Semantic search
| Entered date | Site | Region | Scram | Reactor type | Event description | |
|---|---|---|---|---|---|---|
| ENS 56887 | 13 December 2023 05:50:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | The following information was provided by the licensee via phone and email: At 0102 CST, while operating at 100 percent (reactor) power, River Bend Station experienced an automatic reactor scram caused by a turbine trip signal. The cause of the turbine trip signal is not known at this time and is being investigated. At 0108, reactor core isolation cooling (RCIC) was initiated due to a loss of reactor feed pumps following feedwater heater string isolation. At 0114, reactor water level control was transferred back to feedwater and RCIC was secured. Reactor water level is being maintained by feedwater pumps and reactor pressure is being maintained by turbine bypass valves. The scram was uncomplicated and all other plant systems responded as designed. This event is being reported under 10 CFR 50.72(b)(2)(iv)(B), as any event or condition that results in actuation of the reactor protection system (RPS) when the reactor is critical and 10 CFR 50.72(b)(3)(iv)(A) specified system actuation as result of expected post scram (reactor water) level 3 isolations and manual initiation of RCIC. No radiological releases have occurred due to this event from the unit. The NRC Senior Resident Inspector has been notified of this event. The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: The cause of the turbine trip, while still under investigation, was likely due to an electrical transient involving the main generator. Walkdowns in the switchyard post-scram identified damage to one of the output breaker disconnects. |
| ENS 56863 | 18 November 2023 02:51:00 | River Bend | NRC Region 4 | Manual Scram | GE-6 | The following information was provided by the licensee via phone and email: On November 17, 2023, at 2215 CST, River Bend Station (RBS) was operating at 30 percent reactor power performing plant startup activities when an isolation of low-pressure feedwater string `A' occurred. The team entered applicable alternate operating procedures and inserted control rods to exit the restricted region of the power to flow map. Feedwater temperature continued to lower until it challenged the prohibited region of the AOP-0007 graph requiring a reactor scram. The team inserted a manual reactor scram at 2355 from 24 percent reactor power. All control rods fully inserted and there were no complications. All systems responded as designed. Currently RBS Unit 1 is stable with reactor level being maintained 10 to 51 inches with feed and condensate, and pressure being maintained 500 to 1090 psig using steam drains. This event is being reported under 10 CFR 50.72(b)(2)(iv)(B), as any event or condition that results in actuation of the Reactor Protection System (RPS) when the reactor is critical and 10 CFR 50.72(b)(3)(iv)(A) Specified System Actuation as result of Group 3 isolations. The NRC Senior Resident inspector has been notified. No radiological releases have occurred due to this event from the unit. The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: The electric plant is in a normal lineup for current plant conditions with all emergency diesel generators available. The cause of the initial isolation of low-pressure feedwater string "A" is still under investigation. |
| ENS 55169 | 2 April 2021 14:29:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | At 1017 CDT on April 2, 2021, while operating at 85 percent power, River Bend Station experienced an automatic reactor scram caused by a turbine trip signal. The cause of the turbine trip signal is not known at this time and is being investigated. Reactor water level is being maintained by feedwater pumps and reactor pressure is being maintained by turbine bypass valves. The scram was uncomplicated and all plant systems responded as designed. This event is being reported under 10 CFR 50.72(b)(2)(iv)(B), as any event or condition that results in actuation of the Reactor Protection System (RPS) when the reactor is critical and 10 CFR 50.72(b)(3)(iv)(A) Specified System Actuation as result of expected post scram level 3 isolations. No radiological releases have occurred due to this event from the unit. The NRC Resident Inspector has been notified of this event. |
| ENS 55154 | 25 March 2021 13:37:00 | River Bend | NRC Region 4 | Manual Scram | GE-6 | On March 25, 2021 at 0901 CDT, River Bend Station Unit 1 (RBS) was operating at 93 (percent) reactor power (limited by 100 (percent) recirculation flow) when condenser vacuum began to lower due to ARC-AOV1A, Steam Jet Air Ejector Suction Valve, going closed. At 0918 CDT, a manual reactor SCRAM was inserted at approximately 80 (percent) reactor power due to condenser vacuum continuing to lower. After the SCRAM, all systems responded as designed and condenser vacuum was restored by starting a mechanical vacuum pump. The cause of the Steam Jet Air Ejector Suction Valve closure is unknown at this time and being investigated. Currently RBS is stable, and pressure is being maintained using Turbine Bypass Valves. The Main Steam Isolation Valves remained opened throughout the event. This event is being reported under 10 CFR 50.72(b)(2)(iv)(B), as any event or condition that results in actuation of the Reactor Protection System (RPS) when the reactor is critical and 10 CFR 50.72 (b)(3)(iv)(A) Specified System Actuation as result of expected post SCRAM level 3 isolations. No radiological releases have occurred due to this event from the unit. NRC Resident Inspector has been notified of this event. |
