In a normally functioning plant, coolant water is circulated out of the reactors and chilled.

CNN: STORY HIGHLIGHTS

The ammonia coolant for the power channel, one of eight used to supply electricity to the station, would likely have run out by late Friday morning had it not been shut down, NASA said.

CNN: SHARE THIS

The ammonia coolant for the power channel, one of eight used to supply electricity to the station, is likely to run out by late Friday morning and it will be shut down, NASA said.

CNN: SHARE THIS