05000364/LER-2010-001
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 04-30-2010 |
|---|---|
| Report date: | 06-17-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 45889 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 3642010001R00 - NRC Website | |
Westinghouse -- Pressurized Water Reactor Energy Industry Identification Codes are identified in the text as [XX]
Description of Event
On April 30, 2010 at 21:00, an unplanned Loss of Off-Site Power (LOSP) on A-train 4160 volt emergency Bus 2F [EB] occurred during a scheduled outage test, Safety Injection (SI) with LOSP. The Emergency Diesel Generator (EDG) 1-2A [EK] was being shutdown following the actuation portion of the test. When the B2F Sequencer (A-train) was reset, the EDG output breaker (DF08-2) unexpectedly opened to generate the LOSP signal on 4160 volt Bus 2F. As a result, the B2F Sequencer functioned to automatically re-close DF08-2 and start both the 2A Motor Driven Auxiliary Feedwater (MDAFW) [BA] pump and 2A High Head Safety Injection (HHSI) [BQ] pump. All systems functioned as designed for this condition, and core cooling was maintained throughout by the B-train 2B Residual Heat Removal (RHR) [BP] pump. Flow to the reactor core was maintained. Unit 1 was not affected and remained at 100 % power during the event.
A recent design change was implemented to assure EDG sequencer reliability during all modes of EDG operation. Subsequent to this design change, the necessary procedure change had not been properly incorporated in the test procedure. Test guidance relied upon transitioning to the System Operating Procedure (SOP) for operating the newly installed Test Trip Override Switch (TTOS) located on the B2F Sequencer. However, the transition was not at the correct location in the test procedure. Once recognized, SOP procedure guidance was used and the B2F Sequencer TTOS was operated before resetting the sequencer, and the restoration section was completed without further complications.
In accordance with 10 CFR 50.72(b)(3)(iv)(A) for a valid actuation of the auxiliary feedwater and emergency core cooling systems, an eight hour non-emergency report was issued on May 1, 2010 at 01:01, Event Notification number 45889.
Cause of Event
A recent design change was implemented to assure EDG sequencer reliability during all modes of EDG operation. Subsequent to this design change, the necessary procedure change had not been properly incorporated in the test procedure. Test guidance relied upon transitioning to the System Operating Procedure (SOP) for operating the newly installed Test Trip Override Switch (TTOS) located on the B2F Sequencer. However, the transition was not at the correct location in the test 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.
PRINTED ON RECYCLED PAPER)NRC FORM 366A (9-2007) R=1.1.■� The Farley onsite standby power source is provided from four EDGs (1-2A, 1B, 2B, and 1C). The continuous service rating of 1C EDG is 2,850 kW and 4,075 kW for EDGs 1-2A, 1B, and 2B. EDG 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 2F Emergency Bus. When resetting the B2F Sequencer, the failure to operate the TTOS on the B2F Sequencer caused the EDG output breaker (DF08-2) to open. Sensing the LOSP condition, the B2F Sequencer properly functioned to re-close DF08-2 and sequentially start and connect loads on emergency Bus 2F. Both the 2A MDAFW pump and 2A HHSI pump sequentially started as designed 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 B-train 2B EDG was operable and the 2B RHR pump was in operation throughout the event.
Corrective Action The SI with LOSP test procedure was completed satisfactorily once the TTOS was properly operated.
MDAFW Pump 2A and HHSI Pump 2A were secured. The 4160 volt Bus 2F was aligned to the normal offsite power supply.
An enhanced Apparent Cause Determination was performed and corrective actions developed to address the failure to properly revise the test procedure after the design change.
SNC Operating Experience (OE) on the event has been issued.
Additional Information
Previous Similar Events:
PRINTED ON RECYCLED PAPER)NRC FORM 366A (9-2007)