|Entered date||Site||Region||Scram||Reactor type||Event description|
|ENS 53953||24 March 2019 05:23:00||Hatch||NRC Region 2||Manual Scram||At 0159 (EDT), with Unit 2 in Mode 1 at 25 percent power, the reactor was manually tripped due to degrading condenser vacuum. After the turbine was tripped, the station service electrical buses did not transfer to alternate supply resulting in loss of the condensate feedwater system and level being controlled by the RCIC system. Operators responded and stabilized the plant. Reactor water level is being maintained via the RCIC system. Pressure is being controlled and decay heat is being removed by the HPCI system in pressure control mode. Unit 1 is not affected. Additionally, an actuation of the primary containment isolation system occurred during the reactor scram. The reason for the actuation was a group II isolation signal was received on reactor water level and a group I isolation was received on decreasing vacuum. Due to the Reactor Protection System actuation while critical, this event is being reported as a four-hour, non- emergency notification per 10 CFR 50.72(b)(2)(iv)(B). Additionally, this event is being reported in accordance with 10 CFR 50.72(b)(3)(iv)(A) as an event that results in a valid actuation of the primary containment isolation system. There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified.|
|ENS 52696||20 April 2017 05:57:00||Hatch||NRC Region 2||Automatic Scram||GE-4||On 04/20/2017 at 0302 EST during a reactor startup, a reactor scram resulted from upscale spike on two Intermediate Range Monitors (IRMs), 1C51K601A and 1C51K601B. IRM A, 1C51K601A is in Reactor Protection System Channel A and IRM B, 1C51K601B is in Reactor Protection System Channel B. All control rods fully inserted. No PCIS (Primary Containment Isolation System) actuations occurred and none were expected to occur based upon plant condition following the reactor scram. Investigation is in progress. Condition was not due to a true flux event. This event is reportable per 10 CFR 50.72(b)(2)(iv)(B) as an event or condition that resulted in actuation of the reactor protection system (RPS) when the reactor is critical except when the actuation results from and is part of a pre-planned sequence during testing or reactor operation. CR 10356172 The NRC Resident has been notified. The reactor was at 0.5% (percent) power at the time of the event and will remain in Hot Shutdown pending the results of the root cause investigation.|
|ENS 48738||10 February 2013 09:11:00||Hatch||NRC Region 2||Manual Scram||GE-4||During normal power operations, the crew observed condensate/feedwater conductivity begin to increase at approximately 0530 EST on 02/10/13. The crew responded to the associated alarm response procedures and entered abnormal operating procedure 34AB-N61-001-1 due to degrading reactor water chemistry parameters. A power reduction (from 100%) was initiated at 0555 EST in accordance with station procedures for responding to a suspected condenser tube leak. At 0700 EST, a manual reactor SCRAM (from approximately 47%) was inserted due to the elevated reactor water conductivity in accordance with station abnormal operating procedures. All rods inserted completely and no complications were encountered following the reactor SCRAM, normal feedwater injection remained available. Following the SCRAM, a Group 2 Primary Containment Isolation Signal (PCIS) was received as a result of reactor water level lowering below +3 inches. The lowest reactor water level observed was (minus) 2 inches and was restored to normal operating levels utilizing normal feedwater injection. Following restoration of reactor water level to the normal operating level, the Group 2 PCIS signal was reset. No ECCS injection systems actuated as a result of the reactor SCRAM. The SCRAM was uncomplicated and the plant is stable. Decay heat removal is to the main condenser via the turbine bypass valves. The plant is in a normal offsite electrical power shutdown alignment. Efforts are in progress to isolate the condenser in-leakage. There was no impact on Unit 2. The licensee has notified the NRC Resident Inspector.|
|ENS 47369||24 October 2011 17:01:00||Hatch||NRC Region 2||Manual Scram||GE-4||While performing a startup of HNP-2, after reaching criticality, the crew observed erratic indications on two Intermediate Range Monitors (IRMs), 2C51K601A and 2C51K601C. IRM 2C51K601A had been spiking and was subsequently bypassed. The 2C51K601C was spiking downscale and could not be bypassed due to the 2C51K601A being bypassed already. Both IRMs are in the 'A' RPS trip system. At the time when the second IRM was acting erratic, the crew identified the condition as both IRMs in the same quadrant and did not continue withdrawal of control rods. As a result of not withdrawing control rods, reactor power began to decrease and the crew conservatively inserted a manual reactor scram to shutdown the reactor. All rods did fully insert into the core. No PCIS (Primary Containment Isolation System) actuations occurred and none were expected to occur based on plant conditions following the scram. At this time, investigation is in progress, but the investigation and corrective actions have not yet been completed. The crew is maintaining HNP-2 in Hot Standby (Mode 3) at this time. The licensee informed the NRC Resident Inspector.|
