The workers were moving the equipment from the turbine building at an Entergy Arkansas plant in Russellville, about 70 miles northwest of Little Rock. The three injured workers were taken to a hospital. The company stressed that there is no danger to the public.
The Arkansas Nuclear One plant provides about 30 percent of the state's energy demand, according to Entergy.
"We are deeply saddened by what has happened today," said Jeff Forbes, Entergy's chief nuclear officer. "Our greatest sympathy is with the family and friends of the employee who lost his life, and with those who sustained injuries."
Entergy's two nuclear reactors were shut down after the accident.
The plant was placed under an "unusual event classification," which is the lowest of four emergency classifications designated by the Nuclear Regulatory Commission.
Entergy provides electricity to 2.8 million customers in Arkansas, Louisiana, Mississippi and Texas.