Deep Isolation Reaches Over 100 Issued Patents, Strengthening Global Leadership in Nuclear Waste Disposal Innovation

Expanded international patent portfolio supports commercialization of integrated storage, transportation and disposal solutions

BERKELEY, CA, May 26, 2026 – Deep Isolation Nuclear, Inc. (“Deep Isolation” or the “Company”), a leading innovator in nuclear waste disposal technology, today announced that it has reached more than 100 issued patents worldwide, marking a major milestone in the Company’s effort to develop safe, scalable and cost-effective solutions for the permanent disposal of spent nuclear fuel and high-level radioactive waste.

This achievement reflects Deep Isolation’s strategy to build an integrated intellectual property footprint that protects every stage of the nuclear waste disposal lifecycle. Collectively, the patent portfolio is designed to support an end-to-end disposal ecosystem, including repository architecture, advanced methods for geologic site characterization, canister and packaging systems, emplacement and retrieval technologies, and closure and repository monitoring systems.

“Our patent portfolio reflects a decade of scientific research, engineering development and operational planning focused on solving one of the nuclear industry’s most critical challenges,” said Rod Baltzer, CEO of Deep Isolation. “Surpassing 100 issued patents demonstrates the depth and breadth of our innovation strategy and reinforces our commitment to delivering practical disposal solutions.”

Deep Isolation’s patents support its directional drilling-based disposal technology, which is designed to isolate nuclear waste deep underground in horizontal, slanted, or vertical borehole repositories. The portfolio also includes technologies related to the Company’s Universal Canister System (UCS), a unique packaging platform engineered to support integrated storage, transportation and disposal for waste from advanced reactor and recycling technologies as well as spent nuclear fuel from the existing light water reactor fleet. Deep Isolation’s intellectual property includes patents and applications across major nuclear markets including North America, Europe and Asia.

The milestone comes as governments and advanced reactor developers increasingly prioritize long-term waste management strategies alongside nuclear deployment plans. As interest in nuclear energy continues to grow globally, Deep Isolation and its supply chain partners stand ready to support energy generators with IP embedded in a safe, scalable, licensing-ready disposal solution. 

“Deep Isolation has developed a comprehensive intellectual property portfolio in advanced nuclear waste management,” said Eric Knox, Vice President of Strategic Development at Amentum. “Their portfolio is supported by detailed engineering, prototyping, testing and supply-chain capabilities – which is why we are excited about working with other supply chain partners to deliver a full-scale, at-depth Commercial Pilot for Deep Isolation’s solution at Cameron, Texas.”

About Deep Isolation

Deep Isolation is the first company to undertake development of technologies for nuclear waste disposal in deep boreholes. When commercialized, Deep Isolation’s solution will offer a unique solution to help countries identify, plan for and complete the necessary steps to dispose of their nuclear waste inventories. With over 100 patents issued to date, Deep Isolation’s technology is being designed to leverage proven drilling practices to allow safe isolation of waste deep underground in horizontal, vertical, or slanted borehole repositories. Deep Isolation’s Universal Canister System was developed through a three-year project funded by the U.S. Department of Energy’s Advanced Research Projects Agency–Energy and is engineered to support integrated management of spent fuel and high-level radioactive waste from legacy and advanced reactors across storage, transportation, and eventual disposal.  In January 2026, Deep Isolation launched a full-scale, at-depth deep borehole Commercialization Pilot for its solution at Cameron, Texas, in collaboration with the Deep Borehole Demonstration Center, Halliburton (NYSE: HAL), Amentum (NYSE: AMTM), NAC International, and Occlusion Nuclear Solutions.

###

For more information, visit: deepisolation.com 

Media Contact:
Sophie McCallum
media@deepisolation.com

Investor Contact:
Caldwell Bailey
InvestorRelations@deepisolation.com

Forward-Looking Statements

Statements contained in this news release that are not historical facts are “forward-looking information” or “forward-looking statements” (collectively, “forward-looking statements”) within the meaning of Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934, as amended. Forward-looking statements include, but are not limited to, statements regarding our plans, objectives and expectations for our business, the future growth of our business and the nuclear energy and nuclear waste disposal industries as a whole, and future benefits expected to arise from our strategic partnerships. In certain cases, forward-looking statements can be identified by the use of words and phrases or variations of words and phrases or statements such as “may,” “should,” “expect,” “intend,” “plan,” “anticipate,” “believe,” “estimate,” “predict,” “will,” “could,” “project,” “target,” “potential,” “continue” and similar expressions. Forward-looking statements are based on management’s belief and assumptions, including current expectations and projections about future events and trends, and on information currently available to management. 

