In 1966, the Sacromento Municipal Utility District (SMUD) purchased 2,100 acres in southeast Sacramento County for a nuclear power plant. Rancho Seco was built in Clay Station, California, 25 miles south east of Sacramento, California. This 2772 MWt Babcock and Wilcox pressurized water reactor (916 MWe) achieved initial criticality on September 16, 1976, and entered commercial operation on April 17, 1977.

Rancho Seco had a poor operating history, and a lifetime capacity average of only 39%. Due to this poor operating history and increasing costs, the plant was closed by public vote on June 6, 1989, even though its operating license did not expire until October 11, 2008. Decommissioning activites are currently underway.

The Rancho Seco Nuclear Plant, located in Sacramento, California, was a 913 MWe PWR owned by the Sacramento Municipal Utility District (the District). This single unit facility is comprised of a pressurized water reactor with two independent primary coolant loops, each of which contains two coolant pumps and a steam generator, and an electrically heated pressurizer. The system is housed in a steel-lined, post-tensioned concrete cylinder with a hemispherical dome and a flat, reinforced concrete base mat. A welded steel liner plate, anchored to the inside face of the containment, served as a leaktight membrane. The station operated from 1975 to 1989, when it was shut down by a state public referendum. Plant staff has decreased to 150 employees from a peak employment level of 700; the unit is currently in custodial SAFSTOR.  

The initial SAFSTOR decision included the plan to store spent fuel in the wet storage pool until 1997. This would provide sufficient time to construct an Independent Spent Fuel Storage Installation (ISFSI) for on-site spent fuel storage until a federal repository would be available. Actual decommissioning activities, including site restoration, were to begin in 2008 and be completed by 2011. It was in 1991 that TLG first estimated such a decommissioning program (at $328 million), with assumed low-level waste (LLW) burial at a "Southwest Compact" burial facility (for California and Arizona). However, the development of the proposed Ward Valley site has proceeded slowly because of public intervention. The fact that the Department of the Interior (who owned the land) would not transfer it to California until extensive safety studies and environmental assessments were performed has also contributed to delay. During this time, the projected cost for LLW disposal at Ward Valley escalated at about $100 per year because of interest charges and licensing fees.

Due to such escalating costs, TLG prepared an updated evaluation by 1995. This study would provide the District with the financial forecasts and technical considerations needed to assess the viability of accelerating the decommissioning process. TLG recommended that the District initiate decommissioning activities using state-of-the-art decontamination methods to free release as much of the contaminated materials as possible. Maximum use of off-site waste processors and recyclers would reduce the overall decommissioning costs by millions of dollars. The accelerated scenario was developed as an alternative to the SAFSTOR program delineated within the District's 1991 Decommissioning Plan. A limited demonstration program of removal activities was initiated to determine whether the existing staff could cost-effectively manage the work. The District authorized a total site budget of $15 million per year, which could include incremental decommissioning activities.

The schedule originally developed for the 1995 estimate included a SAFSTOR dormancy period until April 2007, followed by 18 months of preparation and approximately 39 months of deferred decontamination and dismantling. These milestone dates and durations were retained in TLG's 1999 cost update and still remain the fixed schedule for program operations. On the other hand, completing the transfer of spent fuel to the on-site dry storage facility (ISFSI) was revised from November 1999 to July 2000 to reflect delays incurred in system component delivery. As of May 2000, it does not appear hopeful that the transfer will be completed by July. The ISFSI facility has been constructed, and all necessary cask handling equipment has been delivered; however, the casks are not expected for at least another year.

SMUD will redevelop the site when decommissioning is complete. In the early 1970s, a nearby pond was expanded to a 160-acre lake to serve as an emergency backup water supply for the Rancho Seco plant. Surrounding the lake is 400 acres of recreational area originally operated by the county for daytime activities. Over the years the county developed fishing, picnicing, and camping facilities, and then transferred its operation and maintenance responsibilities to SMUD by 1994. To reassure nearby neighbors, farmers, and visitors, SMUD maintains a testing program for non-detectable levels of radiation within a 10-mile radius of the plant.

This level of radiation detection is also being applied to every item being dismantled or scrapped during decommissioning. Failure to meet the criteria requires that the material be disposed of in a radioactive material depository. Asbestos in the cooling towers and within the secondary side buildings has all been removed. Secondary side systems, including the moisture separators, diesel-generators, steam piping and related components have been removed and shipped to recyclers for decontamination and release or burial. Having completed the turbine building staff is now performing "incremental decommissioning" on the auxiliary building.