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| Report date | Site | Event description | |
|---|---|---|---|
| 05000353/LER-2016-001 | 27 July 2016 | Limerick | A manual actuation of the reactor protection system (RPS) when the reactor was critical was initiated during Plant Process Computer (PPC) modification testing at power. A modification wiring design error caused an actuation of both reactor recirculation pump (RRP) trip relays when a circuit isolation switch was closed. The direct cause of the event was a circuit wiring design error implemented in the field that caused energization of the RRP adjustable speed drive (ASD) trip coils. The root cause of the event was a failure of station personnel to appropriately apply Technical Human Performance (THU) error prevention techniques to identify the design error and prevent its installation and testing as part of the modification. The isolation switch for the mis-wired circuit was opened to enable reset of the ASD trip coils. The 2A and 2B ASDs were returned to service. The corrective actions are to change the circuit design to correct the design error. The human performance aspects of the event will be addressed through several management actions that include reinforcement of proper standards and behaviors related to THU error techniques with station personnel. |
| 05000352/LER-2016-003 | 18 May 2016 | Limerick | Reactor coolant system pressure boundary leakage was identified by a drywell leak inspection team during a planned shutdown for a Unit 1 refueling outage. This event resulted in a plant shutdown required by Technical Specifications. The Unit 1 'A' RHR Shutdown Cooling Return Check Valve equalizing line developed a crack at the toe of a weld due to high cyclic fatigue induced by vibration from the reactor recirculation system. The Unit 1 welds were reworked to EPRI 2x1 at select locations on the "A" and "B" RHR Shutdown Cooling Return check valve equalizing lines for HV-051-1F050A and 50B. The similar Unit 2 welds on equalizing lines for HV-051-2F050A and 50B will be examined and reinforced. The scope will be added into the next refueling outage (2R14) currently scheduled for April 2017. |
| 05000352/LER-2016-002 | 11 April 2016 | Limerick | The Unit 1 Division 1 125 VDC Safeguard Battery was rendered inoperable due to installation of temporary seismic restraints that had not been approved for use. This historical issue was identified during a preventive maintenance activity to replace the battery. The investigation identified fifteen reportable events over a three year period. The cause was incomplete scoping of the engineering analysis performed to support battery cell replacements. The analysis did not include the impact of battery replacement activities on the battery rack. The battery cell rack support strategy was revised and a technical evaluation was performed for the seismic qualification of the battery rack during battery cell replacement. The battery cell replacement procedure (M-095-005) will be revised to address the updated technical evaluation and ensure seismic qualification of the battery rack is maintained during maintenance activities. |
| 05000352/LER-2016-001 | 23 March 2016 | Limerick | Unit 1 reactor enclosure secondary containment integrity was briefly declared inoperable when both doors on a reactor enclosure 201' elevation pipe tunnel airlock were simultaneously opened. The cause of the event was a degraded closing mechanism on the airlock inboard door. The airlock doors were closed to restore reactor enclosure secondary containment integrity. The degraded inboard door closing mechanism was repaired. |
| 05000352/LER-2015-002 | 22 October 2015 | Limerick | While operating at full power, a degraded Standby Gas Treatment System (SGTS) subsystem differential pressure (dP) control instrument failed upscale. The subsystem was determined to be operable at the time of the failure. After the corrective maintenance activity it was determined that the failed instrument caused the subsystem to be inoperable. The OB SGTS subsystem was determined to have been inoperable for a period that exceeded the SGTS Technical Specification (TS) allowable outage time (AOT) based on firm evidence regarding the time of the instrument failure. The cause of the OB SGTS subsystem inoperability was a degraded SGTS dP control instrument. The degraded SGTS dP control instrument was replaced and the OB SGTS subsystem was restored to operable status. |
| 05000352/LER-2015-001 | 24 April 2015 | Limerick | A valid automatic actuation of the reactor protection system (RPS) occurred due to a high reactor pressure condition following an unexpected closure of the 1C Inboard main steam isolation valve (MSIV). The cause of the event was that an undersized fitting was installed on the air supply tubing to the 1C Inboard MSIV, which was not capable of withstanding existing cyclic stresses. The fitting failed due to cyclic fatigue. An inspection of Unit 1 inboard (I/B) and Outboard (O/B) MSIV Primary Containment Instrument Gas (PCIG)/Instrument Air tubing was performed to verify that the correct fittings are installed as specified by the design drawings or subsequent evaluation. The inspection of Unit 2 will occur during the in progress refueling outage. The failed fitting connection was replaced with a more robust fitting that is suitable for the application. |
| 05000353/LER-2014-007 | 4 February 2015 | Limerick | A worker failed to verify that the inboard door was closed prior to opening the outboard door when traversing from the reactor enclosure to the refuel floor. The outboard door was closed in less than 10 seconds. This event resulted in a brief inoperability of reactor enclosure secondary containment integrity. The cause of the event was that the technician failed to use proper human performance fundamentals to make sure the blue light was off prior to proceeding and opening the second door in the airlock. The airlock doors were immediately closed to restore reactor enclosure secondary containment integrity. The workers involved were coached and lessons learned were communicated to the site. |
| 05000353/LER-2014-006 | 2 October 2014 | Limerick | A worker failed to physically challenge the latch on the inboard reactor enclosure airlock door when traversing from the refuel floor into the reactor enclosure. The next worker to use the airlock opened the outboard door causing the inboard door to open due to differential pressure across the door. The outboard door was closed in less than 10 seconds. This event resulted in a brief inoperability of reactor enclosure secondary containment integrity. The event was caused by a degraded airlock door self-closing feature on the inboard airlock door. A contributing cause was a worker failure to verify that the inboard airlock door was latched fully closed. The worker failed to properly use the self-check fundamental. The airlock doors were immediately closed to restore reactor enclosure secondary containment integrity and the degraded door self-closing feature was repaired. The worker was coached regarding use of the self-check fundamental. The lessons learned were communicated to the site. |
| 05000353/LER-2014-005 | 23 June 2014 | Limerick | One emergency core cooling system (ECCS) actuation instrumentation channel was determined to have been inoperable for a period that exceeded the Technical Specification (TS) action allowed completion time. The as-found setpoint exceeded the required limit during three consecutive 18-month calibration surveillance tests. The channel was one of two redundant high pressure coolant injection (HPCI) system suppression pool high level channels. The apparent cause of the event was a less than adequate review of the issue report that identified three setpoint drift events on a degraded HPCI level transmitter. The degraded HPCI suppression pool level transmitter was replaced. A Plant Engineering briefing was conducted to reinforce prompt and thorough evaluation of potential system operability and regulatory impacts of repetitive TS instrument recalibrations. |
| 05000353/LER-2014-004 | 3 June 2014 | Limerick | Workers simultaneously opened both doors of a reactor enclosure personnel airlock when transporting material through the airlock. One worker opened the outboard airlock door before the inboard airlock door was properly closed and latched. Both doors were closed in less than 10 seconds. This event resulted in a brief inoperability of reactor enclosure secondary containment integrity. The event was caused by the workers' failure to verify the inboard airlock door was latched fully closed prior to opening the outboard airlock door. The workers failed to properly use the self-check fundamental. The airlock doors were closed to restore reactor enclosure secondary containment integrity. The workers were coached regarding use of the self-check fundamental. The lessons learned were communicated to the site. |
| 05000353/LER-2014-003 | 19 May 2014 | Limerick | Workers simultaneously opened both doors of a reactor enclosure personnel airlock when transporting equipment through the airlock. One worker opened the Unit 1 airlock door and the other worker opened the Unit 2 airlock door before the Unit 1 door was fully closed. Both doors were closed in less than 10 seconds. This event resulted in a brief inoperability of reactor enclosure secondary containment integrity. The cause of the event was a worker deviated from the pre-job briefing instructions regarding one worker being responsible to open and close the airlock doors while the other workers were responsible for pushing the cart through the open door. When the worker deviated from the briefing instructions the worker did not adhere to the airlock door policy. This event was not prevented by the design of the reactor enclosure airlocks since there is no mechanical interlock and the door open indicating light does not prevent simultaneous opening of both airlock doors. The affected airlock doors were closed to restore reactor enclosure secondary containment integrity. The worker was coached regarding compliance with the responsibilities assigned at the pre-job brief and airlock door use. The lessons learned were communicated to the site. |
| 05000352/LER-2014-004 | 5 May 2014 | Limerick | A valid manual actuation of the reactor protection system (RPS) was initiated due to an unexpected closure of all six main turbine intercept valves (TVs). The cause of the main turbine IVs closure was due to a degraded Electro-hydraulic Control (EHC) 30 VDC house power supply. The Unit 1 EHC system was replaced with a Digital EHC (DEHC) system during the subsequent refueling outage 1R15. The Unit 2 EHC system is scheduled to be replaced with a DEHC system during the next refueling outage 2R13 in April 2015. The Unit 2 EHC house and permanent magnet generator (PMG) power supplies as-found voltages were verified to be within the calibration procedure limits and the as-left voltages were adjusted to the middle of the procedure acceptable band during the planned maintenance outage 2M49. |
| 05000352/LER-2014-003 | 28 March 2014 | Limerick | A worker allowed both doors of a reactor enclosure personnel airlock to be open simultaneously. Both doors were closed in less than 10 seconds. This event resulted in a brief inoperability of reactor enclosure secondary containment integrity. The cause of this event was failure of the worker to self check. The worker opened the outboard airlock door prior to allowing the inboard airlock door to go full closed. This event was not prevented by the design of the reactor enclosure airlocks. The affected airlock doors were closed to restore reactor enclosure secondary containment integrity. |
| 05000353/LER-2014-002 | 7 March 2014 | Limerick | Two workers simultaneously opened both doors of a reactor enclosure personnel airlock when entering the airlock. One worker opened the inboard airlock door and the other worker opened the outboard airlock door. Both doors were closed in less than 10 seconds. This event resulted in a brief inoperability of reactor enclosure secondary containment integrity. This event was not prevented by the design of the reactor enclosure airlocks. The affected airlock doors were closed to restore reactor enclosure secondary containment integrity. |
| 05000352/LER-2014-001 | 8 January 2014 | Limerick | Two workers simultaneously opened both doors of a reactor enclosure personnel airlock when entering the airlock at the same time. One worker opened the inboard airlock door and the other worker opened the outboard airlock door. Both doors were closed in less than 10 seconds. This event resulted in a brief inoperability of reactor enclosure secondary containment integrity. This event was caused by a weakness in the design of the reactor enclosure airlocks. A modification is being evaluated for the airlock doors. |
| 05000353/LER-2013-002 | 31 October 2013 | Limerick | Both airlock doors were opened simultaneously when moving equipment through a reactor enclosure airlock causing an unplanned inoperability of reactor enclosure secondary containment integrity. This event was caused by a non-functional airlock door open indicating light not providing the correct door status. The non- functional door open indicating light magnetic switch has been replaced. A review was conducted and no other non-functional door open indicating lights were identified. A periodic routine test of the airlock door open indicating lights will be implemented to identify non-functional door open indicating lights. |
| 05000353/LER-2013-001 | 12 June 2013 | Limerick | A valid manual actuation of the reactor protection system (RPS) occurred during a refueling outage with all control rods inserted. The manual actuation of the RPS system was initiated when the mode switch was placed in the "Shutdown" position following an automatic actuation of RPS. The event was initiated by an unplanned automatic actuation of the turbine stop valve closed trip logic during an RPS surveillance test. The automatic RPS' system actuation was caused by a failure to follow the existing procedure change processes. A corrective action was completed which reinforced the requirements for partial procedure use and temporary procedure changes. The corrective action also established expectations for the review and approval of partial procedures and temporary procedure changes. |
| 05000352/LER-2012-003 | 21 May 2013 | Limerick | A valid manual actuation of the primary containment isolation system was initiated in response to a low delta pressure condition in the reactor enclosure secondary containment. The manual actuation affected primary containment isolation valves in more than one system. The cause of the event was a trip of the reactor enclosure ventilation system. Operators initiated a "B" manual secondary containment isolation as directed by the low delta pressure alarm procedure. The cause of the ventilation system trip was due to degraded performance of the reactor enclosure equipment compartment exhaust (REECE) flow transmitter. The degraded REECE flow transmitter was replaced and the system was tested successfully. The reactor enclosure ventilation system was restored to service and continues to operate normally. |
| 05000352/LER-2013-001 | 20 May 2013 | Limerick | The high pressure coolant injection (HPCI) system was rendered inoperable during a pump, valve, and flow surveillance test. The cause of the HPCI inoperability was a turbine lithe oil system bellows actuated pressure switch failure which resulted in an oil leak. The apparent cause of the pressure switch bellows failure was corrosion and cyclic stresses fatigue. The failed pressure switch was replaced and the HPCI system was tested successfully. Additionally, a similar service pressure switch will be replaced. A review of HPCI and reactor core isolation cooling (RCIC) turbine lube oil system components will be performed to determine if any additional components are potentially susceptible to failure as a result of historical exposure to oil with high moisture content. |
| 05000352/LER-2012-009 | 3 December 2012 | Limerick | An unprotected control cable was identified during a detailed logic and cable routing review for the Multiple Spurious Operations T (MSO) 5f scenario. T The review identified that a D22 Emergency Diesel Generator T (EDG) T output breaker control cable could fail due to postulated fire damage in fire area 067W. The event was caused by an error during the Fire Safe Shutdown T (FSSD) T analysis. T The D22 EDG output breaker control logic was rewired to eliminate the deficiency. |
| 05000352/LER-2012-008 | 12 November 2012 | Limerick | During planned surveillance testing three of four isolation instrumentation channel response times exceeded the Technical Specification T (TS) maximum limit of less than or equal to 0.5 seconds for main steam line T (MSL) T high flow. T The response time test failures were caused by a failure to proceduralize the method of replacement relay selection to ensure the fastest contact release times. T This caused the overall as-left logic response time to lose margin to the TS limit. T The affected relays in the 1A, T 10 and 1D MSL flow channels were replaced. T The relay testing and/or replacement procedure will be revised to include a step-by-step method of selecting relays with the shortest contact release times upon de-energization of the relay. A new stock code will be created for new relays that have been response time tested and found to be acceptable for this application. |
| 05000352/LER-2012-007 | 19 October 2012 | Limerick | Multiple primary containment isolation valves T (PCIVs) were declared inoperable following identification of a closing circuit design deficiency. T Overall, 15 Unit 1 PCIVs and 15 Unit 2 PCIVs were affected. T The deficiency resulted in a potential failure of affected PCIVs to fully close during a loss of coolant accident (LOCA) with offsite power available. T The original design for certain PCIVs contained a design flaw that could potentially prevent the equipment from performing the intended safety function. Following the identification of the design deficiency a design change was implemented on 24 affected PCIVs T (12 per unit). T The design change installed a jumper which removed the LS-8 contact feature. T Three Unit 1 affected Containment Atmospheric Control (CAC) system drywell purge PCIVs' stroke times were reduced to remove the vulnerability. T Three inoperable Unit 2 affected CAC drywell purge PCIVs' stroke times will be reduced to remove the vulnerability. |
| 05000352/LER-2012-002 | 18 September 2012 | Limerick | A transformer failure and subsequent low voltage condition resulted in a loss of the main generator stator cooling water system. T The loss of stator cooling water resulted in an automatic trip of both reactor recirculation pumps which required a valid manual actuation of the reactor protection system. T The transformer failure was caused by partial current discharge T (corona effect). T The partial current discharge was caused by a manufacturing defect resulting in improper insulation of the High Voltage line rod where it passes through the polyester support board. T The faulted transformer was replaced. |
| 05000352/LER-2012-006 | 17 September 2012 | Limerick | A valid manual actuation of the reactor protection system was initiated during an outage with all control rods inserted. T The reactor mode switch was repositioned from "Shutdown" to "Refuel" during preparation to perform control rod exercising. T The mode switch was returned to "Shutdown" when it was identified that the required nuclear instrumentation surveillance tests were not in surveillance. T The cause of the event was a personnel error caused by a test weakness. T The "Pre-control Rod Withdrawal Check and CRD Exercise OPCONs 3,4 With No Core Alterations" surveillance test does not have verification steps to ensure that the Surveillance Test Coordinator T (STC) T input is accurate. T The "Pre-control Rod Withdrawal Check and CRD Exercise OPCONs 3,4 With No Core Alterations" surveillance test Attachment 2 will be revised to add an additional Work Management signoff for a peer check of the STC input. T The T notes and body of Attachment 2 will be revised to improve human factoring. |
| 05000352/LER-2012-005 | 17 September 2012 | Limerick | A valid manual actuation of the reactor protection system was initiated due to an automatic trip of both reactor recirculation pumps. T The reactor recirculation pumps tripped due to a loss of stator cooling water following a failure of a connection in a 13 kV/480 VAC non-safeguard load center air termination cabinet. T An Unusual Event was declared due to flash-over damage on the failed transformer air termination cabinet which was classified as an explosion within the protected area boundary. T The cause of the failed transformer was a high voltage connection clamp that was larger than the 13 kV cable size and the cable was not installed properly. T The cable in use was a solid conductor and the clamp used was designed for stranded cable. T This resulted in overheating and subsequent failure of the connection which damaged the cable and the load center transformer. T The investigation determined that this connection is not disturbed during routine maintenance. T Therefore, this is believed to be a manufacturing issue. T The 124A load center transformer supply cable was upgraded to a stranded cable with a crimped lug connection. T The faulted 124A load center transformer was replaced and returned to service. Similar load center transformers will be upgraded to stranded cable with crimped lug connections. |
| 05000352/LER-2012-004 | 10 September 2012 | Limerick | An instrument pipe used to sense main turbine first stage pressure developed a leak that caused inoperability of two instruments in the reactor protection system. T The Reactor Protection System Instrumentation Technical Specification one-hour action to place the affected trip systems in the tripped condition was not met. T The instruments' reactor protection system function is to bypass the turbine stop valve closure and turbine control valve fast closure trip functions when turbine first stage pressure is equivalent to a thermal power of less than 29.5 percent. T The instrument also bypasses the turbine stop valve closure and turbine control valve fast closure trip functions in the end-of-cycle recirculation pump trip logic. T The cause of the event was vibration induced fatigue of the affected instrument pipe. T The failed instrument pipe was repaired. T The "turbine control valve/stop valve scram bypassed" alarm response procedure was revised to direct a power reduction if trip unit status can not be determined within 15 minutes. T A modification will be installed to address vibration induced fatigue on the affected instrument piping. |
| 05000353/LER-2012-001 | 9 July 2012 | Limerick | The Unit 2 Division 2 redundant reactivity control system was determined to be inoperable due to instrument signal drift on a reactor pressure vessel pressure channel. T An investigation determined that the channel was inoperable for a time longer than permitted by the Technical Specifications. T The apparent cause of the unplanned inoperability of the affected channel was a premature failure of the reactor pressure analog trip module (ATM) card. The ATM card failure was most likely due to a failure of the U1- amplifier sub-component on the card. T The degraded card was replaced, calibrated and tested successfully. T The Daily Surveillance Log/OPCONS 1,2,3 RRCS channel check has been revised to ensure unacceptable RRCS channel signal drift will be identified and evaluated as required. |
| 05000353/LER-2011-003 | 22 June 2012 | Limerick | The reactor core isolation cooling system was rendered inoperable due to valve seat leakage on two feedwater long path flush motor operated valves. The valves failed to fully close when long path flushing was secured during a refueling outage. This was later detected during an investigation for a loss in main generator electrical output. The valve indicating lights indicated the valves were full closed. The cause of the event was degradation and design of the long-path recirculation valves. The corrective actions planned are valve in-body maintenance, diagnostic testing, a preventive maintenance scope revision, and long-path recirculation operating procedure revision. The valves were restored to the full closed position which restored the reactor core isolation cooling system and the primary containment isolation valve to operable. Main generator output increased to normal. |
| 05000352/LER-2012-001 | 19 April 2012 | Limerick | Three of eight main steam isolation valves (MSIVs) exceeded the 5 second maximum closing time requirement during the Unit 1 MSIV cold shutdown valve test. The apparent cause of the test failure was that valve stroke times were not always optimized following prior test failures. A contributing cause was the inherent inaccuracies in valve stroke timing practices. An additional contributing cause is the HV-041-1F028B MSIV pneumatic manifold is causing an extended delay time prior to valve motion. The cold shutdown valve test was performed successfully prior to restart. The test will be revised to require valve stoke time adjustment if the as-found stroke time exceeds pre-established test limits. The HV-041- 1F028B MSIV manifold has been scheduled for replacement in the next Unit 1 refueling outage (1R15) in spring 2014. MSIV stroke timing method improvements for timing accuracy will be investigated, benchmarked and incorporated as necessary. |
| 05000352/LER-2011-003 | 22 August 2011 | Limerick | The high pressure coolant injection system turbine control valve failed to fully close as expected when the system was secured following surveillance testing. A subsequent inspection identified that the No.1 control valve sub-assembly was degraded to the degree that the system safety function could not be assured. The cause of the turbine control valve failure to fully close was binding between the pilot venturi valve and the venturi valve guide. The failure of the lifting beam to venturi valve stem anti- rotation pin initiated accelerated wear of the valve assembly parts, which led to intermittent binding of the parts during turbine operation and turbine control valve No. 1 valve sub-assembly was reworked to replace all damaged parts. The procedure that directs periodic inspection of the turbine control valve assembly will be revised to require non-intrusive inspection of No.1 control valve assembly each refueling outage and to require disassembly of the turbine control valve assembly for detailed inspection of all valve sub-assemblies and replacement of any worn or suspect parts at each turbine major inspection. |
| 05000353/LER-2011-005 | 27 July 2011 | Limerick | A manual actuation of the reactor protection syStem was performed following trips of both reactor recirculation pumps. The pumps tripped due to a failure of a main turbine first stage pressUre trip unit. The cause of the event was a loose wiper terminal on a trip unit potentiometer. The degraded trip unit was replaced and a preventive maintenance activity will be implemented for replacement of similar trip units. (10.2010) |
| 05000352/LER-2011-001 | 7 July 2011 | Limerick | The 1B Reactor Enclosure Recirculation System Subsystem was inoperable for a period that exceeded the Technical Specification allowed outage time. This occurred due to the time from removal of the charcoal sample to the time the unsatisfactory results of the vendor analysis were obtained exceeding the 7-day Technical Specification allowed outage time for one subsystem being inoperable. The sample analysis was completed within 31 days after removal as specified by the surveillance requirement. The affected charcoal bed was replaced and the subsystem was returned to operable status within 5 days of receiving the unsatisfactory sample results. |
| 05000353/LER-2011-002 | 22 April 2011 | Limerick | A manual actuation of the reactor protection system was initiated following an automatic trip of both reactor recirculation pumps. The pumps tripped due to a main generator stator cooling water high temperature actuation which also resulted in an automatic main turbine electro-hydraulic control load set runback. The root cause of the event was a failure to properly control a degraded stator cooling water temperature control valve that required manual operator action in lieu of an automatic control function. The automatic temperature control valve was repaired. The "Adverse Condition Monitoring and Contingency Planning" and "Operational and Technical Decision Making Process" procedures will be revised regarding actions required to substitute a manual operator action for an automatic control function. |
| 05000352/LER-2010-002 | 10 February 2011 | Limerick | The High Pressure Coolant Injection system was rendered inoperable due to a failure of the overspeed mechanism to reset during a periodic test. The cause of the failure to reset was most likely a temporary blockage of the overspeed trip mechanism piston drain port. The condition was corrected by flushing the overspeed trip mechanism during troubleshooting activities. |