Forward-looking statements in this or any other news release are subject to a number of risks, uncertainties, and assumptions that could cause actual results to be materially different from those expressed or implied by such forward-looking statements. Such risks, uncertainties, and assumptions are subject to a number of factors, including, among others: the failure of a market to develop for our deep borehole disposal solutions as quickly as we expect or at all; a failure of demand for our solution to develop sufficiently; regulatory and legal developments, including issues relating to obtaining regulatory approvals or permissions on the timelines we expect or at all; our lack of profitability; delays or failure in our initiative to complete a full-scale, at-depth demonstration of our Universal Canister System and our deep borehole solution; our failure to enter into contracts with customers or, once we do enter into contracts, to continue such contractual relationships or to receive new contract awards; our dependency on governmental contracts and awards and our ability to finalize negotiations on same; our failure to manage our growth effectively or to execute our business plan; our failure to sustain and expand relationships with governmental entities and strategic partners; a failure in the assumptions or analyses we have used in supporting forecasts or plans; our inability to commercialize our products at scale; the development or deployment of other technologies or solutions supplanting or competing with our technologies; challenges to our intellectual property; failures to protect, maintain, enforce, and enhance our intellectual property, and claims by others of intellectual property infringement; political and public perceptions of nuclear energy, including perceptions as to accidents or other high-profile events involving nuclear power facilities or radioactive materials; our liquidity and ability to raise capital; any inability to control operating and project costs and project delays or other project-related problems; security (including cybersecurity) breaches or disruptions; geopolitical, macroeconomic, domestic events or crises, including supply chain disruptions and other risks and uncertainties outside of our control; weather and effects of climate change; and litigation or legal proceedings that may be brought against us. 

The foregoing is not an exhaustive list of all the factors that may cause any forward-looking statements to prove inaccurate or our actual results to differ materially from our expectations and forecasts. Moreover, we operate in a highly regulated environment. New risks emerge from time to time. It is not possible for our management to predict all risks, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements we may make. In light of these risks, uncertainties, and assumptions, the future events and trends discussed in this release may not occur and actual results could differ materially and adversely from those anticipated or implied in the forward-looking statements, and we cannot guarantee future results, performance, or achievements. Accordingly, readers should not place undue reliance on forward-looking statements. We undertake no obligation to update any forward-looking statements for any reason after the date of this release or to conform these statements to actual results or revised expectations, except as required by law. 

Additional information concerning the factors above and other factors will be found in the Company’s public filings with the Securities and Exchange Commission (the “SEC”), including the sections titled “Forward-Looking Statements” and “Risk Factors” in the Company’s Reports on Form 10-K and 10-Q for the fiscal year ended December 31, 2025 and the quarter ending March 31, 2026, respectively, as filed with the SEC, our Form S-1, originally filed August 18, 2025 and subsequently amended, our Proxy Statement for our 2026 Annual Meeting as filed on April 29, 2026, and in filings with the SEC that will be made in the future.

The Company’s SEC filings are available free of charge at www.sec.gov or upon written request to Deep Isolation at InvestorRelations@deepisolation.com or CorpSec@deepisolation.com.

### 


While mined deep geological repositories remain the standard for large-scale commercial spent nuclear fuel disposal, deep borehole disposal has emerged as a viable, modular disposal alternative, particularly for the diverse, non-traditional waste forms generated by advanced microreactors and SMRs. Jesse Sloan, Executive Vice President of Engineering at Deep Isolation, explained this disposal method, and the objectives of the Deep Borehole Demonstration Project. 

