ENS 50831
ENS Event | |
|---|---|
08:04 Feb 19, 2015 | |
| Title | Secondary Containment Building Declared Inoperable Due to Ventilation System Trip |
| Event Description | At 0304 EST on February 19, 2015, Fermi 2 experienced a trip of the Reactor Building Ventilation (RB) (HVAC) during plant operations associated with very cold temperatures outside. At the time of the trip, outside air temperature was -1 degrees Fahrenheit and RB HVAC tripped due to a Freeze-Stat actuation [a freeze protection feature].
The plant Technical Specifications require that Secondary Containment pressure be maintained greater than or equal to -0.125 inches of vacuum water gauge (TS SR 3.6.4.1.1). This specification was not maintained and the highest pressure observed was -0.11 inches of vacuum water gauge. Subsequently, at 0450, during restoration activities, RB pressure degraded again to higher than -0.125 inches of vacuum water gauge for 38 seconds. The lowest observed pressure was -0.11 inches of vacuum water gauge. RB HVAC has been restored by resetting the Freeze-Stat and the Standby Gas Treatment System (SGTS) has been placed back in a standby condition. The technical specification requirement is to maintain secondary containment at -0.125 inches of vacuum water gauge for secondary containment operability. 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.
After reviewing the events that occurred on February 19, 2015 against the accident analyses in Chapter 15 of the UFSAR and design functions of the Standby Gas Treatment System and Secondary Containment structure, it is concluded that a condition that could have prevented the fulfillment of a safety function to control the release of radioactive material did not occur as a result of momentarily exceeding the Technical Specification for Secondary Containment vacuum after a loss of the normal Reactor Building Ventilation System. The Fermi 2 accident analysis for a LOCA does not assume that secondary containment is under vacuum throughout the duration of an accident and contains conservative leakage assumptions to bound the effects of a postulated ground level release. The accident analysis credits the operation of the Standby Gas Treatment System (SGTS); both divisions of SGTS were operable at the time of the event. Although secondary containment was declared inoperable due to exceeding the Technical Specification value for secondary containment vacuum, the structural integrity of the secondary containment was not degraded at the time. Upon receipt of an accident signal, SGTS would have automatically started and restored secondary containment vacuum to within the bounding analyses of Chapter 15 of the UFSAR. Secondary containment was capable of performing its design function of minimizing any ground level release of radioactive material by maintaining boundary integrity so that the SGTS may draw a vacuum in the Reactor Building and filter radioactive material at all times. The event reported in EN 50831 did not result in a condition that could have prevented the fulfillment of a safety function to control the release of radioactive material. This event report is being retracted. The licensee informed the NRC Resident Inspector. Notified R3DO (Skokowski).
Upon further review of NUREG-1022 section 3.2.7, the original Non-Emergency Event Notification, 50831, remains valid. The NRC Resident Inspect has been informed. Notified R3DO (McCraw). |
| 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:+1.85 h0.0771 days <br />0.011 weeks <br />0.00253 months <br />) | |
| Opened: | Brett Jebbia 09:55 Feb 19, 2015 |
| NRC Officer: | Howie Crouch |
| Last Updated: | Apr 15, 2015 |
| 50831 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |