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On November 10, 2010, at approximately 051 … 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. </br>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. </br>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).</br>The (NRC) Resident Inspectors have been notified.C) Resident Inspectors have been notified.
11:18:00, 10 November 2010 +
46,410 +
13:49:00, 10 November 2010 +
11:18:00, 10 November 2010 +
On November 10, 2010, at approximately 051 … 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. </br>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. </br>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).</br>The (NRC) Resident Inspectors have been notified.C) Resident Inspectors have been notified.
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