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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 47511 | 2 December 2011 19:11:00 | 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat | Low Pressure Coolant Injection Inoperable | This condition is being reported in accordance with 10CFR50.72(b)(3)(v) as a condition that could have prevented fulfillment of a safety function. On 12/02/2011 at 1311 CST, the Low Pressure Coolant Injection (LPCI) was declared inoperable when voiding was discovered in the 'B' Residual Heat Removal (RHR) inject vent line. Initial review of this condition for immediate reportability under 50.72(b)(3)(v), event or condition that could have prevented fulfillment of a safety function, concluded the condition was not reportable based on the availability of other Emergency Core Cooling Systems (ECCS). Specifically, Core Spray and HPCI were both available to perform the function of emergency core cooling. On 12/03/2011 at 1650 CST, LPCI was declared operable based on further examinations to determine extent of voiding, system filling and venting and completion of supporting engineering evaluations. Subsequent reviews determined that the reportability decision under 50.72(b)(3)(v) as a event or condition that could have prevented fulfillment of a safety function should be based on safety function at the system level, rather than at the ECCS function level. The decision to report the inoperability of LPCI under 50.72(b)(3)(v) was made at 1319 CST on 12/08/2011. The licensee has notified the NRC Resident Inspector. | Core Spray Residual Heat Removal Emergency Core Cooling System Low Pressure Coolant Injection | |
| ENS 47448 | 16 November 2011 22:22:00 | 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat | Rhr Capability Affected Due to Both Trains of River Water Supply Hvac Systems Inoperable | At 1622 (CST) on November 16, 2011, NextEra Energy Duane Arnold declared the 'A' River Water Supply inoperable following discovery that the HVAC damper controller was installed in reverse. This would have closed the HVAC intake dampers on high temperature instead of opening them. At this time, the 'B' River Water Supply system was already inoperable for HVAC damper maintenance. This resulted in entering TS 3.7.2 Condition B for both River Water Supply systems inoperable (required action to restore a train or be shutdown in 12 hours). Both trains of River Water Supply inoperability potentially affect the plant capability to remove residual heat. Therefore, this event is being reported pursuant to the requirements of 10CFR 50.72(b)(3)(v)(B). At 1735 (CST) on November 16, 2011 Post Maintenance testing on the 'B' River Water Supply HVAC Dampers was completed and 'B' River Water Supply was declared operable, restoring the capability to remove residual heat. The NRC Resident Inspector has been notified.
The licensee is retracting this report based on the following: The purpose of this notification is to retract a previous report made on 11/16/2011 at 19:04 (ET) (EN 47448). Notification of the event to the NRC was initially made as a result of declaring both trains of the River Water Supply (RWS) system inoperable following the discovery that the HVAC damper controller was installed incorrectly. Subsequent to the initial report, NextEra Energy Duane Arnold (NextEra) has determined that the RWS system was capable of performing its safety function and was fully operable during the period that the HVAC controller was incorrectly configured. Specifically, based on the environmental conditions that existed during the period from November 8, 2011 to November 16, 2011, the non-TS RWS Intake HVAC system was Functional, but Degraded. This event is not considered a Safety System Functional Failure or a Condition Prohibited by TS and is not reportable to the NRC as a Licensee Event Report (LER) per 10 CFR 50.73. The NRC Senior Resident Inspector has been notified. Notified R3DO (Orth). | HVAC | |
| ENS 47142 | 11 August 2011 08:27:00 | 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown | Initiation of Technical Specification Required Shutdown | At 0327 (CDT) on August 11, 2011, NextEra Energy Duane Arnold commenced a reactor shutdown as required by TS 3.7.2.B for both River Water Supply subsystems inoperable. At 0008 (CDT), both River Water Supply subsystems were declared inoperable as a result of high differential pressure across the intake travelling screens. TS 3.7.2.B requires that one River Water Supply subsystem be restored or commence reactor shutdown. While the River Water Supply system is currently supplying rated flow, high differential pressure across the travelling screens indicates the potential for eventual degraded flow. This event is being reported pursuant to the requirements of 10 CFR 50.72(b)(2)(i), as a TS required shutdown. Additionally, the current condition of both trains of River Water Supply inoperable also potentially affects the plant capability to remove residual heat. Therefore, this event is also being reported under 10 CFR 50.72(b )(3)(v)(B), as an event that could prevent fulfillment of a safety function. The NRC Resident Inspector has been notified. | 05000331/LER-2011-002 | |
| ENS 46410 | 10 November 2010 11:18:00 | 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat | Rhr Pump Tripped While Operating in Shutdown Cooling Mode | On November 10, 2010, at approximately 0518 hours, with the plant in Mode 5 during Refueling Outage (RFO) 22, the 'A' Residual Heat Removal (RHR) pump tripped while operating in the shutdown cooling mode resulting in an interruption of the primary means of decay heat removal for approximately 30 minutes. During this period the maximum increase in reactor temperature was approximately 2 degrees Fahrenheit with a calculated time to boil of approximately 33.9 hours. There was no loss of decay heat removal due to the fact that both trains of Fuel Pool Cooling system and the Reactor Water Cleanup system remained in service. At the time of this event, the plant was in the process of restoring motive power to MO-1909, Outboard Shutdown Cooling Isolation valve. Motive power had previously been isolated to the valve as part of a preplanned evolution of transferring the power supply to 'B' Reactor Protection System (RPS). Due to a failure to isolate the control power to MO-1909 when RPS power had been