ENS 41850

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v t e ENS Event
15:30 Jul 18, 2005
Title	Electrical Alignment Results in Single Failure Vulnerability
Event Description	Event: Keowee Hydro Station provides emergency power to the three Oconee units via two independent emergency power paths designated as the Overhead Path and the Underground Path. Either of the two Keowee Hydro Units (KHU) can be dedicated to either path, and Keowee Operations rotates which unit is aligned to which path, nominally on a monthly basis. On 7-18-05, as part of a corrective action from a previous event, Oconee reviewed power configurations for Keowee components/circuits with alternate power sources and discovered an alignment which presented a single failure vulnerability which could impact both paths. A review of Keowee Operating Procedures revealed that KHU-1 was designated as the normal source for control relays associated with the overhead path regardless of which unit was aligned to the underground path. KHU-1 was currently aligned to the underground path. It was determined that a postulated single failure of that DC power source would prevent KHU-1 from starting (which would affect the underground path) and would also prevent the main output Air Circuit Breakers from closing in the overhead path. As a result, Operations declared entry at 1130 hours0.0131 days <br />0.314 hours <br />0.00187 weeks <br />4.29965e-4 months <br /> [EDT] into Technical Specification (TS) 3.8.1 condition C for the Overhead power path being inoperable (a 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> allowed completion time). A review of available information indicates that this condition has existed whenever KHU-1 was dedicated to the underground path. This condition is being reported as an unanalyzed condition per guidance in NUREG 1022 section 3.2.4. Initial Safety Significance: The postulated single failure has not occurred. If the postulated single failure occurred during a design basis event, it is expected that, without credit for Operator intervention, both KHUs would fail. Operations would have been able to realign the KHU-2 to the Underground path and/or to have started and aligned a combustion turbine at Lee Steam Station. Such actions would be adequate for LOOP and station blackout scenarios, but would not be adequate for LOCA/LOOP scenarios. Therefore, the potential single failure condition being reported could have potentially resulted in a loss of safety function. Corrective Action(s): The immediate corrective action was to realign the affected DC control circuit power source to KHU-2, which was aligned to the overhead Path. The TS condition was exited at 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br /> [EDT] when this realignment was complete. The licensee notified the NRC Resident Inspector.

ENS 41850 +/-
Where
Oconee South Carolina (NRC Region 2)
Reporting

10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
Time - Person (Reporting Time:+0.38 h0.0158 days <br />0.00226 weeks <br />5.20524e-4 months <br />)
Opened:	Randy Todd 15:53 Jul 18, 2005
NRC Officer:	Mike Ripley
Last Updated:	Jul 18, 2005
41850 - NRC Website
v • d • e

v t e Emergency Notification System
Oconee with 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
WEEKMONTHYEAR2020-01-07T18:41:00 [Table view]
[ENS list for Oconee]

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