ENS 52437
ENS Event | |
|---|---|
15:10 Dec 15, 2016 | |
| Title | Secondary Containment Momentary Low Pressure |
| Event Description | On December 15, 2016, at 1010 EST, the startup of the Reactor Building HVAC [Heating Ventilation and Air Conditioning] system resulted in the Technical Specification (TS) for secondary containment pressure boundary not being met for approximately 1 second. The maximum secondary containment pressure observed during that time was approximately 0.044 inches of vacuum water gauge.
Secondary containment pressure was returned to within the TS operability limit of 0.125 inches of vacuum water gauge (TS SR 3.6.4. 1.1) by Reactor Building HVAC and Standby Gas Treatment System already in operation. There were no radiological releases associated with this event. Declaring secondary containment inoperable is reportable under 10CFR50.72(b)(3)(v)(C) as an event or condition that could have prevented the fulfillment of a safety function needed to control the release of radioactive material. The licensee has notified the NRC Resident Inspector.
In this event notification, DTE Electric Company (DTE) reported conditions whereby the Fermi 2 secondary containment was believed to have exceeded Technical Specification Surveillance Requirements due to high winds. DTE hereby retracts this event notification as the Fermi 2 secondary containment has been determined to have been operable during this event as described below. The Fermi 2 secondary containment pressure is maintained at a pressure less than the external pressure to contain, dilute, hold up, and reduce the activity level of fission products prior to release to the environment, and to isolate and contain fission products that are released during a Design Basis Accident or certain operations. Secondary containment pressure is monitored by a number of differential pressure (dP) sensors. High wind gusts have resulted in momentary negative pressure on the leeward side of the building, causing a more positive pressure indication from one or more dP sensors. The secondary containment building pressure remains relatively constant during these 'wind events.' In December 2016, DTE implemented a software design change to display a 120-second rolling average for secondary containment dP indication. A 120-second rolling average recorded every second provides the operator a more accurate report of actual secondary containment conditions, while mitigating the signal noise and wind gust effects. The conditions associated with the subject event notification were re-reviewed in light of the improved secondary containment dP indication and it was determined that the Fermi 2 secondary containment was operable during this event. Specifically, the secondary containment pressure did not exceed Technical Specification Surveillance Requirements during this event. In summary, the above event notification is retracted because the Fermi 2 secondary containment was determined to have been fully operable during the conditions identified in the subject report. The licensee notified the NRC Resident Inspector. Notified R3DO (Stoedter). |
| 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:+-3.38 h-0.141 days <br />-0.0201 weeks <br />-0.00463 months <br />) | |
| Opened: | Kelley Belenky 11:47 Dec 15, 2016 |
| NRC Officer: | Vince Klco |
| Last Updated: | Mar 17, 2017 |
| 52437 - NRC Website | |
Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |