05000296/LER-2010-002
| Browns Ferry Nuclear Plant Unit 3 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2962010002R00 - NRC Website | |
I. PLANT CONDITION(S)
At the time of discovery, Browns Ferry Nuclear (BFN) Plant Units 1, 2, and 3 were at 100 percent power (3458 MWT).
II. DESCRIPTION OF EVENT
A. Event:
On April 20, 2010, at approximately 1140 hours0.0132 days <br />0.317 hours <br />0.00188 weeks <br />4.3377e-4 months <br /> Central Daylight Time (CDT), the 3B Standby Liquid Control (SLC) Pump [BR] failed to start during the performance of the quarterly SLC Pump Functional Test, 3-SI-4.4.A.1, "Standby Liquid Control Pump Functional Test." For the test, Operations personnel had declared both SLC subsystems inoperable in accordance with the procedure and entered Technical Specifications (TS) Limiting Conditions for Operation (LCO) 3.1.7 Actions for both SLC subsystems inoperable (Action B, which requires restoration of one subsystem to operable status within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />) and for one SLC subsystem inoperable (Action A, which requires both subsystems restored to operable status within 7 days).
Operations personnel promptly returned the 3A SLC Pump to operable status and, by 1202 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.57361e-4 months <br />, exited Action B. Action B was re-entered at 1409 hours0.0163 days <br />0.391 hours <br />0.00233 weeks <br />5.361245e-4 months <br /> CDT to complete the surveillance testing, and, at 1518 hours0.0176 days <br />0.422 hours <br />0.00251 weeks <br />5.77599e-4 months <br /> CDT, after successful testing of the 3B SLC Pump, Operations personnel declared both SLC subsystems operable and exited TS LCO 3.1.7 Actions B and A.
The cause of this event was the inoperability of the 3B SLC Pump motor breaker discovered when the pump failed to start. The 3B SLC Pump failed to start because the pump breaker racking shaft sleeve was not fully engaged which interlocked the breaker from closing. The breaker's racking sleeve failed to engage while the breaker was being racked in at approximately 0127 hours0.00147 days <br />0.0353 hours <br />2.099868e-4 weeks <br />4.83235e-5 months <br /> CDT on March 29, 2010, during a refueling outage. Unit 3 entered TS LCO 3.1.7 applicability (Mode 2) at approximately 2048 hours0.0237 days <br />0.569 hours <br />0.00339 weeks <br />7.79264e-4 months <br /> CDT on April 6, 2010, during startup after the refueling outage. Therefore, SLC Subsystem B was inoperable from approximately 2048 hours0.0237 days <br />0.569 hours <br />0.00339 weeks <br />7.79264e-4 months <br /> CDT on April 6, 2010, to approximately 1518 hours0.0176 days <br />0.422 hours <br />0.00251 weeks <br />5.77599e-4 months <br /> CDT on April 20, 2010, which is longer than the 7 day Completion Time allowed by Condition A Required Action A.1. SLC subsystem A was verified operable during this period.
The Tennessee Valley Authority (TVA) is submitting this report in accordance with 10 CFR 50.73(a)(2)(i)(B), any operation or condition which was prohibited by the plant's Technical Specifications.
B. Inoperable Structures. Components. or Systems that Contributed to the Event:
None
C. Dates and Approximate Times of Maior Occurrences:
March 29, 2010, at 0127 hours0.00147 days <br />0.0353 hours <br />2.099868e-4 weeks <br />4.83235e-5 months <br /> CDT�Operations personnel racked in the 3B SLC Pump breaker.
April 6, 2010, at 2048 hours0.0237 days <br />0.569 hours <br />0.00339 weeks <br />7.79264e-4 months <br /> CDT Operations personnel prepared Unit 3 for startup from a refueling outage and entered TS LCO 3.1.7 applicability.
April 20, 2010, at 0830 hours0.00961 days <br />0.231 hours <br />0.00137 weeks <br />3.15815e-4 months <br /> CDT Operations personnel commenced performance of surveillance 3-SI-4.4.A.1, "Standby Liquid Control Pump Functional Test.
April 20, 2010, at 0954 hours0.011 days <br />0.265 hours <br />0.00158 weeks <br />3.62997e-4 months <br /> CDT For the performance of 3-SI-4.4.A.1, Operations personnel declared both SLC subsystems inoperable and entered TS LCO 3.1.7 Action A and B for one and two SLC subsystems inoperable, respectively.
April 20, 2010, at 1140 hours0.0132 days <br />0.317 hours <br />0.00188 weeks <br />4.3377e-4 months <br /> CDT The 3B SLC Pump failed to start during the performance of 3-SI-4.4.A.1.
April 20, 2010, at 1157 hours0.0134 days <br />0.321 hours <br />0.00191 weeks <br />4.402385e-4 months <br /> CDT Operations personnel reviewed satisfactory testing of the 3A SLC Pump and commenced restoration to normal pbr 3-SI-4.4.A.1. Operations personnel observed and reported that the breaker for the 3B SLC Pump was tripped.