| ENS 54849 | 21 August 2020 12:53:00 | River Bend | NRC Region 4 | Manual Scram | On August 21, 2020 at 0908 CDT, River Bend Station was operating at 100% reactor power when reactor recirculation pump 'B' tripped. At 0918 CDT, a manual reactor scram was inserted at 67% reactor power after receiving indications of thermal hydraulic instability as indicated by flux oscillations on the period based detection system (PBDS) and average power range monitors (APRMs). All control rods fully inserted and there were no complications. All systems responded as designed. Currently River Bend Station Unit 1 is stable and pressure is being maintained using turbine bypass valves. This event is being reported under 10 CFR 50.72(b)(2)(iv)(B), as any event or condition that results in actuation of the reactor protection system (RPS) when the reactor is critical and 10 CFR 50.72 (b)(3)(iv)(A) Specified System Actuation as result of Group 3 isolations. NRC Resident Inspector has been briefed on this event. No radiological releases have occurred due to this event from the unit. | |
| ENS 54096 | 1 June 2019 03:15:00 | River Bend | NRC Region 4 | Manual Scram | At 2345 CDT at River Bend Station (RBS) Unit 1, a manual Reactor scram was inserted in anticipation of receiving an automatic Reactor Water Level 3 (9.7") scram due to the isolation of the 'B' Heater String with the 'A' Heater String already isolated. The 'B' heater string isolation caused loss of suction and subsequent trip of the running Feed Water Pumps 'A' and 'C'. All control rods fully inserted with no issues. Subsequently Reactor level was controlled by the Reactor Core Isolation Cooling (RCIC) system. Feed Water Pump 'C' was restored 4 minutes after the initial trip and the RCIC system secured. Currently RBS-1 is stable and is being cooled down using Turbine Bypass Valves. No radiological releases have occurred due to this event from the unit. The plant is currently under a normal shutdown electrical lineup. The licensee notified the NRC Resident Inspector.
This amended event notification is being made to provide additional information that was not included in the original notification made on 6/1/19 at 0315 EDT. This event was reportable under 10 CFR 50.72(b)(3)(iv)(A) which was not annotated or described in the original report. Forty-two minutes after the Feed Water Pump 'C' was started, the pump tripped causing a Reactor Water Level 3 (9.7") RPS actuation. Feed Water was restored five minutes later using the Feed Water Pump 'A'. The NRC Resident Inspector has been notified. Notified the R4DO (Warnick). | |
| ENS 53732 | 10 November 2018 04:35:00 | River Bend | NRC Region 4 | Automatic Scram | At 0046 CST, River Bend Station experienced an automatic reactor scram on high reactor pressure. Initial indications are that the cause of the scram was an uncommanded closure of the #3 turbine control valve. The plant is stable with reactor water level in the normal level band of 10-51 inches being maintained with feedwater and condensate. Reactor pressure is in the prescribed band of 500-1090 psig, being maintained with turbine bypass valves and steam line drains. No injection systems were actuated either manually or automatically as a result of the event. The reactor scrammed on a Reactor Pressure High scram signal. A Reactor Level 3 signal resulted from the normal post-scram water level response. All systems responded as designed. This event is being reported in accordance with 10 CFR 50.72(b)(2)(iv)(B) as an automatic RPS actuation with the reactor critical. All control rods fully inserted. The Unit is in a normal shutdown electrical alignment. All control rods inserted properly and all systems functioned as designed. The licensee is investigating the cause of the event. The licensee notified the NRC resident inspector. | |
| ENS 53192 | 1 February 2018 14:23:00 | River Bend | NRC Region 4 | Manual Scram | GE-6 | At 1057 CST on February 1, 2018 with the unit in Mode 1 at approximately 27% power, a manual actuation of the Reactor Protection System (RPS) was initiated due to an unexpected trip of the B Recirc Pump with A Recirc Pump in fast speed. B Recirc Pump tripped during transfer from slow to fast speed resulting in single loop operation. Operators were unable to reconcile differing indications of core flow. This resulted in a conservative decision to initiate a manual scram. The cause of the B Recirc Pump trip and the apparent issues with core flow indication are under investigation. The plant is currently stable in Mode 3. The plant response to the scram was as expected. All control rods (fully) inserted as expected; the feedwater system is maintaining reactor vessel water level in the normal control band and reactor pressure is being maintained with steam line drains and main turbine bypass valves. The NRC Senior Resident (Inspector) has been notified.
