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 Report dateSiteEvent description
05000237/LER-2013-00929 January 2014Dresden
05000249/LER-2013-00127 January 2014Dresden

On 11/28/13, at 0258 hours, the Control room received a Unit 2 interlock door alarm. Operations sent an equipment operator to investigate; and found a Radiation Protection Technician (RPT) and laborers in the area of the alarming interlock removing lead blankets.

entered into Technical Specifications 3.6.4.1 Condition A. The doors were closed and the Technical Specifications Condition was exited.

The cause of this event was determined to be a failure to recognize a hazard while proceeding in the face of uncertainty.

Specifically, the RPT did not recognize that there was a change in plant conditions (i.e., the restoration of the X-Area as part of the Secondary Containment boundary) and decided that it was permissible to override the door interlocks by using an emergency manual push-button. As a result of this event, Radiation Protection will be reviewing the proper use of human performance tools and will be revising procedures to enhance the notifications made to the Radiation Protection Department.

This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(C), any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.

klOr Cr101111 ncc tni and e APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/3112e Reported lessons learned are incorporated Into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by intemet e-mall to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB.10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not _ required to respond to, the information collection

05000237/LER-2013-00715 January 2014Dresden

At 10:19:02 CST on November 16, 2013, indication was received in the Control Room that two Secondary Containment doors, in one access opening, were open simultaneously. A worker, staged in the interlock, reported that while opening the Reactor Building side door the Turbine Building side door opened several inches. With two interlock doors open simultaneously, Technical Specifications 3.6.4.1, Surveillance Requirement 3.6.4.1.2, was not met. With the Surveillance Requirement not met, Secondary Containment was declared inoperable, and entry into Technical Specifications 3.6.4.1 Condition A was made. The doors were immediately closed and the Technical Specifications Condition was exited.

The apparent cause evaluation identified that the apparent cause of this event was an interlock circuit relay malfunction. Dresden engineering has completed the engineering change, and the modification is currently awaiting installation.

This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(C), any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.

- 007 - 00 2013

05000237/LER-2013-00513 January 2014Dresden

On November 14, 2013, with Unit 2 shutdown for refueling outage D2R23, both the 2-0220-58B Feed Water Inboard Check Valve and the 2-0220-62B Feed Water Outboard Check Valve failed Local Leak Rate Testing (LLRT) acceptance criteria. Specifically, the "as-found" leak rate for both valves was above the administrative acceptance criteria of 45.0 scfh, and based upon the leakage rate observed, leakage was also determined to exceed the limits for primary containment leakage as specified in TS 5.5.12.c.

During testing, the in-series Feed Water "B" Loop Containment Isolation valve volumes could not be pressurized with full flow service air through the test tap configuration. The injected air immediately passed through the check valve and out the test vent tap, indicating that the valve disc was not fully seated. The cause of this event was determined to be that best practices, for installation and testing of the valves in order to maximize reliability, had not been implemented. The station has subsequently developed and implemented valve maintenance and testing best practices. Additionally, the station is evaluating long term actions to enhance the design and testing of the Feed Water check valves.

This event is being reported in accordance with 10 CFR 50.73(a)(2)(ii)(A) and 10 CFR 50.73(a)(2)(v)(C).

05000237/LER-2013-0046 January 2014Dresden

interlock doors were open simultaneously. A door operator operated the turbine side door hand switch allowing personnel traffic to enter the interlock. Simultaneously, the reactor building side door swung open.

With two interlock doors open simultaneously, Technical Specifications 3.6.4.1, Surveillance Requirement 3.6.4.1.2, was not met. With the Surveillance Requirement not met, Secondary Containment was declared inoperable, and entry into Technical Specifications 3.6.4.1 Condition A was made. The doors were immediately closed and the Technical Specifications Condition was exited. The apparent cause evaluation identified that the apparent cause of this event was an inadequate design specification of a limit switch.

Based upon the short duration of the secondary containment doors being opened simultaneously and that the Secondary Containment differential pressure remained negative during the course of this event, this event is of low safety significance.

This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(C), any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.

05000237/LER-2013-00120 December 2013Dresden

On 6/28/2013, from 07:49:07 to 07:49:14, control room operators received a control room alarm indicating that the unit 2/3 emergency diesel generator (EDG) interlock doors were open simultaneously. Individuals were able to enter the interlock, from two directions, at the same time. With two interlock doors open simultaneously, Technical Specifications 3.6.4.1, Surveillance Requirement 3.6.4.1.2, was not met. With the Surveillance Requirement not met, Secondary Containment was declared inoperable, and entry into Technical Specifications 3.6.4.1 Condition A was made. The doors were immediately closed and the Technical Specifications Condition was exited. Based upon the investigation performed, the failure mechanism for this event was determined to be an isolated and rare premature failure of the latch bolt monitor.

Based upon the short duration of the secondary containment doors being opened simultaneously and that the Secondary Containment differential pressure remained negative during the course of this event, this event is of low safety significance.

This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(C), any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.

05000249/LER-2011-00113 June 2011Dresden

On January 15, 2011, during control rod exercising Technical Specifications (TS) surveillance testing on Dresden Nuclear Power Station (DNPS) Unit 3, it was observed by control room personnel, that at times, the Rod Block Monitor (RBM) count circuit appeared to display too many local power range monitor (LPRM) inputs when a control rod having three LPRM strings was selected. Based on the information at the time, the crew concluded that the RBM remained operable.

During subsequent troubleshooting on January 21, 2011, it was determined that both RBM channels had been inoperable since January 15, 2011 due to a failed circuit card. TS 3.3.2.1 Condition B required a channel to be placed in trip within one (1) hour. However on January 15, 2011, the operators did not properly identify this inoperability. Therefore the required action was not completed within the completion time specified by the plant's TS. The failed card was replaced on January 21, 2011, and the system returned to an operable condition.

A subsequent causal investigation determined that a knowledge deficiency in conjunction with improper procedure usage resulted in an error in determining the operability of the RBM. Training Requests were submitted to perform a review of this event and the function of the count circuit meter.

The RBM upscale rod block is not credited in the analysis of a rod withdrawal error and therefore the safety significance of the failure of the relay card is minimal. Health and safety of the public was not compromised as a result of this condition.

05000237/LER-2009-00231 March 2010Dresden

On March 15, 2009, at approximately 2025 hours (CDT), with Unit 2 at approximately 100 percent power, Dresden Nuclear Power Station Operations personnel discovered during a maintenance activity that motor operated valve 2-2301-6, Unit 2 High Pressure Coolant Injection Suction Valve, would not close. The valve is a normally open valve and is required to close during the transfer of High Pressure Coolant Injection System pump suction from the Condensate Storage Tanks to the Torus to prevent high Torus water level. Troubleshooting and diagnostic testing identified that the valve's failure to close was attributed to valve internal binding.

The Root Cause of this event was that when the valve was in the full open position, the center of gravity of the solid gate valve disc extends past the end of the in-body valve guides, which caused the disc to tip and bind with the in-body guides.

A contributing cause to this event is increased stem friction. The higher than normal thrust associated with the binding caused a loss of stem lubricant through extrusion, which increased the friction at the stem and stem nut interface.

The in-body valve guides were lengthened into bonnet to ensure the valve disc's center of gravity is supported by guides when the valve is in the Open position. Preventative maintenance activities for motor operated valve stem lubrication were revised, as needed, to ensure that the frequency does not exceed two-years for the motor operated valve program valves with horizontal disc/stem orientation that exhibit internal binding.

The safety significance of the event is minimal. An evaluation concluded that HPCI would have operated long enough to fulfill its safety function. A review of the actual Torus water levels during this time frame identified that the Torus would not have exceed its structural design values during a postulated accident. Therefore, the consequences of this event had minimal impact on the health and safety of the public and reactor safety.