|ENS 45148||23 June 2009 05:08:00||Hatch||NRC Region 2||Automatic Scram||GE-4||(The reactor automatically scrammed) on a Main Turbine Trip >27.6% rated thermal power. The main turbine trip was due to reactor high level. Post scram, reactor level decreased to approximately -26 inches. Reactor water level was restored with the condensate system. Both reactor recirc pumps tripped as required on EOC RPT Logic when the main turbine tripped. Both pumps have been restarted. A Group 2 isolation was received at +3 inches reactor water level with all valves closing as required. Investigation as to the cause of the transient is underway. All rods inserted during the scram. No relief valves actuated during the transient. Decay heat is being removed via turbine bypass valves to the main condenser. The plant is within normal shutdown temperature and pressure limits. The electrical grid is stable and the plant is in a normal shutdown electrical lineup. The Group 2 has been reset. There was no effect on Unit 1. The licensee has notified the NRC Resident Inspector.|
|ENS 45145||20 June 2009 15:47:00||Hatch||NRC Region 2||Automatic Scram||GE-4||Plant Hatch Unit 2 experienced a full reactor scram from the main generator protection circuitry (generator runback circuit). Preliminary indications are that a main generator high temperature signal was received, initiating the generator protection (runback) circuitry and a high reactor pressure scram signal was received during the turbine/generator runback. Investigations into the cause of the generator high temperature signal are ongoing. Reactor water level was recovered using the reactor feed system, and reactor pressure was controlled using main turbine bypass valves. All control rods inserted, as expected, during the scram. Other than the cause of the main generator high temperature signal, all systems functioned as expected. Unit is currently at 837 psig; 540 degrees F in Mode 3. Electrical system is in a normal lineup. The licensee informed the NRC Resident Inspector.|
|ENS 44679||22 November 2008 12:26:00||Hatch||NRC Region 2||Manual Scram||GE-4||Manual Rx Scram initiated due to a loss of condensate/feedwater. Condensate Booster Pump 1A tripped due to low suction pressure and then both Reactor Feed-pumps tripped. Both HPCI and RCIC initiated on low level and restored reactor water level to normal band 5 to 50 inches. Both Reactor Water Recirculation Pumps tripped due to low level at RWL (Reactor Water Level) - 60". Lowest RWL was approximately minus 70 inches and a group two isolation occurred at RWL 3 inches. All group two 2 valves closed as required. The cause of the low condensate booster suction pressure is under investigation. Rods fully inserted on the scram. No safety or relief valves lifted after the scram. Reactor water level is being maintained with normal feed and decay heat is being removed to the main condenser. The plant is in its normal shutdown electrical lineup. The licensee notified the NRC Resident Inspector.|
|ENS 44337||4 July 2008 10:04:00||Hatch||NRC Region 2||Automatic Scram||GE-4||A Turbine Trip greater than 30% power caused a Reactor Trip (Scram), both Recirculation Pumps tripped. A low level (Reactor Vessel Water Level) of approximately 2 inches caused a Group 2 containment valve isolation signal, all valves closed as required. The cause of the Turbine Trip is under investigation All control rods fully inserted with no ECCS actuations. Unit 1 is currently stable in mode 3 (Hot Shutdown) with decay heat being removed via the bypass. Following the scram, one SRV lifted and reseated. At the time of the transient, an EHC pump autostart was in progress, however, there is no indication that this was the cause of the turbine trip. Unit 1 is in a normal shutdown electrical lineup. The licensee informed the NRC Resident Inspector.|
|ENS 44046||7 March 2008 17:21:00||Hatch||NRC Region 2||Automatic Scram||GE-4||Unit 2 RPS actuation / unplanned scram with subsequent ECCS discharge to the RCS at 1446 hrs. on 3/07/08. Unit 2 scrammed on Low RPV water level of 3 inches above instrument zero as a result of a loss of condensate feedwater. Water level decreased to approximately 60 inches below instrument zero as a result of the loss of feedwater. (Top of active fuel is approximately 150 inches below instrument zero.) The cause of the loss of feedwater is presently under investigation. At 35 inches below instrument zero, HPCI and RCIC actuated and restored water level. HPCI oscillations were experienced and the system was taken to manual control, at which time the flow oscillations abated. All other systems functioned as required. A team has been assembled to investigate and determine the cause of the initiating event of the loss of feedwater. During the scram, all rods inserted into the core. There were no safety relief valve actuations as a result of the transient. RPV level was restored and is being maintained using control rod drive flow. The electrical grid is stable with normal offsite power supplying safety loads. Decay heat is being removed using the turbine bypass valves to condenser. The licensee has notified the NRC Resident Inspector.|
|ENS 41725||23 May 2005 20:07:00||Hatch||NRC Region 2||Manual Scram||GE-4|
Based on increasing conductivity in the reactor vessel and condenser hotwell, a power reduction was initiated from 100 percent power. A manual scram was inserted at 57 percent RTP and 49 percent Core Flow based on Chemistry recommendations due to sulfates and chlorides in the hotwell. Following the scram a reduction in reactor water level to -28 inches resulted in a Primary Containment Group 2 Isolation (ESF) occurring. All isolations and systems responded as expected. Current plant status is Hot Shutdown with plans to proceed to cold shutdown. All control rods fully inserted and decay heat is being removed with the bypass valves into the condenser. The licensee notified the NRC Resident Inspector.
