The nuclear power plant near Richland was supplying electricity to the grid again Thursday.
It reconnected to the grid at 4:30 a.m. and within three hours was at 24 percent power, said Energy Northwest spokesman John Dobken.
The Columbia Generating Station had its first scram, or unplanned shutdown, in more than six years Monday afternoon.
The control room received an indication that a system used to cool large pumps and other equipment had lost water. A valve being tested had not been properly isolated and the water had been sent down sideline piping.
Before the scram, the power plant had set generation records in December and January.
Scrams are not uncommon. The nation has 99 operating nuclear power reactions, and collectively, they had more than 110 scrams in the last two years, according to Energy Northwest.
At full power the plant produces enough electricity to supply a city the size of Seattle.