The cooling towers at Rancho Seco were demolished years ago, but the land they stood on in Sacramento County, California, never fully left the energy business. Spent nuclear fuel still sits in sealed dry casks under federal watch. Now the Sacramento Municipal Utility District, the public utility that owns the property, plans to fill a neighboring parcel with roughly 100 battery energy storage system (BESS) units, a project called Dry Creek Energy Storage that would rank among the larger grid batteries in the state.
If completed as proposed, the installation would transform a site defined by a 1989 reactor shutdown and decades of decommissioning into an active node on California’s electricity grid, storing power generated by solar and wind farms and dispatching it when demand spikes or generation drops. The project sits at the intersection of two regulatory worlds: California’s aggressive push to add grid-scale storage and the federal government’s open-ended obligation to monitor spent nuclear fuel that has nowhere else to go.
What the regulatory record confirms
California’s state clearinghouse lists Dry Creek Energy Storage under tracking number SCH 2017092042. A Notice of Determination filed under the California Environmental Quality Act describes the physical scope: grading, approximately 100 BESS units, trenching and electrical collection lines, and perimeter fencing. The filing notes that an Environmental Impact Report and a subsequent addendum were prepared before the determination was posted. The project also holds California Department of Fish and Wildlife Incidental Take Permit No. 2081-2025-043-02, issued because construction is expected to affect habitat used by state-listed species.
That habitat impact is quantified in the permit record. The Notice of Determination documents permanent losses to upland dispersal and foraging habitat on the project footprint. In practical terms, the battery installation will replace open ground that wildlife currently uses for movement and feeding. California’s endangered species process is designed to offset that cost through conditions such as habitat preservation or compensatory mitigation on other land.
On the federal side, the Rancho Seco site has never dropped off the regulatory map. The U.S. Nuclear Regulatory Commission maintains a dedicated portal compiling Rancho Seco reports, including Radioactive Effluent and Environmental Reports tied to the former plant. The portal tracks effluent reports, radiological environmental operating reports, and groundwater monitoring questionnaires. Those reporting streams confirm that measurable radiological oversight continues at the property even as new construction is planned nearby.
Spent fuel from the reactor remains on site in an Independent Spent Fuel Storage Installation (ISFSI), a configuration the NRC describes in its dry-cask backgrounder. The Rancho Seco ISFSI operates under the NRC’s general license provisions for spent fuel storage, meaning SMUD maintains the installation in compliance with federal regulations without holding a site-specific license for the storage facility itself. ISFSIs use sealed canisters placed inside concrete or steel overpacks to hold used fuel assemblies after a reactor’s spent fuel pool is no longer available. Because the federal government has not established a permanent repository for commercial spent fuel, the casks at Rancho Seco will remain indefinitely, sharing the broader property with the incoming battery arrays.
Why California wants batteries on sites like this
California law requires the state’s electricity supply to reach 100 percent clean energy by 2045, and regulators have identified grid-scale battery storage as a critical bridge technology. Solar farms across the Central Valley produce far more electricity than the grid can absorb during midday hours, then drop to zero output after sunset. Batteries capture that surplus and release it during evening peaks, reducing the state’s reliance on natural gas peaker plants.
The California Public Utilities Commission has ordered utilities to procure tens of thousands of megawatts of new storage and clean generation capacity through the mid-2030s. SMUD, as a municipally owned utility, is not directly subject to CPUC procurement orders, but it operates under its own board-adopted 2030 Zero Carbon Plan, which calls for eliminating carbon from its power supply by 2030. Large battery projects like Dry Creek fit squarely within that timeline.
Siting a battery facility on land already zoned for energy infrastructure and connected to transmission lines offers practical advantages. The Rancho Seco property has existing road access, electrical interconnection points, and a land-use history that simplifies permitting compared to undeveloped agricultural or wildland parcels. Those efficiencies help explain why a former nuclear site is attractive for a technology that did not exist at commercial scale when the reactor was operating.
What remains uncertain
The figure of 640 megawatt-hours that appears in the headline and in broader coverage of this project does not appear in any primary regulatory filing currently available through the state clearinghouse or the NRC portal. SMUD’s own integrated resource planning documents and board presentations have described large-scale storage targets for the Rancho Seco property, and the 640 MWh figure is consistent with the physical scope of roughly 100 BESS units described in the CEQA record. However, the CEQA filings themselves do not publish a nameplate energy capacity or a megawatt power rating. Until a utility filing, interconnection study, or engineering specification confirms that figure in a binding document, it should be treated as a planning-level estimate rather than a verified nameplate rating.
The commercial structure is also opaque in the public record reviewed as of June 2026. No filing in the state clearinghouse identifies a signed interconnection agreement, power purchase contract, or commercial operation date. Whether the battery installation will feed exclusively into SMUD’s local network or participate in the broader California Independent System Operator wholesale market has not been specified.
The physical relationship between the battery project’s construction footprint and the ISFSI’s security perimeter raises questions that neither the state nor federal filings fully resolve. NRC regulations impose buffer zones and access restrictions around spent fuel storage areas, yet the CEQA documents do not describe how grading and trenching will be staged relative to the federally controlled portion of the site. Any radiological baseline data collected before or during battery construction has not appeared in the NRC’s Rancho Seco reporting portal, so the scope of pre-construction monitoring is unclear.
Fire safety is another gap. Lithium-ion battery installations have experienced thermal runaway events at facilities elsewhere in the U.S., including a 2021 incident at a storage site in Moss Landing, California, that forced evacuations and raised questions about suppression protocols for large-scale BESS projects. The Dry Creek CEQA addendum does not include fire suppression or ventilation specifications for the approximately 100 units described in the project scope. Local fire authorities typically require detailed plans before issuing construction permits, but those documents have not yet entered the public record.
Two risk-managed technologies sharing one property for decades
What makes Dry Creek unusual is not the battery technology itself, which is being deployed at dozens of sites across California, but the co-location with a federally regulated spent fuel installation. The ISFSI and the BESS project each carry their own emergency planning requirements, security protocols, and long-term monitoring obligations. How those frameworks will overlap in practice over the coming decades is a question the existing record raises but does not answer.
Shared concerns include construction traffic routing, emergency responder coordination, and the division of responsibility between local agencies and federal regulators if an incident spans both the battery area and the ISFSI. SMUD, as the site owner, will need to demonstrate to both state and federal regulators that the two uses can coexist without compromising the safety margins built into either system.
For Sacramento County residents and ratepayers, the project represents a tangible test of whether legacy nuclear sites can be repurposed for the storage infrastructure California’s grid increasingly demands. The regulatory filings confirm that both uses are real and permitted. The harder question is how emergency planning, security coordination, and land stewardship will evolve as new grid hardware is layered onto a property still bound by nuclear-era obligations. That question will play out over years of construction and operation.
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*This article was researched with the help of AI, with human editors creating the final content.
