A Rancho Seco nuclear power plant worker was exposed to a high dose of radiation, officials said. Carl Andognini, Sacramento Municipal Utility District nuclear chief, said a microscopic piece of radioactive cobalt was discovered on the clothing of a Rancho Seco welder. Andognini said that under the worst possible assessment of exposure, the unidentified worker received a dose of 450 rems, six times the legal lifetime skin dose of 75 rems.