ENS 41140
ENS Event | |
|---|---|
21:30 Oct 19, 2004 | |
| Title | Standby Emergency Electrical Power Paths Inoperable For 41 Minutes |
| Event Description | The Keowee Hydro Units provide the emergency power source for the Oconee Units. At 0357 on 10/19/04, Keowee Unit 1 (and the overhead emergency power path) was declared inoperable in order to perform scheduled maintenance. At 1730, Keowee Unit 2 (and the underground emergency power path) was declared inoperable due to the loss of breaker control power associated with Keowee Unit 2 auxiliaries. At 1811, as required by Technical Specification 3.8.1 condition I, both standby buses were energized from a Lee Combustion Turbine via an isolated power path. At 1828, a Operability Verification of Keowee Unit 2 to the overhead emergency power path was performed with all acceptance criteria met. At 1904, Keowee Unit 2 to the overhead emergency power path was declared operable. Technical Specification 3.8.1 condition I was exited.
Initial Safety Significance: Between times 1730 to 1811, both on site emergency power paths were inoperable. During this time period a condition existed that could have prevented the fulfillment of the safety function of systems that are needed to mitigate the consequences of an accident. Corrective Action(s): At 1828, an Operability Verification of Keowee Unit 2 to the overhead emergency power path was performed with all acceptance criteria met. At 1904, Keowee Unit 2 to the overhead emergency power path was declared operable. Technical Specification 3.8.1. condition I was exited. A team is established to investigate the loss of breaker control power associated with Keowee Unit 2 auxiliaries. The licensee will notify the NRC Resident Inspector.
The Keowee Hydro Units (KHUs) provide the emergency power source for the three Oconee Units. On 10/20/04 at 0135 Oconee made a notification to the NRC of a loss of safety function. Reference Event Number: 41140. The event was due to an unexpected failure on KHU 2. At the time of the event, KHU 1 was out of service for planned maintenance and was in the early stages of testing for return to service. Each KHU can be aligned to either an overhead or an underground power path to supply emergency power to Oconee. At 1730, KHU 2 and the underground emergency power path were declared inoperable due to the loss of breaker control power associated with KHU 2 auxiliaries while aligned to the underground path. By the Oconee Technical Specification 3.8.1 Bases, this breaker (ACB-8) is required to be operable in order to consider KHU 2 operable while aligned to the underground path. Since KHU 2 did not meet the TS configuration, and since KHU 1 testing was not complete, both trains were inoperable and the event was reported as a loss of safety function. At 1811, as required by Technical Specification 3.8.1 condition I, both standby buses were energized from a Lee Combustion Turbine via a dedicated power path. KHU 2 was re-aligned to the overhead path and its associated auxiliary power breaker (ACB-6). The event was terminated at 1904 when KHU 2 was declared operable to the overhead emergency power path after completion of an Operability Verification test. Justification for conclusion that there was no loss of safely function while KHU 2 was declared inoperable (approximately one hour duration): KHUs are capable of 'black start', i.e. starting and operating on battery power alone. Therefore, if there had been an event resulting in an emergency start signal during the one hour interval of vulnerability, KHU 2 would have been able to start and operate for approximately one hour with the loss of control power to ACB-8. Operations procedures include guidance to close breaker ACB-8 manually using a maintenance closure handle. These steps would have been performed approximately 30 minutes into the postulated event. Based on the results of testing and troubleshooting of ACB-8, Oconee has concluded that ACB-8 could have been closed manually and, once closed, would have successfully provided auxiliary power for the duration of any event. Thus Oconee concludes that KHU 2 should be considered available, with reasonable expectation for performing its safety function during this event. Therefore Oconee has concluded that this event was not a reportable loss of safety function and Event Number 41140 is withdrawn. The resident inspector and R2DO (Bonser) have been notified. |
| Where | |
|---|---|
Oconee  South Carolina (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+4.08 h0.17 days <br />0.0243 weeks <br />0.00559 months <br />) | |
| Opened: | David Younge 01:35 Oct 20, 2004 |
| NRC Officer: | Mike Ripley |
| Last Updated: | Oct 26, 2004 |
| 41140 - 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 %) |