A release of radioactive contaminants at the Vermont Yankee nuclear power plant led to a brief evacuation of 25 workers, regulators and utility officials said.
The release occurred Monday while the cover of a reactor vessel was being removed for refueling, said Robert Williams, spokesman for the utility company Entergy Nuclear.
The cover was placed too close to a fan, which spread airborne contaminants, Williams said.
Williams says the workers were evacuated from the top floor of the reactor building but returned about four hours later after they were checked for exposure to radiation.
The workers, both Entergy employees and contractors, were exposed to a "very minor" amount of radiation that was below their yearly exposure limits, said William Irwin, radiological health chief for the Vermont Department of Health.
"There was never any issue of public health," Irwin said.
The release came during the power plant's regular refueling and maintenance outage, which is scheduled to last three weeks.
The Federal Nuclear Regulatory Commission is investigating, spokesman Neil Sheehan said.