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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 54071 | 18 May 2019 03:03:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Manual Reactor Scram Due to Degrading Condenser Vacuum | On Friday, May 17, 2019 at 2303 (EDT), with the reactor at 70 (percent) core thermal power, Pilgrim Nuclear Power Station initiated a manual reactor scram due to degrading condenser vacuum as a result of the trip of Seawater Pump B. All control rods inserted as designed. The plant is in hot shutdown. Plant safety systems responded as designed. Pressure is being controlled using the Mechanical Hydraulic Control System and Main Condenser. Reactor water level is being maintained with the feedwater and condensate system. During the manual reactor scram, the plant experienced the following isolation signals as designed: "Group 2 Isolation: Miscellaneous containment isolation valves Group 6 Isolation: Reactor Water Clean-up Reactor Building Isolation Actuation Due to the Reactor Protection System actuation while critical, this event is being reported as a four-hour, non-emergency notification in accordance with 10 CFR 50.72(b)(2)(iv)(B), 'any event that results in actuation of the reactor protection system (RPS) when the reactor is critical...' This notification is also being made in accordance with 10 CFR 50.72(b)(3)(iv)(A), 'Any event or condition that results in valid actuation of any of the systems listed in paragraph (b)(3)(iv)(B) of this section...' (B)(2) 'General containment isolation signals affecting containment isolation valves in more than one system or multiple main steam isolation valves (MSIVs).' This event has no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. The licensee will notify the Massachusetts Emergency Management Agency. | Feedwater Reactor Protection System Main Steam Isolation Valve Main Condenser Control Rod | |
| ENS 53648 | 5 October 2018 04:00:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Automatic Reactor Scram Due to Low Reactor Water Level | On Friday, October 5, 2018 at 1209 hours, with the reactor at 100 percent core thermal power, Pilgrim Nuclear Power Station (PNPS) automatically tripped due to reactor water level perturbation and receipt of a low reactor water level Reactor Protection System (RPS) signal. The cause of the low reactor water level is under investigation. The plant is in hot shutdown. All other plant systems responded as designed. Pressure is being controlled using the Mechanical Hydraulic Control System and Main Condenser. Reactor water level is being maintained with the feedwater and condensate system. During the automatic reactor scram the plant experienced the following isolation signals as designed: Group 2 Isolation: Miscellaneous containment isolation valves Group 6 Isolation: Reactor Water Clean-up Reactor Building Isolation System Actuation Due to the RPS actuation while critical, this event is being reported as a four-hour, non-emergency notification in accordance with 10 CFR 50.72(b)(2)(iv)(B), 'any event that results in actuation of the reactor protection system (RPS) when the reactor is critical.' This notification is also being made in accordance with 10 CFR 50.72(b)(3)(iv)(A), 'Any event or condition that results in valid actuation of any of the systems listed in paragraph (b)(3)(iv)(B) of this section ... ' (B)(2) 'General containment isolation signals affecting containment isolation valves in more than one system.' This event has no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. The licensee will notify the Massachusetts Emergency Management Agency. | Feedwater Reactor Protection System Main Condenser | |
| ENS 53147 | 4 January 2018 19:10:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Manual Reactor Scram Due to Partial Loss of Offsite Power During Winter Storm | On January 4, 2018, at 1410 hours EST, with the reactor at approximately 100 percent power and steady state conditions, the winter storm across the Northeast caused the loss of offsite 345 kV Line 342. Reactor power was reduced to approximately 81 percent and a procedurally required manual reactor scram was initiated. All control rods fully inserted. As a result of the reactor scram, indicated reactor water level decreased, as expected, to less than +12 inches resulting in automatic actuation of the Primary Containment Isolation Systems for Group II - Primary Containment Isolation and Reactor Building Isolation System, and Group VI - Reactor Water Cleanup System. Reactor Water Level was restored to the normal operating band. The Primary Containment Isolation Systems have been reset. The Reactor Protection System signal has been reset. Following the reactor scram, the non-safety related Control Rod Drive Pump "B" tripped on low suction pressure. Control Rod Drive Pump "A" was placed in service. All other systems operated as expected, in accordance with design. This event is reportable per the requirements of Title 10, Code of Federal Regulations (CFR) 50.72 (b)(2)(iv)(B) - "RPS Actuation" and 10 CFR 50.72 (b)(3)(iv)(A) - "Specified System Actuation. This event had no impact on the health and/or safety of the public. The NRC Resident Inspector has been notified. The main steam isolation valves are open with decay heat being removed via steam to the main condenser. Offsite power is still available from 345kV line 355. As a contingency, emergency diesel generators are running and powering safety busses per licensee procedure. The licensee notified the Commonwealth of Massachusetts. The licensee will be notifying the town of Plymouth as part of their local notifications. The licensee will be issuing a press release. | Reactor Protection System Emergency Diesel Generator Main Steam Isolation Valve Primary Containment Isolation System Primary containment Reactor Water Cleanup Main Condenser Control Rod | |
| ENS 52223 | 6 September 2016 12:27:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Manual Reactor Scram Due to High Reactor Water Level | On Tuesday, September 6, 2016 at 0827 (EDT), with the reactor at 91% core thermal power (CTP), Pilgrim Nuclear Power Station (PNPS) operators initiated a manual reactor scram due to high reactor water level resulting from feedwater level control oscillation. Other than the feedwater level control oscillations, all other plant systems responded as designed. Plant cooldown is in progress using the High Pressure Coolant Injection System in the pressure control mode. The plant is in hot shutdown. The cause of the feed water level control oscillations is under investigation. This event has no impact on the health and safety of the public. Subsequent to the manual reactor scram the plant experienced the following isolation signals: Group 1 Isolation: Main Steam Isolation Valves Group 2 Isolation: Miscellaneous containment isolation valves Group 6 Isolation: Reactor Water Clean-up Reactor Building (Ventilation) Isolation Actuation The licensee has notified the NRC Senior Resident Inspector. This notification is being made in accordance with 10 CFR 50.72(b)(2)(iv)(B), 'any event that results in actuation of the reactor protection system (RPS) when the reactor is critical...'. This notification is also being made in accordance with 10 CFR 50.72(b)(3)(iv)(A), 'Any event or condition that results in valid actuation of any of the systems listed in paragraph (b)(3)(iv)(B) of this section...' (B)(2) 'General containment isolation signals affecting containment isolation valves in more than one system or multiple main steam isolation valves (MSIVs).' All rods were inserted. The plant is stable with normal off-site power line-up. The licensee will notify the Commonwealth of Massachusetts. | Feedwater High Pressure Coolant Injection Reactor Protection System Main Steam Isolation Valve | |
| ENS 51338 | 22 August 2015 20:28:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Reactor Scram Due to a Single Msiv Closure | On Saturday, August 22, 2015, at 1628 (EDT), with the reactor at 100% core thermal power (CTP) the Pilgrim Nuclear Power Station (PNPS) experienced an automatic reactor scram signal due to the rapid closure of one main steam isolation valve (MSIV). Other than the MSIV all other plant systems responded as designed. Plant cooldown is in progress using steam bypass to the main condenser. The plant is in hot shutdown. The cause of the MSIV closure is still under investigation. This event has no impact on the health and safety of the public. The licensee has notified the NRC Senior Resident Inspector. This notification is being made in accordance with 10 CFR 50.72(b)(2)(iv)(B), 'Any event that results in actuation of the reactor protection system (RPS) when the reactor is critical'. Subsequent to the reactor scram the plant experienced the following isolation signals: - Group 2 Isolation: Miscellaneous containment isolation valves
- Group 6 Isolation: Reactor Water Clean-up
- Reactor Building Isolation Actuation
This notification is also being made in accordance with 10 CFR 50.72(b)(3)(iv)(A), 'Any event or condition that results in valid actuation of any of the systems listed in paragraph (b)(3)(iv)(B) of this section' (B)(2) 'General containment isolation signals affecting containment isolation valves in more than one system or multiple main steam isolation valves (MSIVs).' Plant response was considered normal and the plant is in a stable shutdown / cooldown condition. The license will be notifying the Commonwealth of Massachusetts. | Reactor Protection System Main Steam Isolation Valve Main Condenser | |
| ENS 51087 | 22 May 2015 14:02:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation | Manual Reactor Scram Due to Loss of Condenser Vacuum | On Friday, May 22, 2015 at 1002 EDT, with the Reactor Mode Select Switch in the Start-Up position and the reactor at approximately 3 percent core thermal power, while returning to power from Refueling Outage Number 20, a manual reactor scram was inserted due to degrading main condenser vacuum. The cause of the degraded vacuum is currently under investigation. Following the reactor scram, all rods were verified to be fully inserted and no Emergency Operating Procedure entry conditions existed. All plant systems responded as designed. Currently reactor pressure is being maintained at 400 psig with the Mechanical Hydraulic Control System (turbine by-pass valves). Reactor water level is being maintained in normal bands with the Condensate and Feedwater System. Off-site power is being supplied to the station by the Startup Transformer (normal power supply for shutdown operations). This event had no impact on the health and/or safety of the public. The NRC Resident Inspector is on-site and has been notified. The licensee has notified the Massachusetts Emergency Management Agency. The licensee will be issuing a press release.
The following was provided by the licensee as clarifying information to the first paragraph of the original event notification: As a conservative measure, the operating crew had previously started reducing power from 20 percent core thermal power when it was first noticed that main condenser vacuum was degrading. This was well before any low condenser vacuum alarms were received. During the shutdown, after already securing the main turbine, the operating crew established benchmark values for degrading condenser vacuum for a normal plant shutdown and for a manual reactor scram should vacuum continue to decline to preclude an automatic scram. The licensee notified the NRC Resident Inspector. Notified R1DO (Dwyer). | Feedwater Main Turbine Main Condenser | |
| ENS 50769 | 27 January 2015 09:02:00 | 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Automatic Reactor Scram on Turbine Trip Due to Loss of Offsite Power | On Tuesday January 27, 2015 at 0402 hours, with the Pilgrim Nuclear Power Station (PNPS) Reactor Mode Select Switch (RMSS) in Run and reactor power approximately 52% an automatic reactor scram signal was received due to the automatic trip of the main turbine that was initiated by the opening of the main generator breaker, ACB-104. The event occurred during winter storm 'Juno.' Prior to the event off-site transmission Line 355 was de-energized due (to) weather conditions and its associated PNPS switchyard breakers (ACB-105, a main generator breaker and ACB-102), were open. Per station procedures, reactor power was being lowered, a reactor protection system bus had been placed onto a back-up power supply, the Emergency Diesel Generators had been started and were powering the associated safety related 4 KV buses. The second off-site transmission Line 342 de-energized and the associated PNPS switchyard breakers (ACB-104 main generator breaker and ACB-103) opened. The Shutdown Transformer off-site power supply has remained available throughout this event. All control rods were verified to be fully inserted. Per plant design, Primary Containment Isolation System (PCIS) Group lI sampling systems, Group VI Reactor Water Clean-up (RWCU) system and Reactor Building Isolation System (RBIS) isolations occurred. Currently, the EDG's are powering the safety related 4KV buses, reactor water level is being maintained by the Reactor Core Isolation Cooling (RCIC) system and reactor pressure is being maintained by High Pressure Coolant Injection (HPCI) system. The station is conducting a plant cool down at this time. All systems responded as designed with the exception of a non-safety-related diesel air compressor, K-117 that failed to start. The licensee will notify the State and local governments and plans on issuing a press release. The NRC Resident Inspector has been informed. | High Pressure Coolant Injection Reactor Protection System Emergency Diesel Generator Primary Containment Isolation System Reactor Core Isolation Cooling Main Turbine Control Rod | 05000293/LER-2015-001 |
| ENS 49454 | 19 October 2013 07:31:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Group 1 Isolation Due to High Reactor Water Level | On Saturday, October 19, 2013 at 0331 hours, with the reactor critical at approximately 1% core thermal power and the mode switch in start-up, a high reactor water level condition resulted in a main turbine trip and a valid Group 1 isolation signal. As a result, the Main Steam Isolation Valves (MSIVs) closed. The plant was in start-up from a forced outage. The initial plant conditions were reactor pressure at approximately 280 psig with a corresponding reactor coolant temperature for that pressure. Currently reactor pressure and water level are being maintained with the MSIVs closed in normal bands. The reactor is being cooled down in preparation for operation in shutdown cooling. Off-site power is supplying station power from the Start-up Transformer (normal power supply for shutdown operations). All plant systems responded as designed. The cause of the increase in reactor water level is currently under investigation. This event had no impact on the health and/or safety of the public. The USNRC Senior Resident Inspector has been notified. | Main Steam Isolation Valve Shutdown Cooling | 05000293/LER-2013-010 |
| ENS 49296 | 22 August 2013 11:55:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation 10 CFR 50.72(b)(2)(iv)(A), System Actuation - ECCS Discharge | Reactor Protection Actuation (Scram) | On Thursday, August 22, 2013 at 0755 hours (EDT), with the reactor critical at approximately 98% core thermal power, and the mode switch in RUN, a manual reactor scram was inserted due to lowering reactor water level. The cause of the lowering reactor water level was due to the trip of all three Feedwater Pumps. The cause of the Feedwater Pump trip event is currently under investigation. Following the reactor scram, all control rods were verified to be fully inserted. All 4kV busses transferred to the Startup Transformer as designed. Following the scram the reactor water level lowered to +12 inches initiating the Primary Containment Isolation System (Group II, Reactor Building Isolation System (RBIS); and Group VI - Reactor Water Cleanup System) automatically as per design. Reactor water level lowered to -46 inches initiating Primary Containment Isolation System Group I - Main Steam Isolation Valves (MSIVs); Emergency Core Cooling Systems (ECCS) actuated which included automatic start and injection of the High Pressure Coolant Injection (HPCI) System and the Reactor Core Isolation Cooling (RCIC) System and an automatic start of the Emergency Diesel Generators as designed. Reactor water level was promptly restored to normal level. Currently a cooldown is in progress with reactor pressure is being maintained by the HPCI System operating in the pressure control mode and reactor water level is being maintained by the RCIC System. Reactor Water Clean-up System and normal reactor building ventilation have been restored. Off-site power is being supplied to the station by the Start-up Transformer (normal power supply for shutdown operations). This event had no impact on the health and/or safety of the public. The USNRC Senior Resident Inspector has been notified. This 4-hour notification is being made in accordance with 10 CFR 50.72 (b)(2)(iv)(A) and (B). The plant is transferring from decay heat removal to the torus to decay heat removal to the main condenser. Reactor pressure is 371 psig. Initial indications are that a main feedwater power supply breaker tripped. | Feedwater High Pressure Coolant Injection Emergency Diesel Generator Main Steam Isolation Valve Primary Containment Isolation System Reactor Core Isolation Cooling Reactor Building Ventilation Reactor Water Cleanup Emergency Core Cooling System Decay Heat Removal Main Condenser Control Rod | 05000293/LER-2013-008 |
