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This is a synopsis of initial information received via phone: On December 27, 2019, at 0705 EST, while Unit 2 was at 100 percent (Mode 1), the 'A' Main Feedwater Pump tripped due to an unknown cause. The reactor was manually tripped and is currently at zero (0) percent power (Mode 3). Decay heat is being removed via Auxiliary Feedwater. The 'B' Feedwater pump is operable. There was no impact on Unit 3. The licensee notified the NRC Resident Inspector. Additionally, Connecticut Department of Environmental Protection, Waterford Dispatch, and East Lyme Emergency Management Division will be notified.

• * * UPDATE ON 12/27/2019 AT 1330 EST FROM JASON PARIS TO CATY NOLAN * * *

This is an update to NRC Event Number 54457. At 0704 EST, on 12/27/2019, with Millstone Unit 2 operating at 100 percent power, operators inserted a manual reactor trip. The trip was initiated due to a trip of the 'A' Main Feedwater Pump. The Auxiliary Feedwater System (AFW) automatically actuated as required. All control and shutdown rods fully inserted. All safety systems responded as designed. No primary or secondary safety valves actuated during or after the transient. Unit 2 is currently stable at normal operating pressure and temperature in Mode 3, Hot Standby. Reactor Coolant System (RCS) temperature is being maintained by the steam dump system with all Reactor Coolant Pumps (RCPs) in service. Main Feedwater has been secured, and Auxiliary Feedwater is in service. The electrical system is in normal alignment. There was no impact on Unit 3. There was no impact to the health and safety of the public or plant personnel. Due to Reactor Protection System (RPS) actuation while critical, this event was reported as a four hour, non-emergency notification per 10 CFR 50.72(b)(2)(iv)(B); and an eight hour non-emergency notification in accordance with 10 CFR 50.72(b)(3)(iv)(A) as an event that resulted in a valid actuation of the AFW system. The licensee will notify the NRC Resident Inspector of the update. Notified R1DO (Cherubini).

At 0638 EDT on 5/15/2016, an Unusual Event (EAL GU.2) was declared on Millstone Unit 3 due to a Main Generator hydrogen gas leak into the Turbine Building. At 0645 EDT, operators manually tripped the reactor. All rods inserted. All systems functioned as expected following the reactor trip. Operators are currently venting the remaining hydrogen from the generator through the normal vent path. There is no safety related equipment out-of-service. The plant is in a normal post-trip electrical line-up. All Emergency Diesel Generators are available. The licensee notified the State of Connecticut and the NRC Resident Inspector. Notified DHS SWO, FEMA Ops Center, and DHS NICC Watch Officer. Notified via E-mail FEMA National Watch Center and NuclearSSA.

• * * UPDATE FROM MIKE CICCONE TO HOWIE CROUCH AT 1044 EDT ON 5/15/16 * * *

At 0949 EDT, the licensee terminated the Unusual Event. At 0645 EDT on 5/15/16, a manual reactor trip was initiated at Millstone Unit 3 due to a hydrogen leak from the main generator. As expected, Auxiliary Feedwater System (AFW) initiated on the reactor trip. The trip was uncomplicated and the plant is currently in Mode 3 with a normal electric lineup and decay heat is being removed via steam dumps to the condenser. The cause of the hydrogen leakage is under investigation. This is reportable under 10 CFR 50.72(b)(2)(iv)(B) - RPS actuation while critical, and 10 CFR 50.72 (b)(3)(iv)(A) - valid specified system actuation. The licensee has notified Waterford Township, the State of Connecticut and the NRC Resident Inspector. Notified R1DO (Burritt), NRR ET (McDermott), NRR EO (Morris), IRD (Grant), DHS SWO, FEMA Ops Center, DHS NICC, FEMA National Watch Center (email) and NuclearSSA (email).

At 0702 EDT on 5/25/14, Millstone Units 2 and 3 experienced a loss of offsite power and subsequent trip of both units. An Unusual Event was declared by Millstone Units 2 and 3 at 0715 EDT. Power is currently being supplied to all emergency busses by the emergency diesel generators. Offsite power is not available. At this time, it appears that the loss of offsite power is due to a localized issue in the Millstone switchyard. The surrounding areas were not affected. A decision was made to take the NRC to monitoring mode at 0749 EDT with Region 1 in the lead. Notified DHS SWO, FEMA Ops Center, NICC Watch Officer, DOE Ops Center, USDA Ops Center, HHS Ops Center, and Nuclear SSA via email.

• * * UPDATE FROM MICHAEL CICCONE TO DANIEL MILLS AT 1330 EDT * * *

The loss of offsite power was due to one main line coming into the plant shorting to ground. Emergency plan procedures have been implemented, natural circulation has been established, and the plant is stable. Offsite electrical power has been restored to both Unit 2 and Unit 3. Emergency diesel generators have been secured, and plant equipment has been restored to a normal line up. Extended loss of instrument air following the loss of offsite power complicated the recovery actions. The normal reactor coolant system letdown flow path was not able to be established. This resulted in the rupture of the pressurizer relief tank rupture disk inside containment. The relief valve on the volume control tank lifted when restoring normal letdown. This caused the primary drains transfer tank to overflow into the auxiliary building. This overflow path has been isolated. Supplementary leakage collection system radiation monitor HVR-RE19B, and auxiliary building normal ventilation radiation monitor HVR-RE10B, are indicating normal levels. Notified R1DO (Gray), R1DRA (Lew), NRR EO (Kokajko), IRD MOC (Grant).