This event was initially reported under 10 CFR 72(b)(2)(iv)(B) as a manual actuation of the RPS due to an unexpected trip of the B Reactor Recirculation Pump with the A Reactor Recirculation Pump running in fast speed (Single Loop Operations). Operations was unable to reconcile differing indications of core flow and made the conservative decision to perform a planned shutdown in accordance with normal operating procedures. Therefore, this event 'resulted from and was part of a pre-planned sequence during testing or reactor operation' as specified in 10 CFR 50.72(b)(2)(iv)(B), 10 CFR 50.73(a)(2)(iv)(A) and NUREG-1022 Section 3.2.6. Consequently, this event is not reportable as an actuation of RPS. The NRC Resident Inspector has been notified. R4DO (Groom) has been notified. |
| ENS 52915 | 18 August 2017 23:41:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | At 2055 CDT on August 18, 2017, an automatic actuation of the reactor protection system occurred while the plant was operating at 100 percent power. No plant parameters requiring the actuation of the emergency diesel generators or the emergency core cooling system were exceeded. The main feedwater system remained in service following the scram to maintain reactor water level, and the main condenser remained available as the normal heat sink. The scram occurred after a planned swap of the main feedwater master controller channels in preparation for scheduled surveillance testing. When the channel swap was actuated, the feedwater regulating valves moved to the fully open position. The scram signal originated in the high-flux detection function of the average power range monitors, apparently from the rapid increase in feedwater flow. The cause of the apparent feedwater controller malfunction is under investigation. The NRC Resident Inspector has been notified. No safety relief valves opened. Decay heat is being removed via steam to the main condenser using the bypass valves and steam drains. The licensee intends to go to Cold Shutdown to investigate the malfunction. |
| ENS 52825 | 23 June 2017 23:58:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | While performing a scheduled generator voltage regulator test, River Bend Station experienced an automatic scram when the main generator tripped. It is unknown at this time why the main generator tripped. There were no equipment issues that materially impacted post scram operator response. The intention at this time is to go to cold shutdown while the cause of the trip is investigated. All rods inserted during the scram. Reactor water level is being maintained via normal feedwater with decay heat being removed via turbine bypass valves to the main condenser. The electrical grid is stable and supplying plant loads via the normal shutdown electrical lineup. The licensee has notified the NRC Resident Inspector. |
| ENS 52602 | 10 March 2017 11:41:00 | River Bend | NRC Region 4 | Manual Scram | GE-6 | At 0714 CST on March 10, 2017, with the unit in Mode 1 at approximately 17% power, a manual actuation of the reactor protection system (RPS) was initiated due to rising reactor pressure caused by the closure of the Main Turbine Control Valves (MTCV's). The cause of the closure of the MTCV's is under investigation. The unit is currently stable in Mode 3. All control rods inserted as expected; water level control is stable in the normal control band and reactor pressure is being maintained with steam line drains (aligned to the main condenser). The NRC Senior Resident Inspector has been notified. |
| ENS 51644 | 9 January 2016 07:04:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | On 1/9/16 at 0237 (CST), River Bend Station sustained a reactor scram during a lightning storm. An electrical transient occurred resulting in a full main steam isolation (MSIV) (Group 6) and a Division II Balance of Plant isolation signal. During the scram, level 8 occurred immediately which tripped the feed pumps. A level 3 signal occurred also during the scram. Subsequent level 3 was received three times due to isolated vessel level control. The plant was stabilized and all spurious isolation signals reset, then the MSIVs were restored. The plant is now stable in Mode 3 and plant walkdowns are occurring to assess the transient. During the scram, all rods inserted into the core. The plant was initially cooled down using safety relief valves. Offsite power is available and the plant is in its normal shutdown electrical lineup. The licensee has notified the NRC Resident Inspector. |
| ENS 51568 | 27 November 2015 09:23:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | At 0431 CST on November 27, 2015, an automatic reactor scram occurred following the trip of the main generator. The generator trip was apparently caused by a partial loss of offsite power, which resulted from a differential ground on the north bus of the local 230 kV switchyard. The ground signal caused the reserve station service line no. 1 to de-energize, which tripped the Division 1 offsite power source to station, as well as the main generator. The plant responded as designed as follows: The Division 1 emergency diesel generator started and tied to the bus restoring Division 1 emergency power. The Division 3 emergency diesel generator started and tied to the bus, restoring power on the Division 3 switchgear. The reactor protection system tripped as designed. Reactor water level was controlled normally with condensate and feed water. A level 3 reactor water level scram signal occurred as expected, and RPV (Reactor Pressure Vessel) water level was restored to normal level band. Reactor pressure was controlled by the bypass valve system, and a normal cool down was initiated. The reactor is being taken to cold shutdown pending an investigation of the event. The loss of power also resulted in a partial loss of normal service water cooling to the plant, and emergency service water cooling automatically initiated per design. At the time of event, the reactor protection system was aligned to the backup power supply, which was momentarily lost. This resulted in multiple system isolations including reactor water clean up, and outboard balance of plant isolations. These isolations were initiated due to loss of offsite power, and all responded as designed. The isolation resulted in a loss of the running decay heat removal pump for the spent fuel pool. The standby pump is available for service and being aligned for service. The plant is currently stable in hot shutdown. Transmission and distribution personnel are currently investigating the ground in the 230 kV switchyard. All control rods inserted. The licensee has notified the NRC Resident Inspector. |
| ENS 51112 | 2 June 2015 02:00:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | At 2111 (CDT) River Bend Nuclear Station sustained an Automatic Reactor Scram due to low Reactor Water Level (Level 3). The plant is currently stable, with level being maintained in a normal band of 10 - 51 inches with Condensate and Feedwater. Reactor Pressure is in the prescribed band of 500-1090 psig. The plant is in Mode 3, Hot Shutdown, and will remain in Mode 3 until investigation of the scram is complete. The transient began with a trip of Reactor Feed Pump 'A', followed by a Reactor Scram and a trip of Reactor Feed Pump 'C'. Reactor water level was recovered with Reactor Feed Pump 'B' to a normal post scram level band. There was a problem noted with the Reactor Feedwater Master Level Controller; this was mitigated by the Operator placing the controller to manual. There was no subsequent Level transient. Reactor Pressure was stabilized in normal pressure band with Turbine bypass valves. During the transient, a Reactor Recirculating Flow Control Valve Runback was not received as expected. Reactor Recirculating Pump 'A' responded as expected to transient (switching to low pump speed), Reactor Recirculating Pump 'B' tripped during transient. A Level 3 isolation signal was received, all expected isolations occurred. The cause of the transient is currently under investigation. The reactor is stable in Mode 3 with decay heat being removed via turbine bypass valves, and a normal electrical line up. The NRC Resident Inspector has been notified.
