ENS 48055
ENS Event | |
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17:53 Jun 28, 2012 | |
Title | Loss of One of Two Offsite Power Sources |
Event Description | At 1353 EDT on 06/28/2012, Susquehanna Steam Electric Station experienced a loss of power from one of two offsite power sources when transformer 20 shutdown automatically. All ESS [Engineered Safeguards System] electrical busses fed by this transformer automatically transferred to the other offsite power source (transformer 10). Additionally, startup bus 20, which is normally fed from transformer 20, automatically transferred to transformer 10.
On each unit, multiple system containment isolation valves closed as a result of the electrical transient. Operators were able to reset and restore each system. On unit one, residual heat removal (RHR) shutdown cooling ceased operation during the transient. Shutdown cooling was restored within one hour by control room operators in accordance with off-normal procedures. Unit two remained at 100% power throughout the event. This incident is being reported as an unplanned actuation of systems that mitigate the consequences of significant events per 10 CFR 50.72(b)(3)(iv)(A). The licensee is in a 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> LCO on Unit 2 as a result of the loss of offsite power. All emergency diesels generators are available. The licensee is investigating the cause of the transformer 20 shutdown. The NRC Resident Inspector and the Pennsylvania Emergency Management Agency (PEMA) have been notified. |
Where | |
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Susquehanna Pennsylvania (NRC Region 1) | |
Reporting | |
10 CFR 50.72(b)(3)(iv)(A), System Actuation | |
LER: | 05000387/LER-2012-008 |
Time - Person (Reporting Time:+2.85 h0.119 days <br />0.017 weeks <br />0.0039 months <br />) | |
Opened: | Darvin Duttry 20:44 Jun 28, 2012 |
NRC Officer: | Joe O'Hara |
Last Updated: | Jun 28, 2012 |
48055 - NRC Website
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Unit 1 | |
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Reactor critical | Not Critical |
Scram | No |
Before | Cold Shutdown (0 %) |
After | Cold Shutdown (0 %) |
Unit 2 | |
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Reactor critical | Critical |
Scram | No |
Before | Power Operation (100 %) |
After | Power Operation (100 %) |