• * * UPDATE FROM MICHAEL CICCONE TO DANIEL MILLS AT 1548 EDT * * *

At 1414 EDT the licensee terminated the Unusual Event. Notified R1DO (Gray), R1DRA (Lew), NRR EO (Kokajko), IRD MOC (Grant), DHS SWO, FEMA Ops Center, NICC Watch Officer, DOE Ops Center, USDA Ops Center, HHS Ops Center, and Nuclear SSA via email.

At 2236 on 10/11/08 while reducing power for a planned refueling outage, "C" Steam Generator water level decreased and the turbine tripped. The reactor tripped on the turbine trip. Auxiliary feedwater initiated as expected and decay heat is being removed via the condenser steam dumps. All control rods fully inserted. No significant safety equipment is out of service and all safety buses are being supplied by offsite power. Emergency Diesel generators are available if needed. No PORVs or primary/secondary relief valves lifted. The licensee is evaluating cause of steam generator level excursion. Unit 2 is unaffected.

The licensee notified the NRC Resident Inspector.

The licensee entered an Unusual Event after an automatic reactor trip due to a loss of offsite power per EAL Designation PU-1. Currently the plant is stable in Mode 3 with power being supplied to the "A" & "B" Emergency Diesel Generators (EDG) running supplying power to the safety buses. Decay heat is being removed by the motor driven Auxiliary Feedwater Pump supplying water to the steam generators exhausting to atmosphere via atmospheric relief valves. There are no primary to secondary tube leaks. NRC Resident Inspector has been notified.

• * * UPDATE FROM SKIP JORDAN TO JOHN KNOKE AT1252 EDT ON 05/25/08 * * *

At 1252 EDT the licensee terminated from their Unusual Event. After the loss of offsite power due to a failure of the Reserve Station Service Transformer (RSST) the licensee began to troubleshoot the problem as well as beginning to restore offsite power. At 1106 on 5/24/08 a cross-tie from Unit 3 was connected to Unit 2 and "A" EDG was secured. At 0950 on 5/25/08 the RSST was powered up and the non-vital busses were energized. At 1136 the "B" and "D" Reactor Coolant Pumps were started. At 1230 the vital bus was energized and the "A" EDG was secured. The licensee notified the NRC Resident Inspector. Notifications to: R1 (Marc Dupas, David Lew), R1DO (Mel Gray), NRR EO (Fred Brown), IRD MOC (William Gott), DHS (Fred Hill), FEMA (Dan Sullivan), USDA (Amanda Jimenez,), HHS (Mason Pyle), DOE (Julia Muse). The NRC Resident Inspector was notified.

The licensee was performing maintenance on "D" Steam Generator Low Level bistables when 4 (four) out of 8 (eight) trip control breakers opened possibly due to a 24 V DC power supply transient to 2 (two) of 4 (four) logic matrix relays. The reactor trip logic was verified to be functional and capable of processing valid reactor trip signals. The actuation was invalid as no plant transient occurred and no process variable was exceeded which would otherwise have required a reactor trip. The licensee notified the State and the NRC Resident Inspector.

• * * RETRACTION ON 08/14/06 AT 0947 ET BY M. EWER TO MACKINNON * * *

Upon further review, the initial notification of this event is determined to have been conservative. A review of NUREG 1022, Rev. 2, 'Event Reporting Guidelines, 10 CFR 50.72 and 50.73,' as well as the supporting comments in the notice of final rulemaking for changes to 10 CFR Parts 50 and 72 contained in the Federal Register on October 25, 2000, indicates that these documents stress the need for reporting of system actuations. As stated in NUREG 1022, 'actuation of multichannel actuation systems is defined as actuation of enough channels to complete the minimum actuation logic. Therefore, single channel actuation logic,' Per the final rulemaking, 'the principal reason for reporting an actuation of one of these systems is that it is indicative of an unplanned plant transient that the NRC needs to evaluate to determine if action is necessary to address a safety problem.' In the event described in CR-06-06880, a portion of the RPS actuation sufficiently to cause four of the eight TCBs to open (i.e, a half trip), but not enough channels actuated to complete the minimum actuation logic for RPS (i.e, insufficient channels to fulfill the safety function of the RPS to deenergized the control rod drive mechanisms to shutdown the reactor). There was no unplanned plant transient as a result of the half trip. Determination Based on the above assessment, this condition in NOT reportable per 10 CFR 50.73(a)(2)(iv)(A) as an actuation of any of the systems listed in paragraph 10 CFR 50.73(a)(2)(iv)(B). Accordingly, the report of a 4 hour non-emergency event under 10 CFR 50.72(b)(2)(iv)(b) for a half RPS trip actuation should be withdrawn. R1DO (Lorson) notified. The NRC Resident Inspector will be notified by the licensee of this retraction.

At 09:23 the licensee indicated that several Main Steam Relief Valves lifted and stayed open. A high pressure flow signal from the secondary Steam Generator caused initiation of Unit 3 Safety Injection, which in turn caused the Reactor to trip. All rods fully inserted as required. Activation of the Safety Injection subsequently caused the Pressurizer level to go solid. About 30 minutes into the event the primary Reactor Coolant and Main Steam Systems stabilized, including the Pressurizer level and pressure. During the initial briefing, about 09:35, the licensee reported that all secondary Safety Relief Valves have reseated. Decay heat is being directed to the Atmospheric Dumps due to the Main Condenser not being available. The licensee is attempting to establish ERDS. Initial assessment of this incident is believed not to be security related, however, follow-up is being conducted to verify same. At 09:48, NRC management made a decision to enter into Monitoring Mode. At about 11:15 the licensee indicated that a valve in the Charging System indicated some leakage, therefore it was isolated. Licensee stated that no radiological releases and no S/G tube leakage was indicated. Licensee notified State and local emergency response agencies. They will notify the NRC Resident Inspector. Notified DHS (Doyle), FEMA (Biscue), DOE (Smith), USDA (Magners), and HHS (Hogan).

• * * UPDATE FROM D. DODSON TO W. GOTT 1328 EDT 04/17/05 * * *

At approximately 0830 on April 17, 2005 Millstone Unit 3 experienced an automatic reactor trip from full power. The Reactor is in a stable shutdown condition and is proceeding to Mode 5 cold shutdown. No release of radioactivity other than those minor releases associated with normal plant operation has occurred. There were no personnel injuries associated with the event. In addition to the Reactor Trip, half-train Safety Injection (SI) and half-train Main Steam Isolation (MSI) actuations occurred. Control room personnel were successful at manually initiating full SI and MSI. SI has since been terminated and RCS pressure control has been restored. Multiple steam line safety valves (MSSV) lifted with at least one MSSV indicating a failure to reclose. As a result, an ALERT was declared at approximately 0853 due to the failure of at least one MSSV failing to reclose. All MSSVs are currently closed. Auxiliary Feedwater (AFW) actuated automatically as expected, however, the turbine driven auxiliary feedwater pump (TDAFWP) tripped on start-up and was subsequently reset locally. Both motor driven auxiliary feedwater pumps (MDAFWPs) operated as expected to maintain steam generator water levels. Due to the additional inventory injected to the Reactor Coolant System (RCS) as a result of the SI actuation, the pressurizer filled and a primary system safety valve (PSSV) actuated at a lower than expected pressure. All PSSVs are currently closed, however, there is indication of leakage past either a PSSV or Pilot Operated Relief Valve (PORV). Upon alignment of the Charging system to Refueling Water Storage Tank recirculation flow path, 2 valves had indication of packing leakage. Those packing leaks have been terminated. The cause of the event is under investigation. The licensee has issued a press release. The licensee will notify the NRC Resident Inspector. Notified R1 DO (J. White) and IRD Manager (T. McGinty)

• * * UPDATE FROM D. DODSON TO W. GOTT AT 1915 ON 04/17/05 * * *

The previously reported time of the Alert declaration should be corrected to read 08:42. Millstone Unit 3 entered Mode 4 (Hot Shutdown) at approximately 19:03 on April 17, 2005. The event at Millstone Unit 3 was terminated at 19:05. The cause of the event is under investigation. A recovery plan is being formulated. Internal NRC notifications, DHS (Frost), NRC/EPA (Threatt), FEMA (Erwin), DOE (Morone), USDA (Smeltzer), HHS (Desi) The licensee will notify the NRC Resident Inspector. At 23:45 the Agency exited Monitoring Mode and entered into Normal Mode.

While rolling the turbine when at 20% power they experienced an over speed turbine trip. During a second attempt when at 23% power, the turbine had high vibration so they manually tripped the reactor. Cause for the vibration is being investigated since a new rotor had just been installed in the turbine. All rods fully inserted during the reactor trip and no ECCS injection occurred or primary relief valves lifted. The licensee notified the NRC Resident, the State of Connecticut and Local agencies

• * * UPDATE AT 1423 EST ON 11/28/03 FROM FRANKS TO GOTT * * *

The following clarifying information was provided by the licensee. While at 23% power of a scheduled power ascension following a refueling outage, Millstone Unit 2 performed a required manual reactor trip when main turbine vibration reached a trip set point of 12 MILS. The main turbine vibrations were anticipated during the power ascension due to a newly installed low pressure "Mono-Block" rotor. All control rods fully inserted during the reactor trip and no ECCS injection occurred or primary relief valves lifted. The overspeed trip discussed in the original report was a test conducted prior to placing the main turbine on the grid. Notified R1DO (Dimitriadis). The licensee will notify the NRC Residence Inspector.