ENS 41652
ENS Event | |
|---|---|
12:32 Apr 29, 2005 | |
| Title | Minimum Switchyard Voltage Requirements Not Met |
| Event Description | At 0732 [CDT] on April 29, 2005 Quad Cities Station was notified that the calculated post-LOCA switchyard voltage was below the minimum acceptable value required to ensure offsite power would remain available following a design basis accident. As a result, both offsite power sources were declared inoperable and the appropriate Technical Specification Actions were taken for both Units. The ability of the Emergency Diesel Generators to fulfill their design function was not affected by this condition. This event is being reported in accordance with 10CFR50.72(b)(3)(v)(D) as a condition that could have prevented the fulfillment of a safety function given the predicted post-LOCA switchyard voltage. The condition was exited at 0836 [CDT] on April 29, 2005.
The required minimum post-accident switchyard voltage is 352.9 KV (Unit 1) and 351.0 KV (Unit 2) while the projected post accident voltage, which prompted this notification, was 347.9 KV. During this timeframe, actual switchyard voltage was approximately 358 KV. The licensee notified the NRC Resident Inspector.
The purpose of this report is to retract ENS report #41652 (April 29, 2005), ENS report 41766 (June 11, 2005), and ENS report #41801 (June 27, 2005). The reports were made following notification that the switchyard predicted voltage was below the required value necessary to ensure that offsite power would remain available following a design basis accident. For each event, both sources of offsite power were declared inoperable, the appropriate Technical Specification required actions were taken for the units, and an ENS notification was made for a condition that could have prevented the fulfillment of a safety function. Each Quad Cities unit has two sources of off-site power. For a specific unit, one source is from the switchyard through the unit's Reserve Auxiliary Transformer (RAT) and the second source is from the switchyard through the opposite unit's RAT. Following further analysis of the loading on the RATs during an accident, it was determined that only one source of offsite power to each unit should have been considered inoperable. The analysis determined that because the RAT for the non-accident unit (i.e., the offsite source supplied through the opposite unit) would be carrying a much smaller load, it would not be subject to a degraded voltage condition and resultant isolation from the grid. Therefore, an accident on one unit would not affect the operability of the source of offsite power supplied through the opposite unit's RAT. As a result, only the source of offsite power supplied through the unit's RAT was inoperable. With one source of offsite power available at all times, there was no condition present that could have prevented fulfillment of a safety function, and therefore, these events are not reportable. The licensee notified the NRC Resident Inspector. Notified R3 DO (R. Lanksbury) |
| Where | |
|---|---|
Quad Cities  Illinois (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+-0.53 h-0.0221 days <br />-0.00315 weeks <br />-7.25994e-4 months <br />) | |
| Opened: | Jim Stortz 12:00 Apr 29, 2005 |
| NRC Officer: | Arlon Costa |
| Last Updated: | Aug 9, 2005 |
| 41652 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (85 %) |
| After | Power Operation (85 %) |
Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (85 %) |
| After | Power Operation (85 %) |