Semantic search
| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 56866 | 20 November 2023 15:56:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | HPCI Declared Inoperable | The following information was provided by the licensee via email: At 0956 (CST) on November 20, 2023, accumulated gas was identified in the Dresden Unit 2 high pressure coolant injection (HPCI) system discharge header. As a result, the HPCI system was declared inoperable. Since HPCI is a single-train system, this is a condition that could have prevented the fulfillment of a safety function; therefore, this condition is being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(v)(D). The HPCI system was subsequently vented, and the accumulated gas has been removed, restoring the Dresden Unit 2 HPCI system to an operable status. All other emergency core cooling systems remained operable during this time period. There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: The licensee administratively verified the isolation condenser was operable after declaring HPCI inoperable as required by technical specifications. The licensee stated there was no increase in plant risk. The cause of gas accumulating in the Dresden Unit 2 HPCI discharge header is under investigation, and this issue has been entered into the licensee's corrective action program. | High Pressure Coolant Injection Emergency Core Cooling System | |
| ENS 53204 | 12 February 2018 18:00:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | En Revision Imported Date 10/14/2019 | EN Revision Text: UNANALYZED CONDITION FOR TORNADO GENERATED MISSILES On February 12, 2018, during evaluation of protection for Technical Specifications (TS) equipment from the damaging effects of tornado generated missiles, Dresden Station identified a non-conforming condition in the plant design such that specific TS equipment is considered to not be adequately protected from tornado generated missiles. Tornado generated missiles could strike the Unit 2, Unit 2/3, and Unit 3 Emergency Diesel Generator main fuel oil tank vents. This could result in crimping of the vents, which would affect the ability of the main fuel oil tanks to perform their function if a tornado would occur. This condition is reportable in accordance with 10 CFR 50.72(b)(3)(ii)(B) as a condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety and 10 CFR 50.72(b)(3)(v)(D) as a condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. This condition is being addressed in accordance with NRC enforcement guidance provided in Enforcement Guidance Memorandum (EGM) 15-002, 'Enforcement Discretion for Tornado-Generated Missile Protection Noncompliance,' and DSS-ISG-2016-01, 'Clarification of Licensee Actions in Receipt of Enforcement Discretion' per Enforcement Guidance Memorandum EGM 15-002, 'Enforcement Discretion for Tornado-Generated Missile Protection Noncompliance,' Revision 1. Compensatory measures have been implemented in accordance with these documents. The NRC Resident Inspector has been informed of this notification.
The purpose of this notification is to retract event notification 53204 made on February 12, 2018, for Dresden Station. Additional review determined that the current design of all three Emergency Diesel Generators and associated Main Fuel Oil Storage Tanks Vents is consistent with the licensing basis for Dresden Station. There was no non-conformance of Dresden's tornado missile protection design, and the EDGs were operable at the time the event notification was made. Therefore, this event does not meet the criteria of 10 CFR 50.72(b)(3)(ii)(B) and 10 CFR 50.72(b)(3)(v)(D). The ENS 53204 report is being retracted. The NRC Resident Inspector has been informed of this notification." Notified R3DO (Hills). | Emergency Diesel Generator | |
| ENS 52964 | 12 September 2017 16:31:00 | 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Standby Liquid Control System Piping Failure | On September 12, 2017 at 1131 CDT, both Unit 3 Standby Liquid Control system (SLC) subsystems were declared inoperable for a through wall leak on the common discharge piping. With both subsystems inoperable, the SLC system was unable to fulfill its safety function. This event is reportable under 10 CFR 50.72(b)(3)(v)(A) for an event or condition that could have prevented the fulfillment of a safety function of a system that is needed to shut down the reactor and maintain it in a safe shutdown condition and under 10 CFR 50.72(b)(3)(v)(D) for a system that was unavailable for accident mitigation. The NRC Resident Inspector has been notified. With both trains of SLC inoperable, the licensee entered an 8-hr. action statement to restore at least one train to operability. If unable to do so, then the plant will enter a 12-hr. shutdown action statement. | Standby Liquid Control | |
| ENS 52253 | 19 September 2016 20:50:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Control Room Emergency Ventilation Charcoal Not Meeting Acceptance Criteria | At 1550 (CDT) on September 19, 2016, Dresden received the Methyl Iodide Penetration test results for the Control Room Emergency Ventilation (CREVS) charcoal. The test results did not meet technical specification acceptance criteria. This results in the inoperability of CREVS. CREVS is a single train system and therefore is reportable per 10CFR50.72(b)(3)(v)(D). The Air Filtration Unit (AFU) is required to operate during a design basis accident to maintain Main Control Room habitability. This places unit 2 and unit 3 in a 7 day LCORA (Limiting Condition of Operation Required Action) per Tech Spec 3.7.4 Required Action A.1. The licensee notified the NRC Resident Inspector.
