05000341/LER-2010-002
| Docket Number6 6 2010 2010 - 002 -000 08 03 2010 05000 | |
| Event date: | 6-6-2010 |
|---|---|
| Report date: | 08-03-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 45979 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(a)(1)(i), Emergency Class Declaration |
| 3412010002R00 - NRC Website | |
Initial Plant Conditions:
Mode � 1 Reactor Power� 100 percent
Description of the Event
At 0238 hours0.00275 days <br />0.0661 hours <br />3.935185e-4 weeks <br />9.0559e-5 months <br />, on June 6, 2010, severe weather caused a loss of 345kV Division II offsite power.
A Turbine Control Valve (TCV) fast closure occurred and the Reactor Protection System (RPS) [JD] initiated a reactor scram as a result of the turbine trip [TA]. All control rods fully inserted into the reactor core. Reactor Pressure Vessel (RPV) Level 3 isolation groups for Residual Heat Removal (group 4), Drywell Sumps (group 13) and Transversing Incore Probes (group 15) [JM] isolated as designed. RPV level reached 142 inches above Top of Active Fuel (TAF). Reactor Core Isolation Cooling (RCIC) [BN] was manually started to maintain RPV level. RPV Pressure was controlled on the Turbine Bypass Valves (BPV) and as expected no Safety Relief Valves (SRVs) operated since no significant increases in pressure occurred. Decay heat was removed using the main condenser. An Unusual Event due to Natural Destruction Phenomena Affecting the Protected Area was declared at 0253 hours0.00293 days <br />0.0703 hours <br />4.183201e-4 weeks <br />9.62665e-5 months <br />.
Additionally, two of the three. Division I 120 kV offsite supply lines were lost due to the storm.
Division I buses were powered by the remaining offsite feed. The Division II Emergency Diesel Generators (EDGs) [DG] started automatically and fed the Division II buses.
The National Weather Service identified a Category EF1 tornado in the area of the Fermi 2 station when the Division II offsite power was lost.
At 0417 hours0.00483 days <br />0.116 hours <br />6.894841e-4 weeks <br />1.586685e-4 months <br />, an Alert was declared due to Natural Destruction Phenomena Affecting the Plant Vital Area. Physical damage to the Auxiliary Building [NF] was identified during station inspection following the high wind condition. The damaged structures included the Auxiliary Building, Turbine Building roof, South Turbine Building roll up door and the Cooling Towers. On June 7, 2010, at 0220, the Alert was terminated.
The Main Generator was synchronized to the grid at 1921 hours0.0222 days <br />0.534 hours <br />0.00318 weeks <br />7.309405e-4 months <br />, on June 16, 2010, following repairs to offsite power feeds and station structures.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event or condition that resulted in a valid actuation of RPS and other plant Engineered Safety Features and 10 CFR 50.73(a)(2)(iii) Natural Phenomenon.
All safety related equipment functioned as expected in response to the scram. All control rods were verified to have fully inserted following the scram. All reactor parameters were maintained well within analyzed limits. Turbine Bypass Valves opened to control reactor pressure. No significant increase in reactor pressure occurred as a result of the event; as such, no SRVs lifted.
Reactor vessel water level decreased as expected from the normal level of 196 inches to approximately 142 inches. As a result of the loss of Division II power, the feedwater system was not immediately available following the scram but could have been restored if needed. RCIC and Standby Feedwater were utilized to control water level in the RPV. No Emergency Core Cooling Systems (ECCS) were challenged. Reactor vessel Level 3 Containment Group isolations were received per design. EDGs 13 and 14 automatically started as designed and provided power to Division II safety related busses 65E and 65F.
An Unusual Event and Alert were declared in accordance with the Emergency Plan (Reference Emergency Notification 45979).
There was no change in radiological risk following the event. The Division I Standby Gas Treatment System (SGTS) was initiated to maintain Secondary Containment in accordance with operating procedures. The Division I SGTS Stationary Iodine Particulate and Noble Gas (SPING) radiation monitors, monitored the SGTS exhaust stack with no anomalies noted. There was no active release in progress from the Turbine Building HVAC, Radwaste HVAC, or Reactor Building HVAC exhaust stacks.
Cause of the Event
A category EF1 tornado caused a Reactor Scram, loss of Division II offsite power, and the release of a blow-out panel on the Auxiliary Building.
Corrective Actions
The damage to 120 kV Division I and 345 kV Division II offsite power was repaired and all offsite circuits were restored prior to Reactor restart. Repairs were also made to important station structures including the Auxiliary Building east wall, the Turbine Building roof and south roll up door and the Cooling Towers.
Materials from the openings in the Auxiliary Building wall and Turbine Building roof were surveyed to verify no radioactive material was present. Interior surfaces near the openings were also checked for contamination. Grab samples for airborne activity were also taken in the vicinity of each opening.
All operating air monitoring filters were removed and analyzed for radionuclides. No radionuclide activity was detected.
Additional Information
A. Failed Components: None B. Previous LERs on Similar Problems: There have been no previous events involving a tornado.