05000327/LER-2010-001
| Docket Numbersequential Revmonth Day Year Year Month Day Year | |
| Event date: | 04-05-2010 |
|---|---|
| Report date: | 06-04-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3272010001R00 - NRC Website | |
I. PLANT CONDITION(S)
SQN, Units 1 and 2 were operating at approximately 100 percent power at the time the spent fuel pool (SFP) [EllS code DA] back-up pump [EllS code P] common spare (C-S) breaker [EllS code BKR] was placed into service without arc chutes [EllS code CHT] and phase barriers.
II. DESCRIPTION OF EVENT
A. Event:
On April 4, 2010 at 1030 Eastern Daylight Time (EDT), Electrical Maintenance notified Operations personnel in the main control room (MCR) that the normal supply breaker for the SFP back-up pump C-S failed the inspection requirements of Technical Requirements Manual (TRM) 3.8.3.3. TRM Limiting Condition for Operation (LCO) 3.8.3.3 states that all circuit breakers actuated by fault currents that are used as isolation devices protecting 1 E busses from nonqualified loads shall be operable.
Action b states that with one or more of the above required circuit breakers inoperable either trip the inoperable circuit breaker(s), rack-out the circuit breaker(s) within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, and verify the circuit breaker(s) to be racked out once per 7 days. MCR operators entered TRM LCO 3.8.3.3, Action b for SQN, Units 1 and 2. At SQN, circuit breakers actuated by fault currents are used as isolation devices. The operability of these circuit breakers ensures that the 1 E busses will be protected in the event of faults in nonqualified loads powered by the busses.
On April 5, 2010 at 0038 EDT, Electrical Maintenance completed the repairs on the SFP back-up pump C-S breaker. At 0100 EDT the SFP back-up pump C-S breaker was returned to service following repairs and successful testing. The MCR operators exited TRM 3.8.3.3, Action b. At 0130 EDT Operations placed the SFP back-up pump C-S in service. At 1145 EDT Electrical Maintenance notified the MCR operators that the SFP back-up pump C-S breaker was installed without arc chutes and phase barriers. As a result, the MCR operators entered TRM LCO 3.8.3.3, Action b, for the circuit breaker being inoperable and entered Technical Specification (TS) LCO 3.8.2.1, Action a, because the 480-volt Shutdown Board 2A1-A, for SQN, Units 1 and 2 was considered inoperable. TS LCO 3.8.2.1 states that the following ac electrical boards (480-volt Shutdown Board 2A1-A is listed here) shall be operable and energized with tie breakers open between redundant boards. Action a states that with less than the above complement of ac boards operable and energized, restore the inoperable boards to operable status within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> or be in at least hot standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in cold shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. The shutdown board was considered inoperable because of the unknown affects of the breaker being installed without the arc chutes or the phase barriers on the shutdown board. If the breaker had actuated as designed, without the arc chutes and phase barriers installed, it could have an adverse affect on the shutdown board.
At the time of discovery, SQN, Units 1 and 2 had exceeded the TS LCO action time of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> specified in TS LCO 3.8.2.1, Action a. This event is reportable in accordance with 10 CFR 50.73 (a)(2)(i)(B) as an event in which SQN, Units 1 and 2 were operated in a condition prohibited by TSs.
B. Inoperable Structures, Components, or Systems that Contributed to the Event:
None.
C. Dates and Approximate Times of Major Occurrences:
Date Description April 2, 2010 A work order was initiated to test the SFP back-up pump C-S circuit breaker. The activity was planned and merged with the weekend schedule.
April 3, 2010 The work order was reviewed by Electrical Maintenance for task performance. The Electrical Maintenance technician identified that steps required to complete the scope of work were missing, but failed to make the required notifications to have the work order corrected.
April 3, 2010 The breaker was removed and transported to the breaker shop for testing.
April 4, 2010 at The MCR operators were notified that the breaker for the 1030 EDT SFP back-up pump failed the direct trip actuator test.
Operation's personnel entered TRM LCO 3.8.3.3, Action b, for SQN, Units 1 and 2 because the breaker was inoperable.
April 5, 2010 at Electrical Maintenance completed repairs on breaker.
0038 EDT Maintenance personnel placed the breaker in the cubicle in Shutdown Board 2A1-A.
April 5, 2010 at Operators racked in the breaker for the SFP back-up pump 0100 EDT C-S. The breaker met its post maintenance testing requirements and acceptance criteria. Operation's personnel exited TRM 3.8.3.3, Action b, for SQN, Units 1 and 2.
April 5, 2010 at Electrical Maintenance personnel notified the MCR 1145 EDT operators that the SFP back-up pump C-S breaker was installed without arc chutes and phase barriers.
Operation's personnel entered TRM LCO 3.8.3.3, Action b, for SQN, Units 1 and 2 because the breaker was inoperable. Also, the operators entered TS LCO 3.82.1, Action a, because the 480-volt Shutdown Board 2A1-A was potentially inoperable for SQN, Units 1 and 2.
April 5, 2010 at A pre-job brief was held to perform a one-time only 1700 EDT procedure change to open the transfer switch under load.
April 5, 2010 at SFP back-up pump C-S breaker was disconnected and 1800 EDT racked out. MCR operators exited TS LCO 3.8.2.1, Action a, for SQN, Units 1 and 2.
D. Other Systems or Secondary Functions Affected:
Because the breaker for the SFP back-up pump was inoperable as a result of the missing arc chutes and phase barriers, Shutdown Board 2A1-A was considered inoperable.
E. Method of Discovery:
An Electrical Maintenance technician discovered arc chutes in the Electrical Maintenance shop and notified management. It was determined that the arc chutes and phase barriers had not been installed on the SFP back-up pump C-S breaker. Electrical Maintenance notified the MCR operators that the SFP back-up pump C-S breaker was installed without arc chutes and phase barriers.
F. Operator Actions:
Following Electrical Maintenance's notification that the SFP back-up pump C-S breaker had been installed without the required arc chutes and phase barriers, Operation's personnel entered TRM LCO 3.8.3.3, Action b, for the circuit breaker being inoperable and entered TS LCO 3.8.2.1, Action a, because of the resulting inoperability of the 480-volt Shutdown Board 2A1-A.
G. Safety System Responses:
No safety system response was required.
III.� CAUSE OF THE EVENT A. Direct Cause:
The immediate cause was Electrical Maintenance personnel failed to install the SFP back-up pump C-S breaker arc chutes and phase barriers.
B. Root Cause:
The root cause of the event was determined to be that a less than adequate process exists for conducting technical reviews. At SQN, technical reviews are independent reviews of work order instructions. The steps required to return the breaker to an operable state were omitted from the work order and were not noted during the technical review of the work order.
C. Contributing Factor:
The significant contributing cause of the event was the failure of the Electrical Maintenance technician to stop work when the work order was identified as being inadequate for the task to be performed.
IV.� ANALYSIS OF THE EVENT On April 5, 2010 at 1145 EDT, Electrical Maintenance notified MCR operators that the SFP back-up pump C-S breaker was installed without arc chutes and phase barriers. As a result, MCR operators entered TRM LCO 3.8.3.3, Action b, for the circuit breaker being inoperable and entered TS LCO 3.8.2.1, Action a, because of the inoperability of the 480-volt Shutdown Board 2A1-A, for SQN, Units 1 and 2. At the time of discovery, SQN, Units 1 and 2 had exceeded the TS LCO action time of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> specified in TS LCO 3.8.2.1, Action a.
The shutdown board was considered inoperable because of the unknown affects of the breaker being installed without the arc chutes or the phase barriers on the shutdown board. If the breaker had actuated as designed, without the arc chutes and phase barriers installed, it could have an adverse affect on the shutdown board. However, opening of the SFP back-up pump C-S breaker did not affect its ability to function as required nor did it affect the shutdown board or other components.
The safety consequences of the event involve assessment of the potential effects of the SFP back-up pump C-S breaker tripping when called upon to protect the 480 volt Shutdown Board 2A1-A. In the event the breaker caused damage to the shutdown board, the feeder breaker to the shutdown board would open, limiting the loss of electrical equipment to the shutdown board. During the period of time the 480 volt Shutdown Board 2A1-A was inoperable, calibration activities on the A Common Station Service Transformer resulted in an offsite power source being inoperable but available for a short time. Based on a review of Operator logs, no other components associated with the other shutdown boards were out of service. For transients in which offsite power is a limiting consideration, the SQN UFSAR accident analysis assumptions include loss of all offsite power with an initiating event. These transients also assume a single failure of one diesel generator. Since both diesel generators were operable during the time the 2A1-A 480v Shutdown Board was inoperable, SQN remained within the assumptions of the UFSAR.
V. ASSESSMENT OF SAFETY CONSEQUENCES
Based on the above "Analysis of The Event," this event did not adversely affect the health and safety of plant personnel or the general public.
VI.0 CORRECTIVE ACTIONS
A. Immediate Corrective Actions:
Corrective actions included Operations transferring loads from the 480-volt Shutdown Board 2A1-A and opening the feeder circuit breaker to allow the SFP back-up pump C-S breaker to be removed from service in order to exit TS LCO 3.8.2.1, Action a.
All Electrical Maintenance work was suspended, Electrical Maintenance personnel were briefed on the event and lessons learned, and the Maintenance Manager ordered a directive to all Maintenance personnel that all emergent work and work associated with TS systems, structures, or components performed less frequently than quarterly, that is performed on the off shifts, will have maintenance supervisor oversight. In addition, the Electrical Maintenance technician will receive appropriate disciplinary actions.
B. Corrective Actions to Prevent Recurrence:
The corrective actions are being managed through the Tennessee Valley Authority and the SQN Corrective Action Program.
Maintenance & Modifications Department Procedure-1, Maintenance Management System, will be revised to clarify the requirements for an independent qualified review and technical review of work orders and include a detailed independent qualified review and technical review checklist for use with work orders.
VII. ADDITIONAL INFORMATION
A. Failed Components:
None.
B. Previous LERs on Similar Events:
A review of previous reportable events within the last three years did not identify any previous similar events.
C. Additional Information:
None.
D. Safety System Functional Failure:
This event did not result in a safety system functional failure in accordance with 10 CFR 50.73(a)(2)(v).
E. Unplanned Scram with Complications:
This condition did not result in an unplanned scram with complications.
VIII. COMMITMENTS
None.