At 2231 on 6/1/15, Reactor Water Cleanup System isolated on High Reactor Water Cleanup System Heat Exchanger room temperature due to loss of Turbine Building chill water during the initial transient. All Reactor Water Cleanup System Valves isolated as expected. Reactor Water Cleanup was the only system affected by this isolation signal. The licensee has notified the NRC Resident Inspector. Notified R4DO (Whitten). |
| ENS 51003 | 22 April 2015 14:18:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | On February 24, 2015, at approximately 1702 CDT, while the plant was in cold shutdown, power was lost on the Division 1 reactor protection system (RPS) bus. This event resulted in the automatic closure of the Division 1 primary containment isolation valves in the residual heat removal (RHR) and reactor water cleanup systems. Additionally, the primary containment atmospheric monitoring system automatically actuated, and ventilation systems in the fuel building, auxiliary building, and control building shifted to emergency mode. The closure of the isolation valves in the residual heat removal system caused an automatic trip of the 'A' RHR pump, which had been in the shutdown cooling alignment. The equipment response to the isolation signal was as expected. This event is being reported in accordance with 10 CFR 50.73(a)(1) as an invalid actuation of the Division 1 primary containment isolation system. The isolation was promptly diagnosed as having resulted from a trip of the output breaker of the RPS motor generator (MG) set 'A,' and not from a valid signal. Operators implemented the appropriate response procedures to align power to the bus via the alternate source, and began restoring the affected systems. The 'A' RHR pump was re-started within twelve minutes, during which time coolant temperature increased approximately seven degrees to a maximum of approximately 100F. Other affected systems were restored over the next few hours. The causal analysis concluded that the MG set output breaker tripped due to an overly conservative setpoint on the overvoltage trip relay. The low trip setpoint was a latent condition that had existed since the output voltage was raised in 1988 at the recommendation of the vendor, but at which time the trip setpoint was not changed. To correct this condition, the MG overvoltage trip setpoint was raised to restore adequate operating margin to the normal MG output voltage. At the time of the event, the plant was in MODE 5 with the reactor cavity flooded to greater than 23 feet above the vessel flange. The shutdown cooling system was promptly restored to service. This event was of minimal safety significance to the health and safety of employees and the public. The licensee has notified the NRC Resident Inspector. |
| ENS 50546 | 17 October 2014 07:46:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | At 0303 (CDT), River Bend Nuclear Station sustained a reactor scram due to high Average Power Range Monitor (APRM) flux, suspected due to a malfunction of the Electrohydraulic Control System. Reactor recirculation pump 'B' tripped, reactor recirculation pump 'A' responded appropriately. All other systems responded appropriately except for loss of feed water due to low suction pressure trip from isolating the condensate demineralizers. Reactor water level did not get out of level band. Condensate demineralizers and feedwater were restored to service. Level 3 (isolation) was initiated due to scram. (One) system, Suppression Pool Cooling isolated accordingly due to level 3 signal. Currently the plant is in mode 3, hot shutdown. Plant will remain in mode 3 until investigation of scram is complete. During the scram, all rods inserted into the core. No relief valves lifted as a result of the transient. All safety equipment is available although reactor core isolation cooling is functional but inoperable due to an earlier issue discovered during a surveillance test. The reactor is at normal pressure and temperature for Mode 3. The cause of the high APRM flux and the identified anomalies are under investigation. The licensee has notified the NRC Resident Inspector.
