|Entered date||Site||Region||Scram||Reactor type||Event description|
|ENS 54976||1 November 2020 09:34:00||Cooper||NRC Region 4||Manual Scram||GE-4||On November 1, 2020, at 0534 CST the reactor was manually scrammed due to an un-isolable leak on the Turbine High Pressure Fluid System. Initial power level when the leak was identified was 100 percent. Power was lowered commencing at 0525 in accordance with shutdown procedures. The Reactor Operator scrammed the reactor at 0534 from approximately 75 percent power. Following the scram, Reactor vessel water level lowered to approximately -20 inches on the Wide Range Instruments, and was subsequently recovered to normal post scram range (approximately 36 inches) using the Reactor Feedwater system. Group 2 Isolation occurred due to Reactor vessel level reaching the isolation setpoint (3 inches). The plant is stable in MODE 3 and proceeding to cold shutdown. The Main Condenser remained available throughout the evolution and condenser vacuum is currently being maintained by the Mechanical Vacuum Pumps. Pressure is being controlled using the steam line drains to the main condenser. All control rods fully inserted and there were no complications. All systems responded as designed. The Turbine High Pressure Fluid System has been secured. This event is reportable under 10 CFR 50.72(b)(2)(iv)(B) due to RPS Actuation-Critical and 50.72(b)(3)(iv)(A) Valid Specified System Actuation. The licensee has notified the NRC Resident Inspector.|
|ENS 45489||11 November 2009 22:34:00||Cooper||NRC Region 4||Manual Scram||GE-4||On November 11, 2009, at 1743 CST the reactor was manually scrammed following a manual trip of the main turbine due to an un-isolable leak on the Turbine High Pressure Fluid System (TGF) governor valve 3. Initial power level when the leak was identified was approximately 70%. Power was lowered commencing at 1405 in accordance with shutdown procedures. The reactor operator scrammed the reactor at 17:43 from approximately 15% power when directed by the shutdown procedure to place the reactor in a condition to support repairs to the TGF system. In preparation for the scram, level was raised to the range specified in the shutdown procedure (approximately 46 inches). Following the scram, reactor vessel water level lowered to approximately 15 inches on the narrow range instruments, and was subsequently recovered to normal post scram range (approximately 40 inches) using the reactor feedwater system. All control rods fully inserted. No group isolations occurred since level did not reach the isolation setpoint (3 inches). At 1920, the inboard MSIVs were manually closed to stabilize plant cool down and maintain the plant in mode 3. The main condenser remained available throughout the evolution and condenser vacuum is currently being maintained by the mechanical vacuum pumps. Pressure is being controlled using the steam line drains to the main condenser. All equipment operated as expected and there were no difficulties encountered during the evolution. The TGF System has been secured and is in the process of being tagged out for repair. This event is reportable under 10CFR50.72(b)(2)(iv)(B) due to a non planned reactor scram while critical. The licensee has notified the NRC Resident Inspector. The plant is in its normal shutdown electrical lineup.|
|ENS 45482||6 November 2009 23:22:00||Cooper||NRC Region 4||Manual Scram||GE-4||On November 6, 2009, at 1930 CST the reactor was manually scrammed following a manual trip of the Main Turbine due to an un-isolable leak on the Turbine High Pressure Fluid System (TGF). The RO (Reactor Operator) scrammed the reactor when (reactor vessel water) level lowered below 12 inches on the Narrow Range Instruments. All Control Rods fully inserted and a Group 2 Isolation occurred when level reached 3 inches on the Narrow Range Instruments. Reactor level lowered to approximately 22 inches on the Wide Range Instruments and was recovered in a slow and deliberate manner in order to minimize the effect on the cool down rate because of low levels of decay heat in the fuel. The Reactor Feed System was used to initially recover level. At 2043, the plant was in Mode 3 with the inboard MSIVs manually closed and level and pressure being controlled by RCIC. The MSIVs were closed to minimize the cool down rate and RCIC was started manually for level and pressure control. The Main Condenser remained available throughout the evolution and condenser vacuum is currently being maintained by the Mechanical Vacuum Pumps. The Group 2 Isolation was verified with no discrepancies and was reset at approximately 2010. All equipment operated as expected and there were no difficulties encountered during the evolution. The TGF System has been secured and is in the process of being tagged out for repair. The licensee has notified the NRC Resident Inspector.|
|ENS 44402||9 August 2008 05:24:00||Cooper||NRC Region 4||Manual Scram||GE-4||While performing main turbine reheat stop valve surveillance testing, Reheat Stop Valve 1RV 1A failed to reopen simultaneously with a Moisture Separator C high level alarm. Plant alarm response procedures require a reactor scram in this situation. Operating crew inserted a manual scram at 0204 CDT. Immediately after the scram, RPV level responded as expected and dropped below the Group 2 containment isolation setpoint. All rods inserted fully. RPV level is being controlled with RFP A and the startup valves. RPV pressure is being controlled on the bypass valves. The Group 2 isolation was complete with no anomalies. This report is being submitted pursuant to 50.72(b)(2) for RPS actuation (4 hour report) and 50.72(b)(3) for a valid Group 2 isolation (8 hour report). The scram was characterized as uncomplicated. The lowest reactor vessel water level reached was - 20 inches. No safeties lifted during the transient and all systems functioned as required. The cause of the reheat stop valve failure to reopen is under investigation. The NRC Resident Inspector has been notified.|
|ENS 43870||28 December 2007 02:24:00||Cooper||NRC Region 4||Manual Scram||GE-4||At 2004, while performing a routine surveillance (Manual Scram Functional Test) the operator performing the surveillance identified that the Plant Management Information System (PMIS) terminals in the control room did not respond as expected to the surveillance. The expected response would have displayed an 'RPS channel trip' message. PMIS is the computer system which implements the Safety Parameter Display System (SPDS) and dose determination. Dose determination was available using manual calculations. This system also supports the ERDS (Emergency Response Data System) and the core monitoring system. Additional investigation found that the PMIS displays had stopped updating at 1950. Attempts to cause the system to fail over to the backup computer (the 'A' computer) thus restoring functionality were unsuccessful. Information Technology (IT) personnel were called and responded to the plant. IT personnel manually restarted the 'A' computer and switched the input/output (I/O) devices to the 'A' computer. Personnel have verified the Technical Support Center and Emergency Offsite Facility systems are also functional. Functionality of the SPDS system and its related systems was verified to be restored at 2330. The backup system ('B') remains out of service and will be addressed tomorrow. This event is reported under 50.72(b)(3)xiii, Any event which results in a major loss of emergency assessment capability. The licensee notified the NRC Resident Inspector.|
|ENS 43375||19 May 2007 05:26:00||Cooper||NRC Region 4||Manual Scram||GE-4|
On the evening of 5/10/2007, Cooper began a scheduled down power to accomplish required preventive and corrective maintenance, including replacement of directional control valves on three control rod drive (CRD) hydraulic control units (HCU). HCU 26-27 was hydraulically isolated for maintenance. The plant was in a single recirculation loop configuration to perform corrective maintenance on 'A' Recirculation Motor Generator. A single reactor feed pump was in operation for corrective maintenance to the 'A' Reactor Feed Pump lube oil system. At approximately 0025 CDT on 5/19/2007 reports from the field indicated that a small water leak had developed from the body to bonnet seal of CRD-V-122 for HCU 26-27. The manual isolation valves for the HCU were already closed to isolate the maintenance area. However, due to seat leakage past one or both of the manual isolation valves, the leakage continued and degraded to the point that a visible plume of steam was issuing from the valve. Further, high airborne activity level developed in the vicinity of the HCU bank in the Reactor Building. As a precaution, the Control Room supervisor (CRS) evacuated the Reactor Building at 0125 CDT. At 0200 CDT, the CRS entered the station reactor scram procedure and performed the preparation steps of transferring electrical loads to the startup transformer. At 0212 CDT, the reactor was manually scrammed. All rods inserted normally. A Group 2 containment isolation signal was received on low reactor water level at 3". During the recovery, the remaining reactor feed pump was manually tripped at 50" in accordance with station procedures due to high RPV level conditions.