| ENS 48923 | 15 April 2013 02:17:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Specified System Actuations While Shutting Down | On Sunday, April 14, 2013 at 2217 hours, with the Pilgrim Nuclear Power Station (PNPS) Reactor Mode Select Switch (RMSS) in Start-up, the turbine generator previously removed from service, and the reactor sub-critical on Intermediate Range Monitors Range 2 and lowering, a manual reactor scram was inserted due to reactor pressure lowering beyond established control bands. At the time of the manual reactor scram PNPS was conducting a planned reactor shutdown to commence refueling outage (RFO) -19. All control rods fully inserted and Primary Containment Isolation System Group II (Reactor Building) and Group VI (Reactor Water Cleanup System) actuations occurred as designed due to the expected reactor water level shrink associated with the scram signal. All plant systems responded as designed. Off-site power was unaffected and was supplied by the start-up transformer (normal power supply for refuel and reactor shutdown operations). The Main Steam Isolation Valves (MSIV) were manually closed to terminate the reactor pressure reduction and the High Pressure Coolant Injection (HPCI) system was manually started in the reactor pressure control mode. The Reactor Protection System (RPS) was reset as were the reactor building and reactor water clean-up system isolation signals. Currently, the plant cooldown is continuing with the HPCI system in pressure control and reactor water level being maintained within normal bands with the condensate and feedwater system. The cause of the lowering reactor pressure has not been determined and remains under review. This event had no impact on the health and/or safety of the public. This 8-hour notification is being made in accordance with 10 CFR 50.72 (b)(3)(iv)(A). The NRC Senior Resident Inspector has been notified. The licensee will also be notifying state authorities. | Feedwater High Pressure Coolant Injection Reactor Protection System Main Steam Isolation Valve Primary Containment Isolation System Reactor Water Cleanup Intermediate Range Monitor Control Rod | |
| ENS 48739 | 10 February 2013 19:05:00 | 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Loss of Offsite Power and Subsequent Press Release | On Sunday, February 10, 2013 at 1405 (EST), with the reactor at 0% core thermal power, all control rods fully inserted, and in cold shutdown conditions, the plant experienced a loss of off-site power. With Pilgrim Station aligned to off-site power via the start-up transformer (SUT), a fault on the 'B' phase of the SUT was experienced due to suspected falling ice striking the phase's insulator. This resulted in the tripping of the feeder breaker, ACB-102, and the loss of power to 4160 KV buses A1 through A4. Emergency Diesel Generators (EDGs) 'A' and 'B' auto-started as designed and are powering emergency buses. The loss of off-site power resulted in de-energization of both Reactor Protection System (RPS) channels resulting in a reactor scram signal and isolation of shutdown cooling. At 1418, shutdown cooling was returned to service. All other plant systems responded as designed. Station personnel are in the process of establishing back-up power in accordance with plant procedures. The following press release was made at 1715 hours: 'Offsite power to Pilgrim station was interrupted this afternoon. The plant is in a cold shutdown condition and Pilgrim's diesel generators are providing power to the site. There is no worker or public safety concern. Plant personnel are troubleshooting the cause of the interruption.' This event had no impact on the health and/or safety of the public. The NRC Senior Resident Inspector has been notified. | Reactor Protection System Emergency Diesel Generator Shutdown Cooling Control Rod | 05000293/LER-2013-003 |
| ENS 48736 | 9 February 2013 03:00:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Unusual Event Declared Due to Loss of Offsite Power | Pilgrim Station scrammed on a loss of offsite power. All systems performed as designed. Groups I, II, VI went to completion. Reactor Core Isolation Cooling (RCIC) is injecting to the vessel controlling level. High Pressure Coolant Injection is in pressure control and slowly cooling down. Offsite power was lost multiple times. The Startup Transformer has been declared inoperable. The Unusual Event was declared under EAL SU 1.1 based on loss of offsite power greater than 15 minutes (at 2200 EST). The licensee originally experienced an automatic reactor scram at 2117 EST due to a load reject with a turbine trip/reactor scram due to loss of power. Offsite power availability has been fluctuating in and out to the site. The licensee states that all systems are functioning as required. All rods fully inserted and the reactor is stable in Mode 3. Both Emergency Diesel Generators are providing power to the safety related buses. The loss of offsite power is believed to be weather related. The licensee has notified the State and local authorities and the NRC Resident Inspector. Notified DHS SWO, FEMA, USDA, HHS, DOE, DHS NICC, EPA, and NuclearSSA via email.
