05000341/LER-2012-003
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 06-25-2012 |
|---|---|
| Report date: | 08-24-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 48047 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation |
| 3412012003R00 - NRC Website | |
Initial Plant Conditions:
Mode� 1 Reactor Power�26 percent
Description of the Event
On 6/24/2012 reactor power was reduced to about 20% and the Main Turbine Generator (MTG) [TA/TB] was taken off line to repair Main Unit Transformer 2B [EL]. On 6/25/2012, after completing repairs to the main unit transformer, reactor power was raised to approximately 22% and the unit was synchronized to the power grid [FK] at 1203 EDT. A power ascension began at 1234 EDT using a combination of recirculation flow and control rod pulls to increase reactor power. Feedwater Control [JB] was transferred from Startup Level Control to Single Element Automatic Control at 1300 EDT. Two separate south reactor feed pump vibration alarms (5D28) [IB] were received in the Main Control Room at 1306 and 1312 EDT. Investigation of these alarms revealed no abnormal indications or conditions. At 1322 to 1325 EDT multiple vibration related alarms were received for the south reactor feed pump [SJ], and the pump tripped at 1325 EDT, The north reactor feed pump was started in manual, and multiple Reactor Level High and Low alarms were received as operators worked to control level. A main condenser [SG] pressure increase was identified at 1329 EDT as condenser pressure rose from 0.6 psia to 2,2 psia. At 1330 hours0.0154 days <br />0.369 hours <br />0.0022 weeks <br />5.06065e-4 months <br /> a manual scram was performed by placing the reactor mode switch in shutdown in response to the degrading condenser vacuum.
All rods fully inserted [JC] and operators used the standby feedwater system to restore water level to the normal band. The lowest post scram water level was +154 inches which is below reactor water Level 3 and above Level 2. As expected, the High Pressure Coolant Injection [BJ] and Low Pressure Coolant Injection Systems [BO] did not actuate. No SRVs actuated, and all isolations [JE] and actuations associated with reactor water Level 3 occurred as expected.
Entry into the South Reactor Feed Pump Room after the scram revealed damage to the south reactor feed pump turbine which resulted in main condenser vacuum leaks. The vacuum leaks were isolated and condenser vacuum improved and stabilized at 4 psia following the event. Decay heat was removed using the main condenser via the turbine bypass valves. The south reactor feed pump/turbine is expected to be out of service for an extended time period.
Plant configuration changes were made to isolate the south reactor feed pump/turbine from plant systems and the reactor was restarted using the north reactor feed pump to feed the reactor. A steady 68% power level was achieved on 7/30/2012.
Significant Safety Consequences and Implications This event posed no significant safety implications because the reactor protection and safety related systems functioned as designed following the manual reactor trip. Important safety-related and non-safety related equipment performed as discussed in the description of the event, and plant response was as expected. There was no increase in reactor pressure, and the reactor core was adequately covered and cooled throughout the event.
This event is being reported under 10 CFR 50.73(a)(2)(iv)(A), as an event or condition that resulted in manual actuation of the reactor protection system and a reactor scram. A 4-hour non-emergency notification was made to the NRC Operations Center at 1638 EDT on June 25, 2012 (EN 48047) in accordance with 10 CFR 50.72(b)(2)(iv)(B) for an actuation of the reactor protection system.
Cause of the Event
The direct cause of the event was a degradation in condenser vacuum resulting in a manual scram. The degrading vacuum was caused by vacuum leaks that occurred as the south reactor feed pump was damaged during the event.
The cause of the mechanical failure of the south reactor feed pump is still under investigation.
Corrective Actions
This event was entered into the Fermi 2 Corrective Actions Program. The associated root cause evaluation is still in progress and includes a tear down of the south reactor feed pump and failure analysis. Additional corrective actions may be identified as a result of this effort.
The condition of the north reactor feed pump was assessed and it was determined to be undamaged. Each feed pump was designed to perform at up to 70% feedwater flow. Modifications were performed isolating the south reactor feed pump from its steam and water supplies and from the main condenser, so that the plant could be restarted and run at a lower power level using the north reactor feed pump while the cause of the failure of the south reactor feed pump turbine is investigated and the turbine is rebuilt or replaced. Procedures were revised to reflect running the plant on the north reactor feed pump. Sustained operation at a reduced power level was evaluated and determined to be achievable. Additional monitoring of the north reactor feed pump was performed and additional data gathering equipment has been installed for the north reactor feed pump to assist Engineering in evaluating vibration if needed.
Additional Information
A. Failed Component:
Component: Reactor Feedwater Turbine / Pump Function: Supplies Reactor Feedwater Manufacturer: Imo Delaval, Inc.
Model Number: Type KJDF Reactor Feed Pump Failure Cause: Unknown B. Previous Licensee Event Reports (LERs) on Similar Problems:
There are no other LERs on similar problems noted within the past five years