Rancho Seco Nuclear Generating Station

Rancho Seco Nuclear Generating Station
Country United States
Location Herald, California
Coordinates 38°20′43″N 121°7′18″W / 38.34528°N 121.12167°W / 38.34528; -121.12167Coordinates: 38°20′43″N 121°7′18″W / 38.34528°N 121.12167°W / 38.34528; -121.12167
Status Decommissioned
Commission date April 17, 1975
Decommission date 2009
Construction cost

$375 million in 1974 dollars[1]

($1.46 billion in 2016 dollars[2])
Operator(s) SMUD 1974-present
Nuclear power station
Reactor type Pressurized water reactor
Reactor supplier Babcock & Wilcox
Power generation
Thermal capacity 1 x 2772 MWth
Nameplate capacity 913 MW
Capacity factor <40%[1]

The Rancho Seco Nuclear Generating Station is a decommissioned nuclear power plant built by the Sacramento Municipal Utility District (SMUD) in Herald, California.


In 1966, SMUD purchased 2,100 acres (850 ha) in southeast Sacramento County for a nuclear power plant, which was built in Herald, 25 miles (40 km) south-east of downtown Sacramento.

In the early 1970s, a small pond was expanded to a 160-acre (65 ha) 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 400 acres (160 ha) of recreational area originally operated by the County of Sacramento for day-use activities.

The 2,772 MWt Babcock & Wilcox pressurized water reactor (913 MWe) achieved initial criticality on 16 September 1974 and entered commercial operation on 17 April 1975.

On 20 March 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,[3] 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[4] (Behind the Three Mile Island accident and the cable tray fire at Browns Ferry).

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 7 June 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 3-year span.[5]

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 (11 km) 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 air raid 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 23 October 2009, the Nuclear Regulatory Commission released the majority of the site for unrestricted public use, while approximately 11 acres (4.5 ha) of land including a storage building for low-level radioactive waste and a dry-cask spent fuel storage facility remain under NRC licenses.[6]

The plant cost $375 million[1] when it was built in 1974 ($1.46 billion in 2016 dollars[2]) and it cost about $120 million in 1974 dollars to decommission ($466 million in 2016 dollars[2]), according to the SMUD Rancho Seco Nuclear Education Center.

According to a study published in the open access journal Biomedicine International, the statistically significant drop in cancer rates observed in Sacramento County between 1988 and 2009 may in partly be thanks to the closure of the Rancho Seco plant.[7] However, this conclusion has been disputed by other researchers, noting that drops in cancer rates were observed in the majority of counties in California during the same period, and may therefore be due to other factors unrelated to the Rancho Seco plant.[8]

See also


  1. 1 2 3 Wald, Matthew L. (1989-06-08). "Voters, in a First, Shut Down Nuclear Reactor". The New York Times. ISSN 0362-4331. Archived from the original on 2015-05-25. Retrieved 2016-07-09.
  2. 1 2 3 Thomas, Ryland; Williamson, Samuel H. (2018). "What Was the U.S. GDP Then?". MeasuringWorth. Retrieved January 5, 2018. United States Gross Domestic Product deflator figures follow the Measuring Worth series.
  3. "Policy Issue Information". United States NRC.
  4. "Attachment 2 Policy Issue Information" (PDF). U.S. Nuclear Regulatory Commission. Retrieved 30 August 2010.
  5. http://www.energy-net.org/01NUKE/RSECOT.HTM
  6. "Rancho Seco nuclear power plant ends decommissioning". Power Engineering. PennWell. 2009-10-26. Retrieved 2009-10-30.
  7. Mangano, Joseph J.; Sherman, Janette D. "Open Journal Systems". Retrieved 13 August 2018.
  8. Emery, Robert J. "LETTER TO THE EDITOR Concerning the Article of Mangano and Sherman, "Long-term Local Cancer Reductions Following Nuclear Plant Shutdown"". Retrieved 13 August 2018.
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