Going Nuclear with Justin Huhn and Trevor Hall, May 22, 2026

The Race to Solve Nuclear Waste Storage | Rod Baltzer

Deep Isolation CEO Rod Baltzer joins Going Nuclear to discuss one of the least understood but most important challenges facing the future of nuclear energy: long-term nuclear waste disposal. The conversation explores how Deep Isolation is applying advanced directional drilling technology from the oil and gas sector to create deep borehole disposal systems designed to safely isolate spent nuclear fuel far underground for thousands of years. Rod explains the current bottlenecks surrounding nuclear waste management, the economics of storage and disposal, and why solving the backend of the fuel cycle is becoming increasingly important as small modular reactors and advanced nuclear technologies scale globally. From public market ambitions and international partnerships to the engineering behind disposal canisters and horizontal boreholes, this episode offers a rare deep dive into the future of nuclear waste infrastructure.

Event, May 27-28, 2026 in New York, NY

Bank of America – Power, Utilities and Cleantech Conference

Fireside Chat with Deep Isolation Inc.

Thursday, May 28th, 2026 at 9:00 am Eastern Daylight Time

Speaker

Rod Baltzer
President & CEO, Deep Isolation Inc

Moderator

Ross Fowler
Head of North America Power & Regulated Utilities Equity Research, BofA Securities


The annual conference brings together corporate executives, institutional investors, analysts, and energy industry leaders to discuss trends shaping the power, utilities, and cleantech sectors. Discussions this year are expected to focus on energy infrastructure investment, utility transformation, capital formation, and rising electricity demand driven by AI, electrification, and advanced manufacturing.

Deep Isolation President and CEO Rod Baltzer will join a fireside chat on Thursday, May 28 at 9:00 a.m. EDT with Ross Fowler, Head of North America Power & Regulated Utilities Equity Research at Bank of America Securities, to discuss the growing role of nuclear waste management in supporting advanced nuclear deployment and long-term energy infrastructure planning.

The Advanced Nuclear Podcast, May 18, 2026

Rod Baltzer: Deep Isolation and the Future of Nuclear Waste

In this episode of the Advanced Nuclear Podcast, UCAN Power welcomes Rod Baltzer, CEO of Deep Isolation, for an in‑depth discussion on how deep borehole technology could transform nuclear waste disposal in the United States. Baltzer explains why traditional mined repositories have struggled to deliver timely solutions and how Deep Isolation’s approach—placing nuclear waste deep underground in stable geologic formations—offers a faster, more flexible, and potentially more publicly acceptable alternative. 

Operational Highlights for the First Quarter of 2026

  • Launched a non-radioactive, full-scale, at-depth demonstration of the Company’s deep borehole waste disposal technology at Halliburton’s Drilling Technology Facility near Cameron, TX
  • Successfully completed work under the U.S. Department of Energy Advanced Research Projects Agency-Energy’s (“ARPA-E”) Optimizing Nuclear Waste and Advanced Reactor Disposal Systems (“ONWARDS”), a project led by Oklo, Inc.
  • Selected to participate in ARPA-E’s SCALEUP Ready program, providing up to $20 million to accelerate market adoption of Deep Isolation’s deep borehole waste disposal technology and the first time a company in the nuclear industry has been selected to participate
  • Appointed nuclear industry veteran Ralph L. Hunter to the board of directors on January 23, 2026
  • Appointed Paula Whitten-Doolin as General Counsel on February 3, 2026
  • Appointed Joseph Nelson as Chief Financial Officer on February 17, 2026
  • Appointed nuclear operations leader Matthew Sunseri to its advisory board on March 2, 2026
  • The SEC declared Deep Isolation Nuclear, Inc.’s registration statement on Form S-1 effective on May 7, 2026, allowing the common stock of the Company to be freely tradable

Financial Highlights for the First Quarter of 2026

  • Reported consolidated revenue of $1.4 million
  • Reported research and development expense of approximately $3.5 million related to the start of the non-radioactive, full-scale, at-depth demonstration of our deep borehole waste disposal technology 
  • Had available cash of $22.2 million as of March 31, 2026
  • Reported a net loss of $5.4 million primarily attributable to research and development expenses
  • Total common shares outstanding as of May 12, 2026 of 57,647,613

BERKELEY, CA, May 14, 2026 – Deep Isolation Nuclear, Inc. (“Deep Isolation” or the “Company”), a leading innovator in nuclear waste disposal technology, today announced its operational and financial results for the three-months ended March 31, 2026.

“We are thrilled to be reporting Deep Isolation’s first earnings as a public company,”  said Rod Baltzer, CEO of Deep Isolation. “Our operational momentum in the first quarter was encouraging – breaking ground on our full-scale demonstration project in Cameron, Texas marks a pivotal milestone as we move from the R&D phase toward deployment, showcasing our innovative approach to safe nuclear waste disposal.

“Additionally, our selection for ARPA-E’s SCALEUP Ready program positions us to accelerate commercialization with support from the Department of Energy. These achievements demonstrate our team’s execution capabilities and reinforce Deep Isolation’s leadership in delivering practical solutions for one of the nuclear industry’s most critical challenges. We believe we are entering the market at the exact right time, as the entire nuclear industry is scaling up, gaining momentum  and in need of a scalable waste disposal solution.”

Operational Progress

Deep Isolation advanced several strategic initiatives during the quarter, including the launch of its full-scale technology demonstration program in Cameron, Texas, in collaboration with Halliburton and the Deep Borehole Demonstration Center. The program, which includes collaboration with Westinghouse, NAC International, Occlusion Nuclear Solutions, and Amentum, is designed to demonstrate a fully integrated deep borehole disposal solution for advanced reactor and nuclear recycling waste. The non-radioactive demonstration project is expected to provide operational data and support stakeholder and regulatory confidence as the Company advances commercialization of its technology.

The Company also announced the successful completion of its work under the ARPA-E ONWARDS program, confirming through modeling and analysis that waste streams from advanced reactor fuel recycling are compatible with Deep Isolation’s deep borehole disposal system and can achieve long-term safety performance significantly exceeding target standards. In addition, Deep Isolation was selected for ARPA-E’s SCALEUP Ready program to support commercial deployment of its Universal Canister System, with the Company advancing through the contracting phase for potential funding of up to $20 million to support its Cameron, Texas demonstration project. Deep Isolation is the first company in the nuclear industry to have ever been selected to participate in ARPA-E’s SCALEUP Ready program.

Commercial Progress and Other Company Events

During the quarter, Deep Isolation strengthened its leadership and governance capabilities through several key appointments. The Company appointed Ralph L. Hunter to its Board of Directors, bringing more than 35 years of nuclear industry experience, including senior leadership roles across advanced nuclear development, operations, and policy. Deep Isolation also appointed Paula Whitten-Doolin as General Counsel and Joseph Nelson as Chief Financial Officer to support the Company’s commercialization efforts, public company readiness, and strategic growth initiatives. In addition, the Company appointed nuclear operations leader Matthew Sunseri to its Advisory Board, adding significant expertise in nuclear safety, regulatory strategy, and operational governance as Deep Isolation advances its demonstration and commercialization programs.

On May 8, 2026, the U.S. Securities and Exchange Commission (SEC) declared Deep Isolation’s registration statement on Form S-1 effective, allowing the Company’s common stock to be freely tradable. The Company is actively working with OTC Markets Group, Inc. to enable its shares of common stock to be traded on the OTCQB exchange.  

Financial Summary

For the Three Months EndedFor the Three Months Ended
Amounts in thousands of U.S. dollarsMarch 31, 2026March 31, 2025
Revenue$ 1,447$ 1,520
Research and development expense$ 3,489$ —
Selling, general and administrative expenses$ 2,840$ 993
Net Loss$ (5,416)$ (166)
EBITDA1$ (5,563)$ (135)
Adjusted EBITDA1$ (1,536)$ (135)
Cash$ 22,226$ 2,150

Revenue decreased by approximately $73 thousand, or 5%, for the three months ended March 31, 2026, compared to the three months ended March 31, 2025. The decrease in revenue was primarily attributable to lower revenues at Deep Isolation following the completion of certain projects during 2025, offset by higher revenues at the Company’s subsidiary, Freestone Environmental Services, due to an increase in the number of active contracts.

Research and development expense increased by approximately $3.5 million for the three months ended March 31, 2026, compared to the three months ended March 31, 2025. The increase in research and development expense was attributed to the ordering of long-lead items and front-end engineering work related to the Company’s non-radioactive, full-scale, at-depth demonstration of its deep borehole technologies.

Selling, General and Administrative expenses increased by approximately $1.8 million, or 186%, for the three months ended March 31, 2026, compared to the three months ended March 31, 2025. The increase in selling, general and administrative expenses was primarily attributable to higher accounting, audit, legal and travel expenses along with addition of 4 new employees, including the Chief Financial Officer and General Counsel.

Net loss increased by approximately $5.3 million for the three months ended March 31, 2026, compared to the three months ended March 31, 2025, primarily due to the increases in research and development and selling, general and administrative expenses described above.

EBITDA1 was ($5.6) million for the three months ended March 31, 2026, compared to ($135) thousand for the three months ended March 31, 2025. The decrease in EBITDA was primarily attributed to higher research and development expenses and selling, general, and administrative expenses as described above.

Adjusted EBITDA1 was ($1.5) million for the three months ended March 31, 2026, compared to ($135) thousand for the three months ended March 31, 2025. The decrease in Adjusted EBITDA was primarily attributed to higher selling, general, and administrative expenses as described above.

1 EBITDA and Adjusted EBITDA are non-GAAP financial measures and should not be used in isolation or as a substitute for Deep Isolation’s financial results presented in accordance with Generally Accepted Accounting Principles (“GAAP”). For the definitions and reconciliations of these measures to the most directly comparable financial measures calculated and presented in accordance with GAAP, please refer to Exhibit II at the end of this press release

Conference Call

Deep Isolation will host a conference call to discuss their operational and financial results for the first quarter of 2026 on Thursday May 14, 2026 at 8:30AM ET. The presentation of the Company’s operational and financial results will be followed by a live Q&A session.

A webcast of the conference call will be accessible on Deep Isolation’s investor relations website at https://www.deepisolation.com/investors/. The earnings release and presentation will also be posted to the investor relations website prior to the conference call.

The live conference call may also be accessed by telephone by dialing (877) 704-4453 or (201) 389-0920. For those unable to listen to the live conference call, a replay will be available after the call through the archived webcast on Deep Isolation’s investor relations website or by dialing (844) 512-2921or (412) 317-6671. The access code for the replay is 13760350. The replay will be available for 30 days following the live call.

View Exhibit I: Unaudited Interim Financial Information

View Exhibit II: Non-GAAP Financial Measures: EBITDA and Adjusted EBITDA

About Deep Isolation

Deep Isolation is the first company to undertake development of technologies for nuclear waste disposal in deep boreholes. When commercialized Deep Isolation’s solution will offer a uniquely tailored solution to help countries identify, plan for and complete the necessary steps to dispose of their nuclear waste inventories. With 99 patents issued to date, Deep Isolation’s technology is being designed to leverage proven drilling practices to allow safe isolation of waste deep underground in horizontal, vertical, or slanted borehole repositories. Deep Isolation’s Universal Canister System was developed through a three-year project funded by the U.S. Department of Energy’s Advanced Research Projects Agency—Energy and is engineered to support integrated management of spent fuel and high-level radioactive waste from legacy and advanced reactors across storage, transportation and eventual disposal.

###

For more information, visit: deepisolation.com 

Media Contact:
Sophie McCallum
media@deepisolation.com

Investor Contact:
Caldwell Bailey
InvestorRelations@deepisolation.com

Forward-Looking Statements

Statements contained in this news release that are not historical facts are “forward-looking information” or “forward-looking statements” (collectively, “forward-looking statements”) within the meaning of Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934, as amended. Forward-looking statements include, but are not limited to, statements regarding our plans, objectives and expectations for our business, the future growth of our business and the nuclear energy and nuclear waste disposal industries as a whole, and future benefits expected to arise from our strategic partnerships. In certain cases, forward-looking statements can be identified by the use of words and phrases or variations of words and phrases or statements such as “may,” “should,” “expect,” “intend,” “plan,” “anticipate,” “believe,” “estimate,” “predict,” “will,” “could,” “project,” “target,” “potential,” “continue” and similar expressions. Forward-looking statements are based on management’s belief and assumptions, including current expectations and projections about future events and trends, and on information currently available to management. 

Forward-looking statements in this or any other news release are subject to a number of risks, uncertainties, and assumptions that could cause actual results to be materially different from those expressed or implied by such forward-looking statements. Such risks, uncertainties, and assumptions are subject to a number of factors, including, among others: the failure of a market to develop for our deep borehole disposal solutions as quickly as we expect or at all; a failure of demand for our solution to develop sufficiently; regulatory and legal developments, including issues relating to obtaining regulatory approvals or permissions on the timelines we expect or at all; our lack of profitability; delays or failure in our initiative to complete a full-scale, at-depth demonstration of our Universal Canister System and our deep borehole solution; our failure to enter into contracts with customers or, once we do enter into contracts, to continue such contractual relationships or to receive new contract awards; our dependency on governmental contracts and awards; our  failure to manage our growth effectively or to execute our business plan; a failure to sustain and expand relationships with governmental entities and strategic partners; failure in the assumptions or analyses we have used in supporting forecasts or plans; our inability to commercialize our products at scale; the development or deployment of other technologies or solutions supplanting or competing with our technologies; challenges to our intellectual property; failures to protect, maintain, enforce, and enhance our intellectual property, and claims by others of intellectual property infringement; political and public perceptions of nuclear energy, including perceptions as to accidents or other high-profile events involving nuclear power facilities or radioactive materials; our liquidity and ability to raise capital; any inability to control operating and project costs and project delays or other project-related problems; security (including cybersecurity) breaches or disruptions; geopolitical, macroeconomic, domestic events or crises, including supply chain disruptions and other risks and uncertainties outside of our control; weather and effects of climate change; and litigation or legal proceedings that may be brought against us. 

The foregoing is not an exhaustive list of all the factors that may cause any forward-looking statements to prove inaccurate or our actual results to differ materially from our expectations and forecasts. Moreover, we operate in a highly regulated environment. New risks emerge from time to time. It is not possible for our management to predict all risks, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements we may make. In light of these risks, uncertainties, and assumptions, the future events and trends discussed in this release may not occur and actual results could differ materially and adversely from those anticipated or implied in the forward-looking statements, and we cannot guarantee future results, performance, or achievements. Accordingly, readers should not place undue reliance on forward-looking statements. We undertake no obligation to update any forward-looking statements for any reason after the date of this release or to conform these statements to actual results or revised expectations, except as required by law. ”

Additional information concerning the factors above and other factors will be found in the Company’s public filings with the Securities and Exchange Commission (the “SEC”), including the sections titled “Forward-Looking Statements” and “Risk Factors” in the Company’s Quarterly Report on Form 10-Q for the quarter ended September 30, 2025 filed with the SEC on November 14, 2025, our Form S-1, originally filed August 18, 2025 and subsequently amended, our Proxy Statement for our 2026 Annual Meeting as filed on April 29, 2026, and in filings with the SEC that will be made in the future. The Company’s SEC filings are available free of charge at www.sec.gov or upon written request to Deep Isolation Nuclear at InvestorRelations@deepisolation.com

### 

While all repository concepts aim to achieve the same outcome, long-term isolation of nuclear waste, the way that isolation is achieved depends strongly on the host rock. Different geologic formations control fluid movement, heat transport, and long-term stability in fundamentally different ways. In Part 1, we focused on the processes that govern subsurface behavior over geologic timescales, including how groundwater moves, how transport occurs, and why depth plays such a critical role.

Building on that foundation, this article looks more directly at how specific rock types achieve isolation. Around the world, disposal programs have converged on a small number of host formations, including crystalline rock, shale and argillite, clay, and salt. Each of these formations provides a viable pathway to long-term containment, but they do so through different mechanisms. Understanding those differences is key to how repositories are designed, how sites are evaluated, and why there is no single universal solution for nuclear waste disposal. These differences become clearer when looking at each rock type individually.

Crystalline rock

Fracture-Controlled

Granite and other crystalline basement rocks are extremely strong and geologically stable, having remained largely unchanged for hundreds of millions of years in many regions. The intact rock matrix is very dense, with extremely low permeability, meaning that fluid movement through the rock itself is minimal. These formations are also typically located in tectonically stable settings, where large-scale deformation occurs slowly over geologic time.

The primary challenge in crystalline systems lies in fractures. Over long timescales, tectonic stresses create networks of cracks that can act as pathways for fluid flow. While the rock matrix remains tight, these fractures can be connected in ways that allow groundwater to move more readily. As a result, transport in crystalline formations is often controlled not by the matrix, but by the presence, connectivity, and hydraulic properties of fracture networks.

Because fracture systems can be complex and variable, understanding their geometry and behavior is central to site evaluation. The safety of a crystalline repository depends on identifying regions where fracture connectivity is limited and groundwater movement remains slow over long timescales.

Despite this challenge, crystalline rock remains one of the most widely used host formations for nuclear waste disposal. Its long-term stability provides confidence that geologic conditions will remain predictable over repository-relevant timescales. The high strength of the rock allows for construction at depth, and the low permeability of the matrix helps limit fluid movement outside of fracture pathways.

Crystalline repository concepts therefore rely on a combination of favorable geology and engineered barriers as part of a multi-barrier system. In Sweden and Finland, for example, spent fuel is placed in copper canisters surrounded by bentonite clay. Even if groundwater moves through fractures and reaches the repository, the engineered system provides an additional layer of protection, limiting radionuclide release and transport.

These systems are also supported by decades of research and site characterization. Extensive field studies in countries such as Sweden and Finland have built a detailed understanding of fracture networks, groundwater flow, and long-term system behavior, providing a strong technical and regulatory foundation for implementation. While crystalline systems are often controlled by fractures, other formations behave very differently.

Shale and Argillite

Diffusion-Dominated

Shale and argillite are fine-grained sedimentary rocks formed from compacted mud and clay. Their most important property for disposal is extremely low permeability. The rock matrix is so tight that groundwater flow is negligible, and fluid movement through the formation is largely suppressed.

As a result, transport in shale systems is dominated by diffusion. Instead of water carrying dissolved material through the rock, radionuclides move slowly through the rock matrix, driven by concentration gradients. In practical terms, this means that a radionuclide released into a shale formation may take hundreds of thousands of years to travel only a few meters. Under these conditions, the geology itself provides the primary barrier to transport, with engineered systems playing a supporting role.

In addition to low permeability, shale formations often exhibit self-sealing behavior. Clay minerals within the rock absorb water and expand when disturbed, gradually reducing the size and connectivity of fractures created during drilling or excavation. This tendency to close fractures over time helps maintain low permeability and reinforces long-term isolation.

The main constraints in shale systems are mechanical and thermal. Compared to crystalline rock, shale is generally weaker and more sensitive to stress changes. It can deform or fracture if not properly managed during construction. Thermal loading from radioactive decay must also be carefully controlled, since elevated temperatures can affect both the mechanical properties of the rock and the stability of the surrounding formation.

Shale and argillite formations are being actively studied as host rocks in several national programs. In Canada, for example, significant research has focused on Ordovician-age shale formations in Ontario, where long-term stability, low permeability, and favorable geochemical conditions are being evaluated for repository development. Clay formations share many similarities with shale, but with one important difference.

Clay Formations

Diffusion-Dominated

Clay formations share many of the same advantages as shale, including very low permeability and diffusion-dominated transport. Fluid movement through the rock matrix is extremely slow, and many radionuclides are further immobilized through chemical interactions with clay minerals, which can bind contaminants and limit their mobility.

What distinguishes clay is its mechanical behavior. Unlike more brittle rocks, clay is plastic, meaning it deforms under stress rather than fracturing. Over time, the material can slowly flow and redistribute itself. As a result, openings created during excavation, whether tunnels, boreholes, or stress-induced fractures, tend to close as the surrounding clay creeps back into place. This self-sealing behavior helps restore low permeability and maintain isolation over long timescales.

These properties make clay particularly well suited to repository concepts that rely heavily on the natural barrier. The combination of low permeability, strong sorption capacity, and self-sealing behavior provides multiple mechanisms that act together to limit radionuclide transport.

The primary constraint in clay formations is thermal. Clay conducts heat relatively poorly, so heat generated by radioactive decay can accumulate in the surrounding rock. Elevated temperatures can affect both the mechanical properties of the clay and the stability of the engineered system. Repository designs must therefore manage thermal loading carefully, often by increasing spacing between waste packages or allowing waste to cool prior to emplacement.

