05000424/LER-2005-001, Automatic Reactor Trip Due to Broken Wire Connector
| ML050660274 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 03/02/2005 |
| From: | Grissette D Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-05-0321 LER 05-001-00 | |
| Download: ML050660274 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation |
| 4242005001R00 - NRC Website | |
text
Don E. Grissette Southern Nuclear Vice President Operating Company, Inc.
40 Inverness Center Parkway Post Office Box 1295 Birmingham, Alabama 35201 Tel 205.992.6474 Fax 205.992.0341 SOUTHERNN.Zk March 2, 2005 COMPANY Energy to Serve YourWorldw Docket No.:
50-424 NL-05-0321 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Vogtle Electric Generating Plant - Unit I Licensee Event Report 1-2005-001 Automatic Reactor Trip Due to Broken Wire Connector Ladies and Gentlemen:
In accordance with the requirements of 10 CFR 50.73, Southern Nuclear Operating Company hereby submits a Vogtle Electric Generating Plant licensee event report for a condition that was determined to be reportable on January 11, 2005.
This letter contains no NRC commitments. If you have any questions, please advise.
- Siarely, Don E. Grissette DEG/kgl/daj Enclosure: LER 1-2005-001 cc:
Southern Nuclear Operating Company Mr. J. T. Gasser, Executive Vice President Mr. W. F. Kitchens, General Manager - Plant Vogtle RType: CVC7000 U. S. Nuclear Regulatorv Commission Dr. W. D. Travers, Regional Administrator Mr. C. Gratton, NRR Project Manager - Vogtle Mr. G. J. McCoy, Senior Resident Inspector - Vogtle
Abstract
On January 11, 2005, an automatic turbine trip / reactor trip occurred due to a main generator protective relay lockout. A normal reactor trip sequence ensued and the control room staff responded by transitioning the unit to operation in Mode 3 (Hot Standby).
A continuity check of field connections for the protective relay showed very high resistance through an auxiliary potential transformer which is connected to the secondary of the generator neutral grounding transformer. Inspection of the connection revealed that a wire on a terminal strip in the secondary circuit wiring of the auxiliary potential transformer had failed and disconnected when touched. The high resistance measurement at the potential transformer was apparently due to this failed connection. An analysis of the failed connection determined there was prior damage to the wire at the point where the lug was attached. The damage most likely occurred when the lug was first installed prior to initial plant startup. Over time, the remaining conductors fatigued due to vibration until the high resistance connection developed. As a result of the high resistance the relay sensed an invalid fault. The connection was repaired and the unit was returned to power operation.U.S. NUCLEAR REGULATORY COMMISSION (1.2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL I REVISION YEAR I NUMBER Vogtle Electric Generating Plant - Unit 1 05000-424 2005 001
-- 00 2 OF 4 TEXT (If mnore space is required, use additional copies of NRC Form 366A) (17 A. REQUIREMENT FOR REPORT This report is required per 10 CFR 50.73 (a)(2)(iv) because an unplanned actuation of the reactor protection system occurred.
B. UNIT STATUS AT TIME OF EVENT At the time of this event, Unit I was operating in Mode 1 (power operation) at 100% of rated thermal power. Other than that described herein, there was no inoperable equipment that contributed to the occurrence of this event.
C. DESCRIPTION OF EVENT
On January 11, 2005, at 0719 EST, an automatic turbine trip / reactor trip occurred due to a main generator protective relay lockout. Control rods inserted, main feedwater isolated and the auxiliary feedwater system actuated per the plant design. The control room staff responded by transitioning the unit to normal operation in Mode 3 (Hot Standby).
D. CAUSE OF THE EVENT
Following the reactor trip, a walkdown of the Main Control Room Protective Relay Panel revealed that Main Generator Lockout Relay 386-G3 had rolled and that a target was displayed on relay 364NG.
Subsequent investigations revealed that protective relay 364NG appeared to be in calibration and functioning properly. However, a continuity check of its field connections showed very high resistance through an auxiliary potential transformer which is connected to the secondary of the generator neutral grounding transformer. Once the generator was tagged out and scaffolding erected to access the electrical equipment in the generator dome, an inspection of the protective relaying connections revealed that wire "G4" on a terminal strip in the secondary circuit wiring of the auxiliary potential transformer was damaged after it was touched. The high resistance measured from the relay was apparently due to this failed connection. After repair of the lug and visual inspection of the remaining wiring, the circuit resistance check was satisfactory.
Based on further inspection and analysis, the failed conductor in the main generator dome is attributed to prior damage to the wire at the point where the lug was attached. The lug was the appropriate size and appeared to have been properly crimped. The wire damage may have occurred when the lug was first installed prior to initial plant startup, and it may also have been caused and/orU.S. NUCLEAR REGULATORY COMMISSIONU.S. NUCLEAR REGULATORY COMMISSION (1-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL [REVISION I
YEAR lNUMBER Vogtle Electric Generating Plant - Unit 1 05000-424 2005 001
-- 00 3 OF 4 TEXT (If more space Is required, use additional copies of NRC Form 366A) (17 exacerbated by personnel accessing the generator dome space. Over time, the damaged conductors fatigued due to vibration until a high resistance connection developed. Decreasing voltage to the 364NG relay due to the high resistance connection eventually tripped the relay.
Contributing to the cause of this event was that no specific inspections or testing were performed that may have discovered the degraded connection prior to failure.
E. ANALYSIS OF EVENT
The reactor trip and subsequent AFW actuation occurred as designed. Control room personnel acted appropriately to maintain the proper steam generator water levels during the event and to transition the unit safely into Mode 3.
Based on these considerations, there was no adverse effect on plant safety or on the health and safety of the public as a result of these events.
This event does not represent a safety system functional failure.
F. CORRECTIVE ACTIONS
- 1) The damaged connection was repaired and the unit was returned to power operation.
- 2) Preventive maintenance instructions will be revised to include a specific inspection of electrical and mechanical components within the generator dome area. The instructions will provide details covering all critical components and will be implemented as a close out inspection of the dome area. The generator dome inspections detailed in the revised instructions will be performed during the next refueling outage in each unit. Both are scheduled to be completed in 2005.
G. ADDITIONAL INFORMATION
- 1) Failed Components:
Copper cable #14 AWG - Manufacturer unknown
- 2) Previous Similar Events:
There have been no previous similar events in the last three years.
- 3) Energy Industry Identification System Code:
Main Feedwater System - SJU.S. NUCLEAR REGULATORY COMMISSION I 1-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL REVISION Vogtle Electric Generating Plant - Unit 1 05000-424 2005 lw UB l0 4 OF4 TEXT (if mnore space is required, use additional copies of NRC Form 366A) (17 Auxiliary Feedwater System - BA Control Rod Drive System - JD Main Generator Control Power System - EL