The licensee is retracting this report based on the following: The purpose of this notification is to retract ENS notification 52253 made on September 19th, 2016, for Dresden Nuclear Power Station. After further evaluation and testing, it has been determined that the Control Room Emergency Ventilation System (CREVS) charcoal would have fulfilled its safety function given the Methyl Iodide Penetration test results. The initial tests were performed with a 2 inch bed depth due to a difference in batches used in each charcoal filter, but testing at a 4 inch bed depth is the correct testing methodology for Dresden's configuration. At a 4 inch bed depth, the test results met the Technical Specification acceptance criteria with significant margin. Therefore, this event does not meet the criteria of 10 CFR 50.72(b)(3)(v)(D) and the ENS report is being retracted. The NRC Resident Inspector has been notified. Notified R3DO (Orlikowski). | Control Room Emergency Ventilation | |
| ENS 52046 | 27 June 2016 15:50:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Dresden Unit 3 Declares Alert | At 1050 CDT, (on 6/27/16), an Alert was declared at Dresden Unit 3. The Alert is due to Unit 3 experiencing a fire in the HPCI (High Pressure Coolant Injection) system, auxiliary oil pump motor. The fire is out. This notification is being made per 10 CFR 50.72(a)(1)(i). Dresden Unit 3 is stable and continues to operate at 100% power and HPCI has been declared inoperable. There is no impact on Dresden Unit 2. The licensee has notified the NRC Resident Inspector Notified DHS SWO, FEMA, USDA, HHS, DOE, DHS NICC, EPA, and FEMA National Watch Center, FDA EOC, NuclearSSA via email only.
Termination of MA-5 (Alert). Fire in HPCI room verified extinguished. HPCI system is inoperable. (Technical Specification) TS 3.5.1 condition G in effect, per 10 CFR 50.72(c)(i) - notification of termination of Alert. Dresden Unit 3 terminated the Alert at 1319 CDT, on 6/27/16. Dresden Unit 3 continues to operate at 100% power. The licensee will notify the NRC Resident Inspector. Notified R3DO (Kunowski), NRR (Miller), IRD (Grant), DHS SWO, FEMA, USDA, HHS, DOE, DHS NICC, EPA, and FEMA National Watch Center, FDA EOC, NuclearSSA via email only.
At 1042 (CDT) on 6/27/16, the U3 High Pressure Coolant Injection (HPCI) system was declared inoperable after the Auxiliary Oil Pump failed. This event is reportable per 10CFR50.72(b)(3)(v)(D); any event or condition that at the time of discovery could have prevented fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. This is an eight hour reporting requirement. The Dresden NRC Resident (Inspector) has been notified. Notified R3DO (Kunowski). | High Pressure Coolant Injection | |
| ENS 51934 | 16 May 2016 19:57:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Accident Mitigation - Hpci Declared Inoperable | At 1457 (CDT) on 5-16-16, U-2 (Unit 2) High Pressure Coolant Injection (HPCI) system was declared inoperable after isolation of the system due to a steam leak on the HPCI steam inlet drain pot drain line. The event is reportable per 10CFR50.72(b)(3)(v)(D), Any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences an accident. This is an eight hour report requirement. The Dresden NRC Resident Inspector has been notified. | High Pressure Coolant Injection | |
| ENS 51421 | 24 September 2015 02:00:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | High Pressure Coolant Injection Inoperable Due to Mgu Failure | During surveillance testing of the U2 HPCI (High Pressure Coolant Injection) system, the HPCI motor gear unit (MGU) was positioned from 100 percent to 75 percent demand to satisfy operability testing. The motor gear unit did not respond as system demand was returned to 100 percent. This indicated a failure of the MGU which requires declaration of inoperability of the HPCI System. This is a 14 day LCO. HPCI is a single train system and reportable under SAF 1.8 'Event or condition that could have prevented fulfillment of a safety function.' The licensee will be notifying the NRC Resident Inspector. | High Pressure Coolant Injection | |
| ENS 49591 | 30 November 2013 21:53:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | High Pressure Coolant Injection System Surveillance Test Failure | At 1553 CST on November 30, 2013, during the performance of the High Pressure Coolant Injection (HPCI) fast initiation test, HPCI did not produce the required flow rate as specified by Technical Specification Surveillance Requirement 3.5.1.6. The HPCI subsystem is designed to ensure adequate core cooling when operated with other available Emergency Core Cooling Systems (ECCS), and during this event, all other ECCS systems remained operable. The cause of this event is currently under investigation. This event is being reported in accordance with 10 CFR 50.72(b)(3)(v)(D) as a condition that could have prevented the fulfillment of the safety function of structures or systems needed to mitigate the consequences of an accident. The NRC Resident Inspector has been notified. The flow rate achieved during the test was 3000 gpm and the required minimum flow rate is 5000 gpm. | High Pressure Coolant Injection Emergency Core Cooling System | |
| ENS 48845 | 20 November 2012 00:00:00 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Control Rod Drive Check Valve in Service Leak Test Failure | Control Rod Drive (CRD) Check valves 3-0399-593 and 3-0399-594 are installed on the CRD supply header inside the reactor building to prevent unfiltered radiological release from primary containment past secondary containment through the CRD supply header. The (Design Basis Accident) DBA (Loss of Coolant Accident) LOCA dose analysis does not postulate the CRD supply piping as a release path. These valves were added in response to NRC IN 90-78. Their function is described in the Dresden UFSAR section 4.6.4.6. CRD check valves 3-0399-593 and 3-0399-594 failed their as found In Service Testing (IST) seat leakage test during refuel outage D3R22. Based on the condition of as-found failed seat leakage tests, Engineering determined that CRD check valves 3-0399-593 and 3-0399-594 would not have been able to perform their design functions as described in the UFSAR to maintain the offsite dose and control room dose within regulatory limits. The valves were repaired in D3R22 and successfully retested. The licensee notified the NRC Resident Inspector.
