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ENS 54403 | 21 November 2019 18:25:00 | EN Revision Imported Date : 1/13/2020 UNIT 1 HIGH PRESSURE CORE SPRAY INOPERABLE On 11/21/2019, at 1225 CST, as a result of Division 4 DC bus voltage oscillations, bus voltage lowered to less than the required improved technical specification (ITS) voltage of 127.6 VDC. This resulted in declaring High Pressure Core Spray (HPCS) system inoperable per technical specification LCO 3.8.4 and 3.8.9 actions. Division 4 DC bus voltage was restored to greater than 127.6 VDC at 1227 CST. The HPCS system remains inoperable due to Division 4 DC battery charger inoperability. Since HPCS is an emergency core cooling system and is a single train safety system, this condition is reportable under 10 CFR 50.72(b)(3)(v)(D). The NRC Resident Inspector has been notified. Clinton Power Station has implemented required compensatory actions due to the Division 4 DC battery charger and HPCS remaining inoperable.
The purpose of this notification is to retract a previous report made on 11/21/2019 (EN 54403) under 10 CFR 50.72(b)(3)(v)(D). Subsequent to the initial notification, the event and the NRC guidance in NUREG-1022 pertaining to 10 CFR 50.72(b)(3)(v)(D) were reviewed further. The evaluation determined that the Division 4 DC bus voltage oscillations were caused by a degraded but operable charger. The Division 4 battery remained fully charged during the event and its operability was not impacted. Therefore, the HPCS system remained Operable. Under these circumstances, this event does not represent an inoperability of an accident mitigation system under 10 CFR 50.72(b)(3)(v)(D). Therefore, EN 54403 is retracted. The NRC Resident Inspector has been notified. Notified R3DO (Hanna). | ||
ENS 53824 | 13 January 2019 14:30:00 | En Revision Imported Date 3/8/2019 | EN Revision Text: HIGH PRESSURE CORE SPRAY SELF TEST FAILURE On January 13, 2019, the Self Test System reported a fault associated with the logic system for the High Pressure Core Spray (HPCS) high reactor water level closure function that could prevent the system from performing its safety function. The HPCS system was subsequently declared inoperable with actions taken per LCO (Limiting Condition for Operation) 3.6.1.3 to close and deactivate the 1E12-F004 valve, a primary containment isolation valve. Since HPCS is an emergency core cooling system and is a single train safety system, this condition is reportable under 10 CFR 50.72(b)(3)(v)(D) 'Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.' The NRC Resident Inspector has been notified. HPCS is in a 14-day technical specification LCO action statement.
Testing of the logic system load driver card for the High Pressure Core Spray (HPCS) high reactor water level closure function was completed both on site and at General Electric Hitachi (GEH). This testing determined the cause of the self-test system fault report was limited to the self-test portion of the load driver card and did not impact the ability of HPCS system to perform its specified safety function. Based on the testing results, this event is not reportable under 10 CFR 50.72(b)(3)(v)(D), 'Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.' Therefore, EN 53824 is being retracted. The NRC Resident Inspector has been notified. Notified the R3DO (Hills). | |
ENS 51038 | 4 May 2015 11:15:00 | Loss of Power to the Area Radiation and Process Radiation Local Area Network | At approximately 0615 (CDT) on 5/4/2015, the Area Radiation (AR)/Process Radiation (PR) Local Area Network (LAN) lost power following preparation for a planned Unit Sub 1M outage during the current refueling outage. Preparations for this planned outage included de-energizing the plant process computer data diode uninterruptible power supply that in turn caused a loss of power to the AR/PR LAN. As a result of this power loss, indication was lost in the Main Control Room for the main HVAC and Standby Gas Treatment System effluent radiation monitors without any viable compensatory measure to determine Total Noble Gas Release Rates. The station has determined that this constitutes a major loss of assessment capability per 10 CFR 50.72(b)(3)(xiii). Local radiation monitors continue to function properly. Power to the AR/PR LAN has been restored. Time of restoration was 1159 CDT. There is no impact to current plant operation. The NRC Resident Inspector has been notified.
This event has been reviewed and it was determined that the radioactive release rates displayed on the Safety Parameter Display System screens are obtained directly from the associated radiation monitors (0RIX-PR008 and 0RIX-PR012) and HVAC stack and Standby Gas Treatment System stack flow monitors (0UIX-PR050 and 0UIX-PR051) and are not processed through the AR/PR LAN. As a result, there was no loss of radiation release Emergency Action Level assessment capability with a loss of the AR/PR LAN. Therefore, there was no major loss of emergency assessment capability and this event is not reportable. The NRC Resident Inspector has been notified. Notified R3DO (Lipa) | |
ENS 48269 | 3 September 2012 03:04:00 | Transfer of Emergency Reserve Auxiliary Transformer Isolating Fuel Pool Cooling and Cleanup System, and Fuel Building Ventilation System | At 22:04 CDT on 9/02/2012, the Emergency Reserve Auxiliary Transformer (ERAT) transferred unexpectedly to the Reserve Auxiliary Transformer (RAT). During this transfer, the Fuel Pool Cooling and Cleanup (FC) system pump 'A' tripped and the Fuel Building Ventilation (VF) system isolated. Upper containment pool level dropped below the minimum required level per Technical Specifications (TS) 3.6.2.4 and Secondary Containment differential pressure increased above 0.25 inches vacuum per TS 3.6.4.1. Upper Containment Pool level was restored above the minimum level at 01:27 CDT on 9/3/2012 within the 4 hour completion time. The Upper Containment Pool is a part of the suppression pool makeup system used to ensure the Primary Containment function. Secondary Containment differential pressure was restored at 22:19 on 9/2/2012 when the Standby Gas Treatment System was started. Maintaining secondary containment differential pressure helps to control the release of radioactive material. This event is being reported as a condition that could have prevented the fulfillment of a safety function per 10 CFR 50.72(b)(3)(v)(B) and 10 CFR 50.72(b)(3)(v)(C). The station is currently in a 72-hour action to restore the ERAT to an operable status per TS LCO 3.8.1 Required Action A.2. Plant conditions are stable and actions are underway to repair the ERAT. The NRC Resident (Inspector) has been notified.
Upper Containment Pool level dropped below the normal pool level of 827 feet-3 inches when the Fuel Pool Cooling and Cleanup system pump 'A' tripped, and was initially reported as dropping below the minimum level (825 feet-6 inches) required by Technical Specification (TS) 3.6.2.4. However, subsequent reports from the field confirmed that the lowest level reached was 827 feet 0 inches, which is greater than the minimum required TS level. Therefore, no loss of safety function occurred for the Upper Containment Pool level as a result of this event, and the event is not reportable under 50.72 (b)(3)(v)(B). The NRC Resident (Inspector) has been notified." Notified R3DO (Pelke). | |
ENS 46771 | 20 April 2011 14:15:00 | Watertight Doors Left Ajar Simultaneously During Room Checks | During the performance of operator rounds in the Lake Screenhouse Safe Shutdown System (SX) pump rooms, two water tight doors were left opened simultaneously during the room checks. These two doors opened simultaneously (which) allowed for communication between the Division 1 SX room and Division 2 SX pump room. The operator was in constant attendance in the Division 2 SX pump room during the performance of the equipment checks. During site review, it was determined that a flood in either the Division 1 or Division 2 SX pump rooms would not be isolated to the initiating room, but potentially affect both trains of SX. This could result in a loss of cooling for both Residual Heat Removal systems, therefore, a condition that could have prevented fulfillment of a safety function under 10CFR50.72(b)(3)(v)(B). The NRC Senior Resident has been notified. Offsite power is normal and emergency diesel generators are operable and available. * * * RETRACTION FROM ED TIEDEMANN TO PETE SNYDER ON 6/8/11 AT 1141 EDT * * * A subsequent plant barrier impairment evaluation consistent with Exelon Procedure CC-AA-201, 'Plant Barrier Control Program' has determined that no loss of safety funct ion would have occurred. Each of the following door functions and related postulated events were reviewed for impact: ventilation; flooding, internal and external; high energy line breaks; missiles; radiation protection; and fires. For the condition with the SX pump room water tight doors being open with an operator in the area, the conclusion is an SX division remains protected to ensure that in any of the evaluated events the safety function of SX has been maintained. The licensee has notified the NRC Resident Inspector. | Safe Shutdown |
ENS 43416 | 11 June 2007 01:03:00 | High Pressure Core Spray Declared Inoperable Due to Failed Inverter | At 2003 on 6/10/07, the division 3 Nuclear System Protection System (NSPS) inverter power supply failed for unknown reasons. As a result of this failure, the High Pressure Core Spray (HPCS) system has been declared inoperable. This is a failure of a single train safety system and is reportable under 10 CFR 50.72(b)(3)(v)(D). Troubleshooting has been initiated to determine the cause of this failure. The licensee notified the NRC Resident Inspector.
This event is being retracted. An evaluation was performed and it was determined that no loss of safety function occurred following the failure of the Division 3 NSPS Inverter. The investigation determined that a circuit board failed on the inverter causing a blown fuse. The inverter was found in the reverse transfer position and AC power was automatically transferred to its alternate source, supplying its Division 3 loads. The High Pressure Core Spray system remained fully capable of performing its safety function to start and inject under both LOOP and LOCA conditions. The licensee will notify the NRC Resident Inspector. Notified the R3DO (Lanksbury). | |
ENS 42929 | 24 October 2006 06:42:00 | High Pressure Core Spray (Hpcs) Declared Inoperable for Approx. 3.4 Hours | At 0142 on October 24, 2006, while aligning the High Pressure Core Spray system for surveillance testing of the Reactor Core Isolation Cooling System Storage Tank Level instrumentation, 1E22-F015, the Suppression Pool suction valve for the High Pressure Core Spray pump, failed to stroke fully open. High Pressure Core Spray was declared inoperable as a result. This event is considered a loss of a single train system needed to mitigate the consequences of an accident. The High Pressure Core Spray system was restored to an operable condition at 0506 on October 24, 2006 after the suction valve was successfully stroked open and the HPCS suction source was aligned to the Suppression Pool in accordance with Technical Specification Limiting Condition for Operation 3.5.1. The cause of the event is currently under investigation. All other Emergency Core Cooling systems were fully operable during the time period HPCS was inoperable. The Senior Resident Inspector has been notified by the licensee.