05000237/LER-2009-00722 January 2010DresdenDuring a field walkdown while DNPS Unit 2 was in its fall 2009 refueling outage, it was identified that Reactor Protection System (RPS) Pressure Switches (PS) 2-0504-A, B, C, and D all share a common sensing line with a single isolation valve (2-0504-A/D-HV). A subsequent review found a similar configuration existed on Unit 3. After further review, it was concluded 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 design standard IEEE 279 -1968. Specifically, failure of the common sensing line would bypass these RPS scram functions when reactor power is greater than 38.5 percent. Based on this single point vulnerability, these RPS scram functions could have been disabled if the sensing line failed and therefore this event is reportable per 10 CFR 50.73(a)(2)(v)(A), "Any event or condition that could have prevented the fulfillment of a safety function of structures or systems that are needed to shut down the reactor and maintain it in a safe shutdown condition." For Unit 2, DNPS took actions to restore compliance to the referenced design standard prior to the return to service. For Unit 3, DNPS has performed an operability determination, and the safety function remains operable. Actions to restore compliance for DNPS Unit 3 are scheduled for the next refueling outage.
05000249/LER-2009-0011 December 2009Dresden

On 10/03/2009 at approximately1735 hours while at full power, Unit 3 experienced an automatic reactor scram and Group I primary containment isolation signal. Due to the Group I isolation signal, the inboard and outboard main steam isolation valves closed as designed. Prior to the reactor scram, operators were restoring the reactor water clean-up (RWCU) system per the applicable station procedure.

The Probable Cause for the Group I isolation signal and reactor scram is attributed to a hydraulic pressure transient when restarting the RWCU system due to a latent procedure deficiency.

The procedure for restarting the RWCU has been revised.

During the reactor scram, the shared Unit 2/3 emergency diesel generator automatically started when auxiliary power transferred from the main to the reserve power source.

The safety significance of this event is minimal as plant response and operator actions were consistent with the protection of public health and safety and personnel safety.

05000249/LER-2008-00116 October 2008Dresden

On August 16, 2008, at approximately 2000 hours (CDT), with Unit 3 at approximately 100 percent power, Dresden Nuclear Power Station Operations personnel attempted to pump the Unit 3 drywell floor drain sump, which is used to partially satisfy Surveillance Requirement 3.4.4.1. The pumps started as expected, however, the drywell floor drain sump monitoring system flow integrator indicated no flow. Since the water volume in the drywell floor drain sump could not be measured, the plant was not able to meet Technical Specification 3.4.4, "RCS Operational Leakage." Unit 3 initiated a plant shutdown on August 17, 2008 at approximately 0902 hours (CDT), as the repairs to the system could not be made with Unit 3 online.

Dresden Nuclear Power Station requested a Notice of Enforcement Discretion on August 17, 2008 at approximately 1030 hours (CDT) to allow Unit 3 to remain at power for 7 days to allow time for the processing of an emergency Technical Specification amendment. The NRC granted the Notice of Enforcement Discretion on August 17, 2008 at approximately 1200 hours (CDT). Dresden Nuclear Power Station requested and received an emergency Technical Specification amendment to allow continued power operation with an inoperable Unit 3 drywell floor drain sump monitoring system within the time allowed by the Notice of Enforcement Discretion.

The cause of the event is indeterminate until the drywell floor drain sump monitoring system can be examined during an outage of sufficient duration, but no later than the startup from D3R20.

05000237/LER-2008-00323 June 2008Dresden

On April 23, 2008, at approximately 2300 hours (CDT), with both Units 2 and 3 operating at approximately 100 percent power, the Control Room Emergency Ventilation Air Conditioning System was in operation to perform a post maintenance test. During the activity, the Control Room Emergency Ventilation Air Conditioning System experienced excessive vibration. Technical Specification 3.7.5, "Control Room Emergency Ventilation Air Conditioning (AC) System," was entered. The system was restored to operable status on May 1, 2008. This event is being reported in accordance with 10 CFR 50.73(a)(2)(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," as the Control Room Emergency Ventilation Air Conditioning System is a single train system.

