Fueling the Future of Nuclear

MORGAN:
When most people think about nuclear energy, they think about reactors.

KASE:
Big buildings. Cooling towers. Control rooms.

MORGAN:
But none of that works without fuel.

KASE:
And nuclear fuel isn't just something you load into a reactor and forget about.

MORGAN:
It starts in the ground. It's mined, processed, engineered, and changed by years inside a reactor.

KASE:
And then - eventually - it comes out the other side.

MORGAN:
Which raises a whole new set of questions.

KASE:
What do we do with it? Can we reuse it? And how do we do all of that responsibly?

MORGAN:
Today, we're talking about the nuclear fuel cycle - what it is, why it matters, and how Oak Ridge National Laboratory and its partners are working to improve it.

KASE:
Hello everyone, and welcome to The Sound of Science - the podcast highlighting the voices behind the breakthroughs at Oak Ridge National Laboratory.

MORGAN:
We're your hosts, Morgan McCorkle -

KASE:
-and Kase Clapp.

MORGAN:
This is the second episode in our nuclear miniseries. In the last episode, we zoomed out - looking at why nuclear energy is having a moment, and why so much of that momentum is centered here in East Tennessee.

KASE:
Today, we're zooming way in - on the fuel itself.

MORGAN:
So let's start with the basics. When people talk about the "nuclear fuel cycle," what do they actually mean?

KASE:
At the highest level, it's the full life of nuclear fuel - from beginning to end.

MORGAN:
Uranium is mined from the ground.

KASE:
It's processed and enriched.

MORGAN:
It's fabricated into fuel and used inside a reactor to generate electricity.

KASE:
And then, once it's been used, that fuel has to go somewhere.

MORGAN:
In the U.S., we mostly treat that fuel as waste - what's called an "open" or "once-through" fuel cycle.

KASE:
Other countries recycle fuel, recovering usable material through chemical processing - a "closed" fuel cycle.

MORGAN:
It's a lot to cover - so let's get started.

MUSIC TRANSITION

KASE:
To understand how fuel works inside a reactor, we talked to Andy Nelson.

MORGAN:
He leads the Nuclear Energy and Fuel Cycle division at Oak Ridge National Laboratory.

KASE:
And when Andy talks about nuclear fuel, he often starts with a phrase that sounds almost dismissive - but really isn't.

ANDY NELSON:

If we treat the fuel as a pile of hot rocks, I can't really ask it to do all that much. I mean, it just makes heat.

MORGAN:
That idea - fuel as just a hot pile of rocks - is how nuclear fuel is often talked about.

KASE:
And it's not wrong, exactly. Fuel does make heat.

MORGAN:
But Andy says that framing misses what's really happening inside a reactor - and what fuel could be doing.

KASE:
Because once fuel goes into a reactor, it doesn't stay the same.

MORGAN
It's changing - constantly.

NELSON:

You have fissions happening. You have all these new fission products coming in. So what that means is your chemistry is changing and evolving continuously.

If you have any key material property you need - thermal conductivity comes to mind - if you're trying to get this pile of hot rocks to eject heat into your coolant, well, I don't need to only understand what my thermal conductivity is on day zero. I need to continuously understand for years and years how it's evolving.

MORGAN:
So instead of a static object…

KASE:
Fuel becomes a living materials problem - under extreme conditions.

NELSON:

When I think about the field of nuclear fuel development, what it really means is combining all of these challenges of applied materials science with solid state physics when you're having damage happening to the material.

And then really, if I want to understand the properties, I have materials in extremes - all those standard things that we at Oak Ridge love to focus on from a material science standpoint.

MORGAN:
That complexity is why nuclear fuel development has historically taken so long.

NELSON:

The number we usually throw around is two or three decades from the point at which you or I have an idea on a whiteboard, to the point that you could have a fuel vendor manufacturing, licensing, using that fuel form.

