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| Entered date | Event description | |
|---|---|---|
| ENS 52295 | 12 October 2016 15:17:00 | At 1338 CDT, a spurious electrical fault on a unit substation motor control center caused a spurious feedwater isolation and required a manual reactor trip on Unit 2 Byron Station due to lowering steam generator level. Auxiliary feedwater automatically actuated to supply feedwater flow and is maintaining steam generator level within procedurally required levels. The motor control center fault resulted in feedwater isolations on two of four steam generators. All rods inserted during the trip. Decay heat is being removed via the steam dumps to condenser. Plant response to the trip was uncomplicated. Unit 2 is in a normal shutdown electrical lineup with power available from offsite. The grid is stable. Byron Station Unit 1 is at 95% power and stable and was unaffected by the transient on Unit 2. The cause of the motor control center fault is under investigation. The licensee has notified the NRC Resident Inspector and will be issuing a press release concerning the manual reactor trip. |
| ENS 51958 | 25 May 2016 16:00:00 | On May 25, 2016, during evaluation of protection for Technical Specification (TS) equipment from the damaging effects of tornados, Byron Station identified non-conforming conditions in the plant design such that specific TS equipment on both units is considered to not be adequately protected from tornado missiles. Each of the following reportable conditions is postulated by tornado missiles entering openings through the wall that separates the Auxiliary Building and the Turbine Building: The following items could be impacted by tornado missiles entering the 0A and 0B (common) MCR (main control room) turbine building intake openings: Main control room pressurization, main control room ductwork and dampers, chilled water to the VC (control room ventilation) coils, main control room radiation monitors. The following items could be impacted by tornado missiles entering the Division 11 and 21 MEER (miscellaneous electrical equipment rooms) rooms: Exhaust from the MEER (affects room cooling and MCR pressure), exhaust from a battery room, conduits and cabinets associated with the battery chargers and DC bus. The following items could be impacted by tornado missiles entering the Division 12 and 22 MEER rooms: Exhaust from the MEER (affects room cooling and MCR pressure), MEER supply fan and ductwork, battery room exhaust, and the instrument inverter cabinets. The RWST (refueling water storage tank) roof access opening Bilco hatch is fabricated from sheet metal that is not designed to prevent all postulated tornado missiles from entering the tank. The tank pressure boundary is 24" thick concrete and is designed to withstand an external tornado missile impact. Thus a missile that enters the tank will not adversely impact the tank pressure boundary. The following items could be impacted by tornado missiles entering the RWST roof access: The 6" RWST recirculation pipe, 3" overflow pipe, and 24" suction pipe. This piping is located inside the tank and they are approximately 130 degrees around the tank away from the hatch opening. This condition creates a potential LOSF (loss of safety function) with the Byron Essential Service Water Cooling Towers (UHS) (ultimate heat sink) with the discovery that the power and control cables to four of eight cooling tower fans can be damaged by tornado missiles penetrating through wall openings. This condition is reportable per 10 CFR 50.72(b)(3)(ii)(B) for any event or condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety, and per 10 CFR 50.72(b)(3)(v)(D) for any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. These conditions are being addressed in accordance with EGM 15-002 and DSS-ISG-2016-01 (enforcement discretion and interim guidance documents). The licensee has notified the NRC Resident Inspector. |
| ENS 47644 | 6 February 2012 20:40:00 | Unit 2 had been connected to the grid at 1431 CST today following a recent forced outage and was in the process of power ascension in accordance with plant procedures. At approximately 25% reactor power (approximately 240 MWe), the operators were transferring main feed flow to the steam generator lower nozzle through the feedwater isolation valves, (i.e. 2FW009A, B, C, D). 2FW009C was the first valve to be opened due to previously experienced problems with this valve being stuck in the seat. No issues were experienced during the opening of 2FW009C. Upon opening of 2FW009C, the 2C steam generator level began to rise as expected. The operators throttled back feedwater flow to control steam generator level. However, the 2C steam generator level increased to the High-High level setpoint of 80.8% (p-14). Since the reactor was below 30% (P-8), no automatic reactor trip signal was generated. However, the turbine automatically tripped, a feedwater isolation signal was initiated, and 2C Main Feedwater pump trip occurred as designed. With no main feedwater flow available, the operators manually tripped the reactor and entry into procedure 2BEP 0, Reactor Trip or Safety Injection Unit 2 was entered. The operators then manually started the 2A and 2B Auxiliary Feedwater pumps to supply water to the steam generators prior to reaching the Low-Low steam generator level setpoint of 36.3%. Transition from 2BEP 0 to 2BEP ES-0.1, Reactor Trip Response, was completed and the emergency procedures were exited. Unit 2 is being maintained in a stable condition in Mode 3. The NRC Resident Inspector has been informed. |
| ENS 43807 | 27 November 2007 10:30:00 | An ALERT was declared at 0915 CST. A nitrogen freeze seal was being used on a 3 inch pipe in the 1B RHR and 1B Containment Spray pump room. A leak developed on the freeze seal jacket. This created an oxygen deficient atmosphere (less than 19.5 percent oxygen). The nitrogen supply was isolated. And the room was evacuated. The alert was declared in accordance with Emergency Action Level (EAL) "hazard alert #7 (HA7)." Additional ventilation was being placed in the area to restore normal oxygen levels. EAL table entry HA7 is for "Release of toxic or flammable gases within or restricting access to a vital area which jeopardizes operation of systems required to maintain safe operations or establish or maintain safe shutdown. No personnel injuries occurred. Oxygen levels were returned to acceptable levels at 0933 CST. The licensee notified the NRC Resident Inspector.
The ALERT was terminated at 1103 CST. Notified IRD (McDermott), R3DO (Lipa), DHS SWO (Mary Anne), FEMA (Dan Sullivan), DOE (Anthony Parsons), EPA (Ms Ross), USDA (Andrew Watts), and USDA (Rick Turner). |