Police and the Nebraska Public Power District are investigating the death of a worker at the Cooper nuclear plant Tuesday, although the circumstances suggest he died from natural causes.The control room received a report at 7:38 a.m. that a radiological technician was found unresponsive on the reactor's refueling floor. EMTs and sheriff's office personnel arrived on site but found that the man had died, according to a report filed with the Nuclear Regulatory Commission. Although he was working in a contaminated area, he was wearing appropriate safety gear and contamination was not found on his body.The Nemaha County Sheriff's Office did not suspect foul play or an industrial accident, the Lincoln Journal Star reported. Police identified the man as Ronald Nurney, 66, from Smithfield, Va. He was a Bartlett Nuclear contractor who had worked at Cooper in the past.A release from NPPD said the death was believed to be the result of natural causes. Nonetheless, the plant is investigating the incident and has notified the Occupational Safety and Health Administration.