Based on an evaluation of the current plant design and the overly conservative assumptions made in the 1996 dose estimate, the dose that would be experienced as a result of a DBA LOCA with LOOP (Loss of Offsite Power) due to back leakage through the control rod drive system to the condensate storage tanks (CST) has been reassessed. The initial estimations of dose did not consider the as-built piping configuration of the CRD system. The backflow would be greatly reduced due to the lower differential pressure between the Drywell and CSTs that would exist following a DBA-LOOP. This differential pressure experienced following a DBA-LOOP would not result in a significant backflow due to excess flow check valves and restricting orifices in the current CRD piping configuration. Additionally, in the event that any backflow did occur, the volume of water in the CST would provide a high decontamination factor and dilution. Therefore backflows that could be experienced following a DBA-LOOP would not produce doses that would exceed current limits. Based on this assessment, the unanalyzed condition that was reported on March 22 (EN 48845) is being retracted. The Licensee has notified the NRC Resident Inspector. Notified R3DO (Kozak). | Secondary containment Primary containment Control Rod | |
| ENS 48009 | 10 June 2012 08:00:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Hpci Declared Inoperable Due to Leakage | On Sunday June 10, 2012 at 0112 (Central Time), a through-wall leak was discovered on a piping elbow upstream of the High Pressure Coolant Injection (HPCI) Inlet Drain Pot Inboard Drain valve to the Main Condenser, AOV 3-2301-29. This piping elbow is safety-related, ASME Code Class 2 piping. Dresden Technical Requirements Manual 3.4.a, Condition B requires the leak to be isolated which renders the HPCI system inoperable. The Unit 3 HPCI system was isolated and declared inoperable at 0300 (Central Time), and Technical Specification 3.5.1 Condition G has been entered. The HPCI system is a single train system. The event is being reported pursuant to 10 CFR 50.72(b)(3)(v)(D), any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. The licensee notified the NRC Resident Inspector. | High Pressure Coolant Injection Main Condenser | |
| ENS 47947 | 22 May 2012 15:55:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Hpci Declared Inoperable | At 1055 hours (CDT) on 5/22/2012, a through-wall leak was discovered on the Unit 2 High Pressure Coolant Injection (HPCI) inlet drain pot piping. This is a safety-related, ASME Code Class 2 piping. Dresden Technical Requirements Manual 3.4.a, Condition B requires the leak to be isolated which renders the HPCI system inoperable. The Unit 2 HPCI system was isolated and declared inoperable at 1141 CDT and Technical Specification 3.5.1 condition G was entered. The event is reportable pursuant to 10 CFR 50.72(b)(3)(v)(D), Any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. The licensee notified the NRC Resident Inspector. | High Pressure Coolant Injection | |
| ENS 47370 | 24 October 2011 15:35:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Accident Mitigation Systems Out of Service Due to Maintenance Error | On 10/24/11 at 1035 CDT, a maintenance technician performing a field walk-down of a clearance order inadvertently opened the bus potential fuse drawer for Unit 2 Safety Related Bus 23. This caused all loads of Bus 23 to receive an undervoltage (UV) load shed signal. Division I Containment Cooling Service Water (CCSW) pumps are powered from Bus 23 and are currently aligned to the Main Control Room Emergency Ventilation (CREV) Air Conditioning system. On a loss of CCSW, the CREV Air Conditioning system is inoperable due to a loss of its emergency cooling water supply. This condition affects both Dresden Units 2 and 3. This condition lasted for approximately 7 seconds before the bus potential fuse drawer was reinserted and the Bus 23 UV condition cleared. This event is reportable under 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 of structures or systems that are needed to mitigate the consequences of an accident. The licensee notified the NRC Resident Inspector. | Service water Control Room Emergency Ventilation | |
