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At 2307 EDT on April 21, 2019, in Mode 1 at approximately 100 percent reactor power, Unit 1 automatically tripped due to a Main Turbine Trip. The Main Turbine Trip was a result of two out of three level instruments sensing a false high reactor water level. All control rods inserted as expected during the scram. Safety Relief Valves G and K lifted per design. The same level instruments that failed also tripped both Reactor Feed Pumps. As a result, reactor water level dropped below the Low Level 1 and 2 actuation setpoints. Per design, the Low Level 1 signal resulted in Group 2 (i.e., floor and equipment drain isolation valves), Group 6 (i.e., monitoring and sampling isolation valves) and Group 8 (i.e., shutdown cooling isolation valves) isolations. The Low Level 2 signals resulted in Group 3 (i.e. Reactor Water Cleanup) isolation, a secondary containment isolation signal, and an auto start of Standby Gas Treatment and Control Room Emergency Ventilation. Also, the Low Level 2 resulted in (high pressure coolant injection) HPCI and (reactor core isolation cooling system) RCIC automatically starting and injecting into the vessel. All systems responded as designed. This event is being reported in accordance with 10 CFR 50.72(b)(2)(iv)(B) for RPS actuation and 10 CFR 50.72(b)(3)(iv)(A) as an event that results in valid actuations of the Primary Containment Isolation System. There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. Decay heat is currently being removed via the turbine bypass valves. Condensate and feed water are maintaining water level. The reactor is still at saturation temperature and 475 psi, lowering slowly. The reactor is still in a normal electrical lineup. There was no impact to Unit 2 as a result of this event.

• * * UPDATE ON 04/22/19 AT 0220 EDT FROM ALAN SCHULTZ TO JEFFREY WHITED * * *

The licensee updated the event report to include a 4-Hr Non-Emergency Notification in accordance with 10 CFR 50.72(b)(2)(iv)(A) for Emergency Core Cooling System, HPCI, Discharge to the Reactor Coolant System. Notified R2DO (Dickson), NRR EO (Miller) and IR MOC (Gott).

On April 7, 2018, at 0836 EDT, with Unit 1 in Mode 1 at approximately 100 percent power, the reactor automatically tripped during testing of the stator cooling system. The trip was uncomplicated with all systems responding normally. No safety-related equipment was inoperable at the time of the event. Due to the Reactor Protection System (RPS) actuation while critical, this event is being reported as a four-hour, non-emergency notification per 10 CFR 50.72(b)(2)(iv)(B).

Operations responded using Emergency Operating Procedures and stabilized the plant in Mode 3. Reactor water level being maintained via normal feedwater system. Decay heat is being removed through the bypass valves.

Reactor water level reached low level 1 (LL1) as a result of the reactor trip. The LL1 signal causes a Group 2 (i.e., floor and equipment drain isolation valves), Group 6 (i.e., monitoring and sampling isolation valves) and Group 8 (i.e., shutdown cooling isolation valves) isolations. The LL1 isolations occurred as designed; the Group 8 valves were closed at the time of the event. Due to the Primary Containment Isolation System (PCIS) actuation, this event is also being reported as an eight-hour, non-emergency notification in accordance with 10 CFR 50.72(b)(3)(iv)(A) as an event that results in a valid actuation of the PCIS. Unit 2 was not affected. There was no impact on the health and safety of the public or plant personnel. The safety significance of this event is minimal. The automatic reactor trip was not complicated and all safety-related systems operated as designed. Investigation of the cause of the Reactor Protection System actuation is in progress. The licensee notified the NRC Resident Inspector.

At 2319 hours EST, a manual Reactor Protection System (RPS) actuation was inserted on Unit 1 in anticipation of a loss of condenser vacuum. Shortly before the manual RPS actuation, Circulating Water Intake Pump (CWIP) 1B tripped due to high delta-pressure across the intake traveling screen. This caused the trip of the remaining pumps. Previously, at 1859 hours, balance of plant (BOP) bus Common C unexpectedly de-energized. This caused loss of power to the CWIP traveling screen motors which, in turn, lead to the high delta-pressure across the traveling screen(s). All control rods inserted properly. As a result of the scram, reactor water level reached the Low Level 1 actuation set point and Primary Containment (i.e., Group 6) isolation occurred. All systems functioned as designed. The High Pressure Coolant Injection (HPCI) system is being used, as needed, for pressure control. The Reactor Core Isolation Cooling (RCIC) system is being used, as needed, for level control. No Safety/Relief Valves (SRVs) actuated as a result of the manual RPS actuation. The manual RPS actuation is reportable in accordance with 10CFR50.72(b)(2)(iv)(B) and 10CFR50.72(b)(3)(iv)(A). The actuation of the HPCI and RCIC systems and the Group 6 isolation are reportable in accordance with 10CFR50.72(b)(3)(iv)(A). The unit is currently in Mode 3 with a cooldown in progress. The licensee notified the NRC Resident Inspector. Notified R2DO (Ernstes).

