Deep Isolation Validates Borehole Disposal for Recycled Nuclear Fuel Waste, Completing ARPA-E Partnership With Oklo
Berkeley-based Deep Isolation has confirmed that high-level waste from spent fuel electrorefining is compatible with deep borehole disposal, completing a multi-year ARPA-E ONWARDS project led by Oklo that could reshape the back end of the advanced reactor fuel cycle.
Deep Isolation Nuclear, a Berkeley, California-based company developing deep borehole disposal technology for radioactive waste, announced on March 24 that it has completed its contribution to an ARPA-E project validating that high-level waste from advanced reactor fuel recycling can be safely disposed of in deep boreholes. The work was carried out under the Optimizing Nuclear Waste and Advanced Reactor Disposal Systems (ONWARDS) program, on a project led by Oklo Inc. titled “Enabling the Near Term Commercialization of an Electrorefining Facility to Close the Metal Fuel Cycle.”
The collaboration also involved Argonne National Laboratory and Idaho National Laboratory, and focused on determining whether waste streams produced by the Argonne-baseline electrorefining process — a method for partitioning spent metal fuel — are physically and radiologically compatible with permanent isolation in Deep Isolation’s borehole repository design.
Technical Findings
Deep Isolation’s physics-based modeling examined the behavior of high-level waste disposed of in its borehole system within generic shale and granitic host rock formations. According to the company’s announcement, the results showed long-term safety levels that surpassed the targets established during model development, with projected radiological exposure levels falling “several orders of magnitude below” established dose standards.
The analysis specifically assessed waste forms partitioned through Argonne’s electrorefining baseline process, confirming their compatibility with Deep Isolation’s disposal approach. The company has developed a Universal Canister System through a separate three-year DOE-funded effort under the ARPA-E ONWARDS program, designed to accommodate a range of advanced reactor waste forms in both borehole and mined repository settings.
How Borehole Disposal Works
Deep Isolation’s approach leverages standard drilling practices from the oil and gas industry to place sealed waste canisters deep underground in horizontal, vertical, or slanted boreholes. The company claims to be the first to pursue commercial development of borehole disposal technology for nuclear waste and holds 99 patents related to the system.
The concept differs from conventional mined geological repositories — such as Finland’s Onkalo facility or the long-stalled U.S. Yucca Mountain project — by using narrower, deeper holes drilled into stable rock formations rather than large excavated tunnels. In a 2019 demonstration at a commercial drilling facility, Deep Isolation successfully placed and retrieved a prototype disposal canister from a deep horizontal drillhole in front of more than 40 international observers.
Regulatory and Policy Context
Despite the technical validation, a significant legal barrier remains. Current U.S. federal law does not authorize the use of borehole repositories for the disposal of high-level radioactive waste. The Nuclear Waste Policy Act of 1982 and its 1987 amendments directed the development of a mined geologic repository, which led to the designation of Yucca Mountain — a project that has been effectively frozen since 2010 due to political opposition.
Deep Isolation’s results provide what the company describes as a “technical foundation for closing the metal fuel cycle,” but realizing commercial deployment would require congressional action to authorize borehole disposal as a legally recognized pathway for high-level waste.
The findings arrive as the U.S. nuclear industry enters a period of renewed expansion. The Department of Energy’s Nuclear Lifecycle Innovation Campus initiative, launched in January 2026, has drawn interest from more than two dozen states willing to host fuel cycle facilities, and Oklo has announced plans to design and operate a spent fuel recycling facility in Oak Ridge, Tennessee. Jesse Sloane, Deep Isolation’s Executive Vice President of Engineering, stated that the collaboration with Oklo “represents an important step forward for the advanced reactor ecosystem” by pairing fuel recycling innovation with geologic disposal technology.
Whether borehole disposal moves from validated concept to licensed reality will depend on whether policymakers choose to expand the disposal options available under federal law — a question that grows more pressing as advanced reactors and their associated waste streams move closer to commercial operation.