Event Notification Report for February 28, 1999

- AUTO Rx TRIP FROM 60% DUE TO MAIN TURBINE TRIP DUE TO LOW AUTO STOP OIL PRESSURE -

AT 0130 ON 02/28/99, THE UNIT 1 REACTOR AUTO TRIPPED FROM 60% POWER DUE TO A MAIN TURBINE TRIP (WITH REACTOR POWER ABOVE THE P-9 SETPOINT OF 50% POWER) DUE TO LOW AUTO STOP OIL PRESSURE. ALL CONTROL RODS INSERTED COMPLETELY. THE AUXILIARY FEEDWATER SYSTEM AUTO STARTED TO MAINTAIN STEAM GENERATORS AT NORMAL WATER LEVELS. NO SAFETY OR RELIEF VALVES LIFTED AND STEAM IS BEING DUMPED TO THE MAIN CONDENSER. UNIT 1 IS STABLE IN MODE 3 (HOT STANDBY). THE LICENSEE IS INVESTIGATING THE CAUSE OF THE LOW AUTO STOP OIL PRESSURE.

THE LICENSEE PLANS TO INFORM THE NRC RESIDENT INSPECTOR.

UNIT PLACED IN UNANALYZED CONDITION DUE TO CLOSURE OF CONTAINMENT ISOLATION VALVE

At 0400 CST on 02/28/99, the plant was incorrectly placed in an unanalyzed condition when a manual valve between the reactor coolant drain tank and the chemical volume control holdup tank was closed. This manual valve was located downstream of two containment isolation valves that had failed timing tests, and the manual valve was being relied upon to maintain containment integrity in accordance with NRC Generic Letter 96-06. However, when the manual valve was closed, overpressure protection for that line was lost. The valve subsequently was reopened, restoring the penetration at 0800 CST on 02/28/99. The reportability of this condition was identified at 1650 CST. The NRC resident inspector has been informed of this notification.

UNIT OUTSIDE OF DESIGN BASIS DUE TO SHEARED VALVE STEM IN RHR SYSTEM

"On 2/11/99 the Unit 1 'B' RHR Loop was removed from service for a scheduled maintenance work window. During the system restoration at 2330 Hrs, it was identified that the keepfill system did not respond as expected. An investigation into the degraded keepfill condition was initiated. An Operability Determination was performed and it was determined that the RHR system was operable with the degraded keepfill system.

"On 2/16/99 at 0400 hrs, the Unit 1 'A' RHR Loop was removed from service to perform a scheduled maintenance work window. The 'A' RHR Loop was returned to service at 2115 hrs on 2/16/99 and is currently operable.

"On 2/26/99, after further trouble shooting of the degraded keepfill condition on the 'B' RHR Loop it was determined that the most likely cause was the RHR Loop 'B' Injection Flow Control Valve, HVI51F017B, being failed closed. The 'B' RHR Loop was declared inoperable at 1600 Hrs on 2/26/99. The valve was inspected and found to have the stem sheared from the disk. Following a review of the time line of the events, it was identified that both the 'A' and 'B' RHR Loops were inoperable from 0400 hrs to 2115 hrs on 2/16/99 during the scheduled maintenance work windows for the 'A' RHR Loop.

"This report is being made due to the Plant being Outside of the Design Basis requiring a 1 Hr ENS Notification under 10CFR50.72(b)(1)(ii)(B) and a Loss of a Safety System requiring a 4 Hr ENS notification under 1OCFR50.72(b)(2)(iii)(B)."

The NRC resident inspector has been informed of this notification.

-AUTO Rx TRIP ON HIGH RCS PRESSURE DUE TO MAIN TURBINE CONTROL VALVES FAILING CLOSED-

At 1609 on 02/28/99, the Unit 2 electro-hydraulic control system lost various power supplies. Main steam pressure increased from a normal 900 psig to 942 psig and reactor power increased from 100% to 100.4%. The main turbine control valves had throttled closed for unknown reasons causing the main steam pressure to increase. Main feedwater was throttled to reduce main steam header pressure since the turbine header pressure control station had no effect. Unit 2 was stabilized at 98.5% power with the main steam pressure at 938 psig and the main feedwater master control stations and the reactor control station in manual.

At 2040 on 02/28/99, Unit 2 automatically tripped from 98% power due to a reactor protection system actuation (reactor coolant system high pressure trip). All control rods inserted completely. The main steam code safety valves lifted to dump steam to the atmosphere for approximately 10 minutes. Plant operators verified that the valves reseated properly. Steam is being dumped to the main condenser. The main feedwater system remained operational throughout the event. The reactor control station was in automatic at the time of the trip. Unit 2 is stable in hot shutdown mode.

The licensee is investigating the cause of the main turbine control valves failing closed and plans to make necessary repairs.

Units 1 and 3 remain at 100% power and were unaffected by this event.

The licensee notified the NRC Resident Inspector.