| ENS 47151 | 12 August 2011 19:29:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | High Pressure Coolant Injection System Inoperable Due to Valve Body Leak | On Friday August 12, 2011 at 1429 CDT, a through-wall leak was discovered on the body of the High Pressure Coolant Injection (HPCI) Inlet Drain Pot Inboard Drain valve to the Main Condenser, AOV 2-2301-29. This is a safety-related, ASME Code Class 2 valve. Dresden Technical Requirements Manual 3.4.a, Condition B requires the leak to be isolated which renders the HPCI System Inoperable. The Unit 2 HPCI system was isolated and declared inoperable at 1646 CDT, and Technical Specification 3.5.1 Condition G has been entered. The HPCI system is a single train system. The event is being reported pursuant to 10 CFR 50.72(b)(3)(v)(D), 'any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.' T.S. 3.5.1 condition G is a 14 day LCO and the utility can make the repair at power. The unit is in a normal electrical lineup with offsite power available and all EDG's are operable. There was a slight increase in plant risk to "yellow" as a result of this issue. The NRC Resident Inspector has been notified. | High Pressure Coolant Injection Main Condenser | |
| ENS 46440 | 26 November 2010 23:34:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | High Pressure Coolant Injection Declared Inoperable Due to a Steam Leak | While performing the High Pressure Coolant Injection (HPCI) high pressure run required by SR 3.5.1.6 following Unit 3 refueling outage D3R21, a steam leak developed from the HPCI turbine. The steam leak resulted in a HPCI room high temperature alarm and the HPCI turbine was manually tripped. The U3 HPCI system was declared inoperable and Tech Spec LCO 3.5.1 condition G.1 and G.2 were entered. The condition is being reported in accordance with 10 CFR 50.72 (b)(3)(v)(D) as a condition that at the time of discovery could have prevented the fulfillment of the safety function of a system that is needed to mitigate the consequences of an accident. Maintenance activities are currently in progress to restore system to operable status. The failure resulted in the licensee entering a 14-day LCO action statement for restoration. The licensee has notified the NRC Resident Inspector. | High Pressure Coolant Injection | |
| ENS 46253 | 15 September 2010 08:13:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Hpci Declared Inoperable During Surveillance Testing | In preparation for quarterly valve testing, the High Pressure Coolant Injection system was declared inoperable and the technical specification required actions were implemented. The system was available for on-line risk. During the testing, the inboard steam isolation valve was stroked closed and reopened and operated properly. The valve was reclosed to continue with valve testing. When an attempt was made to reopen the inboard isolation valve, the valve failed to indicate full open. The system remained inoperable due to the valve malfunction. Therefore, the condition is being reported in accordance with 10 CFR 50.72 (b)(3)(v)(D) as a condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. Maintenance activities are currently in progress to restore the system to the operable status. The licensee entered a 14-day Limiting Condition of Operation per Technical Specification 3.5.1. The licensee notified the NRC Resident Inspector.
On September 15, 2010, the NRC Operation Center was notified of Event Number 46253 that described a failure of the High Pressure Coolant Injection (HPCI) system inboard steam isolation valve to fully reopen using the Main Control Room (MCR) control switch. At the time, it was not readily apparent that the system was capable of performing its intended safety function. Therefore, the condition was reported in accordance with 10 CFR 50.72 (b)(3)(v)(D) as a condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. Troubleshooting identified that a contact in the control switch circuit had malfunctioned. This contact is bypassed during an initiation signal. Therefore the valve would have opened fully in the event the HPCI system received an initiation signal. In light of these findings, the HPCI function was not impaired as a result of the contact malfunction and would have been capable of performing its safety function. Therefore, the notification associated with Event Number 46253 is being retracted. The NRC Resident Inspector has been notified. R3DO (Dave Passehl) has been notified. | High Pressure Coolant Injection | |
| ENS 45844 | 15 April 2010 16:19:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | High Pressure Coolant Injection Declared Inoperable Due to Voiding in Discharge Piping | The Unit 2 HPCI (High Pressure Coolant Injection) system was declared inoperable due to failure to meet acceptance criteria for air voiding in the discharge piping. UT (Ultrasonic Testing) inspection identified an air void of approximately 0.515 cubic ft. HPCI remains available and on-line risk remains green. The HPCI discharge piping has been vented. Preliminary post venting UT inspections indicate current void volume is less than acceptance criteria. Certified UT inspectors have been dispatched to validate preliminary UT results. The event is being reported under 10CFR50.72(b)(3)(v)(D). The NRC Senior Resident Inspector has been informed of the event. The acceptance criteria for voids is less than or equal to 0.052 cubic ft.
