05000424/LER-2012-002
| Docket Number Sequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 04-14-2012 |
|---|---|
| Report date: | 06-13-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 47836 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 4242012002R00 - NRC Website | |
A. REQUIREMENT FOR REPORT
This report is required per 10 CFR 50.73(a)(2)(iv)(A) due to an unplanned manual actuation of the Reactor Protection System (RPS) [JC] and an automatic actuation of the Auxiliary Feedwater System (AFW) [BA].
B. UNIT STATUS AT TIME OF EVENT
At the time of this event, Unit 1 was in Mode 1 at 100 percent rated thermal power.
C. DESCRIPTION OF EVENT
On April 14, 2012, with Unit 1 operating in Mode 1 at 100 percent rated thermal power at approximately 1346 hours0.0156 days <br />0.374 hours <br />0.00223 weeks <br />5.12153e-4 months <br /> EDT, Unit 1 operators noted a feedwater flow abnormality and initiated a manual reactor trip due to the loss of flow from the 1B MFP. The Reactor Trip System, the Engineered Safety Feature Actuation System, and other responding equipment performed as expected. The plant was stabilized in Mode 3.
In accordance with 10 CFR 50.72(b)(2)(iv)(B) which specifies the reporting requirements for a manual actuation of the RPS on Unit 1, a 4-hour non-emergency notification was made on April 14, 2012, at 1612 EDT (Event Notification 47836).
D. CAUSE OF EVENT
The apparent cause of the event was a failed "Position 5" circuit board judged to be due to component aging in the MFP turbine speed control circuit. A "Position 5" circuit board's function within the MFP controller is to process feedback signals from the pilot valve position, operating valve position and shaft speed. Its failure impacted the control signal provided to the MFP speed governor thus resulting in steam generator flow mismatches. The failed board has been shipped to a vendor for a detailed failure analysis. The controller board is obsolete and no longer has vendor support from the original manufacturer.
E. SAFETY ASSESSMENT
When the reactor was manually tripped all rods fully inserted. As a result of the reactor trip, the turbine tripped, the Feedwater System isolated and the AFW system actuated in accordance with plant design. Control room operators responded appropriately to control feedwater to the steam generators and the plant was stabilized in Mode 3. Results of the analysis discussed in Final Safety Analysis Report for Plant Vogtle, Chapter 15.2.7, Loss of Normal Feedwater Flow bound this event and show that a loss of normal feedwater does not adversely affect the core, the Reactor Coolant System, or the steam system. The auxiliary feedwater capacity is such that reactor coolant inventory is not relieved from the pressurizer relief or safety valves. Based upon these considerations, there was no adverse effect on plant safety or on the health and safety of the public as a result of this event.
F. CORRECTIVE ACTION
The prompt corrective action was to replace the subject "Position 5" circuit board. In addition, the failure of the circuit board was entered into the Corrective Action Program in order to track a longer term solution.
G. ADDITIONAL INFORMATION
1) Failed Components:
Component: MDT-20 Control System Manufacturer: GE 2) Previous Similar Events:
A review of Licensee Event Reports for the past three years did not identify another instance in which there was a manual reactor trip following the loss of feedwater pump at Vogtle Electric Generating Plant due to a failure of a circuit board in the feedwater control system.
3) Energy Industry Identification System Code:
Plant Protection System - JC Solid State Protection System - JG Auxiliary Feedwater System - BA Feedwater System — SJ 4) Commitment Information:
This report does not create any new permanent licensing commitments.