05000425/LER-2004-004, Unit 2 Automatic Reactor Trip Followed by Safety Injection
| ML050210160 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 01/18/2005 |
| From: | Grissette D Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-05-0040 LER 04-004-00 | |
| Download: ML050210160 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation |
| 4252004004R00 - NRC Website | |
text
Don E. Grissette Vice President Southern Nuclear Operating Company, Inc.
40 Inverness Center Parkway Post Office Box 1295 Birmingham, Alabama 35201 Tel 205.992.6474 Fax 205.992.0341 SOUTHERNNA COMPANY Energy to Serve Your World' January 18, 2005 Docket No.: 50425 NL-05-0040 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Vogtle Electric Generating Plant Licensee Event Report 2-2004-004 Automatic Reactor Trip Followed by Safety Injection 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 November 20, 2004.
If you have any questions, please advise.
Don E. Grissette DEG/RJF/daj Enclosure: LER 2-2004-004 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 Regulatory Commission Dr. W. D. Travers, Regional Administrator Mr. C. Gratton, NRR Project Manager - Vogtle Mr. G. J. McCoy, Senior Resident Inspector-Vogtle D,--
Abstract
On November 20, 2004, 'B' Train Solid State Protection System Testing was in progress with the 'B' Train in the "inhibit mode" for testing. Operators performing the test erroneously operated the 'A' Train Solid State Protection multiplexer test switch which disabled 'A' Train SSPS completing the logic for an automatic reactor trip at 1140 EST. Subsequent to the trip, the Loop 2 Tavg instrument channel failed at its full power value causing a full-open steam dump demand. Control room personnel responded to the decreasing reactor coolant system (RCS) temperature by initiating a Main Steamline Isolation, but the pressure drop was sufficient to result in an automatic Safety Injection (SI) actuation. As designed, the SI signal initiated a Control Room Isolation, a Containment Ventilation Isolation, and a Phase A Containment Isolation. After RCS pressure recovered, control room personnel secured Safety Injection and transitioned the unit to normal operation in Mode 3 (Hot Standby).
The cause of the reactor trip was human error in that the operator erroneously manipulated a test switch on the 'A' Train SSPS. The cause of the SI was the failure of a lead-lag circuit card that lead to the failure of the Loop 2 Tavg circuitry and subsequent full opening of the steam dump valves and RCS pressure drop. A number of actions were implemented to address the human performance errors and the failed lead-lag card was replaced and test satisfactorily.U.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 NUMBER Vogtle Electric Generating Plant - Unit 2 05000-425.
2004 004 00 2 OF 4 TEXT (If more space is required, use additional copies of NRC Form 366A) (17 A. REQUIREMENT FOR REPORT This event is reportable per 10 CFR 50.73 (a)(2)(iv) because an unplanned reactor protection system actuation occurred and multiple unplanned engineered safety features (ESF) actuations occurred.
B. UNIT STATUS AT TIME OF EVENT At the time of this event, Unit 2 was operating at 100 percent 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 November 20, 2004, personnel were performing testing per 14421-2, "Solid State Protection System and Reactor Trip Breaker Train 'B' Operability Test." Solid State Protection System (SSPS)
Train 'B' was in the 'inhibit' mode for testing. Two operators were performing a step which directs the placement of the multiplexer test switch to the 'A+B' position. However, the operators were erroneously located at the 'A' Train SSPS, instead of the 'B' Train SSPS. They identified the switch, performed a peer check, and placed the 'A' Train SSPS multiplexer test switch in the 'A+B' position.
This required the test switch to pass through the 'inhibit' position resulting in a 2 out of 2 General Warning signal for both SSPS trains being in the "inhibit" mode and completed the logic for an automatic reactor trip at 1140 EST. All rods inserted, main feedwater isolated, and the Auxiliary Feedwater System (AFW) actuated as designed to supply feedwater to the steam generators (SGs).
Following the reactor trip, it was discovered that the Loop 2 Tavg instrument, 2T42 1, was failed at its full power value, causing a full-open demand for the steam dump valves. The opening of the steam dump valves led to a rapid drop in reactor coolant system (RCS) temperature and pressure. Control room personnel responded to the decreasing RCS temperature by initiating a Main Steamline Isolation, and the steam dump valves automatically closed as RCS temperature decreased to 550 degrees F. However, the RCS pressure drop to 1833 psig was below the 1870 psig setpoint for initiating an automatic Safety Injection (SI) actuation, which occurred at 1140 EST. The SI signal initiated a Control Room Isolation, a Containment Ventilation Isolation, and a Phase A Containment Isolation, as designed. After RCS pressure had risen to 2235 psig (normal operating pressure),
control room personnel stopped the Safety Injection at 1155 EST. The unit was transitioned to normal operation in Mode 3 (Hot Standby), and personnel reset the various ESF actuation components and signals. A review of charts and recordings verified that, other than 2T421, the various systems' components actuated as required. The NRC Operations Center was notified of these events at 1512 EST.U.S. NUCLEAR REGULATORY COMMISSION (1-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (6)
PAGE (3)
YEAR I
SEQUENTIAL REVISION YEAR NUMBER Vogtle Electric Generating Plant - Unit 2 05000-425 2004 004 00 3 OF 4 TEXT (If more space is required, use additional copies of NRC Form 366A) (17
D. CAUSE OF EVENT
The cause of this reactor trip was human performance errors by the operators performing the SSPS testing in not applying human performance tools and proper peer checking. A number of factors contributed to the occurrence of these errors, including:
- 1. A lack of physical barriers to reduce the potential for error,
- 2. The lack of train designators on some critical procedure steps.
The cause of the Safety Injection was the failure of a lead-lag circuit card that led to a failure of the Loop 2 Tavg circuitry, full opening of the steam dump valves, and the subsequent drop in RCS pressure. The circuit card will be evaluated to determine the failure mechanism. A revised LER will be submitted to address the findings of this failure analysis.
E. ANALYSIS OF EVENT
The reactor trip and subsequent ESF actuations occurred as designed. Control room personnel acted appropriately to maintain the proper steam generator water levels during the events and to isolate the main steamline, thereby mitigating further loss of RCS pressure.
Based on these considerations, there wvas 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
I. The involved operators were removed from active duty status until a remediation program was completed. This program included briefing of all operating crews, generating a summary document of the event to be used for future briefings, a re-qualification in the use of human performance tools, and an interview with the Operations Dept. manager.
- 2. Procedures 14421-1/2 were changed to require the opposite train SSPS cabinets to be locked when performing this testing in the future.
- 3. Procedures 14421-1/2 were also revised to add train designators throughout the text of the procedure.
- - U.S. NUCLEAR REGULATORY COMMISSION (1-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET II 11 11 11 ~
TEXT (if more space is required, use additional copies of NRC Form 366A) (I7
- 4. Broadness reviews are being performed to address the placement of physical barriers and the use of train designators in procedures in order to prevent future human performance events.
- 5. The lead-lag circuit card will be evaluated to determine the failure mechanism. Results are expected to be available by June 15, 2005, and appropriate follow-up actions will be taken.
G. ADDITIONAL INFORMATION
- 1. Failed Components:
7300 NLLI lead-lag circuit card manufactured by Westinghouse Electric Corporation.
Part # 2837A18G01.
2. Previous Similar Events
There have been no previous similar events in the last three years.
- 3. Energy Industry Identification System Code:
Reactor Coolant System - AB Safety Injection System - BQ Solid State Protection System - JG Main Feedwater System - SJ Auxiliary Feedwater System - BA Main Steam System - SB Control Room Ventilation System - VI Containment Isolation System - JM Containment Ventilation Isolation System - JM Integrated Plant Computer System - ID