PNO-III-08-011, D. C. Cook - Unit 1 Manual Trip Due to Main Turbine Generator Fire and Significant Fire Suppression System Degradation
| ML082660516 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 09/22/2008 |
| From: | Ross Telson Division of Nuclear Materials Safety III |
| To: | |
| References | |
| PNO-III-08-011 | |
| Download: ML082660516 (2) | |
September 22, 2008 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE -- PNO-III-08-011 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information is as initially received without verification or evaluation, and is basically all that is known by the Region III staff on this date.
Facility DC Cook Nuclear Plant Indiana Michigan Power Company American Electric Power (AEP)
Bridgeman, MI Docket: 50-315 License: DPR-58 Licensee Emergency Classification X Notification of Unusual Event
__ Alert
__ Site Area Emergency
__ General Emergency
__ Not Applicable
SUBJECT:
DC COOK UNIT 1 UNIT MANUAL TRIP DUE TO MAIN TURBINE GENERATOR FIRE AND SIGNIFICANT FIRE SUPPRESSION SYSTEM DEGRADATION DESCRIPTION:
At 8:05 p.m. EDT on September 20, 2008, with the DC Cook Units 1 and 2 at full power, a malfunction in the Unit 1 main turbine generator (TG) led to high vibrations and loud rumbling that caused operators to manually trip the Unit 1 reactor and TG and to break main condenser vacuum. Breaking vacuum helped stop the TG but resulted in loss of the secondary power conversion system (e.g., main feed water system and condenser bypass valves). A TG hydrogen fire resulted when high TG vibration apparently caused TG hydrogen seals to fail.
Portions of the Unit 1 TG fire suppression system automatically actuated. Operators actuated manual portions of the system and called for both site and local fire departments which responded. It was determined that all reactor safety systems operated as designed (e.g. all control rods fully inserted and the auxiliary feed water system activated), and the steam generator atmospheric relief valves operated to remove decay heat.
At 8:18 p.m., the licensee declared a notification of unusual event (NOUE), the lowest of four emergency classifications, for a fire in the Protected Area lasting more than 15 minutes and a flammable gas release that affected plant operation. The fire was extinguished by 8:30 p.m. At 8:46 p.m., the NRC entered Monitoring Mode.
At 9:25 p.m., a fire system low pressure alarm signaled a problem with the system. Operators stopped the sites three fire pumps. The site fire protection header had ruptured and one of the sites two fire protection storage tanks had been pumped dry. By 11:09 p.m., operators had isolated the rupture and established alternate fire water supplies. By approximately 2;00 a.m.
one of the three fire pumps (a motor-driven unit) was restored to operable status. A second fire pump (one of the two diesel-driven units) was restored to operable status mid-day Sunday.
The licensee inspected Unit 2 as though it had been subjected to a seismic event because the turbine building had experienced vibrations associated with the Unit 1 TG failure. No apparent damage was observed on Unit 2.
At 4:09 a.m, the licensee completed preliminary plant evaluations and exited the NOUE. At 4:17 a.m., the NRC exited monitoring mode. There were no personnel injuries.
Unit 1 has since been cooled down and depressurized. It entered Mode 5 on 3:27 a.m.
Monday, September 22. Unit 2 continues to operate at full power.
The NRC sent a fire protection inspector to the site Sunday afternoon and intends to launch a Special Inspection Team today. The onsite inspectors continue to monitor licensee activities associated with full restoration of the site-wide fire protection system and investigation into the causes of both the TG failure and fire suppression system failure.
The State of Michigan has been notified. The information in this preliminary notification has been reviewed with licensee management.
This information is current as of 7:30 a.m. (CDT) on September 22, 2008.
CONTACT:
Ross Telson (630) 829-9619