ENS 46410
ENS Event | |
|---|---|
11:18 Nov 10, 2010 | |
| Title | Rhr Pump Tripped While Operating in Shutdown Cooling Mode |
| Event Description | On November 10, 2010, at approximately 0518 hours0.006 days <br />0.144 hours <br />8.564815e-4 weeks <br />1.97099e-4 months <br />, 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 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />. 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. |
| Where | |
|---|---|
Duane Arnold  Iowa (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat | |
| LER: | 05000331/LER-2010-005 |
| Time - Person (Reporting Time:+2.52 h0.105 days <br />0.015 weeks <br />0.00345 months <br />) | |
| Opened: | Bob Murrell 13:49 Nov 10, 2010 |
| NRC Officer: | John Knoke |
| Last Updated: | Nov 10, 2010 |
| 46410 - NRC Website
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WEEKMONTHYEARENS 475112011-12-02T19:11:0002 December 2011 19:11:00
[Table view]10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat Low Pressure Coolant Injection Inoperable ENS 474482011-11-16T22:22:00016 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 ENS 471422011-08-11T08:27:00011 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 ENS 464102010-11-10T11:18:00010 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 ENS 431852007-02-24T23:56:00024 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 ENS 426802006-07-01T04:37:0001 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 2011-08-11T08:27:00 | |