Semantic search
| Entered date | Event description | |
|---|---|---|
| ENS 41782 | 17 June 2005 15:02:00 | At 1120 hours (CDT) on June 17, 2005, the Unit 1 reactor automatically scrammed from 85% power due to a valid high reactor pressure signal. The maximum reactor pressure was approximately 1044 psig during the event. All control rods inserted to their full-in position. Initial indications are that the reactor pressure increase was caused by a malfunction in the Electro-Hydraulic Control (EHC) system, which resulted in closure of the main turbine control valves. The main turbine bypass valves (nine) opened as expected in response to the pressure increase. No reactor pressure vessel safety or relief valves were required to actuate during the event. Reactor water level decreased to approximately -20 inches, which resulted in automatic Group 2 and 3 isolations as expected. All systems responded properly to the event. Unit 1 is in Mode 3 with a cooldown in progress and reactor water level in the normal level band. An investigation into the Unit 1 scram is in progress. Unit 2 remains at 94% power. This report is being made in accordance with 10CFR 50.72(b)(2)(iv)(B) and 10CFR50.72(b)(3)(iv)(A). The licensee notified the NRC Resident Inspector. |
| ENS 41652 | 29 April 2005 12:00:00 | 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) |
| ENS 40625 | 30 March 2004 10:40:00 | At 0740 hours (CST) during testing of the turbine thrust bearing wear detector, a main turbine trip occurred. This resulted in an automatic reactor scram due to turbine stop valve closure. Following the scram all Group II (Primary Containment) and Group III (Reactor Water Cleanup) isolations occurred as expected. All essential equipment functioned as required. Unit 2 remains in Mode 3 with reactor water level in the normal level band. An investigation into the Unit 2 turbine trip is in progress. Unit 1 was unaffected by the event and remains at 85% power. All control rods fully inserted. Decay heat is being removed via steam to the main condenser using the bypass valves. The Licensee notified the NRC Resident inspector. |