Kaiser-Hill Co. officials on Thursday said they have completed the $7 billion Rocky Flats cleanup - a major milestone in the former nuclear- trigger plant's transformation into a public wildlife refuge. The cleanup is the largest completed on a U.S. Department of Energy or federal Superfund toxic-waste site, project managers said. More than 21 tons of weapons- grade nuclear material was removed, enough radioactive waste to fill a string of rail cars 90 miles long.