05000410/LER-2003-002
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4102003002R00 - NRC Website | |
I. Description of Event
On August 14, 2003 at approximately 1611 hours0.0186 days <br />0.448 hours <br />0.00266 weeks <br />6.129855e-4 months <br />, Nine Mile Point Unit 2 (NMP2) automatically scrammed from 100% rated thermal power. The scram resulted from a turbine control valve fast closure trip that was generated as the electrohydraulic system (ERG) attempted to control turbine speed and reactor pressure by re-positioning turbine control and turbine bypass valves in response to a severe disturbance in the electric grid.
As a result of the grid disturbance, undervoltage conditions occurred on each of three emergency buses. Because of the undervoltage conditions, at approximately 1612 hours0.0187 days <br />0.448 hours <br />0.00267 weeks <br />6.13366e-4 months <br /> each of the three divisional (Division 1, 2, and 3) emergency diesel generators (EDG) automatically started and powered its associated emergency bus, as designed.
Although there was never an actual loss of 115 KV off-site power (both off-site 115 KV lines remained energized), the fluctuations in voltage were such that the grid was deemed unstable and the Emergency Action Levels for an Unusual Event (UE) were deemed to be met. At 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> a UE was declared because of grid instability. After grid stability had been established, operators began transferring the emergency buses to off-site power and securing the associated EDG. Division 1 and Division 3 emergency buses were aligned to off-site power through their normal transformer. The Division 2 emergency bus was aligned to off-site power through an alternate transformer that required additional load transfers to maintain divisional separation. The Division 1 EDG was secured at 0137 hours0.00159 days <br />0.0381 hours <br />2.265212e-4 weeks <br />5.21285e-5 months <br /> on August 15, 2003, the Division 3 EDG was secured at 0401 hours0.00464 days <br />0.111 hours <br />6.630291e-4 weeks <br />1.525805e-4 months <br /> on August 15, 2003 and the Division 2 EDG was secured at 0712 hours0.00824 days <br />0.198 hours <br />0.00118 weeks <br />2.70916e-4 months <br /> on August 15, 2003. The UE was terminated at 0734 hours0.0085 days <br />0.204 hours <br />0.00121 weeks <br />2.79287e-4 months <br /> on August 15, 2003 after off-site power was restored to all three emergency buses.
After the scram, the turbine tripped as a result of high reactor vessel water level. The high water level occurred because the electrical transient had caused the feedwater flow control valves to lock up at approximately 55% open.
The high reactor vessel water level also tripped the running feedwater pump, 2FWS-P1C, as designed. Operators had previously tripped feedwater pump 2FWS-P1B due to increasing reactor water vessel level. Feedwater pump FWS-P1C had been left running while preparations were being made to start reactor core isolation cooling (RCIC).
Because the feedwater flow control valves had locked up, operators used RCIC to maintain reactor water level.
Reactor pressure was controlled using the turbine bypass valves.
NMP2 remained in hot shutdown until the unit was restarted.
Ii. Cause of Event A severe disturbance in the electric grid, affecting parts of the northeastern United States and southern Ontario in Canada, caused the cycling of the turbine control valves and turbine bypass valves leading to a reactor scram.
WIC FORM 36.6A (1.2C01) ill. Analysis of Event This event is reportable In accordance with 10 CFR 50.73 (a)(2)(iv)(A) because of the reactor scram while critical and because of the automatic start of the EDGs.
No Emergency Core Coating Systems actuated or should have actuated.
All rods fully Inserted on the scram.
All three EDGs started and ran as designed.
Based on the above, the event did not pose a threat to the health and safety of the public.
IV. Corrective Actions
None.
V. Additional information 1. Failed Components:
None 2. Previous similar events:
None 3. Identification of components referred to in this Licensee Event Report:
Components IEEE 805 System ID � IEEE 803A Function Feedwater System SJ N/A Main Steam System SB N/A Main Turbine System TA N/A Turbine Bypass System JI N/A Turbine Control System TG N/A Reactor Core Isolation Cooling BN N/A Emergency Buses EB N/A Non-Emergency Buses EA N/A Recirculation System AD N/A Reactor Core AC N/A Emergency Diesel Generator EK N/A 115 KV Off-site Power System FK N/A Control Rod Drive System AA N/A Turbine TA TRB Control rod AA ROD Bus EA, EB BU Pump AD, AA P Valve SB, SJ, .11 ISV, PCV Reactor Vessel AD RPV