Following the void identification, an engineering evaluation was initiated to determine the impact of the non-condensable gas pocket identified in the HPCI piping. The evaluation was completed and the following results were obtained. The pocket of non-condensable gas in the HPCI discharge piping did not adversely affect the ability of the system to maintain peak cladding temperatures below required limits. The pressure that would have been experienced during an initiation of the system was determined to be within the design pressure of the system. Additionally, the potential force imbalances that would be experienced during a system initiation were determined to be within the piping design allowables. Based on the engineering evaluation, the pocket of non-condensable gas did not have a detrimental effect on HPCI system operation. The ability of the HPCI system to perform its intended safety function was maintained throughout this condition. Therefore, the above notification is being retracted. The NRC Resident Inspector has been notified. Notified R3DO(Pelke) | High Pressure Coolant Injection | |
| ENS 45525 | 28 November 2009 04:05:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Turbine Valve Trips Did Not Meet Tech Specs | At 2205 on Nov 27, 2009, at the Dresden Nuclear Power Station (DNPS) it was determined that Technical Specification RPS functions 8 and 9, 'Turbine Stop Valve - Closure' and 'Turbine Control Valve Fast Closure, Trip Oil Pressure - Low' are susceptible to single point vulnerability due to a nonconformance to a design standard (IEEE- 279 1968). Based on this single point vulnerability, these RPS functions could potentially have prevented the fulfillment of their respective safety function and therefore this event is reportable per 10 CFR 50.72(b)(3)(v)(D), 'an event or condition that could have prevented the fulfillment of a safety function-mitigate the consequences of an accident.' The station has performed an operability determination, and the safety function remains operable. Actions to restore compliance to referenced design standard are in progress. The licensee has informed the NRC Resident Inspector. | ||
| ENS 44168 | 25 April 2008 16:30:00 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Non-Conservative Core Spray Flow in Dresden Nuclear Power Station Loca Analysis | Exelon Generation Company, LLC (EGC) has been informed of a change in the vendor calculation of Peak Cladding Temperature (PCT) for Dresden Nuclear Power Station (DNPS) Unit 2. On April 24, 2008, Westinghouse initially notified EGC of a potential non-conservatism with respect to the assumed core spray (CS) flow in the Westinghouse 10 CFR 50, Appendix K LOCA analysis for DNPS Unit 2. Based on further discussions with Westinghouse, EGC confirmed the error on April 25, 2008, at 1130. In selecting the limiting plant configuration for the DNPS Appendix K LOCA model, Westinghouse used the net flow at the CS sparger, instead of the runout flow minus leakage outside the shroud. As a result, Westinghouse used an incorrect input for CS flow for the ECCS LOCA analysis. Westinghouse has evaluated the impact of correcting the assumed CS flow on the DNPS Unit 2 limiting large break LOCA analysis. Preliminary results indicate an increase of 80 degrees F in the PCT value. This results in a final PCT value of 2230 degrees F, which is in excess of 10 CFR 50.46 (b)(1) limits. However, preliminary calculation results also indicate that a 3 percent reduction in the MAPLGHR limit would offset the 80 degree F increase in the limiting PCT. Dresden Unit 2 has been operating with more than 3 percent margin in MAPLHGR since November 2007 (i.e., the start of the current operating cycle - D2C21). Administrative limits wilt be established to maintain these margins. The LOCA analysis of record for DNPS Unit 3 utilizes the correct CS shroud leakage and CS flow delivered to the vessel through the CS sparger. Therefore, this non-conservatism does not affect DNPS Unit 3. Currently, there is sufficient operating margin for DNPS Unit 2 to ensure the PCT limit would not be exceeded. There are no other 10 CFR 50.46 ECCS criteria for DNPS Unit 2 that are impacted. This notification is being made as a result of the 10 CFR 50.45 (a)(3)(ii) requirement to report this issue in accordance with 10 CFR 50.72 (i.e., 10 CFR 50.72(b)(3)(ii)(B)). The licensee notified the NRC Resident Inspector. | Core Spray | |
| ENS 44140 | 15 April 2008 12:00:00 | 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | High Pressure Coolant Injection Declared Inoperable | Unit 2 HPCI (High Pressure Coolant Injection) System was declared inoperable due to discovery of a failed flow controller. The controller failure would prevent HPCI from achieving rated flow (safety function). Investigation into cause of failure and preparation for controller replacement are in progress. This event is being reported under 10CFR50.72(b)(3)(v)(B & D). The licensee notified the NRC Resident Inspector. The licensee indicated the Isolation Condenser is operable. A 14 day LCO is in effect. | High Pressure Coolant Injection | |
| ENS 43526 | 26 July 2007 22:06:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Accident Mitigation Report - Unit 2 Hpci Isolated Due to Small Bore Steam Leak | At 1706 hours on 07/26/07, a through wall leak was identified on the U2 High Pressure Coolant Injection (HPCI) Inlet Drain Pot drain piping. This piping is ASME Code class 2 piping and as required by the Technical Requirements Manual the piping was isolated which resulted in isolation of the U2 HPCI System. U2 HPCI was declared inoperable. This event is reportable under 10CFR50.72(b)(3)(v)(D). Piping repair preparations are in progress. During the performance of operator rounds, the licensee noticed a puddle of fluid on the deck and wet lagging overhead. Upon removal of the lagging, the licensee noticed a small steam leak in a 1" small bore line. The licensee is currently in a 14 day LCO under technical specification 3.5.1 F(1) and F(2). The licensee is currently developing a work package to repair or replace the line. The licensee notified the NRC Resident Inspector. | High Pressure Coolant Injection | |
| ENS 43209 | 3 March 2007 01:12:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Unit 3 Hpci Inoperable Due to Pinhole Leak on the Steam Side | At 1912 hours on 03/02/07, a through wall leak was identified on the U3 High Pressure Coolant Injection (HPCI) Inlet Drain Pot drain piping. This piping is ASME Code class 2 piping and as required by the Technical Requirements Manual the piping was isolated which resulted in isolation of the U3 HPCI System. U3 HPCI was declared inoperable. This event is reportable under 10CFR50.72(b)(3)(v)(D). Piping repair preparations are in progress. The leak was discovered by a licensed operator on rounds. The Technical Specification is a 14 day LCO. The licensee notified the NRC Resident Inspector. | High Pressure Coolant Injection | |
| ENS 42976 | 9 November 2006 04:54:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Failure of Control Room Hvac to Maintain Control Room Temperature | At 22:54 hours on November 8, 2006, the B Control Room HVAC Refrigeration and Condensing Unit (RCU) failed to maintain proper Control Room temperature and cycling excessively. The RCU is a single train system and therefore is reportable per 10CFR50.72(b)(3)(v)(D). The RCU is required to operate during a design basis accident to maintain Main Control Room habitability/temperature. The Air Filtration Unit (AFU) of CREVS remains operable. This places unit 2 in a 30 day LCORA per Tech Spec 3.7.5 Required Action A.1. The licensee notified the NRC Resident Inspector. | HVAC | |
| ENS 42481 | 6 April 2006 15:39:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | High Pressure Coolant Injection System Declared Inoperable | At 10:39 AM on 4/6/06, Unit 2 HPCI was declared inoperable due to circuit breaker 16 failure on the ESS bus. Circuit breaker 16 opened as a result of temporarily shorting the power supply lead while installing a new HPCI temperature recorder. Trouble shooting is in progress as a result of the failure and restoration will follow. Since circuit breaker 16 provides ESS power to HPCI flow controller, HPCI was declared inoperable. This event is reportable under 1OCFR 5.72(b)(3)(v)(D). The licensee notified the NRC Resident Inspector. | High Pressure Coolant Injection | |
| ENS 42300 | 2 February 2006 01:43:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Inoperable Isolation Condenser | While performing DIS 1300-02, Unit 2 ISO COND Steam/Condensate Line High Flow Calibration, workers attempted to valve in DPIS 2-1349-8, U2 Isolation Condenser Return Line Hi Flow. While opening the low isolation valve the technician noticed a vibration in the sensing line. He proceeded to close the equalizer and open the high isolation. As he opened the high side isolation the DPIS indication started to ramp high. As the indication ramped above about 9 inches the technician closed the high side isolation valve. The Isolation Condenser has been isolated to comply with Technical Specification entered TS 3.3.6.1 C.1 and F.1, Primary Containment Isolation Instrumentation and TS 3.5.3. A.1 & A.2, Isolation Condenser. A prompt investigation has been initiated to determine the cause. A troubleshooting plan is being developed. Per Tech Spec Bases Section 3.5.3, Applicable Safety Analysis, credit is taken for the Isolation Condenser in the loss of Feedwater Transient Analysis. Therefore the event is reportable under 10CFR 50.72.(b)(3)(v)(D). The licensee notified the NRC Resident Inspector. | Feedwater Primary containment | |
| ENS 41791 | 23 June 2005 20:49:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Offsite Power Source Declared Inoperable Due to Low Voltage | At 15:49 hours Central Daylight Savings Time, June 23, 2005, entered DOA 6500-12, Low Switchyard Voltage. Bulk Power Operations reported predicted post Unit trip with LOCA switchyard voltage for Unit 2 is 342.5 KV and for Unit 3 is 342.3 KV. This rendered both Unit 2 and Unit 3 offsite electrical power sources inoperable. This predicted voltage is the value required to support Loss Of Coolant Accident (LOCA) loading. Entered applicable Technical Specification required actions for both Units due to both offsite power sources being declared inoperable for Unit 2 and Unit 3. As of 1744 hours, restored Unit 2 offsite electrical power source to operable status by performing Transformer 86 Tap Changer adjustment per applicable procedure. TR 86 (transformer 86) supplies Unit 2 offsite electrical power. As of 1948 hours, switchyard voltage was restored to operable limits. This restored Unit 3 offsite electrical power source to operable status. This notification is provided in accordance with 10CFR50.72(b)(3)(v)(D) to report a condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. The licensee will notify the NRC Resident Inspector and the state.
The purpose of this report is to retract ENS report 41791 (June 23, 2005) for Dresden Nuclear Power Station (DNPS). The report was made following notification from Bulk Power Operations that the predicted post Unit trip with LOCA switchyard voltage rendered both Unit 2 and Unit 3 offsite electrical power sources inoperable. Both offsite electrical power sources were declared inoperable, the appropriate Technical Specification required actions were taken and an ENS notification was made in accordance with 10CFR 50.72(b) (3)(v)(D) for an event that could have prevented fulfillment of a safety function. In July 2006, DNPS performed a reanalysis of the June 23, 2005 event. The reanalysis determined that the computer model used to determine the required switchyard voltage for the June 23, 2005 event conservatively assumed that the Reserve Auxiliary Transformers (RATs) were supplying all plant 4 kilovolt (Kv) electrical loads and the second source of offsite power for each unit was based on a post unit trip. During normal plant operation the 4kV electrical loads are split between the RATs and the Unit Auxiliary Transformers (UATs). The reanalysis used the split bus configuration and the actual switchyard voltages at the time of the June 23, 2005 event. The reanalysis concluded that the voltages were greater than required, ensuring that the second source of offsite power for each unit would remain operable following a postulated design basis accident. Therefore, there was no condition present on June 23, 2005, that could have prevented fulfillment of a safety function and this event is not reportable under 10CFR 50.72(b)(3)(v)(D). The licensee notified the NRC Resident Inspector. Notified R3 DO (R. Lanksbury) | ||
| ENS 41370 | 4 February 2005 01:15:00 | 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | 4160 Volt Relaying and Metering Single Failure Vulnerability | The licensee provided the following report via facsimile: On February 3, 2005 at 1915 hours, DNPS confirmed a vulnerability with a 4160 VAC relaying and metering current transformer (CT) associated with the Unit and Reserve Auxiliary Transformers (i.e., the UAT and RAT) on both Units. Although the CT is currently fully operable, failure of the CT circuitry will cause the neutral overcurrent relay to trip (and lockout) the main, reserve and tie feed breakers. These combined protective relay trips will act to trip and lock out the circuit breakers supplying feeds to buses 23 (33) and 24 (34), essentially isolating them from their normal and emergency power sources. Emergency power (i.e., the emergency diesel generator) would still be available to safety related buses 23-1 (33-1) and 24-1 (34-1), but the Containment Cooling Service Water (CCSW) system would remain without a power source. If this failure occurred during a LOCA, then the CCSW pumps may not be able to be started within ten minutes. A modification is in progress to eliminate this vulnerability. This event is being reported as a potential loss of safety function (10CFR50.72(b)(3)(v)(B)) and a degraded or unanalyzed condition (10CFR50.72(b)(3)(ii)(B)). The NRC Resident Inspector has been notified. See similar events #41362 (Crystal River), #41366 (LaSalle), and #41369 (Quad Cities). | Service water Emergency Diesel Generator | |
| ENS 40712 | 28 April 2004 17:09:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Control Room Hvac Inoperable | During routine alignment of the Control Room HVAC system it was determined the 2/3-5741-053B damper failed to close as required. The damper is required to close to isolate outside air to the control room for accident conditions. Because of the damper failure the Control Room Emergency Ventilation System (CREVS) was declared inoperable at 1209 on 4/28/04. The CREVS is a single train system utilized to mitigate the consequences of an accident and this event is reportable under 10 CFR 50.72(b)(3)(v)(D). (Exelon Reportability Manual Section - SAF 1.8) The licensee notified the NRC Resident Inspector. | HVAC Control Room Emergency Ventilation | |
| ENS 40671 | 12 April 2004 23:10:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | High Pressure Coolant Injection System (Hpci) Declared Inoperable | High Pressure Coolant Injection System Incapable of Performing its intended Safety Function. This report is being made in accordance with 10 CFR 50.72(b)(3)(v) due the High Pressure Coolant Injection System being incapable of performing its intended safety function. At 1810 hours (CDT) during performance of the functional test of the level instrumentation for the automatic realignment of the High Pressure Coolant Injection system (HPCI) suction sources, plant maintenance person identified that logic circuitry leads had been lifted. The leads not being connected would prevent the automatic realignment of the HPCI suction from its non-safety related source, the Condensate Storage Tank (CST), to its safety related source, the Suppression Pool. Based on preliminary information, the leads were lifted during scheduled maintenance activities on the HPCI system in March. The applicable Technical Specification specified that HPCI be declared inoperable within an hour. Actions were immediately taken to restore the automatic function. The leads were re-landed and the TS condition exited at 1853 hours. The inability of the system to automatically realign due to a CST low level or a Suppression Pool high level is considered to be a condition that would prevent the fulfillment of the safety function of the HPCI system. The licensee is still investigating the cause. The NRC Resident Inspector was notified. | High Pressure Coolant Injection | |
| ENS 40494 | 1 February 2004 10:00:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | High Pressure Coolent Injection Declared Inoperable But Remains Available. | During the Unit 3 scram on 01/30/04 the response of the feedwater level control system caused the RPV (Reactor Pressure Vessel) level to increase higher than expected. RPV level rose above the HPCI steam line. Calculations showed approximately 60 gallons of water entered the steam line. This response could adversely affect the HPCI system should the same type of event occur and FWLC (Feedwater Level Control) respond the same way on Unit 2. Based on this information and no reasonable assurance that the same response will not occur, the Unit 2 HPCI system is conservatively being declared inoperable. HPCI remains available. Entering Tech Spec 3.5.1 Required Action F.1 (Isolation Condenser is OPERABLE) and F.2 (Restore HPCI to Operable status within 14 days). A modification is being prepared to change the response of FWLC to preclude this adverse response during a transient. The NRC Resident Inspector will be notified. | Feedwater Reactor Pressure Vessel | |
| ENS 40311 | 10 November 2003 13:20:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Bypassing the Pressure Suppression Function of the Torus | On 11/10/2003 at 07:20 CST it was discovered, during a control room panel walk-down, that Dresden U2 had primary containment valves 2-1601-56 Torus Purge valve and 2-1601-21 DW (drywell) Purge valve open simultaneously. This valve alignment created a flow path from the Drywell to the Torus, effectively bypassing the pressure suppression function of the torus water volume during a LOCA (Loss of Coolant Accident) condition. This condition placed U2 containment in an unanalyzed condition, not capable of performing the intended design function, which is to mitigate the consequences of a LOCA. The proper valve alignment was restored at 07:26 CST which restored U2 primary containment to operable status per TS (Tech. Spec) 3.6.1.1. A review of plant data identified that this valve arrangement, which bypassed primary containment, had been in effect when U2 entered Mode 2 (Startup) from Mode 4 (Cold Shutdown) at 12:01 on Nov 9, 2003. In addition, this valve line-up existed for a duration greater than that allowed by TS 3.6.1.1 A.1 and B.1 (1 hour). The NRC Resident Inspector was notified of this event by the licensee.
Dresden has performed an engineering evaluation that bounds the plant conditions that existed while the two valves were simultaneously open. The evaluation concluded that the valves would have automatically closed in sufficient time to prevent exceeding the design limits of the primary containment during a postulated Design Basis Accident. Therefore, Dresden retract the ENS call associated with this event. This event will be the subject of an Licensee Event Report in accordance with the requirements of 10 CFR 50.73(a)(2)(i)(B), 'Any event or condition which was prohibited by the plant's Technical Specifications.'" R3DO (Ken Riemer) notified. The NRC Resident Inspector was notified of the above retraction by the Licensee. | Primary containment | |
| ENS 40227 | 7 October 2003 03:15:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Hpci System Inoperability Due to Failed Suppression Pool Level Switch at Dresden Unit 2 | The Unit 2 HPCI system has been declared INOPERABLE due to the failure of a pressure suppression pool high-level switch during surveillance and being unable to maintain the HPCI pump suction lined up to the pressure suppression pool in standby lineup. Per technical specification 3.3.5.1. required action D.2.2. with the high level switch INOPERABLE the HPCI system must have the pump suction aligned to the suppression pool with in 24 hours or declare the HPCI system INOPERABLE when the required action completion time can not be met. The function of the suppression pool high-level switch causes the HPCI pump suction to automatically realign to the suppression pool when the suppression pool reaches the high level set point during an accident. When the pump suction swap to the suppression pool was performed the HPCI gland seal leak off pump began to run automatically. Further investigation determined that there was an unknown input into the HPCI gland seal leak off condenser (GSLO). Normally the GSLO does not have an input while in standby lineup and therefore does not normally operate while the pump suction is aligned to the Pressure Suppression Pool. The GSLO pump would have a discharge flow path with the HPCI system running and therefore would have the ability to maintain its design function. However in the standby line (-up) with the pump suction aligned to the suppression pool the GSLO pump did not have a discharge flow path. This inability to pump the GSLO condenser required the suction be realigned to the condensate storage tank and with the combination of a failed suppression pool high-level switch requires declaration of INOPERABITY of the HPCI system. This is a 14 day LCO. This is a single train system and reportable under SAF 1.8 Event or Condition That Could Have Prevented Fulfillment of a Safety Function. The INOPERABLE HPCI system function can be manually initiated from the main control room. Investigation and troubleshooting into the unknown HPCI GSLO input has been, initiated in parallel with the repairs to the failed suppression high level switch. The licensee intended on notifying the NRC Resident Inspector. |