Pilgrim terminated the Unusual Event and has transitioned to recovery effective at 10:55 AM on 02/10/2013. Offsite power has been restored to safety-related and non-safety-related electrical buses through the station Startup Transformer via a single 345 KV line. The other two offsite power sources remain out of service. The emergency diesel generators have been secured and are in standby. Residual heat removal is in shutdown cooling mode maintaining the reactor in cold shutdown. Fuel Pool Cooling is in service with fuel pool coolant temperatures trending down. The licensee notified State, local authorities and the NRC Resident Inspector. Notified R1 RA (Dean), R1DO (Powell), NRR DIR(Leeds) NRR EO (Evans) and NSIR IRD (Marshall). Notified DHS SWO, FEMA, USDA, HHS, DOE, DHS NICC, EPA, and NuclearSSA via email. | High Pressure Coolant Injection Emergency Diesel Generator Reactor Core Isolation Cooling Shutdown Cooling Residual Heat Removal | |
| ENS 48664 | 10 January 2013 20:34:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation | Reactor Protection Actuation (Scram) - Recirculation Pump Trip | On Thursday, January 10, 2013 at 1534 hour (EST), with the reactor at 100% core thermal power, both recirculation pumps spuriously tripped and a manual reactor scram was inserted as required by station procedures. The cause of the recirculation pump trip is under investigation. Following the reactor scram, all rods were verified to be fully inserted and the Primary Containment Isolation System Group II (Reactor Building) and Group VI (Reactor Water Cleanup System) actuations occurred as designed due to the expected reactor water level shrink associated with the scram signal. All other plant systems responded as designed. Currently reactor pressure is being maintained between 900 and 1050 psig with the Mechanical Hydraulic Control System (turbine by-pass valves). The Reactor Protection System has been reset; Reactor Water Cleanup System and normal reactor building ventilation have been restored. Reactor water level is being maintained in normal bands with the Condensate and Feedwater System. Off-site power is being supplied to the station by the Start-up Transformer (normal power supply for shutdown operations) and the switchyard ring bus has been restored. This event had no impact on the health and/or safety of the public. The USNRC Senior Resident Inspector is on-site and has been notified. This 4-hour notification is being made in accordance with 10 CFR 50.72 (b)(2)(iv)(B). The scram was uncomplicated and decay heat is being released to the main condenser via the turbine by-pass valves. | Feedwater Reactor Protection System Primary Containment Isolation System Reactor Building Ventilation Reactor Water Cleanup Main Condenser | |
| ENS 47945 | 22 May 2012 17:11:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation | Manual Reactor Scram Due to Degrading Condenser Vacuum | On Tuesday, May 22, 2012 at 1311 hours (EDT), with the reactor at approximately 35% core thermal power, during a planned power reduction to support thermal backwash of the main condenser, a manual reactor scram was inserted due to degrading main condenser vacuum. The cause of the degraded vacuum is currently under investigation. Following the reactor scram, all rods were verified to be fully inserted and the Primary Containment Isolation System Group II (Reactor Building) and Group VI (Reactor Water Cleanup System) actuations occurred as designed due to the expected reactor water level shrink associated with the scram signal. Standby Gas Treatment System Train 'B,' which is designed to shutdown 65 seconds after the Group II signal is received if the Standby Gas Treatment Train 'A' is in service, continued to operate until manually secured. With this exception, all other plant systems responded as designed. Currently reactor pressure is being maintained at 920 psig with the Mechanical Hydraulic Control System (turbine by-pass valves). Reactor water level is being maintained in normal bands with the Condensate and Feedwater System. Off-Site power is being supplied to the station by the Start-up Transformer (normal power supply for shutdown operations). This event had no impact on the health and/or safety of the public. The NRC Senior Resident Inspector has been notified." The licensee has notified the Massachusetts Emergency Management Agency. | Feedwater Primary Containment Isolation System Reactor Water Cleanup Standby Gas Treatment System Main Condenser | |
