ENS 43157
ENS Event | |
|---|---|
19:42 Feb 8, 2007 | |
| Title | Raw Water Pumps Declared Inoperable Due To A Potential Failure Of The Pump Breaker Linkages |
| Event Description | On February 8, 2007 at 10:22 CST, Raw Water Pump AC-10C was declared inoperable when the pump breaker experienced a plunger linkage failure during a scheduled pump start for a scheduled rotation. Due to a similar failure of Raw Water Pump AC-10B two weeks earlier, a condition report was initiated for engineering to review the potential for a common failure mode. Engineering reviewed the number of cycles of the breakers for AC-10A and AC-10D both have greater than 1600 cycles. The breaker for AC-10B had over 1200 cycles at the time of its failure and AC-10C was over 1700 cycles. Based on the similar numbers of cycles, engineering has determined that continued operation of AC-10A and AC-10D without breaker failure could not he assured. All other safeguards associated breakers have been verified to have less than 1000 cycles and are not considered to be susceptible to breaker failure at this time. After discussion with engineering, Raw Water Pumps AC-10A and AC-10D were declared inoperable on February 8, 2007 at 13:42 CST based on the number of breaker cycles for these two components in relation to the two breakers that failed.
With three Raw Water Pumps inoperable, Fort Calhoun Station entered Technical Specification 2.0.1 which requires the plant be placed in hot shutdown within six (6) hours. The potential for a common mode failure of the linkage in the 4160 VAC circuit breakers (ABB Combustion Engineering Model No. 5VKBR-250) could have prevented operation of the Raw Water Pumps to fulfill the required design function to remove residual heat during a design basis accident. At 15:22 CST, repairs were completed on Raw Water Pump AC-10C breaker and the pump was declared operable. At 15:34 CST, Technical Specification 2.0.1 was exited and Technical Specification 2.4(1)c, 7-day LCO was entered for the inoperability of Raw Water Pumps AC-10A and AC-10D. The repair of the breakers for AC-10A and AC-10D are scheduled for February 9, 2007. The licensee informed the NRC Resident Inspector.
This communication is meant to supplement the notification of February 8, 2007. The common mode failure of the linkage in the 4160V circuit breaker (ABB Combustion Engineering model number 5VKBR-250) could have prevented the operation of the raw water pumps as required by design. This could have resulted in the inability of the raw water system to remove residual heat during design basis accidents as required. The licensee informed the NRC Resident Inspector. Notified R4DO (Smith).
On February 3, 2007, (Event Number 43157) Fort Calhoun Station reported a condition that, at the time, was believed [to be] a possible common mode failure of the 4160V feeder breakers for the Raw Water (RW) System [redacted]. The circuit breakers for two of the four RW pump feeder breakers had failed. Investigation had determined that the failure mechanism was the same for the two failures. On February 8, it was not known if the other two RW pump breakers could fail by this same mechanism. The component that failed in the circuit breaker was an offset rod that transmitted operation of the circuit breaker to a set of auxiliary switches associated with the circuit breakers. The offset rods of the A and D RW pumps have subsequently been tested. Non destructive testing determined that the rods had no cracks. Destructive testing determined that the rods would not have failed for several hundred operations of the circuit breakers. As a result, the system was capable of performing its design safety function. Therefore, this event is not reportable under 10 CFR 50.72(b)(3)(B) as previously reported and EN 43157 is being retracted. While no verbal report criteria is applicable to this condition it is reportable as an LER under 10 CFR 50.73(a)(2)(vii). The licensee notified the NRC Resident Inspector. R4DO ( Shannon) notified. |
| Where | |
|---|---|
Ft Calhoun  Nebraska (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat | |
| Time - Person (Reporting Time:+-1.03 h-0.0429 days <br />-0.00613 weeks <br />-0.00141 months <br />) | |
| Opened: | Erick Matzke 18:40 Feb 8, 2007 |
| NRC Officer: | Steve Sandin |
| Last Updated: | Mar 15, 2007 |
| 43157 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |