ENS 40457
ENS Event | |
|---|---|
16:20 Jan 19, 2004 | |
| Title | Certain Plant Doors May Not Be Able to Withstand Pressure Created by Main Steam Line Break |
| Event Description | On January 19, 2004, during on-going analysis of the effects of a Main Steam Line Break using new computer models, an issue was raised involving the capability of plant doors. Specifically, the preliminary analysis for a Main Steam Line Break in the Turbine Building determined that certain doors may not be able to withstand the initial pressure wave caused by a guillotine break of the main steam line.
The preliminary analysis indicates that a pressure wave of approximately 2.7 psi is generated from such a main steam line break, which is more than the capability of several doors isolating safety-related equipment from the Turbine Building. The forces generated from this pressure wave could cause failure of the doors leading to both trains of low voltage switchgear, and the resultant steam environment could potentially render all low voltage AC equipment as well the station batteries inoperable. One train of the high voltage switchgear equipment could also be affected due to failure of the door leading to this room. Due to the potential loss of both trains of low voltage electrical distribution as a result of a steam line break, this issue is being reported as a non-emergency, 8-hour report in accordance with 10CFR50.72(b)(3)(ii)(B), a condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety. Current steam line pressures are low enough such that all doors are capable of withstanding any forces resulting from a steam line break. Engineering evaluation of the issue is continuing. The NRC Resident Inspector has been notified of this issue by the licensee. The licensee also plans to make a media/press release regarding this issue.
Further review and evaluation of this issue has determined that the pressure wave from a main steam line break in the Turbine Building results in pressures of less than 1.0 psi. Therefore, the affected doors would be able to withstand this pressure wave with one exception. The one exception is the door to a High Voltage Switchgear Room, which is different from the other doors in that it opens into the Switchgear Room and therefore has a very low capability to withstand a positive pressure in the Turbine Building. However, additional analysis determined that in the event of a main steam line break and possible failure of the door, the resultant environment in the room (i.e., temperature, pressure, and humidity) would be within the capability of the enclosed equipment, and equipment operability would not have been challenged. Accordingly, this issue is no longer considered an unanalyzed condition that would have significantly degraded plant safety, and therefore the notification made per 10CFR50.72(b)(3)(ii)(B) is retracted. Notified R3O (Gardner) and NRR EO (Reis) |
| Where | |
|---|---|
Davis Besse  Ohio (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+-0.82 h-0.0342 days <br />-0.00488 weeks <br />-0.00112 months <br />) | |
| Opened: | Author Lewis 15:31 Jan 19, 2004 |
| NRC Officer: | Gerry Waig |
| Last Updated: | Feb 20, 2004 |
| 40457 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Not Critical |
| Scram | No |
| Before | Hot Shutdown (0 %) |
| After | Hot Shutdown (0 %) |
WEEKMONTHYEARENS 573732024-10-10T14:45:00010 October 2024 14:45:00
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