(CNN) -- The Nuclear Regulatory Commission will investigate an incident at a Nebraska nuclear plant in which three workers were accidentally exposed to radiation, it said in a statement Monday.
The incident occurred April 3, when workers at the Cooper Nuclear Station near Brownville, Nebraska, "removed a long tube contaminated with highly radioactive material through the bottom of the reactor vessel, rather than through the top as is usually done, triggering radiation alarms." The workers put down the tube and immediately left the area, the statement said.
Officials at the facility do not believe the workers received radiation exposures over limits set by the NRC, the commission said.
The facility is operated by the Nebraska Public Power District. Commission inspectors, who began their work Monday, "will look at the circumstances and decision-making by NPPD officials that led to the exposures, review the licensee's response to the event, calculate the exposures the workers received and review corrective actions taken to prevent a recurrence," the commission statement said.
A report will be issued within 45 days, according to the commission.
A nuclear crisis at Japan's Fukushima Daiichi plant, triggered by a March 11 magnitude-9.0 earthquake and subsequent tsunami, has led to a renewed focus on nuclear power in the United States and abroad.