Upon further review of this event, the High Pressure Core Spray (HPCS) system remained operable. Based upon valve motor operator thrust verification testing data and troubleshooting, the cause of the suppression pool suction valve for the HPCS pump stopping in mid-position was determined to be tripping of the open-direction torque switch prior to the open limit switch setpoint. Normally, the condition of the open-direction torque switch has no safety-related consequence since the torque switch is bypassed during design basis events and the valve's motor gearing capability is sufficient to open the valve when the torque switch is bypassed. During this event, as directed by the surveillance test procedure, operators placed the HPCS Motor Operated Valve (MOV) test switch to the test position which resulted in the open-direction torque switch not being bypassed (i.e., was in the circuit) during repositioning of the HPCS suppression pool suction valve. Due to placing the HPCS MOV test switch to test, operators entered the action of Operational Requirements Manual section 2.5.2 (Motor Operated Valves Thermal Overload Protection). The action requires operators to return the MOV test switch to normal (removing the torque switch from the circuit) if an emergency condition occurs requiring valve repositioning. As operators were opening the HPCS suppression pool suction valve for testing, suction for the HPCS pump was aligned from the RCIC storage tank. When the HPCS suction valve from suppression pool stopped in mid-position, the HPCS suction valve from the RCIC storage tank was still fully open (per design, stays full open until the HPCS suppression pool suction valve is full open). Therefore, if an accident occurred requiring HPCS to initiate and inject water into the reactor pressure vessel during this event suction would have initiated from the RCIC storage tank. The HPCS system can take suction from either the RCIC storage tank or the suppression pool, and a HPCS initiation signal does not automatically swap HPCS pump suction from the RCIC storage tank to the suppression pool or vice versa. The operators immediately recognized the HPCS suppression pool suction valve did not fully open. If an accident condition occurred, operators would reposition the HPCS MOV test switch to Normal (to bypass the open torque switch). In the event a condition requiring a HPCS suction transfer to the suppression pool occurred, the suppression pool suction valve would fully open and the RCIC storage tank suction valve would fully close, completing the required suction shift. On this basis, the HPCS system was capable of performing its function to mitigate the consequences of an accident and this issue is not reportable under 10 CFR 50.72(b)(3)(v)(D). The NRC Resident was notified of this retraction. R3DO(Cameron) notified. | |
ENS 40983 | 24 August 2004 14:17:00 | High Pressure Core Spray (Hpcs) Declared Inoperable | At 1128 hours on 8/23/04, the Division 3 Essential Switchgear Heat Removal System (VX) was removed from service and declared inoperable for performance of system flow verification and balance. The test includes an as found flow check on the Division 3 Essential Switchgear Heat Removal System Condensing Unit, rendering the Division 3 VX safety-related chiller 1VX06CC INOPERABLE. The non-safety VX subsystem remained OPERABLE during the test. At 0917 hours on 8/24/04, the non-safety Division 3 VX Heat Removal Supply Fan 1VX04CC, tripped due to the breaker for the safety-related fan being removed for replacement. The Main Control Room received alarm 5042-6A, Auto Trip Pump/Fan. Since both the safety and non-safety subsystems of VX were unavailable Operators declared the High Pressure Core Spray (HPCS) System inoperable per Technical Specification 3.7.2, Action A.1. At 1153 hours, the breaker replacement was complete, 1VX04CC was restored to service, and the HPCS System was declared OPERABLE. The VX System maintains safety-related switchgear, battery and inverter room, and cable spread areas within the design temperature limits of the equipment. The VX system is support system for the HPCS System. With both subsystems of the VX System out of service, the HPCS System may not have been capable of performing its safety function to provide Emergency Core Cooling, aid in depressurization and maintain reactor vessel water level following a loss of coolant accident. An engineering evaluation is currently in progress to determine if the HPCS System would have been capable of performing its safety function with both safety and non-safety subsystems of VX out of service. This issue is being reported in accordance with 10CFR50.72(b)(3)(v)(D), as an event or condition that at the time of discovery could have prevented the fulfillment of the safety function needed to mitigate the consequences of an accident. The NRC Resident Inspector was notified of this event by the licensee.
Upon further review of this event, additional analysis has been performed which bounds the design bases heatup of the associated rooms cooled by the Division III Essential Switchgear Heat Removal System (VX). This analysis concludes that the areas cooled by the Division 3 VX subsystem would not have exceeded design temperatures while the cooling was secured, prior to cooling recovery, and that the supported systems remained operable. Based upon this additional analysis, it can be reasonably concluded that the safety function of High Pressure Core Spray, as a single train safety system, was fulfilled. Therefore this event is not reportable and Event #40983 is being retracted. The NRC Resident Inspector was notified of this retraction by the licensee. R3DO (Clayton) has been notified. | Time of Discovery Reactor Vessel Water Level |