On March 20 , 1978 , a failure of power supply for the plant 's non-nuclear instrumentation system led to steam generator dryout . ( ref NRC LER 312/78 - 001 ) . In an ongoing study of " precursors " that could lead to a nuclear disaster if additional failures were to have occurred , in 2005 the United States Nuclear Regulatory Commission concluded that this event at Rancho Seco was the third most serious safety-related occurrence in the United States ( Behind the Three Mile Island accident and the cable tray fire at Browns Ferry )
Three Mile Island accident
Three Mile Island accident
Rancho Seco Nuclear Generating Station