Clay formations are being actively pursued as host rocks in several national programs. In Belgium, research has focused on the Boom Clay formation, while in France, the Callovo-Oxfordian clay is the basis for the Cigéo repository. Both programs have conducted extensive underground research over multiple decades to characterize the long-term behavior of these systems. Salt represents a fundamentally different end-member in how isolation is achieved.

Salt

Deformation-Dominated

Salt formations are in many ways the most distinctive of the major host rock options. In their intact state, they have extremely low permeability and essentially no connected pore space, meaning there are no continuous pathways for fluid flow. As a result, fluid movement through undisturbed salt is negligible.

What sets salt apart is its mechanical behavior. Under the pressures found at depth, salt deforms continuously over time through a process known as creep. Rather than remaining rigid or fracturing, the rock flows slowly and plastically, redistributing stress and closing any voids that are created. Openings formed during excavation or drilling begin to close almost immediately as the surrounding salt moves inward. Over decades to centuries, this process can encapsulate waste, isolating it within the formation as the salt gradually seals around it.

This behavior provides a powerful containment mechanism. In salt-based repositories, isolation is achieved not only through low permeability, but through the physical closure of the formation itself. The Waste Isolation Pilot Plant (WIPP) in New Mexico is a well-known example of this approach. Operating since 1999, it relies on the long-term creep of salt to isolate transuranic waste by gradually sealing disposal rooms and limiting fluid movement.

The primary complication in salt formations is the presence of brine. Although salt is often described as dry, small pockets of highly saline fluid can exist within the formation. Heat generated by radioactive waste can mobilize this brine, causing it to migrate toward disposal zones. This behavior must be carefully considered in repository design, particularly in selecting canister materials and managing thermal loading.

Salt’s creep behavior can also introduce engineering challenges. While closure is beneficial for long-term isolation, it can complicate operations during emplacement and sealing. In borehole-based concepts, for example, the tendency of salt to deform and close around installed components must be accounted for in both design and installation strategy. While each host rock relies on different mechanisms, the key differences become clearer when viewed side by side.

How they compare

While each host rock relies on different mechanisms, the underlying goal is the same: limit fluid movement and ensure that any radionuclide transport occurs slowly enough to meet long-term safety objectives. The table below summarizes how each formation achieves this.

Rock TypeHow Isolation WorksKey AdvantagesMain ConstraintWhere It’s Being Used
CrystallineLimiting fracture flow + engineered barriersHigh strength, long-term geologic stability, extensive experienceFracture uncertaintySweden, Finland, Canada
Shale / argilliteDiffusion through tight matrixExtremely slow transport, geology carries safety functionHeat sensitivity, lower mechanical strengthCanada
ClayDiffusion + sorption + plastic self-sealingMultiple reinforcing mechanisms, self-sealing behaviorLow thermal conductivityBelgium, France
SaltCreep-dominated closureNear-zero permeability, self-sealing, physical isolationBrine, thermal effects on creepUSA (WIPP)

There’s no single best answer

Every rock type described here has been selected by at least one national disposal program, and for good reason. Each provides a credible, defensible pathway to long-term isolation. The difference lies in how that isolation is achieved.

In crystalline formations, repository designs account for fracture-controlled flow by combining stable host rock with robust engineered barriers. In shale and clay systems, extremely low permeability and diffusion-dominated transport allow the geology itself to carry much of the safety function. In salt, isolation is achieved through both low permeability and creep-driven closure, which gradually encapsulates the waste within the formation.

The appropriate choice for a given country or site depends on several factors, including the available geology, the characteristics of the waste, and the overall repository design. Whether waste is emplaced in mined tunnels or deep boreholes, the underlying principle remains the same: the disposal system should align with, and reinforce, the natural behavior of the host rock.

What is consistent across all these approaches is the underlying logic. Effective repository design does not attempt to overcome the geology, but to work with it. Over geologic timescales, the most durable component of any repository is not the engineered barrier system, but the formation that surrounds it. This reflects the same principle introduced in Part 1: long-term repository performance depends on how engineered systems and geology work together, with the host rock providing the foundation for isolation over geologic timescales.

Subscribe to Receive Our Newsletter

* indicates required

Email Preferences




Contact

For more information about our solution, please contact us.

info@deepisolation.com+1 415 915 6506

Deep Isolation, Inc.
2120 University Avenue, Ste. 623
Berkeley, CA 94704