The question of whether the former Rancho Seco Nuclear Generating Station remains radioactive has a complex answer: both yes and no. The facility, a former nuclear power plant in California, has undergone a thorough decommissioning process that dramatically reduced the site’s environmental footprint. Most of the property has been released for unrestricted public use. However, the most intensely radioactive material—the spent nuclear fuel—is still stored securely on the premises. Understanding the current status requires separating the decommissioned plant structures from the long-term management of nuclear waste and the ongoing environmental monitoring of the surrounding land.
Operational Timeline and Permanent Closure
Rancho Seco, a 913-megawatt pressurized water reactor located in Herald, California, began commercial operation in April 1975. The plant had a troubled operational history characterized by chronic reliability issues and extended outages. Operational challenges, combined with public anxiety following the Three Mile Island accident, led to a public referendum on the plant’s future. On June 7, 1989, voters chose to decommission the plant, making it the first instance in the United States of a public vote closing an operating nuclear reactor.
Following the vote, the Sacramento Municipal Utility District immediately began defueling the reactor, transitioning to active decommissioning in 1997. The physical dismantlement involved removing major plant systems and structures, including the reactor vessel. By 2009, the Nuclear Regulatory Commission (NRC) certified the successful completion of the bulk decommissioning, releasing the vast majority of the 2,100-acre site for unrestricted public use. The NRC officially terminated the operating license in August 2018, confirming the land met federal safety criteria for unrestricted release.
Management of Spent Nuclear Fuel
The primary source of high-level radioactivity at Rancho Seco remains the spent nuclear fuel, contained within a dedicated, heavily protected area. All used fuel assemblies were transferred from the reactor’s spent fuel pool to an Independent Spent Fuel Storage Installation (ISFSI) on the site. This transfer, involving 493 spent fuel assemblies, was completed in August 2002. The ISFSI stores the fuel using dry cask technology within concrete monoliths.
The dry casks are thick, sealed metal canisters placed inside reinforced concrete modules, providing shielding and structural protection. The facility also stores a single canister of Greater-Than-Class C (GTCC) waste, consisting of highly radioactive solid reactor internals. The entire ISFSI occupies a small, fenced-off area of approximately 11 acres and operates under a specific Part 72 license from the NRC. This licensing requires continuous security, monitoring, and financial assurance for the interim management of the high-level radioactive material.
Current Environmental Surveillance
The safety of the surrounding environment is ensured through continuous, mandated environmental surveillance programs. These programs monitor for potential low-level radiation releases into the air, water, and soil surrounding the former plant site. Monitoring includes sampling and testing of groundwater, surface water, local vegetation, and air quality. This ongoing surveillance is conducted in accordance with strict federal regulations and is overseen by the NRC and the California Department of Public Health.
The scientific conclusion from monitoring efforts is that the overall environmental radiation profile is safe for public access. Any detectable environmental releases are kept within the low federal safety limits set for unrestricted use. The regulatory standard requires that radiation distinguishable from natural background levels must not exceed 25 millirems per year. The successful completion of final status surveys and the NRC’s termination of the operating license confirm the land has been remediated to this standard.
Public Access and Site Redevelopment
The transformation of the Rancho Seco site demonstrates public safety following the decommissioning process. Approximately 400 acres of the grounds have been converted into the Rancho Seco Recreational Area. This public park features a lake stocked for fishing and is open for boating and swimming. Visitors can also enjoy camping, hiking, and wildlife viewing in the area.
Beyond recreation, the site has been repurposed for new energy production, including a 600-megawatt natural gas-fired plant and a major solar power facility. Plans for a large battery energy storage system further illustrate the site’s shift toward clean energy infrastructure. The only area that remains strictly off-limits to the public is the small, highly secure ISFSI area containing the spent nuclear fuel, which is clearly fenced and continuously guarded.