ENS 43634
ENS Event | |
|---|---|
20:09 Sep 11, 2007 | |
| Title | Loss of Safety Function - Both Edg'S Unavailable |
| Event Description | This report is being made pursuant to 10CFR50.72(b)(3)(v)(D) Any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of SSCs that are needed to mitigate the consequences of an accident.
Diesel generator #2 (DG2) was inoperable and unavailable for planned maintenance. This was day 2 of a 7 day shutdown LCO. At 1449, Diesel Generator #1 (DG1) was declared inoperable and unavailable at 1509, due to malfunction of the day fuel oil day tank high level shutoff solenoid valve. With both DGs unavailable, the required safety function was not maintained. At time 1645, DG1 was restored to an available status by repairing the diesel fuel oil day lank high level shut off solenoid. At this time DG1 is able to perform the safety function. DG1 was declared operable at 2129. While recovering the DG2 from planned maintenance, the operators were refilling the DG2 day tank and noticed the level increasing in the DG1 day tank. The operators determined that a mechanical failure of the float occurred in the DG1 solenoid valve. The valve should have remained shut to preclude overfilling the tank. The safety function of the valve occurs on a loss of power. On a loss of power, the solenoid valve fails open to allow the tank to be filled. The NRC Senior Resident Inspector has been notified.
This update is being made to correct certain technical inaccuracies in the initial Event Notification [43634] and in the additional information reflected on the NRC website. The corrected initial Event Notification is as follows. This report is being made pursuant to 10CFR50.72(b)(3)(v)(D) Any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of SSCs that are needed to mitigate the consequences of an accident. Diesel generator #2 (DG2) was inoperable and unavailable due to planned maintenance. This was day 2 of a 7 day shutdown LCO. While recovering DG2 from planned maintenance, operators were refilling the DG2 fuel oil (FO) day tank and noticed that level was also increasing in [Diesel generator #1] DG1 FO day tank. The operators determined that the DG1 day tank float valve and FO day tank high level shutoff solenoid valve were both shut as designed, but were leaking by. At 1449, Operators declared DG1 inoperable but available due to leak-by of the FO day tank high level shutoff solenoid valve. At 1509, DG1 was declared unavailable due to operators positioning its Maintenance Lock-Out (MLO) switch to OFF (lock out) for work on the valves. With both DGs unavailable, the required safety function was not maintained. CNS [Cooper Nuclear Station] replaced the FO day tank high level shut off solenoid valve and at 1645, restored DG1 to an available status by repositioning the MLO switch to ON. Subsequently the replacement shutoff solenoid valve was also found to leak by. CNS realigned DG FO transfer systems and declared DG1 operable at 2129. The licensee notified the NRC Resident Inspector. Notified R4DO (Shannon) |
| Where | |
|---|---|
Cooper  Nebraska (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+2.82 h0.118 days <br />0.0168 weeks <br />0.00386 months <br />) | |
| Opened: | Steven Jobe 22:58 Sep 11, 2007 |
| NRC Officer: | Joe O'Hara |
| Last Updated: | Sep 12, 2007 |
| 43634 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |