ENS 47471
ENS Event | |
|---|---|
19:53 Nov 22, 2011 | |
| Title | Inadvertent Actuation of a Drywell-To-Suppression Chamber Vacuum Relief Valve |
| Event Description | This report is being made pursuant to 10CFR50.72 criteria (b)(3)(v)(D), 'Any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.'
At time 1353 CST on 11/22/11, a licensed operator inadvertently bumped the Torus-to-Drywell vacuum relief Master Control Switch for the Drywell-to-Suppression Chamber vacuum relief valves from the 'close' position to the 'open' position. One of the twelve vacuum relief valves controlled by the Master Control Switch indicated an open indication. The other eleven vacuum relief valves did not operate due to having the pneumatics secured to the operator. Immediately upon recognizing the condition, the licensed operator returned the switch to the closed position. The open vacuum relief valve indication changed to the closed indication. From automatic alarm logging, the time that the vacuum relief was open was recorded as six seconds. The vacuum relief valve has a safety function in the closed position to limit the amount of bypass flow to ensure proper containment response on a postulated LOCA event and an open safety function post-LOCA to limit negative differential pressure between the drywell and the suppression chamber. With the valve partially open, the LOCA containment response cannot be assured. This results in declaring the primary containment inoperable. The vacuum relief valve manual operators have air secured during normal operation. With air secured, only one of the twelve valves operated versus all twelve. A valve line-up was performed and all pneumatic supply valves were in the proper line-up. Currently, the only unusual occurrence is why there was sufficient air to the individual vacuum relief valve that caused it to operate in the open direction. This will be resolved within the corrective action program. Currently, all twelve Drywell-to-Suppression Chamber vacuum relief valves are closed and in the normal line-up. [The] NRC Senior Resident Inspector has been notified. |
| 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 | |
| LER: | 05000298/LER-2011-007 |
| Time - Person (Reporting Time:+-1.05 h-0.0438 days <br />-0.00625 weeks <br />-0.00144 months <br />) | |
| Opened: | Brian Stander 18:50 Nov 22, 2011 |
| NRC Officer: | Howie Crouch |
| Last Updated: | Nov 22, 2011 |
| 47471 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |