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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 54988 | 8 November 2020 13:29:00 | 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Unusual Event Due to Earthquake Felt Onsite | Millstone Units 2 & 3 declared an Unusual Event at 0921 EST after an earthquake was felt onsite. The earthquake monitoring instrumentation did not actuate, and there were no station system actuations. No damage has been detected at this time. Millstone has initiated their Abnormal Operating Procedure for an earthquake and performing station walkdowns. The State of Massachusetts has been notified. The Waterford Police and U.S. Coast Guard have contacted the station. The NRC resident has been notified. Notified DHS SWO, FEMA Operations Center, CISA Central, FEMA NWC (email), DHS Nuclear SSA (email), and FEMA NRCC SASC (email).
At 1510 EST on November 8, 2020, Millstone Units 2 & 3 exited the Unusual Event due to the earthquake following plant walkdowns that revealed no damage to plant structures, systems, or components. Station and System walkdowns identified no issues due to the earthquake. Millstone notified the State and local authorities, and the NRC Resident Inspector. Notified R1DO (DeFrancisco), IRD (Grant), NRR (Nieh), R1RA (Lew), NRR EO (Miller), DHS SWO, FEMA Operations Center, CISA Central, FEMA NWC (email), DHS Nuclear SSA (email), and FEMA NRCC SASC (email). | ||
| ENS 53005 | 9 October 2017 18:05:00 | 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Notification of Unusual Event - Flammable Gas in the Turbine Building | While troubleshooting a hydrogen differential pressure gauge, operators found a hydrogen concentration greater than the lower explosive limit (4% hydrogen concentration). The licensee evacuated the turbine building. The licensee is ventilating the area to allow personnel access to isolate and repair the leak. The plant Fire Brigade is on standby. This event was declared for GU-2: release of toxic or flammable gas. The main generator pressure and hydrogen concentration are stable. The licensee notified the NRC Resident Inspector. Notified DHS SWO, FEMA Operations Center, DHS NICC, FEMA NWC (email), DHS Nuclear SSA (email), and FEMA NRCC SASC (email).
The unusual event was terminated at 1617 EDT because the leak was isolated and the hydrogen concentration in the Hydrogen Control Cabinet was zero percent. The licensee notified the NRC Resident Inspector. Notified the R1DO (Jackson), IRD MOC (Stapleton), NRR (King), DHS SWO, FEMA Operations Center, DHS NICC, FEMA NWC (email), DHS Nuclear SSA (email), and FEMA NRCC SASC (email). | ||
| ENS 52904 | 15 August 2017 11:48:00 | 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Unusual Event Due to Fire Alarm in Containment | On August 15, 2017 at 0748 EDT, an Unusual Event was declared at Millstone Unit 2 due to a fire alarm indication in containment that was unable to be verified extinguished within 15 minutes. Current containment parameters do not indicate an actual fire. A containment entry is planned to verify that there is no fire. Unit 2 continues at 100% power. Unit 3 was unaffected. The NRC remains in Normal mode. The licensee notified the NRC Resident Inspector and State and local government agencies. Notified DHS SWO, FEMA Ops Center, DHS NICC. Notified FEMA National Watch and Nuclear SSA via E-mail.
At 0951 EDT, the Unusual Event was terminated. No signs of an actual fire were present upon containment entry. All alarms are cleared and they are investigating the cause of the alarm. The licensee notified the NRC Resident Inspector and State and local government agencies. Notified R1DO (Gray), NRR EO (Miller), and IRD (Gott). Notified DHS SWO, FEMA Ops Center, DHS NICC. Notified FEMA National Watch and Nuclear SSA via E-mail. | ||
| ENS 51929 | 15 May 2016 10:38:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(a)(1)(i), Emergency Class Declaration 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Unusual Event Due to Main Generator Hydrogen Leak in Turbine Building | 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.
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). | Emergency Diesel Generator Auxiliary Feedwater | |
| ENS 51513 | 4 November 2015 16:33:00 | 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Fire on the 'A' Emergency Diesel Generator | At 1133 EST on 11/4/15, an Alert was declared due to a fire in the 'A' Emergency Diesel Generator (EDG) enclosure. Fire caused damage to the safety related EDG and was declared inoperable. The fire is out, and off-site assistance was not necessary. A fire watch has been stationed, and no personnel injuries were reported. The licensee has notified the NRC Resident Inspector. Notified DHS, FEMA, USDA, HHS, DOE, DHS NICC, EPA EOC, FEMA NWC (via email), FDA EOC (via email) and Nuclear SSA (via email).
At 1446 EST on 11/4/15, Millstone Unit 3 terminated the Alert declaration following satisfactory atmospheric samples at the site boundary and notifying the State of Connecticut. The licensee will notify the NRC Resident Inspector. Notified R1DO (Rogge), NRR EO (Morris), and IRD (Grant). Notified DHS, FEMA, USDA, HHS, DOE, DHS NICC, EPA EOC, FEMA NWC (via email), FDA EOC (via email) and Nuclear SSA (via email). | Emergency Diesel Generator | |
| ENS 51448 | 4 October 2015 13:32:00 | 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Unusual Event Declared Due to Identified Rcs Leakage > 25 Gpm | At 0932 EDT on 10/4/15, the licensee declared an Unusual Event for identified RCS (Reactor Coolant System) leakage exceeding 25 gallons per minute (GPM), per EAL BU2, due to a relief valve leaking on the Shutdown Cooling System common header. The RCS leakage was within the capacity of the Charging System. At 0954 EDT the RCS leakage was terminated by isolating the Shutdown Cooling System. The cause of the relief valve failure is unknown and under investigation. The RCS cooldown was terminated and both RCS loops were restored to service for decay heat removal using both Steam Generators and the Main Condenser. Current RCS temperature is 248 degrees F with RCS pressure at 248 psig. All offsite power and EDGs (Emergency Diesel Generators) are available. The licensee intends to repair the relief valve to resume the RCS cooldown using the shutdown cooling system.. The licensee informed State and local agencies and the NRC Resident Inspector. Notified DHS SWO, DHS NICC, FEMA, and Nuclear SSA via email.
The licensee terminated the Unusual Event at 1100 EDT, based on verification that the RCS leakage was stopped. The licensee informed State and local agencies and the NRC Resident Inspector. Notified R1DO (Bower), NRR EO (Morris), and IRD (Gott). Notified DHS SWO, DHS NICC, FEMA, and Nuclear SSA via email. | Steam Generator Shutdown Cooling Decay Heat Removal Main Condenser | |
| ENS 50141 | 25 May 2014 11:02:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(a)(1)(i), Emergency Class Declaration 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Unusual Event Due to Loss of Offsite Power | 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.
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).
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. | Reactor Coolant System Emergency Diesel Generator | 05000336/LER-2014-006 |
| ENS 50142 | 25 May 2014 11:02:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(a)(1)(i), Emergency Class Declaration 10 CFR 50.72(b)(3)(iv)(A), System Actuation 10 CFR 50.72(b)(3)(xiii), Loss of Emergency Preparedness | Unusual Event Due to Loss of Offsite Power | 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.
All EDGs have been secured and offsite power has been restored. The licensee is reporting the loss of two stack radiation monitors - 8168 and 8169. This is reportable under 10CFR50.72(b)(3)(xiii). Notified R1DO (Gray), R1DRA (Lew), NRR EO (Kokajko), IRD MOC (Grant).
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. | Emergency Diesel Generator | 05000336/LER-2014-006 |
| ENS 45498 | 15 November 2009 13:26:00 | 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Unit 2 Declared an Unusual Event Due to a Loss of Annunciators | At 0826 EST, Millstone Unit 2 declared a NOUE, due to a loss of power to the control room main board annunciators. Power was lost to the non-vital power supply, VR-11&21, during heater drain pump post maintenance testing, which caused the loss of power to the main control board annunciators. Charging and letdown systems are secured. Additional watchstanders were stationed during the annunciator outage. Power was restored to the main control board, and the licensee is in the process of terminating the NOUE. The NRC remained in Normal Mode. The NRC Senior Resident Inspector has been notified. The State of Connecticut has been notified.
Millstone Unit 2 terminated the NOUE at 0859 EST after power was restored to the main control board annunciator. Notified R1DO (Cahill), R1RA (Roberts), IRD MOC (Grant), NRR ET (Boger), NRR EO (Bahadur). The NRC Senior Resident Inspector has been notified. The State of Connecticut has been notified as well as DHS and FEMA. | ||
| ENS 44238 | 24 May 2008 13:54:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Loss of Offsite Power | 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.
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. | Steam Generator Emergency Diesel Generator Auxiliary Feedwater | |
| ENS 44121 | 6 April 2008 17:17:00 | 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Unusual Event from Reactor Coolant System Leakage | Millstone unit 2 entered a refueling outage on 4/6/2008. The plant was in the process of placing shutdown cooling in service when at 1236 a 10-15 gpm leak was detected by decreasing pressurizer level. The release path was determined to be from the Reactor Coolant System (RCS) to the Refueling Water Storage Tank (RWST). Pressurizer level is stable and RWST level is rising slowly. Two charging pumps are available for RCS makeup. Decay heat is being removed with Atmospheric Dump Valves. The vent line on the RWST does not contain a radiation monitor and this is an potential unmonitored radiation release path. The Unusual Event was declared at 1317. The leak was terminated at 1320. Monitoring of the potential release path commenced at 1610. The licensee notified the NRC Resident Inspector.
The leak path has been isolated by closing the two air operated ECCS recirc header stops 2-SI-659/660." The Unusual Event was terminated at 1856 and the NRC exited "monitoring mode" at 1920. Notified IRD (Cruz), NRR EO (Quay), and R1DO (Hansell). EPA Incident Report Number: 867171 The licensee notified the NRC Resident Inspector.
Upon further review, the times that the RCS leak occurred and was isolated require correction. The RCS leak occurred at 1243 when valve 2-SI-651 was opened to place shutdown cooling in service. The leak was terminated at 1356 when valve 2-Sl-659 was closed. The NRC Sr. Resident Inspector has been notified. Notified R1DO (Conte). | Reactor Coolant System Shutdown Cooling | |
| ENS 43318 | 25 April 2007 15:01:00 | 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Loss of Offsite Power While Defueled | While the offsite grid operator was performing electrical switching in the switchyard, Millstone 3 experienced a complete loss of offsite power. The "A" emergency diesel generator started and supplied power to the protected vital train electrical buses. Power to Spent Fuel Pool Cooling, Service Water, and Component Cooling Water was restored. Spent Fuel Pool level was not affected. No radiation was released from the plant. Offsite power was restored to the site at approximately 11:50. The NRC did not escalate response mode for this event. The licensee notified the NRC Resident Inspector.
The Unusual Event was terminated at 14:27. The electrical lineup has been restored to the shutdown electrical lineup. The licensee notified the NRC Resident Inspector. Notified FEMA (Dwight Fuller), DHS SWO (John Frost), NRR EO (M.J. Ross-Lee), R1DO (Trapp), R2DO (Payne), R3DO (Passehl), R4DO (Smith), and IRD (Cruz). | Service water Emergency Diesel Generator | |
| ENS 41607 | 17 April 2005 12:42:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(a)(1)(i), Emergency Class Declaration 10 CFR 50.72(b)(3)(iv)(A), System Actuation 10 CFR 50.72(b)(2)(iv)(A), System Actuation - ECCS Discharge | Alert Declared Due to Unit 3 Main Steam Relief Valves Not Reseating After Actuation | 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).
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)
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. | Steam Generator Reactor Coolant System Auxiliary Feedwater Safety Relief Valve Main Condenser Main Steam | |
| ENS 41333 | 14 January 2005 14:55:00 | 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Licensee Reported a Fire in the Turbine Building | The licensee reported that an NOUE was declared at 10:10 due to a fire in the Turbine Building. The fire started approximately at 09:55 and was extinguished at 10:16. The licensee has not yet assessed the damage to the equipment. Offsite assistance was requested but not used. No emergency equipment was affected and there was no adverse affect on plant operations. The cause of the fire was due to an electrical short. The NRC resident Inspector was notified and state and local will be notified.
At 1605, the licensee secured from the unusual event. Notified R1DO (P. Krohn), IRD (P. Wilson), NRREO (W. Ruland) and TAS (Hahn). | ||
| ENS 40245 | 14 October 2003 08:04:00 | 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Unusual Event Declared - Loss of Shutdown Cooling | At 0404 EDT on 10/14/03, Millstone 2 lost shutdown cooling due to the loss of power to vital power bus VA10. Power and shutdown cooling were restored at 0414. Millstone declared an Unusual Event at 0423 due to a greater than 10 degree increase in reactor coolant system temperature. Reactor coolant system temperature increased from 101 degrees to 113 degrees. Power was lost to VA10 while attempting to swap power supplies from inverter 1 to inverter 5. Inverter 1 is now supplying power to VA10. The licensee notified the NRC Resident Inspector.
Millstone 2 exited their Unusual Event at 0532, after completing the abnormal operating procedure and stabilizing plant conditions. Notified R1DO (Bellamy), NRR (Reis), DIRO (McGinty), DHS (Rick DaSilva), and FEMA (David Barden)..
An update to event notification 40245 is being made to reflect that the loss of shutdown cooling is also considered reportable under 10CFR50.72(b)(3)(v). Additionally, further review of plant response following the loss of VA10, indicates that due to an equipment performance issue (failed relay) the containment isolation valves did not respond as expected and were manually closed per procedure. This issue will be investigated and addressed as needed in the LER. The NRC Resident Inspector will be notified Reg1 RDO(McDermott) was notified. | Reactor Coolant System Shutdown Cooling | 05000336/LER-2003-005 |