| ENS 46837 | 10 May 2011 17:15:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation | Reactor Protection System Actuation During Start-Up | At 1315 hours on Tuesday, May 10, 2011, with the Reactor Mode Select Switch in Startup, the Reactor Protection System (RPS) actuated due to a valid Hi-Hi trip signal from the Intermediate Range Monitors (IRMs) of the Neutron Monitoring System. At the time of the RPS actuation, reactor thermal power was four (4)% and control rods were being withdrawn as part of a planned reactor startup from a refueling outage. The RPS actuation signal resulted in a reactor scram. The IRMs were in range 7 when the scram occurred. All control rods automatically inserted in accordance with design. No other ESF actuation signals were generated. The reactor scram was not part of pre-planned test or reactor operation. The cause of the Hi-Hi IRM trip signal is under investigation. This event had no impact on the health and/or safety of the public. The licensee has notified the NRC Senior Resident Inspector. This 4-hour notification is being made in accordance with 10CFR50.72(b)(2)(iv)(B). The unit is in a normal post trip electrical alignment. Decay heat is being removed via the main steam line drains to the main condenser. The licensee will notify the Massachusetts Emergency Management Agency. | Reactor Protection System Intermediate Range Monitor Main Steam Line Main Condenser Control Rod | |
| ENS 46631 | 20 February 2011 15:34:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Reactor Protection System Actuation While Shutdown | On Sunday, February 20, 2011, at 1034 EST with the reactor shutdown and all control rods fully inserted a valid Reactor Protection System (RPS) low reactor water initiation signal (+12 inch) was received. The RPS actuation signal resulted in reactor scram and actuation of the Primary Containment Isolation Systems for Group II - Primary Containment Isolation and Reactor Building Isolation System (RBIS), and Group VI - Reactor Water Cleanup System (RWCU). At the time of the event, a controlled reactor shutdown and cooldown was in progress. The Reactor Mode Selector Switch was in 'Startup' and a cooldown was being controlled using the Mechanical Hydraulic Control (MHC) System. Initial event review indicates that the turbine by-pass valve controlling the cooldown closed causing a 'shrink' on indicated reactor water level to briefly lower to +12 inches (lowest observed water level). Reactor water level was immediately restored, the isolations (Group II and VI) were reset, and the RPS signal was reset at 1135 EST. All systems operated as expected, in accordance with design. This event had no impact on the health and/or safety of the public. The US NRC Senior Resident Inspector was in the Main Control Room at the time of the event. The licensee will be notifying the State. | Reactor Protection System Primary Containment Isolation System Primary containment Reactor Water Cleanup Control Rod | |
| ENS 44737 | 20 December 2008 15:45:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Momentary Loss of 345Kv Offsite Power | At approximately 1045 hours on Saturday, December 20, 2008, while in a Hot Shutdown condition, Pilgrim Station experienced a momentary loss of all 345kV off-site power to the Startup Transformer (SUT). As a result, the following safety system actuations occurred: automatic Reactor Protection System (RPS) actuation (all control rods were previously inserted), automatic start of both Emergency Diesel Generators (EDG) and loading of their respective emergency buses, automatic actuation of Primary Containment Isolation Systems (PCIS) Groups I, II, VI and Reactor Building Ventilation, manual initiation of the High Pressure Coolant Injection (HPCI) system for reactor pressure control, and manual initiation of the Reactor Core Isolation Cooling (RCIC) system for reactor level control. All systems functioned as designed and expected. Because power from an off-site source remained available from the 23kV Shutdown Transformer, the criteria for declaration of an Unusual Event were not met (Pilgrim EAL 6.3.2.1). 345kV power was automatically restored to the Startup Transformer via breaker reclose logic. Restoration of normal on-site power to all 4kV buses is complete and efforts to return systems to normal shutdown alignments are in progress. Current plans are in place to maneuver the plant to a Cold Shutdown condition as necessary to support recovery actions. The NRC Resident was on-site at the time of the event and has been notified. There was no threat to the health or safety of the public as a result of this event. The loss of power was caused by a breaker icing in the onsite switchyard. The switchyard breakers were inspected for icing. The licensee notified the State of Massachusetts. | High Pressure Coolant Injection Reactor Protection System Emergency Diesel Generator Primary Containment Isolation System Reactor Core Isolation Cooling Reactor Building Ventilation Control Rod | 05000293/LER-2008-007 |