April 20, 2010, at 1202 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.57361e-4 months <br /> CDT Unit 3 Operations personnel returned the 3A SLC Pump to operable status and exited Action B.
Operations personnel verified proper position of the 3B SLC Pump breaker.
April 20, 2010, at 1409 hours0.0163 days <br />0.391 hours <br />0.00233 weeks <br />5.361245e-4 months <br /> CDT Operations personnel declared both SLC subsystems inoperable for testing and re-entered Action B.
April 20, 2010, at 1518 hours0.0176 days <br />0.422 hours <br />0.00251 weeks <br />5.77599e-4 months <br /> CDT C Completed 3-SI-4.4.A.1 for the 3B SLC Pump, declared both SLC subsystems operable, and exited TS LCO 3.1.7 Actions B and A.
D. Other Systems or Secondary Functions Affected:
None
E. Method of Discovery:
The 3B Standby Liquid Control pump was found inoperable during the performance of the scheduled quarterly surveillance 3-SI-4.4.A.1, "Standby Liquid Control Pump Functional Test.
F. Operator Actions:
None
G. Safety System Responses:
None
III. CAUSE OF THE EVENT
A. Immediate Cause:
The 3B SLC Pump failed to start.
B. Root Cause:
Operations personnel did not properly implement procedure steps or perform self checking and peer checking when racking in the breaker for the 3B SLC Pump for clearance restoration during a refueling outage.
C. Contributina Factors; The General Electric (GE) type AK breakers racking shaft sleeve failed to spring back fully forward as it is designed to do. While this feature is not relied upon (i.e., the procedural steps ensure the sleeve is positioned fully forward) had it functioned it would have precluded this event.
IV. ANALYSIS OF THE EVENT
The 3B SLC Pump failed to start because the pump breaker was not properly positioned by Operations personnel when racking in the breaker for a clearance restoration step on March 29, 2010, during a refueling outage. The breaker is a 480VAC GE AK 2A-15 type breaker.
When racking this breaker in, it is required for the racking shaft sleeve to slide fully forward with pins on the shaft slide into sleeve notches to be engaged in order for the breaker to be operable. When the breaker was checked after the SLC Pump would not start, it was found with the racking sleeve not fully engaged (fully forward). The racking sleeve is designed to spring return to the forward position. The design feature that includes the racking sleeve has led to a two step procedural action to "Remove the Racking Crank Handle" and "Verify the shaft sleeve slides fully forward" to manually verify the racking sleeve is engaged. If the shaft sleeve had operated as designed, it would have prevented this event.
Two Assistant Unit Operators (AUOs) racked in the breaker for a clearance restoration step on March 29, 2010, during a refueling outage. TVA's investigation found that the AUOs had inappropriately missed the second part of a step in the General Operating Instruction for racking in this type of breaker which requires "VERIFY shaft sleeve slides fully forward." Even though the procedure had two actions in one step, strict procedural adherence and attention to detail would have prevented this event from occurring.
V. ASSESSMENT OF SAFETY CONSEQUENCES
The safety consequences of this event were not significant. The failure of the AUOs to properly position (rack in) the 3B SLC Pump breaker caused the 3B SLC pump (one subsystem) to not be available for its intended safety function for the time period of March 29, 2010, to discovery on April 20, 2010. Although one SLC subsystem was unavailable, the other subsystem (with the 3A SLC pump) was operable during this period and was confirmed by testing to be fully functional and would have been available to perform the required safety function.
During the sequence of events described herein, one SLC subsystem was available for fulfillment of the SLC System safety function; therefore, TVA concludes that there was no significant reduction in the protection of the public as a result of this event.
VI. CORRECTIVE ACTIONS - The corrective actions are being managed with TVA's Corrective Action Program A. Immediate Corrective Actions:
Operations personnel correctly positioned the 3B SLC pump breaker and the breaker was tested satisfactorily. All other safety-related 480VAC GE AK breakers were visually verified by Operations personnel to be correctly positioned.
B. Corrective Actions to Prevent Recurrence:
1. In accordance with TVA policy, appropriate personnel actions were taken for the two AU0s who racked in the breaker for the clearance restoration.
2. Operations Shift Managers briefed their respective crews about this event.
3. The event is scheduled to be added and presented to Licensed and Non-Licensed Operator Requalification Training by July 22, 2010.
4. The GE AK 2A-15 type breakers are being evaluated for design modification or additional procedural controls to enhance the reliability of the racking in procedure.
VII. ADDITIONAL INFORMATION
A. Failed Components:
None B. Previous LERs on Similar Events:
None
C. Additional Information:
Corrective action document for this report is Problem Evaluation Report 225949.
D. Safety System Functional Failure Consideration:
In accordance with NEI 99-02 guidance, this event is not classified as a safety system functional failure.
E. Scram With Complications Consideration:
This event did not include a reactor scram.
VIII. COMMITMENTS
None