The apparent cause is attributed to the lack of lubrication due to the oil in the compressor being displaced by refrigerant. Liquid refrigerant accumulates in the compressor due to liquid floodback during operation and flooded starts. Following the completion of the actions associated with the equipment apparent cause analysis, Plant Engineering will evaluate system operation to determine the effectiveness of the actions taken. Based on this evaluation, if it is determined that system reliability has not been improved, further actions will be developed and implement, as appropriate.

05000249/LER-2006-0019 April 2007Dresden

On November 12, 2006, with Unit 3 in a refuel outage, Dresden Nuclear Power Station Unit 3 was notified that vendor testing had identified three of the four Main Steam Safety Valves removed from the unit during this outage had exceeded their Technical Specification allowable as-found lift setpoint tolerance of plus or minus 1 percent. One of the valves lifted above the allowable lift setpoint tolerance by 0.1 percent and two of the valves lifted below their allowable lift setpoint tolerance by 1.4 percent and 1.5 percent. Additionally, a Target Rock Safety/Relief Valve also removed during the Unit 3 refuel outage, was tested on February 7, 2007 and lifted above the allowable lift setpoint tolerance by 1.9 percent. This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications," and 10 CFR 50.73(a)(2)(vii)(D), "Any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system designed to mitigate the consequences of an accident.

The cause of the event was attributed to setpoint drift. The corrective action to address this issue had been previously initiated. On June 2, 2006, Dresden Nuclear Power Station submitted a request for a change to the Technical Specifications for Units 2 and 3 to increase the allowable as-found Main Steam Safety Valve lift setpoint tolerance from plus or minus 1 percent to 3 percent. This change is currently under review by the Nuclear Regulatory Commission.

05000237/LER-2006-0025 June 2006Dresden

On April 6, 2006, at approximately 1039 hours (CDT), with Unit 2 at approximately 97 percent power, Dresden Nuclear Power Station Instrument Maintenance technicians were installing a new High Pressure Coolant Injection System temperature recorder 2-2340-9 when an energized recorder electrical lead was accidentally shorted to a recorder mounting bracket screw. A consequence of this electrical short was the transfer of the Essential Service System to its emergency power supply from Motor Control Center 28-2 and the trip of Essential Service System circuit 16. This resulted in the High Pressure Coolant Injection System being declared inoperable due to a loss of its automatic function from the loss of power to its flow controller and signal converter. However, the system was available due to control room personnel being able to manually control system operation.

The apparent cause of this event was human performance associated with the technicians' lack of attention to detail in manipulating tools and failure to self-check. Corrective actions addressed the human performance issues through discussions of this event with the IM technicians during department training sessions and the evaluation the technicians during out-of-the-box training for proper use of human performance tools. These corrective actions reinforced the need for self-checking and the use of tape on adjacent metal components when working with energized electrical leads.

05000237/LER-2005-00223 May 2005Dresden

On March 24, 2005, at 0529 hours (CST), with Unit 2 at approximately 96 percent power, two unexpected control room alarms were received for exceeding the Electro-Hydraulic Control System maximum combined flow limit setpoint and open Turbine Bypass Valves. Several seconds later, high flow in the Main Steam System resulted in a signal to close the Main Steam Isolation Valves that initiated an automatic reactor scram. All control rods fully inserted and all other systems responded to the reactor scram as expected, except for non-safety related equipment, the Turbine Generator Lube Oil Pump and the 2B Reactor Feedwater Pump Auxiliary Oil Pump, which did not operate as required.

