ENS 51935
ENS Event | |
|---|---|
01:05 May 17, 2016 | |
| Title | Unanalyzed Condition That Significantly Degrades Plant Safety |
| Event Description | On May 16, 2016 at 2105, Sequoyah Nuclear Power Plant identified a nonconforming condition involving the Emergency Diesel Generator (EDG) fire dampers installed in Units 1 and 2. Specifically, it has been identified that if a tornado causes a differential pressure across the east and west sides of the EDG Building, this could create a high airflow rate through the EDG Building ventilation path. The fire dampers for each EDG bay (required to isolate the space for CO2 fire suppression per SQN Fire Protection Report) have not been analyzed to withstand high air flows resulting from a tornado and could possibly fail in a way that impedes airflow for EDG cooling. This is an unanalyzed condition that could prevent all EDGs from supplying electrical power as designed during a tornado or other similar weather events.
All 4 EDGs are required to be operable by both units' Technical Specifications to provide electrical power to safe shutdown/safety related equipment following accident conditions coincident with a loss of offsite power. The Current Licensing Basis (CLB) requires that tornado effects be considered in the design of safety related SSCs [Systems, Structures, and Components], and it cannot be demonstrated at this time that the described SSCs will withstand the design basis tornado. It has been determined that the CLB may not adequately address possible design basis tornado scenarios. The EDGs are located inside the power plant structure and are currently capable of performing their safety function. The occurrence of such an event is highly unlikely and there is no imminent concern regarding severe weather involving tornadoes. Compensatory measures have been developed to address the associated nonconformance. The condition described above is being reported as an unanalyzed condition that significantly degrades plant safety per 10 CFR 50.72(b)(3)(ii)(B). The NRC Resident Inspector has been notified. |
| Where | |
|---|---|
Sequoyah  Tennessee (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+-3.8 h-0.158 days <br />-0.0226 weeks <br />-0.00521 months <br />) | |
| Opened: | Robert Urbanski 21:17 May 16, 2016 |
| NRC Officer: | Karl Diederich |
| Last Updated: | May 16, 2016 |
| 51935 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 544872020-01-22T03:18:00022 January 2020 03:18:00
[Table view]10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition ENS 521872016-08-17T21:22:00017 August 2016 21:22:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Due to Not Meeting Single Failure Criteria ENS 519942016-06-08T19:26:0008 June 2016 19:26:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition That Could Potentially Degrade Plant Safety ENS 519352016-05-17T01:05:00017 May 2016 01:05:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition That Significantly Degrades Plant Safety ENS 518542016-04-07T19:07:0007 April 2016 19:07:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition - High Pressure Fire Suppression Isolated from Containment ENS 515272015-11-10T20:02:00010 November 2015 20:02:00 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat, 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Due to Debris Dropped Into Reactor Cavity Equipment Pit ENS 502442014-07-01T02:46:0001 July 2014 02:46:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition That Could Have Resulted in an Increased Maximum Flood Level ENS 496902014-01-03T20:00:0003 January 2014 20:00:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Abgts Potentially Inoperable for Both Units Under Worst-Case Conditions ENS 485842012-12-13T00:14:00013 December 2012 00:14:00 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Risk of Possible Flooding to Ercw Building During Design Basis Flood ENS 487252009-07-28T05:00:00028 July 2009 05:00:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition That Could Have Resulted in an Increased Maximum Flood Level ENS 448142009-01-28T19:25:00028 January 2009 19:25:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Related to a Postulated Appendix R Fire Scenario 2020-01-22T03:18:00 | |