05000374/LER-2009-001
| Docket Numbersequential Revmonth Day Year Year Month Day Year 05000Number No. | |
| Event date: | 08-15-2009 |
|---|---|
| Report date: | 10-14-2009 |
| 3742009001R00 - NRC Website | |
A. PLANT AND SYSTEM IDENTIFICATION
General Electric Boiling Water Reactor, 3489 Megawatts Thermal Rated Core Power
CONDITION PRIOR TO EVENT
� Unit(s): 2 Event Date: 8/15/09�Event Time: 1606 � Reactor Mode(s): 1 Power Level(s): 100 Mode(s) Name: Power Operation
B. DESCRIPTION OF EVENT
On August 15, 2009, at 1606 (CDT), Unit 2 was at 100% power performing weekly Main Turbine (TG ) [TA] overspeed surveillance testing. During the surveillance, the Main Turbine unexpectedly tripped on an overspeed signal from the Digital Electro-Hydraulic Control (DEHC) wi system, causing a reactor scram.
The safety significance of the event was minimal. The speed of the Main Turbine was confirmed to have been normal at the time of the trip. All control rods fully inserted, and all systems responded as expected to the scram.
Troubleshooting identified that the cause of the trip was a failed communication chip on a VCMI card in the DEHC system. The VCMI card was replaced, and the Unit was restarted and synchronized to the grid on August 19, 2009. The Unit returned to full power at 2300 CDT on August 20, 2009.
An Emergency Notification System call was made at 1906 CDT on August 15, 2009, in accordance with 10 CFR 50.72(b)(2)(ivXB) due to an event or condition that resulted in the actuation of the reactor protection system when the reactor was critical.
C. CAUSE OF EVENT
Troubleshooting identified that the cause of the trip was a failed communication chip on a VCMI card in the DEHC system. At the time of the trip, there was a diagnostic alarm in, indicating that there was a degraded communication link between the three DEHC control modules. This degraded condition, in combination with inserting a half trip signal during the overspeed surveillance test, completed the turbine trip logic, resulting in a turbine trip/reactor scram.
The diagnostic alarm had been received approximately one week prior to the event. Engineering personnel evaluated system log messages and vendor information in order to understand the impact of the conditions that would cause the alarm. However, the vendor information failed to provide an adequate description of the alarm logic or its potential risk, which has been determined to be the root cause of this event. Contributing causes included inadequate communication between the Station engineers and the vendor that failed to highlight the overall risk that the degraded condition posed to the station, and � operating alarm response procedures that did not adequately warn the operators of the risk associated with the alarm.
D. SAFETY ANALYSIS
The safety significance of the event was minimal. The speed of the Main Turbine was confirmed to have been normal at the time of the trip. All control rods fully inserted, and all systems responded as expected to the scram.
E. CORRECTIVE ACTIONS
Corrective Actions:
- The failed VCMI card was replaced.
Corrective Action to Prevent Recurrence:
- The DEHC vendor will provide the Station with an improved manual with enhanced information on fault codes and their associated risks.
- DEHC alarms will be evaluated for potential impact, and the appropriate alarm procedures will be revised as necessary.
F. PREVIOUS OCCURENCES
A document review found no previous occurrences of a turbine trip/reactor scram due to an erroneous signal from DEHC.
G. COMPONENT FAILURE DATA
General Electric, VCMI Card IS215VCMIH2CA, Serial No. 515F073 _