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| Entered date | Event description | |
|---|---|---|
| ENS 42161 | 21 November 2005 17:42:00 | The Division 3 Emergency Diesel Generator (EDG) was declared INOPERABLE following a trip during a routine monthly surveillance run. As soon as the Division 3 EDG was at full load it tripped off line (output breaker tripped). The Division 3 EDG supplies electrical power to the High Pressure Core Spray System in the event of a loss of offsite power. No problems occurred on the Division 3, 4160 volt, safety related bus. This event is being reported in accordance with 10CFR50.72(b)(3)(v)(B), Event or Condition That Could Have Prevented Fulfillment of a Safety Function for a single-train system failure. The NRC Resident inspector has been notified.
Subsequent trouble-shooting and testing determined that the cause of the engine trip on 11/21/05 was an invalid high coolant temperature trip signal. This trip is bypassed during a Loss of Coolant (LOCA) initiation of the system, therefore, it was determined that the EDG would have been able to perform its safety function during a LOCA. Following a Loss of Offsite Power (LOOP), reactor water level is expected to reach Reactor Pressure Vessel (RPV) Water Level Low Low (Level 2) within 30 seconds of the initiating signal. Once Level 2 is reached, both the EDG and the LOCA Trip bypass signals are actuated. It was determined that the bypass would have occurred prior to the high coolant temperature trip. Based on the above, it was determined that the Division 3 EDG would have been fully capable of performing its safety function under both LOCA and LOOP. The Division 3 EDG was restored to an operable condition at 0214 on 11/22/05. The NRC Senior Resident Inspector has been notified. Notified R3DO (H. Peterson). |
| ENS 40983 | 24 August 2004 17:36:00 | At 1128 hours on 8/23/04, the Division 3 Essential Switchgear Heat Removal System (VX) was removed from service and declared inoperable for performance of system flow verification and balance. The test includes an as found flow check on the Division 3 Essential Switchgear Heat Removal System Condensing Unit, rendering the Division 3 VX safety-related chiller 1VX06CC INOPERABLE. The non-safety VX subsystem remained OPERABLE during the test. At 0917 hours on 8/24/04, the non-safety Division 3 VX Heat Removal Supply Fan 1VX04CC, tripped due to the breaker for the safety-related fan being removed for replacement. The Main Control Room received alarm 5042-6A, Auto Trip Pump/Fan. Since both the safety and non-safety subsystems of VX were unavailable Operators declared the High Pressure Core Spray (HPCS) System inoperable per Technical Specification 3.7.2, Action A.1. At 1153 hours, the breaker replacement was complete, 1VX04CC was restored to service, and the HPCS System was declared OPERABLE. The VX System maintains safety-related switchgear, battery and inverter room, and cable spread areas within the design temperature limits of the equipment. The VX system is support system for the HPCS System. With both subsystems of the VX System out of service, the HPCS System may not have been capable of performing its safety function to provide Emergency Core Cooling, aid in depressurization and maintain reactor vessel water level following a loss of coolant accident. An engineering evaluation is currently in progress to determine if the HPCS System would have been capable of performing its safety function with both safety and non-safety subsystems of VX out of service. This issue is being reported in accordance with 10CFR50.72(b)(3)(v)(D), as an event or condition that at the time of discovery could have prevented the fulfillment of the safety function needed to mitigate the consequences of an accident. The NRC Resident Inspector was notified of this event by the licensee.
Upon further review of this event, additional analysis has been performed which bounds the design bases heatup of the associated rooms cooled by the Division III Essential Switchgear Heat Removal System (VX). This analysis concludes that the areas cooled by the Division 3 VX subsystem would not have exceeded design temperatures while the cooling was secured, prior to cooling recovery, and that the supported systems remained operable. Based upon this additional analysis, it can be reasonably concluded that the safety function of High Pressure Core Spray, as a single train safety system, was fulfilled. Therefore this event is not reportable and Event #40983 is being retracted. The NRC Resident Inspector was notified of this retraction by the licensee. R3DO (Clayton) has been notified. |