BRIDGMAN, Mich. (AP) — A nuclear power plant in southwestern Michigan says a coolant water safety valve opened unexpectedly after one of its reactors was shut down for refueling and maintenance.

Indiana Michigan Power says Cook Nuclear Plant's Unit 1 reactor was shut down early Wednesday as planned, but less than an hour afterward a valve that's part of its reactor coolant supply system opened. Fluid went into a collection tank.

No injuries were reported. The plant notified the Nuclear Regulatory Commission and activated its emergency plan until about 8 a.m.

The plant is along Lake Michigan in Berrien County's Lake Township, near Bridgman. IMP says the reactor is shut down and stable. It says an equipment failure caused the valve to open. Cook's Unit 2 remains at 100 percent power during the shutdown.