The licensee is updating the notification to include an 8 hour notification for a specified system actuation due to the Level 3 isolation signal. Licensee is proceeding to cold shutdown to troubleshoot the EHC system. The licensee will notify the NRC Resident Inspector. Notified R4DO (Haire). |
| ENS 47960 | 24 May 2012 18:04:00 | River Bend | NRC Region 4 | Manual Scram | GE-6 | At 1348 CDT on 5/24/12 with the Reactor at 33% power, River Bend Station operators inserted a manual reactor scram based on loss of high pressure feed to the reactor following a loss of a 13.8 Kv switchgear. The Control Room team observed an electrical transient in the Control Room concurrent with the start of Reactor Feed Pump "B". The crew identified that no high pressure feed was aligned to the reactor and inserted a manual scram. Based on the configuration of the electrical plant during startup, all circulating water and Normal Service Water (NSW) was supplied from NPS-SWG1B. MSIVs were closed based on loss of circulating water and Standby Service Water (SSW) initiated automatically based on loss of NSW. EOP-0001, 'RPV Control' was entered on reactor high pressure and reactor low water level. EOP-0002, 'Primary Containment Control' was entered based on primary containment pressure high and suppression pool level high. EOP-0003, 'Secondary Containment Control', was entered on annulus pressure high. Reactor water level control is being maintained with Reactor Core Isolation Cooling (RCIC). High pressure core spray was manually started but was not required and was subsequently shut down. Pressure control is via RCIC and Safety Relief Valves (SRVs). Safety related busses are aligned to offsite power as normal. They were not affected by the electrical transient. Immediately after the scram at 1350, a report from the Turbine Building indicated smoke was seen around the Reactor Feed Pump 'B' termination cabinet. The Fire Brigade was activated. At 1358, the Fire Brigade reported that there was no fire. A review of the Emergency Action Levels (EALs) was performed. No emergency declaration was required. Initial investigation shows damage to cabling and circuit boards associated with Reactor Feedpump 'B' in the Turbine Building, but no fire was ever observed. In addition, the Technical Support Center (TSC) and Operations Support Center (OSC) lost power. At the time, both facilities continued to be in a state of readiness and emergency functions could be performed. At 1526, power was restored to both facilities, including the ventilation systems. All rods inserted into the core. The unit is stable at 230 psi and 391 degrees F. Reactor pressure is maintained by RCIC and decay heat removal via safety relief valves to the suppression pool. The unit is in a technical specification for suppression pool high level. There were no safety system failures. There is one non safety related 13.8 switchgear out of service due to this event and NNS-Switchgear 2A out of service from an event three days ago. Offsite assistance was not required. The NRC Resident Inspector has been notified. |
| ENS 47940 | 21 May 2012 18:35:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | At 1452 CDT on 5/21/2012 with the reactor at 100% power, River Bend Station experienced a reactor scram resulting from an RPS actuation. Following the scram, reactor water level briefly lowered below level 3. The reactor is stable with pressure and temperature being controlled by the feed water system and main steam bypass valves, respectfully. The cause of the scram was due to a turbine trip/low condenser vacuum. The low vacuum condition resulted from a loss of non-safety related 4160V switchgear that powers two of four circulating water pumps. A suspected spurious Division II isolation of Reactor Core Isolation Cooling (RCIC) was observed. Restoration of RCIC to standby is in progress. A report of a fire in a manhole was received shortly after the scram . Fire Brigade was dispatched and noted a small active fire in a cable tray. The fire was extinguished with fire extinguishers. Power cables are routed through this manhole. The plant is conducting causal investigations to fully understand the cause of the turbine trip. As information becomes available, River Bend Station will provide additional information. All rods are inserted, and the plant is in a normal shutdown electrical lineup with the exception of NNS-Switchgear 2A being deenergized. Offsite assistance was not required to extinguish the fire. The licensee notified the NRC Resident Inspector. |
| ENS 47549 | 23 December 2011 10:10:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | At 0610 CST on 12/23/2011 with the reactor at 100% power, River Bend Station experienced an (automatic) reactor scram resulting from a RPS actuation. Following the scram, reactor water level briefly lowered below level 3, resulting in the automatic closure of containment isolation valves in the suppression pool cooling system. This isolation was confirmed to have occurred as designed. The reactor is stable with pressure and temperature being controlled by the feed water system and main steam bypass valves, respectively. The cause of the scram was due to a turbine trip. Initial indications are that the turbine tripped due to a loss speed sensor. All control rods inserted and Reactor Core Isolation Cooling was manually operated for approximately 1 minute and secured, The plant is conducting causal investigations to fully understand the cause of the turbine trip. As information becomes available River Bend Station will provide additional information. This event is being reported in accordance with 10CFR50.72(b)(iv)(B) as an automatic RPS actuation with the reactor critical. The safety relief valves momentarily lifted immediately following the scram. The plant electrical distribution system is in a normal shutdown configuration. The scram was uncomplicated. The licensee notified the NRC Resident Inspector. |
