At 1235 CST on December 24, 2020, Callaway Plant was in Mode 1 at approximately 90 percent power when a turbine trip/reactor trip, from a vital main generator trip signal, occurred. All safety systems responded as expected with exception of an indication issue with the 'B' Feedwater Isolation Valve, which was confirmed closed, and one intermediate range nuclear instrumentation channel which failed off-scale low following the trip. A valid Feedwater Isolation Signal and Auxiliary Feedwater Actuation Signal were also received as a result of the plant trip. The plant is being maintained stable in Mode 3.
All control rods fully inserted from the reactor trip signal, and decay heat is being removed via the Auxiliary Feedwater and Steam Dump Systems.
Automatic Reactor Scram Due to Main Turbine / Generator Trip
On December 11, 2020 at 1204 CST, Grand Gulf Nuclear Station (GGNS) experienced an Automatic Reactor Scram from 100 percent Reactor Power after a Main Turbine and Generator Trip.
All Control Rods fully inserted and there were no complications. All systems responded as designed.
Reactor pressure is being maintained with Main Turbine Bypass Valves. Reactor water level is being maintained in normal band with the condensate system.
No radiological releases have occurred due to this event from the unit.
NUREG/IA-0521 Analysis with Trace Code of Pkl III Tests G1.2. Study on Heat Transfer Mechanisms in the SG in Presence of Nitrogen, Steam and Water as a Function of the Primary Coolant Inventory in Double Loop Operation