Entergy said in a news release that the 7:45 a.m. accident at its Arkansas Nuclear One power plant in Russellville involved a generator stator that fell while being moved out of a turbine building, Arkansas Online reported.
The (Russellville) Courier reported a person who witnessed the accident said the large piece of equipment fell from a crane.
OzarkFirst.com reported the other three victims suffered injuries that were not life threatening. The names of the victims had not been reported.
The company said the plant's No. 1 unit was in a "refueling outage" and the No. 2 unit automatically shut down because of the incident, which was classified as an unusual event, the lowest of four emergency classifications designed by the Nuclear Regulatory Commission.
Entergy officials said there was no danger to the public and state Health Department official Chris Meyer called it an industrial accident that did not involve any radiation or affect the reactor, Arkansas Online said.
"We are deeply saddened by what has happened today," Jeff Forbes, Entergy's executive vice president and chief nuclear officer, said in the release. "Our greatest sympathy is with the family and friends of the employee who lost his life, and with those who sustained injuries.
"I also want to express my sorrow and support to all those who work at Arkansas Nuclear One. I know this is especially hard on them."
The plant's website the two generating units provide about 30 percent of Arkansas' total energy demand.