| 05000352/LER-2010-001 | 23 August 2010 | Limerick | A valid manual actuation of the reactor protection system was initiated due to an automatic trip of both reactor recirculation pumps. T The event was caused by a failure of a 13 kV cable that powered a non- safeguard 480 VAC load center, a failure of a load center control power undervoltage auxiliary relay to automatically provide control power to the adjacent load center and a failure of a reactor recirculation pump M-G set standby lube oil pump relay. T The faulted 13 kV cable section has been replaced but has not been energized. T The failed undervoltage auxiliary relay has been replaced. The failed reactor recirculation pump M-G set standby lube oil pump relay was replaced. T The north stack ventilation exhaust wide range accident monitor also failed due to the initial electrical distribution voltage transient. T The radiation monitor has been repaired and returned to service. |
| 05000353/LER-2010-001 | 25 June 2010 | Limerick | The Hi-Hi radiation alarm setpoint for the process radiation monitor on the reactor enclosure cooling water system was discovered to be exceeding the Technical Specification allowable value during a review of completed surveillance test documentation. h The required grab samples were not collected during the affected period. h The condition was caused by a less than adequate technical human performance during revision of the surveillance test procedure in 2003. h The affected procedures have been revised to correct the error. |
| 05000352/LER-2009-003 | 26 October 2009 | Limerick | A review of steam leak detection setpoint calculations identified a nonconservative isolation actuation setpoint for the high pressure coolant injection system equipment room high differential temperature isolation. The event was caused by inadequate design controls that allowed less than adequate documentation of design analysis and less than adequate transmittal of design information during a modification and Technical Specification change in 1994. This resulted in an error during the environmental qualification temperature computation for the high pressure coolant injection system equipment room. Upon issue discovery a temporary configuration change was implemented to lower the high pressure coolant injection system equipment room high differential temperature setpoints. This issue is historical. Technical rigor of calculation issues have been addressed by implementation of the post-merger Exelon configuration change process procedures in 2002 and technical task risk/rigor assessments that were implemented in 2004. A license amendment request will be submitted to lower the Technical Specification 3.3.2 high pressure coolant injection system equipment room high differential temperature setpoint. |
| 05000353/LER-2009-002 | 7 July 2009 | Limerick | A condition prohibited by Technical Specifications was identified during a review of main turbine valve testing activities. h In 2008 there were three occasions when the main turbine bypass system was rendered inoperable. h The action to verify the minimum critical power ratio above the limit specified in the Core Operating Limits Report was not completed within one hour as required by Technical Specifications. h The condition prohibited by Technical Specifications was caused by inadequate site documentation for a critical design basis function. The Design Basis Document will be revised to include the design basis function of the stop valve load limit logic. |
| 05000353/LER-2009-001 | 1 June 2009 | Limerick | A valid actuation of the D23 Emergency Diesel Generator bus undervoltage minimum actuation logic occurred following manual operator action to mitigate a bus overvoltage condition during emergency diesel generator testing. T The event was caused by a failure of the emergency diesel generator voltage regulator due to an intermittent failure of the #1 rectifier bank. T The emergency diesel generator voltage regulator was swapped to the #2 rectifier bank and the emergency diesel generator testing was successfully completed. T The #1 rectifier bank is scheduled for replacement. T Testing will be performed on the rectifier to confirm the cause of the failure was due to excessive forward voltage drop across the flyback diode. |
| 05000352/LER-2009-002 | 22 April 2009 | Limerick | The "A" Control Room Emergency Fresh Air Supply System Subsystem was inoperable for a period that exceeded the Technical Specification allowed outage time. T This occurred due to the time from removal of the sample to the time the unsatisfactory results of the vendor analysis were obtained exceeding the 7-day Technical Specification allowed outage time for one subsystem being inoperable. T The sample analysis was completed within 31 days after removal as specified by the surveillance requirement. The affected charcoal bed was replaced and the subsystem was returned to operable status within 3 days of receiving the unsatisfactory sample results. T Charcoal bed age and penetration data have been added as inputs to bed performance monitoring and replacement decision making. |