So if I go back even ten years ago - but certainly before that - if we were a reactor company and we had an idea for a new reactor type, we don't want to bite off two or three decades and who knows how many billions of dollars in development costs.

KASE:
For a long time, that meant reactor designers didn't ask much of fuel beyond one job.

MORGAN:
Be a hot pile of rocks - and do it reliably.

KASE:
What's changing now is the ability to ask more of the fuel - and get answers faster.

NELSON:

What's changed is that we're having the first time some new ideas and new thoughts about not only how we think about qualifying a new fuel material, but again also the tools and the approaches we have to do that.

So we're really focusing a lot at Oak Ridge and in other laboratories around the U.S. on trying to shorten that development cycle timeline down - to get fuel concepts to market quicker.

And you bring together neutrons, material development, and in the modern era, computational techniques to really understand how these materials behave. So it's just a great, wonderful problem for the DOE labs in particular, to bring all these people and capabilities together to address.

MORGAN:
In other words, fuel doesn't have to be just a hot pile of rocks anymore.

KASE:
And that opens the door to entirely new ways of thinking about reactors.

MUSIC

MORGAN:
So if the traditional approach to nuclear fuel is to ask it to do one thing really well -

KASE:
- make heat, reliably, for a long time -

MORGAN:
The next step is asking a bigger question.

KASE:
What if fuel itself could provide additional benefits?

NELSON:

The question that people have been thinking about for a long time is, can we do better than that? Can we have the fuel provide some kind of engineering benefit, whether it's to contain fission products or do other things?

MORGAN:
One answer to that question is a fuel form Oak Ridge is especially well known for - TRISO fuel.

KASE: That's short for TRi-structural ISOtropic particle fuel.

MORGAN:
TRISO isn't a fuel rod like you'd see in a typical light-water reactor.

KASE:
Instead of stacking cylindrical uranium pellets into long tubes, TRISO fuel breaks the fuel into millions of tiny particles - each about the size of a poppy seed.

MORGAN:
Inside each particle is a fuel kernel made of uranium compounds, surrounded by multiple layers of carbon- and ceramic-based coatings that act as a built-in containment system.

NELSON:

It's a much different approach where each fuel particle is about a millimeter in size and has many, many coatings that are all designed for different engineering aspects.

KASE: What makes TRISO special is that even if one particle has a problem, it doesn't compromise the whole fuel assembly - millions of neighbors keep working.

NELSON:

The idea being if you have one flaw, one defect, that's only one small fraction of fuel, and the other millions of particles you have in your core can operate just fine.

MORGAN:
What's striking about TRISO is that, while it feels new, the idea itself isn't.

NELSON:

This really started at Oak Ridge in the late 50s, early 1960s. People started looking at how do I improve on this pile of hot rocks concept. One thing that people figured out or thought about quite early on was, well, I keep having fission products leaking out of my fuel. What if I put a coating on it?

KASE:
That work led to some of the earliest coated particle fuels -

MORGAN:
- developed just down the road from where many of these fuels are still being studied today.

NELSON:

At Oak Ridge in the 60s, up into the early 70s, you saw a lot of really novel work - the first coated particle fuels being developed, in a building about a block away from us right now.

KASE:
The idea didn't disappear because it didn't work.

MORGAN:
It faded because of economics and timing.

NELSON:

Because of the same economic drivers that really slowed nuclear deployment elsewhere in the U.S., that idea kind of fell by the wayside in the 1980s.

KASE:
What's different now is that the industry is ready for it.

MORGAN:
And Oak Ridge is once again helping bring it forward.

NELSON:

So in the early 2000s and actually why I'm at Oak Ridge was that the first gas cooled reactor effort of the modern era, spun back up. And the Department of Energy knew they would need a laboratory to recapitalize the fabrication capabilities. So we here at Oak Ridge reconstituted a lot of that capability to fabricate and characterize TRISO.

KASE:
TRISO is a fundamentally different way of thinking about fuel.

