ENS 42334
ENS Event | |
|---|---|
14:33 Feb 13, 2006 | |
| Title | Loss of Single Power Supply Could Result in Loss of Ventilation for Dc Subsystems in Both Units |
| Event Description | At 09:33 on February 13, 2006, a Susquehanna field operator inadvertently tripped an essential instrument AC panel breaker, while applying an energy control tag. He immediately communicated this condition to the control room, and then closed the breaker to restore power. During the subsequent investigation to determine applicable technical specifications, control room operators discovered that the tripped breaker resulted in a momentary loss of both battery room exhaust subsystems. To comply with the required actions for a loss of both battery room exhaust subsystems, Susquehanna declared all Unit 1 and Unit 2 DC subsystems inoperable, which resulted in LCO 3.0.3.
Although the entry into LCO 3.0.3 is not reportable, Susquehanna did discover an unanalyzed condition on both units that significantly degrades plant safety, which is reportable in accordance with 10CFR50.72(b)(3)(ii). The loss of a single power supply could result in the loss of ventilation and cooling for all DC subsystems on both units, leading to degradation of essential DC power sources. This condition does not meet single failure criteria for safety-related equipment. The licensee notified the NRC Resident Inspector.
The licensee is retracting this report based on the following: At 0933 hours0.0108 days <br />0.259 hours <br />0.00154 weeks <br />3.550065e-4 months <br /> on February 13, 2006, a Susquehanna field operator inadvertently tripped an essential instrument AC panel breaker while applying an energy control tag. The field operator immediately communicated this condition to the control room and was directed to close the breaker to restore power. The breaker trip resulted in a momentary loss of exhaust flow from the Class 1E 125 VDC and 250 VDC battery rooms. In response, operators declared all Unit 1 and Unit 2 batteries inoperable. An ENS notification (# 42334) was initiated in accordance with 10CFR50.72(b)(3)(ii)(B), Unanalyzed Condition that Significantly Affects Plant Safety, because the loss of a single power supply rendered the status of all station essential DC power sources (Batteries) indeterminate and, thus, inoperable. It was believed that this condition did not meet single failure criteria for safety-related equipment. Subsequent analysis of this event has revealed that the battery room exhaust system acted per design. The system's design is consistent with intended logic that ensures single failure proof isolation of the system, in compliance with the single failure criterion, in response to a toxic gas release. The single failure proof design of the battery exhaust system ensures isolation, not continued operation, in the presence of a single failure. The analysis further concluded that a short term loss of battery room exhaust does not compromise a battery's ability to function. The insights obtained through this analysis provide the basis for retraction of the ENS report of February 13, 2006. The licensee informed the NRC Resident Inspector. Notified R1DO(Henderson). |
| Where | |
|---|---|
Susquehanna  Pennsylvania (NRC Region 1) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+2.75 h0.115 days <br />0.0164 weeks <br />0.00377 months <br />) | |
| Opened: | Martin Lichtner 17:18 Feb 13, 2006 |
| NRC Officer: | Bill Huffman |
| Last Updated: | Feb 21, 2006 |
| 42334 - NRC Website
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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 465192011-01-03T18:44:0003 January 2011 18:44:00
[Table view]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 Single Point of Failure Vulnerability Discovered Which Could Potentially Affect Accident Response ENS 423342006-02-13T14:33:00013 February 2006 14:33:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Loss of Single Power Supply Could Result in Loss of Ventilation for Dc Subsystems in Both Units 2011-01-03T18:44:00 | |