The United States has roughly 90,000 metric tons of spent nuclear fuel sitting in temporary storage at reactor sites across the country, with no permanent disposal facility in operation and no clear timeline for one. The federal government’s decades-long effort to open a deep geological repository at Yucca Mountain in Nevada remains politically and legally frozen. Against that backdrop, a California startup called Deep Isolation announced in late March 2026 that federally funded computer modeling shows burying high-level waste from recycled nuclear fuel in deep boreholes could keep radiation exposure levels several orders of magnitude below safety limits set by the Nuclear Regulatory Commission.
The project, conducted in partnership with advanced reactor company Oklo under the Department of Energy’s ARPA-E ONWARDS program, simulated how waste produced by electrorefining and pyroprocessing would behave over thousands of years when sealed inside boreholes drilled into shale and granitic rock. If the modeling holds up under further scrutiny, it could open a new path for disposing of waste from next-generation reactors that the existing regulatory framework was never designed to handle.
What the modeling found
Deep Isolation’s project focused on a specific problem: what happens to high-level waste streams from electrorefining and pyroprocessing when they are sealed inside directional boreholes drilled into two types of generic host rock, shale and granite. According to the company’s announcement of its ARPA-E results, physics-based simulations projected long-term radiation exposure levels several orders of magnitude below the NRC’s dose-based safety limits for geological disposal. That margin is significant because it suggests the concept could tolerate substantial geological uncertainty and still meet regulatory standards.
The ARPA-E ONWARDS program, which funded the work, is specifically aimed at enabling near-term commercialization of electrorefining facilities to close the metal fuel cycle. Oklo’s involvement ties the waste question directly to advanced reactor designs that would produce waste forms different from those generated by the conventional light-water reactors that dominate the current U.S. fleet. If those waste forms can be safely disposed of in boreholes rather than a centralized mined repository, it removes one of the most persistent barriers to licensing and building next-generation nuclear plants.
Deep Isolation’s broader disposal concept, described in its SEC registration statement, involves drilling directional boreholes to significant depth, loading waste canisters, emplacing them in the disposal zone, and sealing the borehole above. The company says the design includes retrieval capability, distinguishing it from permanent, irreversible disposal schemes. The SEC filing, a legally accountable document prepared for investors, also details the company’s intellectual property, partnerships, and business risk factors.
Independent scientific work supports the general plausibility of the approach. A peer-reviewed study published in Nuclear Technology examined post-closure safety modeling for deep borehole disposal, analyzing sensitivity to heat load, borehole depth, geothermal gradient, and host-rock properties. That paper showed that under many plausible geological conditions, radionuclide migration from a sealed borehole can remain extremely limited over long timescales. It does not evaluate the specific waste forms or borehole configurations modeled by Deep Isolation, but it provides a scientific framework for assessing such claims.
The gap between simulation and reality
No one has drilled a full-scale deep borehole for nuclear waste disposal anywhere in the United States. That is the single largest caveat attached to these results.
The DOE tried once. Sandia National Laboratories designed a Deep Borehole Field Test, documented in report SAND2016-9235R and archived through the Office of Scientific and Technical Information. The plan called for drilling to roughly 5 kilometers depth in crystalline basement rock and conducting detailed hydrogeologic, geochemical, geomechanical, and thermal measurements at disposal-relevant depths. The project never reached the drilling stage. Community opposition at proposed sites in South Dakota and North Dakota stalled the effort, and the environmental review (EA-2060) was ultimately withdrawn. DOE’s NEPA portal still lists the proposed assessment as canceled. No replacement federal drilling program targeting a comparable full-scale demonstration has been authorized since.
Without field data from an actual borehole at disposal depth, any safety case remains partly theoretical. Deep Isolation’s results come from simulations of generic rock formations, not site-specific measurements. While physics-based modeling is standard practice in nuclear safety assessment and is used worldwide to evaluate repository concepts, regulators typically require detailed site characterization data before approving a disposal facility. That means measurements of groundwater flow rates, rock permeability, fracture networks, and in situ stress at the specific location where waste would be placed.
The particular waste streams modeled also lack extensive disposal-specific peer review in borehole contexts. Electrorefining and pyroprocessing produce waste forms with different chemical and physical properties than the spent fuel assemblies that most borehole research has considered. Important open questions include how these waste forms hold up under high temperature and pressure over geological time, how canister materials corrode in different geochemical environments, and whether gas generation or chemical alteration could compromise borehole seals.
There is also the matter of who is making the claims. Deep Isolation is a company actively seeking to raise capital, as its SEC filing makes plain. The validation comes from the company’s own reporting of its ARPA-E project, not from an independent federal laboratory or a regulatory finding. ARPA-E funding means expert reviewers judged the project technically promising enough to merit public investment, but that is not the same as regulatory endorsement. No statement from the NRC or DOE confirming the adequacy of these modeling results for licensing purposes appears in available public records, and no license application for a borehole disposal facility is currently under review.
The political and social dimension
Even a technically sound disposal concept faces a gauntlet of political and social challenges that have derailed nuclear waste projects before. Yucca Mountain is the defining example: Congress designated the Nevada site in 1987, DOE spent billions characterizing it, and the NRC began reviewing a license application, yet the project has been effectively dead for over a decade due to state opposition and shifting federal priorities.
Deep boreholes could face similar resistance. Siting any facility that accepts high-level radioactive waste requires community engagement, and the history of the DOE’s own borehole field test shows that even a research drilling project with no actual waste involved can provoke strong local opposition. Proponents argue that boreholes have a smaller surface footprint than mined repositories and could be located in a wider range of geological settings, potentially offering more flexibility in siting. But flexibility in geology does not guarantee flexibility in politics.
Where this stands in May 2026
Three categories of evidence bear on the central question of whether deep boreholes can safely isolate recycled nuclear fuel waste, and they carry different weights.
The strongest foundation is the body of federal research, particularly the Sandia National Laboratories work that established technical parameters for borehole disposal at roughly 5 km depth and laid out a detailed measurement program. This is primary government research conducted by a national laboratory, though it dates to 2016 and describes a test that was never carried out.
Deep Isolation’s ARPA-E results form the second layer. As a corporate communication reporting on federally funded work, the announcement carries real weight, but the specific modeling inputs, boundary conditions, and sensitivity analyses have not yet appeared in peer-reviewed journals. Until independent researchers can examine those details, the reported safety margins should be treated as promising but provisional.
The third layer is the broader peer-reviewed literature on borehole disposal, which consistently shows that under realistic geological conditions, radionuclide transport from a sealed deep borehole can remain far below regulatory limits. This body of work does not validate Deep Isolation’s exact design, but it confirms that the underlying concept has serious scientific support.
Taken together, the evidence supports a cautiously optimistic reading. There is a credible scientific and engineering basis for believing that deep boreholes in suitable rock could provide very high isolation for certain types of high-level waste, including waste from advanced fuel cycles. Deep Isolation’s project adds to that picture by suggesting that modeled exposures for specific electrorefining and pyroprocessing waste streams fall far below regulatory thresholds.
But “promising in simulation” is not the same as “proven and licensable.” The absence of a full-scale demonstration, the lack of site-specific data at disposal depths, and the early stage of independent peer review for these particular waste forms mean the technology has not yet crossed the threshold from concept to operational solution. For policymakers weighing the future of nuclear energy in the United States, and for communities that may one day be asked to host a borehole facility, that distinction matters enormously.
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*This article was researched with the help of AI, with human editors creating the final content.