• * * UPDATE FROM STEWART BYRD TO CHARLES TEAL AT 0741 EST ON 2/23/12 * * *

At 2319 hours EST, a loss of all Circulating Water Intake Pumps caused a lowering vacuum on Unit 1. As previously reported (i.e. Event Notification 47690), a manual Reactor Protection System (RPS) actuation was inserted on Unit 1 at this time. In addition, a valid actuation of the RPS, High Pressure Coolant Injection (HPCI), Reactor Core Isolation Cooling (RCIC), and a Group 6 isolation was reported in accordance with 10CFR50.72(b)(3)(iv)(A). At 2342, Main Condenser vacuum was 15 in. Hg and lowering. All Main Steam Isolation Valves were slow closed in anticipation of Group 1 isolation at this time. This follow-up notification is being made to report the manual actuation of the Group 1 isolation valves in accordance with 10 CFR 50.72(b)(3)(iv)(A). The Group 1 isolation was discussed with the NRC during initial notification of EN 47690, and this follow-up is providing written notification of the MSIV closure. The NRC Resident Inspector has been notified. Notified R2DO (Ernstes).

On May 12, 2005, at 0411 hours, electrical power was lost to the 4160 VAC Emergency Bus E1. Emergency Diesel Generator 1 was inoperable for maintenance at the time of the electrical power loss. This power loss to Emergency Bus E1 affected both Units 1 and 2. Unit 1 The loss of power to E1 resulted in Division 1 Primary Containment Isolation Valve (PCIV) actuations. The actuations included the Primary Containment Isolation System (PCIS) Group 2 (i.e., Drywell Equipment and Floor Drain, Traversing In-core Probe, Residual Heat Removal (RHR) Discharge to Radwaste, and RHR Process Sample), Group 3 (i.e., Reactor Water Cleanup), and Group 6 (i.e., Containment Atmosphere Control/Dilution, Containment Atmosphere Monitoring, and Post Accident Sampling Systems) valves, as well as the Reactor Building Ventilation System isolation (i.e., Secondary Containment isolation) and the automatic start of Standby Gas Treatment (SGT) System train B. The actuations of PCIVs and Reactor Building Ventilation System isolation were complete and the affected equipment responded as designed to the invalid signal (i.e., the valves and dampers that were open, at the time of the event, closed). Additionally, SGT System train B started and functioned successfully. Loss of power to E1 also resulted in entry into LCO 3.0.3 (i.e., be in Mode 2 within 7 hours, Mode 3 within 13 hours, and Mode 4 within 37 hours) due to all required reactor coolant leakage detection instrumentation/systems being inoperable. At 0440 hours, it was discovered that all three Control Room Air Conditioning (AC) subsystems became inoperable due to failure of the control building air compressors and Technical Specification LCO 3.0.3 was entered. At 0515 hours, it was determined that both Control Room Emergency Ventilation (CREV) subsystems became inoperable when the dampers drifted shut. At 0546 hours, a control building air compressor was started and the control room air conditioning and CREV subsystems were returned to operable status. Operators initiated a plant shutdown for Unit 1, as required by Technical Specifications at 0948 hours. Unit 2 Conditions and activities associated with the Control Room AC and CREV systems apply to Unit 2 as well as Unit 1. Reporting Requirements Met by this Notification 10 CFR 50.72(b)(2)(1), the initiation of any nuclear plant shutdown required by the plant's Technical Specifications, applies to Unit 1. 10 CFR 50.72(b)(3)(v)(D), a condition that, at the time of discovery, could have prevented the fulfillment of the safety function of systems that are needed to mitigate the consequences of an accident (i.e., Control Room AC and CREV), applies to both Units 1 and 2. 10 CFR 50.73(a)(i), invalid actuation of general containment isolation signals affecting containment isolation valves in more than one system, applies to Unit 1. INITIAL SAFETY SIGNIFICANCE EVALUATION Currently Unit 2 is operating at steady state with Unit 1 being shut down. Specified systems actuated as designed. No adverse impact to the control room environment occurred during the period (i.e., one hour and 35 minutes) the affected ventilation system was inoperable. The other redundant emergency busses are operable. Prior to the event reactor coolant leakage level for Unit 1 was well within operating limits. The actions as required by the applicable Technical Specifications have been established. CORRECTIVE ACTIONS Activities are currently under way to determine the cause of the E1 power loss and restore electrical power to Emergency Bus E1. Causes and actions to preclude recurrence will be addressed in accordance with the corrective action program and provided to the NRC in the associated licensee event report. The licensee notified the NRC Resident Inspector.

• * * UPDATE ON 05/13/05 @ 0952 BY LEONARD BELLER TO CHAUNCEY GOULD * * *

On May 12, 2005, at 0411 hours, electrical power was lost to the 4160 VAC Emergency Bus E1. Emergency Diesel Generator 1 was inoperable for maintenance at the time of the electrical power loss. This power loss to Emergency Bus E1 affected both Units 1 and 2. A non-emergency notification (Event Number 41692) was made to the NRC Operations Center at 112:2 hours. This follow-up notification discusses plant recovery from the Emergency Bus E1 power loss. Unit 1 Loss of power to E1 resulted in entry, into LCO 3.0.3 (i.e., be in Mode 2 within 7 hours, Mode 3 within 13 hours, and Mode 4 within 39 hours) due to all required reactor coolant system (RCS) leakage detection instrumentation being inoperable. Operators initiated a plant shutdown for Unit 1, as required by Technical Specifications at 0948 hours. A Notice of Enforcement Discretion (NOED) was requested from the NRC to waive compliance with the shutdown requirements associated with RCS leakage detection instrumentation in order to provide more time for an orderly plant shutdown. In lieu of the RCS leakage detection shutdown requirements (i.e., be in Mode 2 by 1111 hours), Unit 1 would adhere to the shutdown requirements associated with loss of Emergency Bus E1 (i.e.,, be in Mode 3 by May 13, 2005, at 0011 hours). The requested NOED was verbally granted by the NRC on May 12, 2005 at 1050 hours, so shutdown activities for Unit 1 continued versus the insertion of a manual reactor scram, with the unit at approximately 65 percent of rated thermal power. Power was restored to Emergency Bus E1 and the LCO associated with RCS leakage detection instrumentation was exited on May 12, 2005 at 1740 hours. The LCO associated with loss of power to Emergency Bus E1 was exited at 2015 hours. Unit 2 The LCO associated with loss of power to Emergency Bus E1 also applied to Unit 2, and was exited at 2015 hours, CORRECTIVE ACTIONS Emergency Diesel Generator 1 was made available, but not operable, on May 13, 2005, at 0117 hours. The licensee notified the NRC Resident Inspector. Reg 2 RDO (Moorman) was notified.

On July 29, 2004, at approximately 0351 hours, testing of Suppression Chamber-to-Drywell vacuum breakers commenced in accordance with Periodic Test 0PT02.3.1, "Suppression Chamber-to-Drywell Vacuum Breaker Operability Test." At 0357 hours, it was determined that vacuum breaker 2-CAC-X18D had an open indication. Technical Specifications (TS) Limiting Condition for Operation (LCO) 3.6.1.6, "Suppression Chamber-to-Drywell Vacuum Breakers," Condition B was entered for one suppression chamber-to-drywell vacuum breaker (2-CAC-X18D) not indicating closed. Required Action B.1 of TS LCO 3.6.1.6 provides 4 hours to verify the vacuum breaker closed. Attempts to confirm the vacuum breaker closed were unsuccessful and at 0757 hours, TS LCO 3.6.1.6 Condition C was entered. Required Action C.1 is to be in Mode 3 (Hot Shutdown) in 12 hours and Required Action C.2 is to be in Mode 4 (Cold Shutdown) in 36 hours. Initiation of the plant shutdown required by TS LCO 3.6.1.6 commenced at 0942 hours. This condition is being reported in accordance with 10 CFR 50.72(b)(2)(i) as the initiation of any nuclear plant shutdown required by the plant's TS. INITIAL SAFETY SIGNIFICANCE EVALUATION The initial safety significance of this condition is considered to be minimal. The actual position of the vacuum breaker cannot be confirmed, however if one vacuum breaker was not closed, communication between the drywell and suppression chamber air space could occur, and as a result, there is a potential, for primary containment overpressurization due to this bypass leakage if a loss of coolant accident were to occur. The plant is currently proceeding to hot shutdown with all Emergency Core Cooling systems operable. CORRECTIVE ACTIONS Determine the required corrective actions after entry into the drywell following shutdown. The safety significance of the event will be reviewed when the actual condition of the vacuum breaker is known. The NRC Resident Inspector has been notified.

• * * UPDATE ON 07/29/04 @ 1654 FROM KEN CHISM TO CHAUNCEY GOULD * * *

On July 29, 2004, at 1517 hours, a manual scram was inserted to shut down the Unit 2 reactor from approximately 23 percent of rated thermal power. The reactor shutdown was implemented to meet the requirements of Technical Specification (TS) Limiting Condition for Operation (LCO) 3.6.1.6 Required Action C.1 to be in Mode 3 in 12 hours. All control rods fully inserted into the core and no ECCS actuation occurred or relief valves lifted. Following the scram, an expected reactor vessel coolant level shrink occurred causing coolant level to decrease below the Low Level 1 setpoint. This coolant level decrease resulted in a Primary Containment Isolation Valve isolation signal to Group 2 (Drywell Equipment and Floor Drain, Traversing In-core Probe, Residual Heat Removal (RHR) Discharge to Radwaste, and RHR Process Sample), Group 6 (Containment Atmosphere Control/Dilution, Containment Atmosphere Monitoring, and Post Accident Sampling System), and Group 8 (RHR Shutdown Cooling Suction and RHR Inboard Injection) isolation valves. The isolation signal closed all of the valves that were open at the time of the expected initiation. The plant is currently in mode 3 and proceeding with a normal cooldown to Mode 4. The NRC Resident Inspection was informed. Notified Reg 2 RDO (Tom Decker).