05000348/LER-2012-003
| Docket Number Sequential Revmonth Day Year Year Month Day Yearnumber No. | |
| Event date: | 04-05-2012 |
|---|---|
| Report date: | 05-31-2012 |
| Initial Reporting | |
| ENS 47809 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 3482012003R00 - NRC Website | |
Westinghouse -- Pressurized Water Reactor Energy Industry Identification Codes are identified in the text as [XX]
Description of Event
On April 5, 2012 at approximately 12:24, with Unit 1 in mode 6, an unplanned loss of power on A-train 4160 volt emergency bus 1F [EK] occurred during a scheduled outage test of the Sl/LOSP signal. Prior to the event, the 1-2A Emergency Diesel Generator (EDG) [EK] was solely aligned to the 1F bus and successfully carrying all the loads per the test sequence. During subsequent restoration steps the 1-2A EDG should have been paralleled to the grid, however, a human performance error was made and this procedure step was not correctly performed. When the B1 F Sequencer Test Trip Override Switch (TTOS) was selected to the 'On' position, the EDG output breaker (DF08-1) opened to generate an LOSP signal on the 1F bus.
As a result, the B1 F Sequencer functioned to automatically re-close DF08-1, and automatically start all LOSP loads. This included the 1C Component Cooling Water Pump (CCW) [CC], the 1A High Head Safety Injection Pump (discharge isolation valve was closed prior to the event) [BQ], and the 1A and 1B Service Water Pumps [BI]. All systems functioned as designed for this condition. Since core cooling was aligned to the A-train prior to the event, the A-train, 1A Residual Heat Removal (RHR) [BP] pump was deenergized when the LOSP occurred. This pump is not an LOSP load and therefore did not automatically restart. The 1A RHR pump was manually restarted one minute after the LOSP to reestablish core cooling after a slight increase in reactor coolant system (RCS) temperature of approximately four degrees. Unit 2 was not affected and remained at 100 percent power during the event.
Once the error was recognized, the surveillance test procedure was property executed to restore off site power and shutdown the 1-2A EDG without further complications.
In accordance with 10 CFR 50.72(b)(3)(iv)(A) for a valid actuation of the emergency core cooling and emergency AC electrical power systems, an eight hour non-emergency report was issued on April 5, 2012 at 17:21, Event Notification 47809.
Cause of Event
The direct cause of the event was the failure to correctly perform a procedural step to parallel the 1-2A EDG with off-site power and return it to automatic standby operation. As a result, when the B1 F Sequencer Test Trip Override Switch (TTOS) was selected to the 'On' position, the EDG output breaker (DF08-1) opened to generate an LOSP signal on the 1F bus. Additional human factor weaknesses were identified in the step structuring at the point of error in the test procedure.
Furthermore, a contributing cause was the failure to identify and brief on critical steps in the procedure.
Safety Assessment This event had no adverse effect on the safety and health of the public. There were no safety system functional failures and all systems functioned as designed.
The Farley onsite standby power source is provided from four EDGs (1-2A, 1B, 2B, and 1C). EDGs 1 2A and 1C are A-Train and EDGs 1B and 2B are B-Train. Farley also has a fifth diesel generator (2C) that serves as a station blackout diesel, which can be manually aligned to supply B-Train power to either unit and power LOSP loads.
During the restoration portion of the test procedure, EDG 1-2A was operating and tied to the 1F Emergency Bus. During subsequent restoration steps the 1-2A EDG should have been paralleled to the grid, however, a human performance error was made and this procedure step was not correctly performed. When the B1 F Sequencer Test Trip Override Switch (TTOS) was selected to the 'On' position, the EDG output breaker (DF08-1) opened to generate an LOSP signal on the 1F bus.
Sensing the LOSP condition, the B1 F Sequencer properly functioned to re-close DF08-1 and sequentially start and connect loads on emergency Bus 1F. Loads are automatically and sequentially started per design to prevent overloading of the EDG. The EDG output breaker closure and sequencing of shutdown loads are required functions of an EDG and therefore had no adverse effect on the safety and health of the public.
The A-train 1A RHR pump was deenergized when the LOSP occurred. This pump is not an LOSP load and therefore did not automatically restart since a safety injection (SI) signal was not present. The 1A RHR pump was manually restarted one minute after the LOSP to reestablish core cooling after a slight increase in reactor coolant system (RCS) temperature of approximately four degrees. The B-train 1B EDG was operable and the B-train 1B RHR pump was available to be started if needed. Since both RHR trains were available and the 1A RHR pump was restarted, a loss of safety function did not occur.
This event is reportable pursuant to 10 CFR 50.73 (a)(2)(iv)(A) for a system actuation.
Corrective Action Once the error was recognized, the surveillance test guidance was properly executed to restore off-site power, shutdown the 1-2A EDG, and successfully complete the SI with LOSP test procedure.
Causal analysis was completed and additional actions to enhance the procedure and improve the identification of critical steps were identified; and will be tracked to closure in the corrective action program (CAP).
Industry Operating Experience (OE) on the event has been issued.
Additional Information
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