'B' RFP was restarted when conditions permitted and is being used to control RPV level. RPV pressure is being controlled by the bypass valves rejecting heat to the main condenser.
This report is being submitted pursuant to 50.72 (2)(iv) for a critical scram and specified system actuation for the Group 2 containment isolation. Currently, the leak into the Reactor Building has stopped. Radiological conditions are being assessed and a repair and recovery plan developed. The Senior Resident Inspector has been informed. The scram was characterized as uncomplicated and all systems functioned as required. No personnel contaminations or off-site releases occurred due to the HCU valve leak.
|ENS 42594||22 May 2006 10:13:00||Cooper||NRC Region 4||Manual Scram||GE-4||CNS was operating at 100% power at 06:51 CDT on May 22, 2006 when Plant Service Air pressure began lowering due to an unknown cause. Additional Service Air Compressors could not be started in time to recover Service Air pressure. A rapid power reduction was performed and at 07:01 the reactor was manually scrammed as a mitigating action due to lowering Plant Service Air pressure. All control rods fully inserted and a Group 2 Isolation occurred due to low Reactor Vessel level as expected following the manual scram. Minimum Reactor level was -20 inches Wide Range. The reactor is currently shutdown and stable with level maintained at 35 inches in the green band on the Narrow Range Indicators with the Feedwater System. Reactor pressure following the scram was stabilized at approximately 900 psig using the Main Condenser Bypass Valves and is slowly lowering. This report is made in accordance with 10CFR50.72 as a 4 Hour Report due to a valid RPS actuation and as an 8 Hour Report due to a valid Group 2 Isolation actuation. All automatic actions functioned as expected. The plant is being maintained in Hot Shutdown while the cause of the Plant Service Air Pressure lowering is being investigated. The NRC Senior Resident inspector has been informed of the event. The scram was characterized as uncomplicated. The licensee is not in any significant tech spec LCO and all systems functioned as required. It was noted that there are 3 service air compressors available and only one of the compressors was running at the time of the event. The licensee does not yet know the cause of the service air pressure loss or why the backup compressors did not autostart. Instrument air pressure was maintained during the event.|
|ENS 42375||26 February 2006 04:32:00||Cooper||NRC Region 4||Manual Scram||GE-4||This report is being made pursuant to 10CFR50.72 (b) (2) (iv) (B) actuation of RPS when the reactor is critical (4 hour report) and 10CFR50.72 (b) (3) (iv) (A) actuation of PCIS group 2 (8 hour report). At 0250 on 2/26/06, Central Standard Time, Cooper Nuclear Station was manually scrammed due to main turbine reheat valve remaining closed following testing concurrent with a high level in the moisture separator. Alarm card procedure for this condition required removing the turbine from service. Subsequent to the scram, reactor vessel level lowered to minus 20 inches wide range indication. This corresponds to approximately 140 inches above the top of the fuel. A primary containment isolation system (PCIS) group 2 isolation occurred as expected due to level transient. All automatic actions occurred as expected. The NRC Senior Resident Inspector has been informed of the event. The reactor scram was uncomplicated, all control rods fully inserted, and no relief or safety valves lifted. The electrical lineup is normal, and the decay heat path is to the main condenser through the turbine bypass valves.|