After further review and evaluation it has been determined that the four hour call made May 23, 2005 per the guidance of 50.72(b)(2)(iv)(B) should be retracted. A review of the event with respect to NUREG 1022 Revision 2 determined that: The manual scram was part of a pre-planned sequence to shut the plant down due to an equipment problem. The manual scram was part of a pre-planned sequence. The guidance to scram the reactor was established by the plant's Abnormal Operating Procedure addressing a condenser tube leak and was part of a preplanned sequence to prevent future equipment and component failures. The Manual Scram was not inserted to protect the plant against an event that presented a challenge to an FSAR analyzed event. In other words, this was not an Anticipated Operational Occurrence, an Accident, or a Special Event as defined in section 15.1.3 of the Unit 2 FSAR. Rather it was part of a plan to shutdown the reactor to protect against future potential equipment problems due to out of limits chemistry parameters. Further justification is provided by the fact that the manual scram was not initiated in anticipation of an automatic scram. Per NUREG 1022 Rev. 2: 'The staff also considers intentional manual actions, in which one or more system components are actuated in response to actual plant conditions resulting from equipment failure or human error, to be reportable because such actions would usually mitigate the consequences of a significant event. This position is consistent with the statement that the commission is interested in events where a system was needed to mitigate the consequences of the event.' However, the reporting requirement itself indicates that actuations that result from pre-planned sequences are not reportable. An example is provided in the NUREG of an equipment problem involving the loss of recirc pumps. In this example it is stated that: 'Even though the reactor scram was in response to an existing written procedure, this event does not involve a preplanned sequence because the loss of the recirc pumps and the resultant off-normal procedure entry were event driven, not pre-planned.' This is similar to our event, however, in the NUREG example, the reactor is scrammed to protect against the possibility of a stability event and stability is an FSAR analyzed event. In our case we were shutting down for chemistry reasons, not an FSAR type event. It is concluded that when the RPS is used to shutdown the reactor as part of a plan for the resolution of equipment problems, and the RPS is not needed to mitigate the consequences of an FSAR analyzed event, i.e., one which threatens a fission product boundary (i.e., fuel cladding, RCPB, primary and secondary containments), the RPS actuation is not reportable under 50.72(b)(2)(iv)(B).
The licensee notified the NRC Resident Inspector. Notified R2DO (Haag).
On May 23, 2005 a four hour report was made per the guidance of 50.72(b)(2)(iv)(B), 'Any event or condition that results in an actuation of the RPS when the reactor is critical except when the actuation results from and is part of a pre-planned sequence during testing or reactor operation.' This was made per event # 41725. The report was made within the four hour time frame of 10 CFR 50.72(b)(2). The four hour report for event # 41725 was retracted on June 6, 2005. After further consideration, the retraction made on June 6, 2005 is being cancelled and the original report re-instated. The licensee notified the NRC Resident Inspector. Notified R2 DO (K. Landis)
|ENS 41070||25 September 2004 02:44:00||Hatch||NRC Region 2||Manual Scram||GE-4||Received Group 2 isolation signal on Low Reactor Water Level during initiation of manual reactor scram during planned shutdown. Reactor Water Level decreased to -0.5 inches. Group 2 isolation setpoint is +3.0 inches. All Group 2 isolation valves closed as required. During the planned shutdown, all control rods fully inserted. Decay heat is being removed to the main condenser via the main turbine bypass valves, ESF and ECCS systems remain available, and the electrical grid is stable. The licensee will notify the NRC Resident Inspector.|