital Rod Position Indication System (DPRI). The digital rod position indication system measures the actual position of each control rod using a detector which consists of discrete coils mounted concentrically with the rod drive pressure housing. The coils are located axially along the pressure housing and magnetically sense the entry and presence of the rod drive shaft through its centerline.

For each detector, the coils are interlaced into two data channels, and are connected to the containment electronics (Data A and B) by separate multi-conductor cables. By emoloying two separate channels of information, the digital rod i

position indication system can continue to function (at reduced accuracy) when one channel fails. Either Data channel is sufficient to satisfy the Tech.

Spec. requirements for Modes 3, 4 and 5.

Repeated data failure alarms had been received on DRPI caused by electrical connector problems in the cables between the Data A and Data B cabinets and I

the sensing coils. The previous failures resulted in loss of indication for individual rods or for Urgent Warning Alarms on either the Dat*a A or Data B channels. The cause of the problem was traced to the removable male connectors on the Individual rod cables located at the connector plate which l

l is atop the Reactor Vessel Head. The connectors (Rowe Part Nos. 2RC6562 &

6RC6563) were found to have loose pins as a result of improper fabrication by the manufacturer, Rowe. During'the replacement of failed connector pins, it was discovered that the connector pins were to be torqued to a specified i

value. This information and a torquing tool were included in the replacement j

pin kit. This information was not available from the other technical information on site.

On January 11, 1987, while the plant was in Mode 3 at 557' and 2235 psig (normal operating temperature and pressure), connectors were checked for loose pins. The reactor trip breakers were closed so that shutdown banks C & D could be maintained fully withdrawn por General Operating Procedure CP-2.

Maintenance I&C technicians started by working on the Data A connectors, one at a time.

Since numerous alarms were expected, DRPI Data A was bypassed in the control room at 1625 on January 10, 1987. The resulting rod position indication from Data B sensors (half accuracy) met the LCO for Tech. Spec.

i 3.1.3.3.

Apparently while working in the area, other connectors for Data B inputs were moved or vibrated, causing an alarm on Data B.

Since Data A was already out of service, this caused DRPI Urgent Failure Alarm at 0232 on January 11, 1987.

Lois of both Data A and Data B meant that the Tech. Spoc.

LCO was no longer met. Therefore, the reactor trip breakers were manually opened per the Action Statement of Technical Specification 3.1.3.1.

All systems responded as expected and the plant stabilised at normal opor uin.t temperature and pressure.

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Subsequently, at 0400 DRPI Data A was restored to service giving at least half accuracy on all rods and thus satisfying the LCO of Tech. Spec. 3.1.3.3.

All required connectors were retightened and restored to service by January 12, 1987. Since that time, no repeat alarms have been received due to loose connectors.

Cause

The manual scram was a result of manual operator action to comply with Technical Specification 3.1.3.3.

The DRPI system became inoperable during the repair of loose electrical connectors on the individual rod cables.

Analysis As stated above, the event resulted from a manufacturer's deficiency that led to unreliable rod position information. The plant was already in Mode 3 and the event had no impact on safety.

This event is reportable in ancordance with 10CFR50.73(a)(2)(fv) which requires reporting of any event or condition that resulted in manual or automatic actuation of any Engineered Safety Feature.

Corrective Action

The root cause of the problem was identified prior to the event. The event occurred during implementation of the corrective action.

Since the completion of corrective action, no repeat alarms have been received due to loose connectors.

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Cp&L Carolina Power & Light Company HARRIS NUCLEAR PROJECT P. O. Box 165 New Hill, NC 27562 FEB 0 61981 l

File Numbert SHF/10-13510C Ref. 10CFR50.73 Letter Numbert HO-870348 (0) l U.S. Nuclear Regulatory Commission-ATTN! NRC Document Control Desk Washington, DC 20555 i

SHEARON HARRIS NUCLEAR POWER PLANT UNIT 1 i

DOCKET No. 50-400 LICENSE NO. NPF-63 LICENSEE EVENT REPORT 87-001 Centlement In accordance with Title 10 to the Code of Federal Regulations, the enclosed Licensee Event Report is submitted. This report fulfills the requirement for a written report within thirty (30) days of a reportable occurrence and is in accordance with the format set forth in NUREC-1022, September 1983.

Very truly yours, b

R. A. Watson Vice President llarris Nuclear Project RAWiskm Enclosure ces Dr. J. N. Crace (NRC - R11)

Mr. C. Maxwell (NRC - SilNPP) l I

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