Entergy Corp. shut down the plant Sunday, one day after operators found a tank leaking faster than federal regulators permit.
Palisades is along Lake Michigan in Van Buren County's Covert Township, 80 miles east-northeast of Chicago. It's had nine shutdowns since September 2011.
The Nuclear Regulatory Commission said Palisades discharged 79 gallons of "very slightly radioactive water" into Lake Michigan. It says there's no health effect.
U.S. Rep Fred Upton, R-St. Joseph called the situation "unacceptable" Tuesday.
Entergy Vice President Terry Young said the New Orleans-based company shares Upton's expectations and is committed to ensuring safety.