| ENS 45369 | 20 September 2009 21:32:00 | River Bend | NRC Region 4 | Manual Scram | GE-6 | At 1747 hours on September 20, 2009, at River Bend Station, during plant shut down for a planned outage, an unplanned manual reactor scram was initiated by plant operators. As part of the planned shutdown, the reactor recirculation pumps were being transferred from fast to slow speed. This transfer did not occur as expected. Instead, the pumps tripped to off. After this occurred, the operators entered the manual reactor scram. Power level was approximately 23 percent at the time of the scram. All other plant equipment and systems performed as expected. Plant personnel are investigating the cause of the pump trip. The plant is proceeding with planned outage activities. All rods fully inserted. Decay heat is being removed via main steam drains and bypass valves to the condenser. Reactor pressure is at 200 psig. The electrical lineup is normal and all safety related equipment is available if required. No safety or relief valves lifted during the manual scram. The licensee has notified the NRC Resident Inspector. |
| ENS 44457 | 1 September 2008 23:33:00 | River Bend | NRC Region 4 | Manual Scram | GE-6 | Voluntary Report of Planned Manual Plant Shutdown. At 1802 on September 1, 2008, River Bend Station (RBS) completed a planned manual shutdown of the unit. This shutdown was determined to be necessary based on the conditions of the grid due to Hurricane Gustav. Evaluation of grid conditions determined that removing the unit from power operation would improve the reliability of the grid and thus the decision was made to shutdown. Offsite power was declared inoperable at 1520 on September 1 based on notification of grid status by the grid operator. It is expected that offsite power will be restored to an operable status within the 24 hour LCO Required Action Completion Time. In addition, damage to turbine building siding was reported. Assessment of this condition is being conducted. RBS had previously activated the Outage Control Center prior to the arrival of Hurricane Gustav. Additional resources are available on site to respond to plant conditions. A comprehensive assessment of the condition of the plant and other site facilities will be completed prior to restart. At this time, a schedule for restart has not been established. The licensee contacted the NRC Resident Inspector. |
| ENS 44347 | 16 July 2008 09:49:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | On June 2, 2008 at 6:24 a.m. CDT power was lost on the reactor protection system (RPS) bus 'A'. The plant was operating at 100 percent power at the time. The loss of RPS bus 'A' interrupted power to containment isolation actuation circuitry. This caused the Division 1 containment isolation valves in various balance of plant systems to automatically close, as designed. Plant operators implemented recovery procedures to shift RPS 'A' to its alternate power supply, and restore the systems affected by the isolation. The containment isolation valves were confirmed to have actuated as required. Plant capacity was not interrupted by the containment isolation signal. As their primary power source, each RPS bus is supplied by its own motor generator set. The investigation of this event found that two resistors on a circuit card in the voltage regulator on the 'A' RPS motor-generator set failed. This had the effect of causing the generator voltage to fluctuate significantly, resulting in a automatic trip of the generator output breaker and a loss of power on the bus. This event is being reported in accordance with 10CFR50.73(a)(2)(iv)(A) as an invalid actuation of the Division I containment isolation actuation system." The licensee informed the NRC Resident Inspector. |
| ENS 44034 | 5 March 2008 17:44:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | At 2:43 p.m. CST, an unplanned automatic reactor scram occurred. The initial investigation determined that the event resulted from an apparent malfunction in the main turbine control system. This had the effect of causing reactor steam pressure to exceed the trip set point for the reactor protection system, initiating the reactor scram signal. All reactor control rods inserted, and the main feedwater system remained in service. Reactor safety-relief valves initially lifted as a result of the pressure transient. Reactor pressure is now being controlled by steam line drains with turbine bypass valves as a backup. There was no condition requiring the actuation of emergency diesel generators or emergency core cooling systems. NRC Resident Inspector has been notified. |
| ENS 43773 | 7 November 2007 07:58:00 | River Bend | NRC Region 4 | Manual Scram | GE-6 | With the plant in Mode 1 at (approximately) 75% power, the Auxiliary boiler and water treatment building 480 volt switchgear (NJS-SWG1J) faulted. The fault resulted in the loss of the NPS A bus (13.8 Kv normal supply), causing condensate and feed pumps to trip. Operators in the control room immediately responded and the plant was manually scrammed at 0306. Both the high pressure core spray (HPCS) and the reactor core isolation cooling (RCIC) systems responded automatically and injected into the vessel (valid ECCS signal). Safety systems responded as expected, including level 2 isolations. The licensee believes a transformer fault may have transferred up the line and caused the loss of normal power supply. RCIC is controlling reactor water level with primary plant pressure approximately 325 psia. Decay heat is being controlled through modulating the SRV's. The licensee has all systems available to place the unit in safe shutdown and cooldown. The licensee has one inoperable EDG and is not in any technical specification action statement at this time. The licensee notified the NRC Resident Inspector.