The root cause of this event is indeterminate. The most probable cause is attributed to an increase in electrical resistance between electrical pins 13 and 22 on the "A54" card within the Electro-Hydraulic Control System. The corrective actions to prevent recurrence are to replace the "A54" card backplane connector, remake all termipoints on the connector for the "A54" card and to rework the remaining connectors between electrical pins 13 and 22. The "A54" card backplane connector was replaced and the all termipoints on the refueling outage.

05000237/LER-2005-0014 April 2005Dresden

On February 3, 2005, at 1915 hours (CST), with Unit 2 at approximately 95 percent power and Unit 3 at approximately 96 percent power, Dresden Nuclear Power Station engineering personnel confirmed that single failure vulnerabilities existed on 4160 Volt Relaying and Metering transformers on both units. The single failure vulnerabilities defeated the independence of the offsite alternating current power supplies. If this failure occurred during a Loss of Coolant Accident, the Containment Cooling Service Water system pumps may not have been able to be started within the required time. The single failure vulnerabilities were removed on February 4, 2005, at 0009 hours, and the effected plant equipment was declared operable.

The root cause of this event was determined to be an existing latent design deficiency. The corrective action to prevent reoccurrence is currently in place in the Configuration Change procedures used to install new designs at Dresden Nuclear Power Station. A preliminary engineering review for similar existing latent design deficiencies found no other similar deficiencies. A corrective action is in place for engineering to complete an extent of condition review of the alternating current, Emergency Diesel Generators, and direct current systems for latent design deficiency conditions similar to this event.

05000249/LER-2004-00619 January 2005Dresden

Dresden Nuclear Power Station, Units 2 and 3, had been experiencing increasing trends in vibration levels on both Main Turbine Generators, bearings 9 and 10 since May 2004. Numerous efforts and reviews during the summer and fall of 2004 were not successful in resolving the vibration. Dresden Unit 3 entered a refueling outage in October 2004 and as part of the outage scope, the Main Turbine Generator was inspected. On October 31, 2004, the inspection identified that the Unit 3 Main Turbine Generator Rotor had a crack in the shaft near the rotor coupling. This finding resulted in the decision to remove Unit 2 from service and conduct an inspection of its rotor shaft. On November 1, 2004, a crack was identified on the Unit 2 rotor shaft. The Unit 2 crack was in the same general location and similar configuration as the Unit 3 crack.

These events are being reported as a Voluntary Licensee Event Report in accordance with the guidance contained in NUREG 1022, Revision 2, "Event Reporting Guidelines 10 CFR 50.72 and 50.73.

The root cause of these events was determined to be intermittent oscillating torsional loading on the generator rotor, which produced a torsional fatigue failure mode. The cause of the intermittent oscillating torsional loading is indeterminate. The cause and source of the intermittent oscillating torsional loading will be investigated through analytic modeling and data acquisition during plant operation.

05000249/LER-2004-00529 November 2004Dresden

On September 29, 2004, at 1235 hours (CDT), with Unit 3 at approximately 100 percent power in Mode 1, it was discovered that 3 of the 4 Unit 3 Isolation Condenser Time Delay Relays exceeded their Allowed Value specified in Technical Specification 3.3.5.2, "Isolation Condenser (IC) System Instrumentation." The event was discovered while performing Surveillance Procedure DIS 1300-08, "Sustained High Reactor Pressure Time Delay Relay Calibration." This event identified that two independent channels of the time delay portion of the Unit 3 Isolation Condenser Initiation Logic were inoperable and is being reported under 10 CFR 50.73(a)(2)(vii), "), "Any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system." Additionally, this event is being reported under 10 CFR 50.73(a)(2)(i)(B), "Operation or condition prohibited by Technical Specifications." The Isolation Condenser Time Delay Relays were previously calibrated on June 16, 2002 by using a stopwatch.

The root cause of the event was due to an ineffective extent of condition review for a corrective action associated with a 1996 event in which stopwatches were determined to not be sensitive enough for calibration checks on components with limited margin. The corrective action to prevent recurrence was to use a strip chart recorder for calibrating the Isolation Condenser Time Delay Relays.