The Department of Energy, in a turnaround, has acknowledged it received reports from Du Pont Co. about nuclear reactor accidents at the Savannah River Plant in South Carolina over a 28-year period. On Friday, department officials had said they hadn't known about the accidents. C. Anson Franklin, assistant secretary for congressional, intergovernmental and public affairs at the Energy Department, said Monday that Du Pont had notified the Energy Department and its predecessor agency, the Atomic Energy Commission, of the incidents.