| 05000352/LER-2009-001 | 13 March 2009 | Limerick | The required and minimum number of accident monitoring instrumentation channels for neutron flux were not maintained operable for periods that exceeded the Technical Specification 3.3.7.5 allowable outage times. T The apparent cause of the event was that the Technical Specification and associated Bases do not clearly identify what instrumentation is required to satisfy the requirement for two operable neutron flux channels during operation in POWER OPERATION (OPCON 1) and STARTUP (OPCON 2) modes. Following this event the licensed operators were trained on this requirement. The Daily Surveillance Log/OPCON 1,2,3 was revised to verify that the required number of SRMs and IRMs remain operable in OPCON 1. T The TS 3.3.7.5 Bases for accident monitoring instrumentation will be revised to clarify the site methods for meeting the accident monitoring instrumentation requirements. T Licensed operator training will be revised to reinforce the requirements for maintaining the accident monitoring instrumentation channels operable. |
| 05000353/LER-2008-001 | 2 February 2009 | Limerick | A valid actuation of the D23 Emergency Diesel Generator bus undervoltage minimum actuation logic occurred following manual operator action to mitigate a bus overvoltage condition during emergency diesel generator post maintenance testing. The event was caused by a failure of the emergency diesel generator voltage regulator due to an intermittent failure of the #1 rectifier bank. The emergency diesel generator voltage regulator was swapped to the #2 rectifier bank and the emergency diesel generator governor tuning was successfully completed. The #1 rectifier bank was replaced and a failure analysis was performed. The failure was primarily caused by looseness at a bolted connection and corrosion at the rectifier flyback diode. |
| 05000352/LER-2008-004 | 31 December 2008 | Limerick | The procedure for performing a remote shutdown during a MCR or cable spreading room fire did not include a step to align the reactor core isolation cooling system suction to the suppression pool. T This alignment is assumed in the plant fire safe shutdown analysis. T The procedure was revised to add the required step. |
| 05000352/LER-2008-003 | 30 December 2008 | Limerick | The High Pressure Coolant Injection system was rendered inoperable due to observed oscillations in the system flow indication. F The condition was corrected by recalibration of a flow transmitter, replacement of a square root converter, and replacement of a degraded inverter in the turbine control system. F Failure analysis will be performed on the degraded inverter. |
| 05000352/LER-2008-002 | 19 May 2008 | Limerick | A valid automatic actuation of the reactor protection system occurred as a result of an invalid power/load unbalance actuation. T This invalid power/load unbalance actuation caused an actuation of the main generator protection lockout relays, which resulted in a Main Turbine trip. T The root cause of this event was the main generator protection relay logic that failed due to a defective relay. T The main generator relay testing procedures will be revised to include a circuit loop signal verification test to ensure reliability of newly installed equipment. |
| 05000352/LER-2008-001 | 12 May 2008 | Limerick | During a refueling outage a control rod was withdrawn with the source range monitor in the affected core quadrant inoperable. The source range monitor was restored to operable and the control rod was inserted. h The root causes of this event were that the control room supervisor and reactor operator failed to ensure the 1C Source Range Monitor was not bypassed and the control room supervisor failed to obtain a peer check by a second senior reactor operator prior to declaring it operable. The source range monitor channel check surveillance test was revised to ensure the source range monitors and intermediate range monitors are inserted and not bypassed. h The site procedure for returning equipment to service will be revised to require a peer check for operability decisions when returning equipment to service. |
| 05000353/LER-2008-002 | 31 March 2008 | Limerick | A valid automatic actuation of the reactor protection system occurred as a result of a phase-to-ground fault at the 2A Main Transformer low voltage (22 kV) bushing connection to the Iso- Phase bus. T The Main Generator neutral overvoltage relay actuated and tripped the generator protection lockout relays, which resulted in a Main Turbine trip. T The cause of the ground fault was overheating of the bolted connection between the Main Transformer bushing and the flexible links that connect the bushing to the Iso-Phase Bus. T The degraded bushings and flexible links were replaced. T The transformer maintenance procedure was revised to provide enhanced direction for assembly of the bolted connection. |