ENS 51202
ENS Event | |
|---|---|
18:35 Jul 7, 2015 | |
| Title | Secondary Containment Pressure Boundary Vacuum Not Maintained within Specifications |
| Event Description | On 7/7/2015 at approximately 1435 EDT, the Technical Specification for Secondary Containment Pressure Boundary was not met when vacuum could not be maintained greater than or equal to -0.125 inches of water gauge for approximately 41 seconds. As part of post-maintenance testing for the non-safety related Reactor Building HVAC Center Exhaust Fan, the fan was started while the safety-related Standby Gas Treatment system was also in operation. Shortly after the fan was started, operators observed degrading vacuum in secondary containment and subsequently secured the center exhaust and supply fans. Vacuum continued to degrade momentarily after the fans were secured, and then returned to a Technical Specification allowable value.
Subsequent inspections discovered that the affected fan was operating in the reverse direction. This is believed to have caused Secondary Containment pressure to increase. Since vacuum could not be maintained with the safety-related Standby Gas Treatment system operating, the plant operated in an unanalyzed condition. The cause of the reverse rotation is under investigation. There were no radiological releases associated with this event. The NRC Senior Resident Inspector has been notified.
Based on plant configuration at the time of the event and further review of the Fermi 2 UFSAR, the plant did not operate in an unanalyzed condition. The Reactor Building HVAC fans would have tripped, as designed, upon receipt of a safety-related Standby Gas Treatment actuation signal during the time of the event. Therefore, the fans' pressurizing effect on secondary containment would have ceased within the time limits assumed in the existing accident analysis. The reporting criteria of 10CFR50.72(b)(3)(v)(C) remains valid. The licensee notified the NRC Resident Inspector. Notified the R3DO (Stone). |
| Where | |
|---|---|
Fermi  Michigan (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | |
| Time - Person (Reporting Time:+-2.47 h-0.103 days <br />-0.0147 weeks <br />-0.00338 months <br />) | |
| Opened: | Chris Robinson 16:07 Jul 7, 2015 |
| NRC Officer: | Vince Klco |
| Last Updated: | Jul 7, 2015 |
| 51202 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |