7:20 am: My alarm goes off and it’s time to feed the dog.

At this point I’m already awake, cleaned up, dressed, and ready to start my day – the dog wakes me up every day before my alarm goes off, so I take him out for a brief walk and start to get a pre-read on my emails.  The Deep Isolation team is dispersed across several time zones, but not many are on the west coast with me.  Because of that, I typically receive a handful of emails with project updates, company news, or client feedback well before I start my workday.  Checking these on my phone while I’m out with the dog helps me ease into the mindset for work.

7:30 am: I pick up where I left off the day before, working on an economic model.

Dog fed and coffee in hand, I sit at my desk in my home office and unlock my work laptop.  A colorful spreadsheet greets me, right where I’d left it the previous afternoon.  Deep Isolation has developed a robust cost model for estimating lifecycle costs for the implementation of a deep borehole repository to aid client studies and proposals.  We recently received updated cost estimates from our drilling partner to widen the range of configurations we could model, and I have been updating our baseline cost model to account for the new data available.  I sip my coffee and get to work updating the formulas that play into the analysis.

8:00 am: I finish the economic model updates and continue with a literature review on environmental and social impact assessments.

As part of one of our international client studies, I’m working on a report deliverable to provide a preliminary environmental and social impact assessment.  It’s imperative that a nuclear waste disposal facility has a strong defensible set of analyses that can prove to regulators and the general public that it will perform as designed, and in a safe manner.  Part of that includes an analysis of the overall impact that the facility will have on the environment and local population – I get back to reading up on similar studies that have been conducted so that I can better direct the direction of this deliverable.

8:45 am: I need a break from reading environmental impact assessments, so I switch to editing a waste disposal plan.

Deep Isolation works with a number of advanced reactor companies and national laboratory researchers on feasibility studies to assess whether our technology can be a good fit for disposing of their waste forms.  I’ve been editing a comprehensive waste disposal plan that’s due to the client in a few months; it lays out repository design considerations, a complete economic assessment, and a preliminary performance and safety assessment.  We’ve received extremely helpful consultant feedback on a previous draft of the waste disposal plan, so I verify that the new report incorporates the recommendations in a polished manner.

9:15 am: I receive an email from a collaborator on our demonstration project, and I switch gears once again to assess the contents.

Our team recently broke ground on a full-scale demonstration project, where we will be drilling a borehole to prototypic depth and emplacing/retrieving multiple nuclear waste canisters.  The team that will be placing the canisters below ground sent along an initial draft of their procedures for us to review.  I read through and add comments and suggested edits to the draft, drawing from my previous knowledge from my time in the Navy executing nuclear procedures.  Although the demonstration will be completely non-radioactive, we intend to operate the same way we would in a realistic scenario.  Much of my procedural review constitutes ensuring that the nuclear operational controls can fit in with the standard oil and gas techniques applied.  Once I finish documenting my recommendations and questions, I let the other team members know that I’m done with my review.

10:00 am: I have a team meeting with external collaborators, so I toss on my headphones and join the meeting.

As a member of a fully remote company working on projects comprised of cross-functional teams, I find that I get the most value from a given time period out of our team video calls – especially for the demonstration project.  Our routine team meetings for this project include project managers, engineers, operators, and other team members from Deep Isolation and our collaborating companies.  Open communication and spread of ideas is promoted; I take notes, ask questions, make suggestions, and am optimistic about the project outcome.

11:00 am: The meeting is finished and I incorporate some of the discussion takeaways into a functional requirements document I’ve been working on.

A project of this scale requires detailed documented requirements and specifications against which design efforts can be based and program test success can be evaluated.  The functional requirements and objectives for our project depend on input from all disciplines on the team, and I get to work changing the wording and content of the document so that we’re set up for success later on.

11:45 am: I step away for a bit to eat some lunch and walk the dog around the neighborhood for a bit of fresh air.

I’ve been on a bit of a bean salad kick recently – drained black beans and chick peas, cherry tomato halves, diced cucumber, pitted kalamata olives, and feta cheese with a olive oil/sherry vinegar/pepperoncini brine/maple syrup dressing.  I highly recommend it, it’s easy to meal prep and quite modular!

12:15 pm: Done with lunch, I head back to my desk and check on how my inbox and task-tracking are going.

I check my emails and ensure they’ve all been read, acknowledged, and categorized appropriately.  I like to sort all emails into applicable folders and keep the main Inbox only for emails that still require action.  This, combined with my physical notebook of tasks and notes helps me to “keep the main thing the main thing” and appropriately prioritize projects and other tasks.  In addition, I update a spreadsheet I use for tracking how I spend my time which will make it easier for me to submit my timesheet later in the week.

12:30 pm: I begin research to find published values for radioactive atoms that will remain in one client’s spent nuclear fuel assemblies at the time of disposal.

As part of a study I’m working on for a client, Deep Isolation is contracting out a computational assessment of how safe our borehole repository will be and how well it will perform in that specific area with that specific type of waste form.  Different types of nuclear reactors use different designs for their nuclear fuel, and after these reactors operate for decades the residual constituents of these nuclear fuel assemblies vary depending on these different designs.  Many types of waste forms have been analyzed in the past to identify what quantities of which radioactive atoms (called radionuclides) remain, and I’m helping to find out what published data exists for the types of fuel our client uses – that way it can be used in the computational models that represent the migration of these radionuclides from where we dispose the waste to the biosphere.

1:30 pm: I send my findings on radionuclide composition to the team member working on the performance model and return to drafting the waste disposal plan I had been working on earlier.

I pull up the draft waste disposal plan report on one of my computer monitors, and on my other monitor I pull up a previously submitted deliverable for the same client and overall project.  Because the waste disposal plan is our essentially our final delivery for this project, some information from previous milestones in the project is briefly incorporated into this report and I’d like to ensure that I’m staying true to our findings while I incorporate feedback that was left in the form of comments on the previous draft.

3:15 pm: I change projects one last time for the day and continue researching and drafting the environmental and social impact assessment.

I pick up where I left off early in the morning and review a few additional sources for the preliminary economic and social impact assessment.  I’m fairly confident that the information I’ve collated from my literature review is sufficient for me to draw initial qualitative conclusions so I begin drafting the applicable section of the report, citing sources as applicable.  Research heavy documentation is a bit more difficult for me to find a working rhythm, but right at the end of my workday I seem to have found my groove.  I highlight a few portions of source documentation that I know will help me the next morning, type a few short notes in my draft document that I know will help me regain my train of thought in the morning, and log out of my laptop for the day.

4:00 pm: I change into workout clothes and head to the gym after a productive day.

I hop in my car, head to the gym, and suffer through a little bit of cardio before my evening.  Maybe I’ll play some video games with my husband and our college friends, maybe I’ll cook dinner and read a book.  Either way, I plan to have an enjoyable evening, get a good night’s sleep, and am excited to take on whatever comes up tomorrow.  No two days are the same for me but I look forward to the excitement brought on by the variety, and am driven by my intellectual curiosity and craving for more information and innovation.

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 Type	How Isolation Works	Key Advantages	Main Constraint	Where It’s Being Used
Crystalline	Limiting fracture flow + engineered barriers	High strength, long-term geologic stability, extensive experience	Fracture uncertainty	Sweden, Finland, Canada
Shale / argillite	Diffusion through tight matrix	Extremely slow transport, geology carries safety function	Heat sensitivity, lower mechanical strength	Canada
Clay	Diffusion + sorption + plastic self-sealing	Multiple reinforcing mechanisms, self-sealing behavior	Low thermal conductivity	Belgium, France
Salt	Creep-dominated closure	Near-zero permeability, self-sealing, physical isolation	Brine, thermal effects on creep	USA (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.

The geology of a repository isn’t just a backdrop; it’s doing most of the work. Here’s how different geologic conditions control the long-term isolation of nuclear waste.

When people think about nuclear waste disposal, they often focus on engineered barriers: thick metal canisters, layers of sealing materials, and complex closure systems. These components are critical for early system performance. But when we consider what the system must do over 100,000 to a million years (i.e., geologic timescales), the focus shifts. Ultimately, it’s the host rock that carries the burden of long-term performance.

Rock formations are not static — they evolve over time under the influence of stress, temperature, fluid movement, and chemical reactions. Minerals dissolve and re-precipitate, fractures can open or gradually seal, and in some formations the rock itself deforms or flows. These processes occur slowly, but over geologic timescales they control how fluids move and how permeability changes at depth. The goal isn’t to find a formation that never changes, but one that evolves in predictable ways that can be understood and modeled.

This is why host rock selection is one of the most consequential decisions in repository design. Over hundreds of thousands to millions of years, it is the geologic system that ultimately ensures isolation. Engineered components play an important role, but they function in support of the natural system.

Key Properties of Geologic Formations

Before discussing the different host rock types (blog 2 of this series), it’s important to first provide an overview of the key geologic parameters that describe the physical and chemical properties of a system, and ultimately its suitability for waste disposal. These parameters control how fluids move, how heat is transported, and how the system responds to long-term changes. While different rock types express these properties in different ways, the underlying metrics are consistent across all repository concepts.

Property	What It Describes	Why It Matters for Disposal
Porosity	Fraction of void space in the rock	Determines fluid storage and influences diffusion pathways
Thermal conductivity	Ability to conduct heat	Governs how heat from radioactive decay dissipates into the surrounding rock
Diffusivity (effective)	Rate of molecular transport through the rock matrix	Controls radionuclide migration in low-permeability systems
Hydraulic gradient	Driving force for groundwater flow	Determines direction and magnitude of fluid movement
Fracture density / connectivity	Presence and linkage of cracks in the rock	Can dominate flow pathways even in otherwise low-permeability formations
Geochemical conditions	Fluid composition, pH, redox state	Influences radionuclide solubility, sorption, and long-term mobility
Mechanical properties (strength, creep)	How rock responds to stress	Affects fracture formation, sealing behavior, and long-term stability
Salinity / fluid density	Dissolved solids in groundwater	Can stabilize deep systems and suppress buoyancy-driven flow

The table above summarizes the key properties used to describe geologic formations in the context of nuclear waste disposal. Each of these parameters represents a different aspect of how the subsurface system behaves, from how fluids move, to how heat is transferred, to how the rock responds to long-term stress. No single property determines whether a formation is suitable for disposal. Instead, it is the combination of these factors and how they evolve over time, that defines system behavior. For example, a rock may have low matrix permeability but still allow faster transport if fractures are well connected. Conversely, formations with higher porosity but strong geochemical retention or self-sealing behavior can still provide effective isolation. Understanding how these properties interact is central to evaluating and comparing different host rock types.

What Is the Rock Actually Trying to Do?

At the most basic level, a host rock must prevent radioactive material from migrating through the subsurface and reaching drinking water, the surface, or anything living. The objective of nuclear waste disposal is long-term safety, specifically limiting the movement of radionuclides so they cannot be transported by groundwater.

This leads to a central question: how does a given rock formation control fluid movement?

There are two primary modes. In some rocks, fluids move mainly through fractures, cracks in the rock that act as pathways for flow. In others, the rock matrix is so tight that fracture flow is minimal, and transport occurs primarily by diffusion, where molecules spread slowly through the rock. The difference in timescales between these two modes is substantial. Fracture flow can move material relatively quickly, while diffusion through dense rock may take hundreds of thousands of years for radionuclides to travel only a few meters.

The goal is not to eliminate movement entirely, but to slow it enough that radionuclides decay before they can travel meaningful distances.

A second important factor is how the rock responds to disturbance. Drilling or excavating a repository inevitably alters the surrounding formation, creating fractures, redistributing stress, and changing permeability. Some rocks can gradually heal this damage over time, either by swelling or by deforming and closing fractures. These self-sealing behaviors can significantly enhance long-term isolation compared to rocks that remain fractured once disturbed. The way these processes play out in practice is strongly influenced by depth.

The Role of Depth

At greater depths, typically kilometers below the surface, groundwater systems begin to behave very differently from what we experience near the surface. The weight of overlying rock increases pressure, temperatures rise due to the Earth’s natural geothermal gradient, and water becomes more saline as it interacts with minerals over long periods of time. These changes affect how water moves. Higher pressures compress pore spaces, reducing permeability, while increased salinity makes the water denser. In many cases, this creates layered systems where denser fluids remain trapped below lighter ones, limiting vertical movement.

As a result, groundwater flow at depth is often much slower and more isolated than near the surface, where rainfall and rivers continuously drive circulation. In deep formations, there may be little to no connection to these surface-driven flow systems. Instead of water actively moving through the rock, transport can be dominated by diffusion, the slow spreading of dissolved substances through the rock matrix. Under these conditions, it can take tens or hundreds of thousands of years for dissolved material to move even short distances.

In some formations, particularly those with very low permeability, these factors combine to create environments that are nearly stagnant. Fluid movement is minimal, and the system is effectively isolated from the surface. This is one of the key reasons deep geologic environments are considered favorable for long-term containment.

Depth is therefore not just a geometric parameter; it directly influences the mechanical, hydraulic, and chemical processes that control subsurface behavior. Elevated pressures affect stress and fracture stability, temperature influences reaction rates and fluid properties, and increased salinity can suppress buoyancy-driven flow. Together, these factors determine how permeability evolves and how fluids, along with any dissolved contaminants, can move over time.

Whether waste is accessed through mined tunnels or deep boreholes, placing it far below the surface situates it within a part of the subsurface where natural conditions are inherently more favorable for long-term containment.

Geology and Long-Term Isolation

Taken together, these processes highlight a central idea: the long-term safety of a repository is ultimately controlled by the natural behavior of the geologic system. Fluid movement, transport mechanisms, and the response of the rock to stress and temperature all work together to determine how effectively waste is isolated over time. The goal is not to engineer a system that overcomes the geology, but to place waste in a setting where the geology itself provides a strong and predictable barrier.

In Part 2, we build on this foundation by looking at how different types of rock formations, including crystalline rock, shale and argillite, clay, and salt, achieve isolation in different ways, and how those differences shape repository design.

By Jessica Chow

The rapid growth of nuclear start-ups in the past two decades indicates the changing nuclear industry: an industry in need of innovation. This industry needs fresh perspectives from professionals excited to engage with nuclear technology, especially in the face of the global challenge of climate change. 

The nuclear start-up life was the topic of a panel I joined recently at the Nuclear Innovation Bootcamp (NIB) in Madison, Wisconsin. Also participating were Tyler Bernstein of Zeno Power Systems, Alexia Mercier of OECD Nuclear Energy Agency, and Andy Morales of FireHydrant. We delved into the intersection of nuclear technology, innovation, and team building in the start-up space. Most of the questions we received from the Bootcamp attendees focused on how to not only succeed in the nuclear start-up space but thrive. Let’s discuss that. 

What does success look like in the nuclear industry? Success looks like the further deployment of nuclear energy technology to fight climate change, continued use of nuclear material for medical purposes, and future innovation in the nuclear industry.

So how do we get there and what changes to how we approach nuclear innovation will be needed to find this success? Based on the NIB panel discussion, it seems that young professionals believe new reactor designs are key to the future success of nuclear energy. It does make sense that young industry professionals who may be unfamiliar with the complex history of nuclear power would focus on the technical aspects of nuclear. But forgoing the industry’s history misses a key opportunity for growth: to find success in the nuclear industry, especially with innovation, we need to learn from the industry’s past, especially as it pertains to its engagement with the public. 

Success for the next generation of nuclear professionals must:

Listen. Learn. Adapt. 

We can pull a great example of this from my co-panelist, Tyler Bernstein of Zeno Power Systems who said, “Something I believe we’ve done well as we’ve grown our team is balancing bringing onboard team members with decades of experience with industry newcomers — who are frequently non-nuclear engineers. We’ve seen this combination work well as those who have more experience can impart wisdom on how things have been in the past, while industry newcomers bring fresh and creative ideas to the table. In fact, our founding team is comprised wholly of newcomers to the nuclear industry; I believe a good part of our success to date is a result of my co-founders and I coming together with new perspectives on old problems.”

Recruiting a diverse team is part of creating a culture where different stakeholders are listened to in a constructive and meaningful way. A diverse team provides an organization with the ability to approach conversations from different perspectives. Many of the attendees at NIB are in the process of starting their own nuclear startups. To empower their success, we must also empower young professionals to build teams diverse in expertise, backgrounds, age, and race. 

There is so much work to be done to prepare young professionals for the complex nuclear industry, but by questioning the traditions of the nuclear industry of the past, we can learn and change to find success in the future. 

A final thank you is deserved by the organizers of the 2022 Nuclear Innovation Bootcamp, especially River Bennett of Nuclear Innovation Alliance, the panel’s moderator for the panel. It is programs such as NIB that provide much-needed resources to the young generation of the nuclear inclusive clean energy future. 

Related posts

*Africa Deserves a Say in Its Clean Energy Future

Meet Monica Mwanje, Advocating for a More Inclusive Nuclear Workforce

By Dr. Ethan Bates

Deep Isolation Director of Systems Engineering Dr. Ethan Bates presented his paper, co-authored with borehole sciences expert John Midgley, titled Features, Events, and Processes Prioritization for Deep Borehole Disposal Concepts in Crystalline Rock and Shale, at the American Nuclear Society Meeting in Anaheim, Calif., earlier this month.

We sat down with Dr. Bates to learn more about these analyses.

Q: What are FEPs? Why are they relevant to the safety analysis of nuclear waste disposal?

FEPs stands for “features, events, and processes” and studying this allows us to categorize phenomena affecting nuclear waste repository performance.  Specifically, events and processes impact the features of the repository, and a screening process is needed to evaluate which of these is important to safety in the long run. This paper generally addresses FEPs for borehole concepts that Deep Isolation (and other institutions) are considering and prioritizes a subset of FEP groups to guide future collaborations. This is to support the safety and feasibility evaluation of deep borehole concepts in a wider range of geologies, including crystalline rock and shale.

Q: What was your motivation for prioritizing features, events, and processes in deep borehole disposal concepts in crystalline rock and shale?

Modern drilling technologies broaden our options for nuclear waste disposal to a wider range of sites, geological environments, depths, and configurations.  In the past, researchers (including myself) focused on crystalline rock as the host rock, but Deep Isolation has shown that equally safe repositories could be constructed in shale using horizontal drilling. This option could be very helpful in the siting process (which can be challenging) but it increases the scope of work required in the early stages of designing borehole repositories. 

To perform a comprehensive evaluation of the safety of a deep borehole repository, we need to analyze all the phenomena, initiating events, and boundary conditions affecting deep borehole repositories over 10,000 years or more.  With limited resources, it’s important to focus our efforts on the FEPs that are assessed to be of greater importance.

Q: What are the high-priority FEPs, and how were they determined?

To streamline the prioritization process, a smaller subset of FEP groups was created. Then, an expert panel (including those from a leading national laboratory) was convened to assess the relative importance of the FEP groups.  The FEP group related to radionuclide transport through the host rock barrier, which varies with depth, was deemed high-priority because in the deep borehole disposal concept this barrier strongly impacts the safety of the repository. Ultimately, three high-priority FEP groups were identified:

• radionuclide transport through the host rock and overlying geologic units;
• seal and plug degradation; and
• radionuclide transport through the disturbed rock zone.

Further evaluation of these FEPs will advance the generic feasibility and safety assessment of deep borehole disposal concepts.

Q: What are the big takeaways from this work?

Early findings on the high priority FEP group related to host rock transport properties show that deep borehole disposal enables wider access to host rocks where diffusion of radionuclides (extremely slow and predictable, relative to advection) is the dominant transport mechanism.  Imagine having a sugar cube at the bottom of a glass of water: With diffusion, the water is not moving and it takes a very long time for the sugar to dissolve into the water.  Having advection is equivalent to stirring the glass and allows for much more rapid transport of the sugar.

Q: What are the next steps?

High- and medium-priority FEPs were identified in this paper to better understand the long-term performance assessment of deep boreholes for nuclear waste disposal. Although a preliminary analysis was conducted on the high-priority FEP group related to host rock properties, additional work is needed to draw general correlations about the depth variation of clay properties.  Future work on the other high priority FEP groups such as transport through the disturbed rock zone and seal and plug degradation might eventually show these FEPs to have a lower significance in the safety case than initially thought, for example, by showing that the repository performs safely even when these features and barriers are conservatively assumed to be degraded. Additional efforts will also go toward the medium priority FEPs such as gas generation in the emplacement zone, transport and dilution in the biosphere, and matrix diffusion, which can act as an important delay mechanism in crystalline rock.

Related posts

*Deep Borehole Expert Joins Deep Isolation

*Sealing of a Deep Horizontal Borehole Repository for Nuclear Waste

By Betsy Madru

In 2012, the U.S. Blue Ribbon Commission on America’s Nuclear Future was formed by the Secretary of Energy to conduct a comprehensive review of policies for managing the back end of the nuclear fuel cycle. One of the Commission’s recommendations was to use consent-based siting approaches to determine a location for a facility to store and dispose of nuclear waste. 

In 2017 the United States Department of Energy developed and requested public comment on the “Draft Consent-Based Siting Process for Consolidated Storage and Disposal Facilities for Spent Nuclear Fuel and High-Level Radioactive Waste.” The incorporation of consent-based siting in DOE’s nuclear waste work is moving the nation’s nuclear waste program in the right direction. 

The DOE has revived its efforts by recently issuing a Request for Information on “Using a Consent-Based Siting Process To Identify Federal Interim Storage Facilities.” This means interested entities had an opportunity to submit their thoughts on how such a process should be conducted to ultimately help the U.S. progress toward a solution. 

Here is an excerpt from Deep Isolation’s RFI response:

“The Department of Energy should lay out a comprehensive plan for development of an entire waste management system that provides flexibility in the strategy and approach for storage, transportation, and disposal. An essential part of any fully integrated plan is continuation of generic work that will be required regardless of the final destination of the material, such as work being done under 180(c) of the NWPA to provide technical and financial training to local state and tribal public safety officials whose jurisdictions are on major transportation routes. Initiating a consent-based siting process for interim storage is an important first step of the Department’s overall plan, but it must be developed against the larger backdrop of a comprehensive system that is grounded in sound science and built on a platform of public trust and confidence.”

“Progress on establishing one or more permanent disposal facilities is critical to efforts to develop an interim storage facility. … If it is assumed that potential interim storage sites will be pursued using a consent-based process, then the hosts of those sites must have reasonable confidence that the sites will, in fact, be “interim” and not become permanent by default. The only way to maintain that balance and assurance is to have a robust integrated waste management system that includes both types of facilities as well as the accompanying safety and regulatory structure to enable success.”

“New regulations for geologic disposal must be built on a solid technical foundation of safety analyses and performance assessments, and must establish regulatory certainty at the outset…. Clarity and certainty about the regulatory process will provide a necessary underpinning for conversations about the siting of disposal facilities.  This will in turn provide greater confidence that interim storage will not become permanent and will allow more open dialogue with prospective host communities and states that is built on a platform of transparency and trust”

Now that responses to the RFI have been submitted, the Office of Nuclear Energy and the U.S. Department of Energy will use the 220 responses submitted to inform development of a consent-based siting process, overall strategy for an integrated waste management system, and possibly a funding opportunity. The DOE has consolidated all the responses and is planning to issue a report of all the findings in the coming months and 

To learn more:

Social Scientist Explains Community Consent

Keeping Nuclear Waste Transportation Safe

What factors influence nuclear waste storage or disposal?