ENS 50663
ENS Event | |
|---|---|
00:30 Dec 10, 2014 | |
| Title | High Energy Line Break Door Found Closed |
| Event Description | At 1830 [CST] on December 9, 2014 Door 410B, a HELB (High Energy Line Break) door between the east and west sides of the ground floor of the reactor building, was found closed. This door is one half of a pair of double doors that are normally open to provide a HELB energy and flooding release path to mitigate postulated HELB events. The closed HELB door has the potential to impact safe shutdown by exposing both divisions of safe shutdown components to unanalyzed environmental conditions. With the potential loss of both divisions of safe shutdown equipment, no safe shutdown path would exist. This condition is being reported as an unanalyzed condition as defined by [10 CFR] 50.72(b)(3)(ii)(B). The HELB door was immediately opened and returned to normal configuration. Door 410A remained open during the time that Door 410B was closed and provided an available, but not yet analyzed, release path that could have mitigated the consequences of this event. The health and safety of the general public was not impacted as a result of this condition.
The NRC Resident Inspector has been notified.
Further analysis has determined that the condition did not significantly degrade plant safety. Door 410B in the Reactor Building was found closed. This door is one half of a pair of double door (Doors 410A and 410B) that normally open to provide a High Energy Line Break (HELB) energy and flooding release path to mitigate postulated HELB events. The condition of one half of the double door closed was not previously analyzed. A subsequent completed engineering evaluation analyzed this condition, Door 410B being closed and Door 410A being open, for the following environmental conditions: peak compartment temperatures, block wall differential pressure, radiation dose, and flooding. The environmental conditions found the Reactor Building in response to Door 410B being closed with 410A being open does not affect the operability of safety related equipment housed within the Reactor Building or the ability to safely shut-down the plant and maintain the plant shutdown condition following a HELB event. The NRC Resident Inspector has been notified. Notified R3DO (Dickson). |
| Where | |
|---|---|
Monticello  Minnesota (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+0.02 h8.333333e-4 days <br />1.190476e-4 weeks <br />2.7396e-5 months <br />) | |
| Opened: | William Stang 00:31 Dec 10, 2014 |
| NRC Officer: | Daniel Mills |
| Last Updated: | Jan 30, 2015 |
| 50663 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (90 %) |
| After | Power Operation (90 %) |