ENS 44910
ENS Event | |
|---|---|
16:25 Mar 16, 2009 | |
| Title | Short Term Loss of Supplemental Spent Fuel Cooling |
| Event Description | On 3/16/2009 at 1225, Unit 2 was in Mode 5 (Refueling), during natural circulation mode to support maintenance on the common suction line to both loops of Residual Heat Removal (RHR) Systems, both Secondary Side Supplemental Spent Fuel Pool Cooling pumps tripped. Earlier on the same day at 0550, the unit had been placed into natural recirculation mode when the RHR Loop 'A' was secured from the Shutdown Cooling mode of operation. In this mode the 'A' loop of Supplemental Spent Fuel Pool Cooling coupled with the 'A' loop of the Fuel Pool Cooling system was designated as the primary decay heat removal system and the 'B' loop of both systems were designated as the backup decay heat removal system. At the time of the secondary pump trips, the RHR Common loop suction was being placed under clearance.
The trip of the Secondary Side pumps caused a loss of the entire ('A' and 'B' loops) Supplemental Spent Fuel Pool Cooling System and resulted in a partial loss of the decay heat removal system. Both 'A' and 'B' loops of the Fuel Pool Cooling System remained in service. In addition, Unit 2 remained in an Active LCO for Technical Specification 3.9.7 due to securing all loops of Shutdown Cooling at 0550. The Supplemental Spent Fuel Pool Cooling system was restored to operation at 1245, and actions to restore RHR to the Shutdown Cooling Mode of operation were in progress. RHR 'A' Loop was restored to on available status at 1259, and placed in the Shutdown Cooling mode of operation at 1447. Based on the combination of systems out of service, and no supporting calculation to ensure Spent Fuel Pool Temperature remains below 150 degrees Fahrenheit (as described In the UFSAR), this could have prevented the fulfillment of the safety function for Decay Heat Removal. The safety significance of the loss of primary decay heat removal was minimal. During the loss of the Supplemental Spent Fuel Pool Cooling system, reactor vessel temperature rose by approximately 0.5 degrees Fahrenheit. Total heatup of the Spent Fuel Pool was less than 2 degree Fahrenheit. Allowed Technical Specification Heatup rate is limited to 100 degrees Fahrenheit per hour which the was not approached, or exceeded, at any time. Calculated time to boil (with no cooling supplied) was greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />; transient was brief in duration and did not challenge time to boil. At all times, the Fuel Pool Cooling System remained in service. There were no challenges to the reactor pressure vessel, or the fuel, due to the loss of decay heat removal. The Supplemental Spent Fuel Pool Cooling System was restored to operation at 1245. RHR was restored to service in the shutdown cooling made of operation at 1447. The licensee has notified the NRC Resident Inspector.
The licensee is retracting this report based on the following: On March 16, 2009, at 2017 hours0.0233 days <br />0.56 hours <br />0.00333 weeks <br />7.674685e-4 months <br />, the Control Room Supervisor made a notification (Event Number 44910) to the NRC Operations Center in accordance with 10 CFR 50.72(b)(3)(v)(B) (i.e., any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to remove residual heat). The notification was made as a result of a loss of the secondary side Supplemental Spent Fuel Pool Cooling (SSFPC) system pumps. At the time of the loss, both loops of Residual Heat Removal (RHR) shutdown cooling were out of service to support maintenance. In this mode, the 'A' loop of the SSFPC system coupled with the 'A' loop of the Fuel Pool Cooling (FPC) system was designated as the primary decay heat removal system and the 'B' loop of both systems were designated as the backup decay heat removal system. Loss of the secondary side SSFPC system pumps impaired the ability to remove decay heat; both the 'A' and 'B' loops of the FPC system remained in service. Basis for Retraction Event Notification 44910 was conservatively made because, although the FPC system remained capable of removing decay heat, there was no documented calculation which demonstrated that the FPC system could maintain the fuel pool and reactor cavity temperature at or below 150 degrees F, as described in the Updated Final Safety Analysis Report. An Engineering Calculation (i.e., 0041-0021. 'Fuel Pool Cooling Heat Removal Capability') demonstrating that the FPC system was capable of maintaining temperature below 150 degrees F, at that point in the outage, has been completed. As such, the March 16, 2009, loss of the secondary side SSFPC system pumps does not represent a condition that could have prevented the fulfillment of a safety function and this event is not reportable under 10 CFR 50.72(b)(3)(v)(B). Investigation of this condition is documented in the corrective action program in Nuclear Condition Report (NCR) 325496. The NRC Resident was notified of this retraction." Notified R2DO (Ernstes). |
| Where | |
|---|---|
Brunswick  North Carolina (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat | |
| Time - Person (Reporting Time:+3.87 h0.161 days <br />0.023 weeks <br />0.0053 months <br />) | |
| Opened: | William Woodbury 20:17 Mar 16, 2009 |
| NRC Officer: | Bill Huffman |
| Last Updated: | Apr 30, 2009 |
| 44910 - NRC Website
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WEEKMONTHYEARENS 449102009-03-16T16:25:00016 March 2009 16:25:00
[Table view]10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat Short Term Loss of Supplemental Spent Fuel Cooling 2009-03-16T16:25:00 | |