transferred, MO-1909 automatically closed when motive power had been restored due the existence of a Primary Containment Isolation System (PCIS) signal that was initiated when 'B' RPS power had been transferred. The closure of MO-1909 resulted in the isolation of the common shutdown cooling pathway, and therefore prevented both the 'A' and the 'B' RHR systems from removing decay heat. Preliminary investigations into this event indicate that the failure to isolate control power to MO-1909 occurred due to an existing procedure deficiency for transferring RPS power supplies. As a result of the closure of MO-1909, Operations entered Abnormal Operating Procedure (AOP) 149, Loss of Decay Heat Removal, and Technical Specification (TS) Limiting Condition for Operations (LCO) 3.9.7 Condition A; Required RHR Shutdown Cooling Subsystem Inoperable and performed the required actions of the AOP and TS. At approximately 0547, shutdown cooling was restored when the 'C' RHR pump was placed in shutdown cooling. TS 3.9.7 and AOP 149 were subsequently exited at 0551. During the duration of this event adequate decay heat removal existed as part of the site's Shutdown Risk Management in that two loops of Fuel Pool Cooling were in-service and Feed and Bleed utilizing the Control Rod Drive pumps was available. Additionally, Reactor Water Cleanup was in service and remained in service for the duration of this event. Note that RHR shutdown cooling was considered available during this event due to the fact that there were no component failures associated with MO-1909 preventing it from being immediately re-opened. This event is being reported as an event or condition that at the time of discovery could have prevented fulfillment of a safety function of structures or systems that are needed to remove residual heat under 10 CFR 50.72 (b)(3)(v)(B). The (NRC) Resident Inspectors have been notified. | Reactor Protection System Primary Containment Isolation System Shutdown Cooling Residual Heat Removal Reactor Water Cleanup Decay Heat Removal Control Rod | 05000331/LER-2010-005 |
| ENS 43185 | 24 February 2007 23:56:00 | 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Loss of Normal Electrical Lineup Due to Grid Instability from Adverse Weather Conditions | Immediate notifications are being made for the following events: 1) Valid RPS non-critical actuation: 8 hour notification per 50.72(b)(3)(iv)(B) 2) Group 1, 2, 3, 4 and 5 isolations: 8 hour notification per 50.72(b)(3)(iv)(B) 3) Loss of decay heat removal (RHR Shutdown Cooling) isolated: 8 hour notification per 50.72(b)(3)(v)(A) 4) Auto start of 'A' Standby Diesel Generator and subsequent pick up of essential buses by both 'A' and 'B' Standby Diesel Generators: 8 hour notification per 50.72(b)(3)(iv)(A). Just prior to the event the plant was in Mode 5 with core alterations in progress and the 'B' Standby Diesel Generator being run manually for post maintenance testing. At 1756 hours on 2/24/2007, core alterations were halted due to indications that the grid was becoming unstable. Freezing rain had been in progress all day. At 1757 hours an electrical transient occurred as some of the offsite lines coming into the switchyard were lost. The 'B' Reactor Protection System (RPS) bus was lost. A full RPS trip occurred from loss of the 'B' RPS bus and too few inputs to the 'A' RPS trip logic. The loss of 'B' RPS power resulted in Groups 1, 2, 3, 4 and 5 isolations. The Group 4 isolation caused a loss of decay heat removal capability (RHR Shutdown Cooling isolated). The 'A' Standby Diesel Generator auto started, but the 1A3 essential bus remained powered from offsite sources. The 'B' SBDG was already running. The 1A4 bus also remained powered from offsite sources. At 1820 hours, a degraded voltage trip signal was received resulting in both emergency diesel generators picking up their respective buses. At present, the essential buses 1A3 and 1A4 are being carried by the emergency diesel generators. Only one of the six lines supplying offsite power to the site is available. Both non-essential buses are being powered from the one offsite line. The emergency buses will remain on the emergency diesel generators until additional offsite lines can be restored. RHR Shutdown Cooling was restored at 1826 hours. The licensee notified the NRC Resident Inspector, State and local officials. | Reactor Protection System Emergency Diesel Generator Shutdown Cooling Decay Heat Removal | |
| ENS 42680 | 1 July 2006 04:37:00 | 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat | Common Cause Degradation to Rhr Service Water Pump Motor Cooling Coils | At 2337 of 06/30/2006, it was determined that 3 out of 4 Residual Heat Removal Service Water (RHRSW) pumps were inoperable due to a common cause. Each of the 3 affected RHRSW pumps contained motor cooling coils that had experienced flow induced erosion which had significantly reduced the wall thickness of the cooling coil material. In some cases, the thinning was sufficient to cause through wall leakage of water into the upper motor bearing oil reservoir and subsequently displace oil out of the reservoir. Currently, 2 of the 3 affected RHRSW pumps have been removed from service for repairs. 1 of those pumps is expected to be returned to service shortly. The 3rd affected pump remains available for use, but has been conservatively declared inoperable based on Engineering evaluation that indicates a common cause failure mechanism likely exists, based on common fabrication methods used for all RHRSW pump motor cooling coils. The 4th (unaffected) RHRSW pump remains Operable because its cooling coil was replaced approximately 1 month ago. Under these conditions, sufficient confidence that the affected RHRSW pumps could perform their post LOCA mission does not exist. With only 1 of the 4 RHRSW pumps remaining Operable, the RHRSW System is not capable of performing its safety function. This event is reportable under 10CFR50.72(b)(3)(v)(B) and 50.73(a)(2)(v)(B). With 3 out of the 4 RHRSW pumps considered inoperable, the licensee is currently in an 8 hour Tech Spec LCO action statement. However, with expected the return of one of these pumps to operable status within the next hour, the LCO will convert to a 7 day action statement. The licensee notified the NRC Resident Inspector. | Service water Residual Heat Removal Service Water |