| ENS 44735 | 19 December 2008 23:31:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Automatic Reactor Scram Due to Load Reject | On December 19, 2008, at 1831 hours with the reactor at 100% core thermal power (CTP) an automatic reactor scram occurred. It appears the scram occurred as a result of a load reject experienced during a severe winter storm. Three of the four safety relief valves opened in response to the event. Primary Containment Isolation System (PCIS) Group 2 (sample valves) and Group 6 (reactor water cleanup system) and the reactor building isolation system (RBIS-secondary containment) isolated as designed (all have since been restored) on the reactor water level +12 inches setpoint due to normal vessel shrink. Initial review indicates all safety-related systems responded as designed. Off-site power has been maintained; however the two 4kv safety related buses (A5&A6) were conservatively placed on the station emergency diesel generators due to potential grid stability concern. Currently, the reactor mode select switch (RMSS) is in the Shutdown position; the reactor scram has been reset; the reactor is being maintained at approximately 940 psig, with pressure being maintained by the main turbine by-pass valves; and reactor water level is being maintained at normal levels of 29 inches with the main condensate and feedwater system. Station maintenance personnel are assessing the status of the station switchyard. Once this activity is complete the duration of the forced outage and recovery plans will be determined. All control rods fully inserted on the scram. The licensee has notified the NRC Resident Inspector. | Feedwater Emergency Diesel Generator Primary Containment Isolation System Main Turbine Reactor Water Cleanup Safety Relief Valve Control Rod | |
| ENS 43479 | 10 July 2007 23:54:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Main Turbine Trip Causing a Reactor Scram | During a planned power reduction to support thermal backwash of the main condenser, an automatic reactor scram resulted from a main turbine trip. The cause for the turbine trip is currently under investigation. Following the reactor scram, the expected reactor level shrink resulted in valid group 2, Reactor Building Ventilation, and group 6, Reactor Water Cleanup System isolations. All safety systems and equipment functioned as designed. A schedule for plant restart has not yet been determined. All control rods fully inserted and no safety relief valves lifted from the scram. Minimum level after the scram was -10 inches. Decay heat is being removed using the main turbine bypass valves to the main condenser and maintaining level using normal reactor feed water. The plant is using the normal shut down electrical lineup and slowly cooling down (currently at 820 psi). The licensee notified the NRC Resident Inspector. | Reactor Building Ventilation Reactor Water Cleanup Safety Relief Valve Main Condenser Control Rod | |
| ENS 43245 | 17 March 2007 20:58:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Group Isolations Following Manual Reactor Scram | On March 17 2007, at approximately 1658 EDT, Group 2 (Reactor Building Ventilation Isolation) and Group 6 (RWCU Isolation) automatic containment isolation signals were received due to low reactor water level following the insertion of a manual scram signal. The manual scram signal was inserted following the reaching of internal administrative limits on changes in unidentified drywell leakage. The receipt of these isolation signals is not unusual following the insertion of a scram signal. The reactor was manually shutdown due to reaching internal administrative limits on changes in unidentified drywell leakage. Prior to the manual shutdown, the leakage had not reached the applicable Technical Specification limits. Drywell leakage as of 1800 EDT was 1.3 GPM identified and 2.59 GPM unidentified with the unit in Hot Shutdown Mode. All safety systems responded as expected. The plant is in a stable condition. Investigation is continuing. The licensee notified the NRC Resident Inspector. | Reactor Building Ventilation | |
| ENS 42414 | 13 March 2006 23:08:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Manual Reactor Scram After Offgas System Failure | During a power ascension, the non-safety Augmented Offgas System experienced a failure which caused a Recombiner high temperature condition. To protect components of the non-safety Augmented Offgas System, station procedures require a manual scram of the reactor when this condition occurs. Station procedures were followed and the reactor was manually scrammed at 18:08. All rods fully inserted and all safety systems performed per design. Primary containment isolation systems responded properly resulting in an automatic isolation of Primary Containment Isolation System Groups 2 and 6 valves and a Reactor Building Isolation due to the transient low reactor water level condition caused by the scram. The plant is in a stable condition. Investigation is continuing. No safety valves lifted on the scram, decay heat is being removed with the bypass valve, normal feed and condensate are maintaining reactor water level, and the electrical grid is stable on the startup transformer. The licensee notified the NRC Resident Inspector. | Primary Containment Isolation System |