The high pressure core spray system was returned to its standby lineup at 0318 (all times are CST). Standby service water was being placed in service at 0701 to raise service water header pressure when standby service water pump 'C' started automatically. NPS 13.8kv switchgear 'A' was restored to service at 1245. The reactor core isolation cooling system, which automatically started at the time of the event, was shutdown at 1645. The Division 3 diesel generator, which automatically started at the time of the event, was restored to its standby lineup at 1429. Shutdown cooling was placed in service with residual heat removal pump 'A', at 1626. The plant entered Mode 4 (cold shutdown) at 1942. The electrical fault that initiated the event has been isolated to a 13.8kv/480v transformer in the turbine building. An investigation is ongoing. The licensee notified the NRC Resident Inspector. Notified the R4DO (Spitzberg) and NRR (Lubinski). |
| ENS 43668 | 27 September 2007 03:48:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | At approximately 2244 on September 26, 2007 an unplanned reactor scram occurred. An Average Power Range Monitor (APRM) surveillance was being performed at the time. This surveillance should not have caused a full scram and the cause of the scram is under investigation. The plant responded to the scram as expected, all control rods fully inserted, and there is no need for emergency injection system operation. Critical parameters are being maintained within prescribed bands and the plant has been stabilized. A level 3 signal was received during this scram which would have caused an isolation but all affected valves were already in the closed position. This event is being reported in accordance with 10CFR50.72(b)(2)(iv)(B) as an event that results in activation of the reactor protection system with the reactor critical. All emergency systems are available and in standby mode. The licensee notified the NRC Resident Inspector. |
| ENS 43345 | 4 May 2007 16:01:00 | River Bend | NRC Region 4 | Manual Scram | GE-6 | At approximately 1256 CDT on May 4, 2007, a manual reactor scram was initiated following the loss of cooling to the no. 2 main transformer. Reactor power at the time of the scram was approximately 70 percent (initially 100% power). Following the scram, reactor water level briefly decreased below Level 3, resulting in the automatic closure of containment isolation valves in the suppression pool cooling system. This isolation was confirmed to have occurred as designed. Reactor pressure and water level control were promptly established. All control rods inserted, and no emergency injection system operation was required. This event is being reported in accordance with 10CFR50.72(b)(2)(iv)(B) as a condition resulting in a manual actuation of the reactor protection system. The NRC Resident Inspector was notified of this event by the licensee. |
| ENS 42921 | 19 October 2006 22:35:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | At 1756 CDT with the plant operating at 100% power, a reactor scram occurred in response to a reactor water level 3 signal from an apparent loss of feedwater. Both feedwater injection lines isolated when isolation valves were inadvertently closed, The cause of the isolation valve closure is under investigation. When reactor water level lowered to level 2, high pressure core spray (HPCS) initiated automatically and recovered water level. The reactor core isolation cooling system (RCIC) was tagged out for maintenance at the time of the event. Following the scram, main steam isolation valves isolated on low main steam header pressure. As a result, reactor pressure control was being controlled with the safety relief valves. SRV pressure control in turn led to EOP entry conditions on containment pressure and suppression pool level. Both feedwater lines were opened, and normal reactor level control was restored. The MSIV's were opened and pressure control was returned to the turbine bypass valves and the main condenser. Initial indications are that all plant equipment functioned as designed with the exception of the 'B' feed pump which experienced an apparent seal failure. The plant is stable in Mode 3. All plant conditions are understood. This event is being reported in accordance with 10CRF50.72(b)(2) as an RPS actuation and an injection of HPCS into the reactor vessel, and in accordance with 10CRF50.72(b)(3) as a loss of safety function of HPCS, as it was manually disabled during recovery from the event. The HPCS Injection valve was manually overridden closed for 76 minutes. In addition,' containment isolation valves in multiple systems actuated in response to the RPV level 2 signal. Reactor vessel water level lowered to below level 2. Decay heat is being removed by normal feedwater to the reactor vessel steaming to the main condenser. Offsite power is available and stable. Emergency Diesel Generators are available. The licensee notified the NRC Resident Inspector.
