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| Entered date | Event description | |
|---|---|---|
| ENS 54035 | 29 April 2019 20:01:00 | During power ascension on April 29, 2019, at 1630 (EDT), Nine Mile Point Unit 1 power and pressure oscillations were observed with reactor power at approximately 82 (percent). At time 1633 (EDT), the reactor was manually scrammed when the scram criteria of greater than 4 (percent) APRM power oscillations were observed in accordance with special operating procedures. All control rods fully inserted and all plant systems responded per design following the scram. Following the manual scram, the High Pressure Coolant Injection (HPCI) System automatically initiated as expected. At Nine Mile Point Unit 1, a HPCI system actuation signal on low Reactor Pressure Vessel (RPV) level is normally received following a reactor scram, due to level shrink. HPCI is a flow control mode of the normal feedwater systems, and is not an Emergency Core Cooling System. At 1633 (50 seconds after the reactor scram), RPV level was restored above the HPCI System low level actuation setpoint and the HPCI System initiation signal was reset. Pressure control was established on the Turbine Bypass Valves, the preferred system. No Electromatic Relief Valves actuated due to this scram. Nine Mile Point Unit 1 is currently in Hot Shutdown, with reactor water level and pressure maintained within normal bands. The offsite grid is stable with no grid restrictions or warnings in effect. The cause of the power oscillations is currently under investigation. The NRC Resident Inspector was notified. The New York State public service commission was notified. |