In 1966, SMUD purchased in southeast Sacramento County for a nuclear power plant, which was built in Herald, south-east of downtown Sacramento. In the early 1970s, a small pond was expanded to a lake to serve as an emergency backup water supply for the station. The lake has always received its water from the Folsom South Canal and has no relationship with the power plant's daily water supply. Surrounding the lake is of recreational area originally operated by the County of Sacramento for day-use activities. The 2,772 MWt Babcock & Wilcoxpressurized water reactor achieved initial criticality on September 16, 1974 and entered commercial operation on April 17, 1975. On March 20, 1978, a power supply failure for the plant's non-nuclear instrumentation system led to steam generator dryout. This triggered an automatic reactor shutdown. In a 2005 document, the United States Nuclear Regulatory Commission indicated that it was the third most serious safety-related occurrence in the United States to date. The plant operated from April 1975 to June 1989, but had a lifetime capacity average of only 39%; it was closed by public vote on June 7, 1989 after multiple referenda that resulted from a long record of multiple annual shut-downs, cost over-runs, mismanagement, multiple accidents that included radioactive steam releases, restarts after unresolved automatic shut-downs, and regular rate increases that included a 92% increase over one three-year span. Operation of the recreational area was assumed by SMUD in 1992. In cooperation with the Nature Conservancy, SMUD dedicated in June 2006 the Howard Ranch Nature Trail, a seven-mile long trail that follows riparian and marsh habitat along Rancho Seco Lake and the adjoining Howard Ranch that once belonged to the owner of the famous racehorse Seabiscuit. All power-generating equipment has been removed from the plant, and the now-empty cooling towers remain a prominent part of the local landscape. Also scattered throughout the area around the plant are abandoned civil defense sirens that at one time would have warned people of a radioactivity release from the station. Additions to SMUD's Rancho Seco property have included massive solar installations and, more recently, the natural gas-fired Cosumnes Power Plant, brought online in 2006. On October 23, 2009, the Nuclear Regulatory Commission released the majority of the site for unrestricted public use, while approximately of land including a storage building for low-level radioactive waste and a dry-cask spent fuel storage facility remain under NRC licenses. The plant cost $375 million when it was built in 1974 and it cost about $120 million in 1974 dollars to decommission, according to the SMUD Rancho Seco Nuclear Education Center.
