This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.

FULTON, MO (KTVI) – Ameren’s Callaway 1 nuclear reactor unexpectedly shut down Wednesday. A release from the Missouri Coalition for the Environment says it was operating at 100% when it shut down just after midnight.

An unexpected main turbine trip caused the shutdown. A report posted to the US Nuclear Regulatory Commission states this, “Caused a reactor trip occurred on 12/03/2014 with the plant operating in Mode 1 at 100 percent power. As part of the plant design, an expected, valid actuation of the Auxiliary Feedwater System occurred in response to the reactor trip. As part of the Auxiliary Feedwater actuation, the ‘B’ Motor Driven Auxiliary Feedwater Pump to ‘D’ Steam Generator throttle valve did not throttle as expected and was manually isolated. All other systems functioned normally in response to the plant conditions. The plant is currently stable in Mode 3 at 0 percent power. Safety related buses are receiving normal off-site power and the grid is currently stable.

All control rods fully inserted on the reactor trip. Steam generator levels are being maintained by the AFW system and decay heat is being removed by the main condenser. No primary or secondary safety relief valves lifted during the transient.”