|ENS 42010||23 September 2005 04:38:00||Cooper||NRC Region 4||Manual Scram||GE-4||At 0040 hours Central Daylight Time, Cooper Nuclear Station was manually scrammed due to degrading main condenser vacuum. Subsequent to the scram, reactor vessel level lowered to minus 20 inches wide range which corresponds to approximately 140 inches above the top of fuel. A Primary Containment Isolation System (PCIS) group 2 isolation occurred as expected due to the level transient. All automatic actions occurred as expected. This report includes both a 4 hour and an 8 hour report. The 4 hour report is being made pursuant to 10CFR50.72(b)(2)(iv)(b), Actuation of RPS when the reactor is critical. The 8 hour report is being made pursuant to 10CFR50.72(b)(3)(iv)(a), Actuation of PCIS group 2 due to expected RPV low level following the scram. The NRC Resident Inspector has been informed of the event. All control rods fully inserted following the scram. All safety-related equipment including Emergency Diesel Generators are operable. Offsite power is stable and available. RPV water level is currently being maintained at approximately 35 inches with feedwater supplied by the condensate pumps. The cause of the degrading main condenser vacuum is unknown and under investigation. The RWCU Heat Exchanger is in service to remove decay heat.|
|ENS 41601||15 April 2005 09:26:00||Cooper||NRC Region 4||Automatic Scram||GE-4||This is both a four hour and eight hour report for the following event: 4 hour Non-Emergency for ECCS Discharge to the RCS and RPS Actuation; 8 hour Non-Emergency for Groups 2 & 6. Also, HPCI (High Pressure Coolant Injection) was placed in pull-to-lock, thereby making HPCI unavailable. At 0436 (hrs.) CDT 04/15/2005, Cooper Nuclear Station experienced a reactor feed water level transient followed by reactor vessel water level low level alarm and an automatic scram. HPCI and RCIC (Reactor Core Isolation Cooling) automatically initiated and injected into the reactor vessel. Groups 2, 3, and 6 actuated on low reactor water level. Both reactor recirculation pumps tripped and RWCU (Reactor Water Clean-Up system) isolated. Reactor vessel water level reached approximately (minus) 70 inches (instrument zero, approximately 90 inches of water remained above the fuel) and recovered after HPCI and RCIC had begun to inject. All post-scram automatic actions were as expected. HPCI was placed in pull-to-lock to prevent over feeding. The plant is being cooled down to establish natural circulation flow and permit recovery of recirculation pumps. Investigation into the cause of the reactor feed water level transient is ongoing. All rods inserted during the scram. No safety relief valves lifted during the transient. All group isolation signals have been reset. The electrical grid is stable. Decay heat is being removed via steam dumps to the main condenser. The licensee has notified the NRC Resident Inspector.|
|ENS 40362||29 November 2003 02:47:00||Cooper||NRC Region 4||Automatic Scram||GE-4||At 2202 CST, a low Reactor Water Level Scram (Level 3) occurred due to lowering feedwater flow. All control rods inserted on the Scram. The Scram resulted in actuation of HPCI and RCIC on low Reactor Water level (Level 2), and the low level ATWS Recirculation Pump Trip (RPT). HPCI and RCIC initiated and both Reactor Recirculation pumps tripped. It is estimated that RCIC injected approximately 500 to 600 gallons, and HPCI injected less than 100 gallons. HPCI was secured early in the transient, and RCIC operated for approximately 2 minutes. Reactor Water level was recovered and maintained with the operating feedwater pump. The Reactor Water low level (Level 3) also resulted in Group 2 (Primary Containment), Group 3 (Reactor Water Cleanup), and Group 6 isolations (Secondary Containment Isolation and Control Room Ventilation system start). All isolations functioned as designed. Initial indications are that Feedwater Pump B speed lowered unexpectedly, causing Reactor Water level to lower. Reactor Water level reached -44 inches (wide range instruments) (120 inches above top of active fuel). The setpoints for HPCI, RCIC, and ATWS-RPT are -33 inches. Plans are to take the unit to Mode 4. The licensee notified the NRC Resident Inspector.|