05000220/LER-2003-002
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2202003002R01 - 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 1 (NMP1) automatically scrammed from 100 percent power. A turbine trip due to load rejection caused the reactor scram with all control rods fully inserting into the core. A large disturbance in the electric grid, affecting parts of the northeastern United States and southern Ontario in Canada caused the turbine to trip on load rejection.
At approximately 1612 hours0.0187 days <br />0.448 hours <br />0.00267 weeks <br />6.13366e-4 months <br />, the grid disturbance resulted in degraded voltage conditions on NMP1 emergency buses. This caused the emergency buses to automatically isolate from off-site 115 KV electrical power, which resulted in the starting and loading of both emergency diesel generators (EDGs). Post scram, non-safety related loads initially remained powered by off-sfte 115 KV power and experienced significant voltage transients. By approximately 1622 hours0.0188 days <br />0.451 hours <br />0.00268 weeks <br />6.17171e-4 months <br />, the voltage transients had led to the loss of all reactor recirculation pumps and circulating water pumps. Loss of the circulating water pumps resulted in the eventual loss of the condenser.
Immediately following the scram, both motor driven feedwater pumps operated in the high pressure coolant injection (HPCI) mode, as designed, to restore reactor vessel water level. After recovery of the water level, the feedwater pumps continued to operate in the HPCI mode until the water level reached the "1-1i-Hr level (approximately one minute after the scram) at which point the feedwater pumps tripped as designed.
Turbine bypass valves (TBVs) and all six electromatic relief valves (ERVs) opened automatically to relieve reactor pressure after the scram. The TBVs relieve to the main condenser and the ERVs relieve to the suppression pool. Operators then manually operated two ERVs as needed to control reactor pressure and to assist In controlling reactor vessel water level.
All main steam isolation valves were manually dosed at 1623 hours0.0188 days <br />0.451 hours <br />0.00268 weeks <br />6.175515e-4 months <br /> and emergency condensers (EC) and ERVs were used to control reactor system pressure and reactor vessel level. The control rod drive injection (CRDI) system provided a source of makeup water to aid in maintaining reactor vessel water level.
Because of continued grid instability, an Unusual Event (UE) was declared at 1633 hours0.0189 days <br />0.454 hours <br />0.0027 weeks <br />6.213565e-4 months <br /> on August 14, 2003.
Although there was never a complete loss of both 115 KV off-site lines, the fluctuations In voltage were such that off-site power was deemed unstable and the Emergency Action Levels for an UE were deemed to be met. The 115 kV voltage transients ultimately led to the loss of the condensate system, which supplies the keep-fill system for the core spray system. Although the keep-fill system was out of service for 11.2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, an analysis of the event confirmed the core spray system remained fully available and operable. The EDGs continued to power the emergency buses until the grid was determined to be stable, at which time the emergency buses were paralleled to off-site power and the EDGs secured. EDG 103 was secured at 2339 hours0.0271 days <br />0.65 hours <br />0.00387 weeks <br />8.899895e-4 months <br /> on August 14, 2003 and EDG 102 was secured at 0016 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> on August 15, 2003. The UE was terminated at 0120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> on August 15, 2003.
NMP1 reached cold shutdown at 0126 hours0.00146 days <br />0.035 hours <br />2.083333e-4 weeks <br />4.7943e-5 months <br /> on August 16, 2003.
U. Cause of Event
A severe disturbance in the electric grid, affecting parts of the northeastern United States and southern Ontario in Canada caused the turbine trip on load rejection leading to the reactor scram.
111. Analysis of Event This event Is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) because of the critical reactor scram and because of the automatic start of the EDGs.
No Emergency Core Cooling Systems actuated or should have actuated.
All control rods fully Inserted on the scram.
Both 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 � J1 � N/A Condenser System � SG � N/A Recirculation System � AD � N/A Reactor Core � AC � N/A Emergency Diesel Generator � EK � N/A Emergency Buses � EB � N/A Non-Emergency Buses � EA � N/A 115 KV Off-site Power System � FK � N/A Circulating Water System � KE � N/A Emergency Condenser � BL � N/A Control Rod Drive System � AA � N/A Suppression Pool � NH � N/A Turbine � TA � TRB Condenser � SG, BL � COND Control rod � AA � ROD Motor � SJ � MO Bus � EA, EB � BU Pump � AD, KE, AA, SD � P Valve � SB, JI � ISV, EV, PCV Reactor Vessel � AD � RPV Condensate System � SD � N/A Core Spray System � BM � N/A