The closure signal to the main feedwater header isolation valves occurred when part of a chart recorder above the isolation valve control switches was dropped by an operator. The operator was attempting to adjust the paper drive mechanism in the recorder, and accidentally dropped the paper cartridge, which struck the 'CLOSE' pushbuttons on the isolation valve control switches. Following the scram, there was a delay in placing the reactor mode switch in the 'SHUTDOWN' position, which is an immediate action required by procedure. Placing the mode switch to 'SHUTDOWN' bypasses the reactor low steam pressure MSIV Isolation. Reactor steam pressure began dropping after the scram, until it reached the MSIV automatic closure setpoint, and the MSIVs isolated, In addition the licensee corrected one of the 10 CFR Section entries from "50.72(b)(3)(v)(A) POT UNABLE TO SAFE SD" to "50.72(b)(3)(v)(D) ACCIDENT MITIGATION." The licensee notified the NRC Resident Inspector. Notified R4 DO (D. Powers) and NRR EO (N. Chokshi) |
| ENS 41339 | 15 January 2005 05:08:00 | River Bend | NRC Region 4 | Manual Scram | GE-6 | At 0212 plant operators inserted a manual reactor scram and tripped the main turbine while at 100% power due to indications and alarms of a generator field ground fault. All rods fully inserted and there were no indications of any relief valves lifting. The reactor water level is being controlled within the normal band with feed pump "C" and reactor pressure is being controlled with bypass valves at 800-1090 psig. Also the "A" heater drain pump tripped during the reactor scram due to the water level in the third port heater. The licensee is investigating the cause. The NRC Resident Inspector was notified. |
| ENS 41082 | 1 October 2004 12:00:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | At 7:30 a.m. (CDT) on October 1, 2004, an automatic reactor scram occurred as a result of an electrical fault on the main generator output lines that caused a main generator trip and turbine trip. All control rods inserted. Approximately 13 minutes prior to the fault, a loss of one station service transformer had occurred. This resulted in an automatic start of the Division 1 diesel generator and a loss of power to some plant auxiliaries, including the feedwater level regulation isolation valves. The loss of reserve station service no. 1, combined with the trip of the main generator, caused a loss of power to two condensate pumps and one main feedwater pump. The remaining two feedwater pumps tripped on low suction pressure. The reactor containment isolation cooling pump (RCIC) steam supply isolated during the scram transient, so the control room operators manually started the high-pressure core spray system (HPCS) pump for level control. The injection valve was closed as level had already reached the high water level isolation setpoint for that valve. It was later reopened manually as level approached the low level setpoint (level 2), which would have automatically opened the valve. The level 2 setpoint was reached briefly after the valve was already open. Reactor pressure is being controlled manually with safety relief valves (SRV's). The main steam isolation valves (MSIV's) were manually closed due to lowering pressure from steam loads in the plant that could not be immediately isolated because of loss of power to their valves. RCIC is also running in CST (condensate storage tank) to CST mode, to augment pressure control. The electrical load center which supplies power to the instrumentation and valves needed for feedwater operation was cross-tied to an alternate power source, and feedwater was restored to operation and is presently controlling reactor water level. During the event, standby service water also initiated. This is the presently known information. Further information will be provided as the investigation continues. The licensee has notified the NRC Resident Inspector. |
| ENS 40957 | 15 August 2004 08:50:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | At 0405 on August 15, 2004, River Bend Station had a loss of 230Kv Line #353 (RSS #2, Port Hudson) feeding the plant's switchyard. This resulted in a generator trip and a reactor scram. Feedwater tripped on a Reactor vessel Level 8 signal. RCIC is operating to control reactor vessel level. SRVs were used to manually control pressure. Mechanical vacuum pump (ARC A) would not start to control condenser vacuum. The MSIVs were manually isolated in anticipation of a Group 6 isolation (low vacuum). There was no ECCS initiation. Power was restored to the mechanical vacuum pump ARC B. Vacuum was restored and main steam lanes are in use for pressure control. We are still investigating the root cause. The following ESF actuations occurred: - Division II Diesel Generator - Standby Gas Treatment System - Annulus Mixing System - Control Building Ventilation System. The licensee will inform the NRC Resident Inspector.
River Bend Station is currently in Mode 3, Hot Shutdown. During the event, offsite power was maintained through Reserve Station Service Line #1 to Division 1 safety related equipment and 'A' balance of plant (BOP) non-safety related equipment. The 230 KV line from the plant's switchyard (RSS Line #2) that was lost during the event has been recovered and the Division 2 bus has been restored to its normal power supply. The Division 2 diesel generator has been secured from operation (and has been placed in standby) During, the event, main condenser vacuum was restored from the main control room by starting the 'B' mechanical vacuum pump. Feedwater Pump 'A' remained available during the event. The circulating water supply to the main condenser remained in operation throughout the event. RCIC (Reactor Core Isolation Cooling) remains in service for reactor vessel level control. The ESF (Emergency Safety Feature) systems have been secured and placed in standby. A root cause team has been assembled to address the cause of the initial failure of the 230 KV Line #353. The licensee has notified the NRC Resident Inspector Notified R4DO (Linda Smith) and NRR EO (Cynthia Carpenter) |
| ENS 40191 | 23 September 2003 02:44:00 | River Bend | NRC Region 4 | Automatic Scram | GE-6 | At 2243 on 9/22/2003 a Reactor scram occurred while performing Main Turbine control valve testing. Preliminary investigations indicate that high Reactor pressure was the signal that caused the scram. As a result of the scram, a Reactor low level 3 (9.7 inch) signal was received as expected from a high power scram due to the rapid coolant shrinkage. All expected actions for the low reactor level 3 (9.7 inch) signal occurred as expected. The plant is stable in Mode 3 (hot shutdown) with level being controlled with the Feedwater System and Reactor pressure being controlled with the Main Turbine Bypass valves. All control rods fully inserted, no ECCS actuations were received, and the electrical grid is stable. The licensee notified the NRC Resident Inspector. |