MORGAN:
Instead of relying on one large barrier, safety is distributed across millions of tiny ones.

KASE:
And that added safety opens the door to new reactor designs.

MORGAN:
Especially when it comes to size and flexibility.

NELSON:

The big difference between a conventional light water reactor and some of the concepts that are being proposed to use TRISO is the size. Much smaller - kilowatt to tens of megawatt size plants - have really latched on to trying to use TRISO for that need.

MORGAN:
Advanced fuels like TRISO aren't about replacing today's reactors.

KASE:
They're about expanding what nuclear energy can do - and where it can be used.

MUSIC TRANSITION

MORGAN:
Up to this point, we've been talking about what fuel does inside a reactor - how it's engineered, how it behaves, and how it's evolving.

KASE:
But eventually, every fuel assembly comes out of the reactor.

MORGAN:
In many ways, that's where the toughest questions begin.

KASE:
Leigh Martin leads ORNL's Integrated Fuel Cycle section.

LEIGH MARTIN:

There are a couple of different ways to look at the fuel cycle. The first one is an open fuel cycle, which is basically where we take uranium out of the ground, refine it, make a fuel with it, put it in a reactor, and then dispose of it without doing anything with it.

The next term that is generally used is a closed fuel cycle, where you take the uranium out of the ground, refine it and make it into fuel, put it in a reactor. But because there is still useful material left in the fuel, we then would perform some kind of limited chemical processing so we can take the useful pieces out of the fuel and put it into new fuel that we can put back into a reactor.

MORGAN:
On the surface, that can sound like an obvious choice.

KASE:
If there's still usable material left in the fuel, why wouldn't you recycle it?

MORGAN:

And looking at the numbers, it sounds like there's a lot of energy left on the table.

MARTIN:

Out of about a ton of material, most of it is still uranium that's left in the fuel afterwards. About five percent of what comes out of the reactor is truly waste.

KASE:
That number - five percent - surprises a lot of people.

MORGAN:
It's one of the strongest arguments for recycling.

KASE:
But Leigh is also quick to point out that the reality is more complicated. Recycling creates its own challenges.

MARTIN:

When it comes out of the reactor, it's basically got all of the periodic table in it. There's still some useful uranium left in the fuel afterwards, but you're left with this smaller amount of material that has a lot of radioisotopes in it.

MORGAN:
So a closed fuel cycle doesn't eliminate waste.

KASE:
It reduces it - but adds complexity.

MORGAN:
That's one of the core R&D challenges Oak Ridge is working on.

KASE:
How do you recover useful material without creating more waste in the process?

MARTIN:

You don't want to take a gram of material and turn it into ten grams of material.

MORGAN:
That's why ORNL researchers are looking at ways to improve long-standing recycling methods.

KASE:
One of the best-known is something called the PUREX process.

MORGAN:
PUREX stands for Plutonium Uranium Redox Extraction.

KASE:
In simple terms, used fuel is dissolved in nitric acid, and chemical solvents are used to selectively separate usable uranium and plutonium from the rest.

MORGAN:
It was originally developed in the mid-20th century - with Oak Ridge scientists helping refine it - and it's still the international standard for separating uranium and plutonium from used nuclear fuel.

KASE:
Countries like France use PUREX at industrial scale as part of a closed fuel cycle.

MARTIN:

The PUREX process is one of my favorite chemical processes. Since that was deployed around 70 years ago, we have not changed it. And there are very few examples in the whole chemical industry where you've developed a process and it's lasted 70 years without any changes.

MORGAN:
Seventy years is an extraordinary lifespan for an industrial process.

KASE:
And now researchers are asking what the next evolution of that recycling process might look like.

MARTIN:

Some of the current research is looking at some alternative processing technologies…instead of dissolving in acid straight away, we basically heat the fuel up.

MORGAN:
That step - heating the fuel first - is designed to deal with some of the most difficult materials early.

MARTIN:

It's very good at handling some of those volatile materials that we were talking about before - tritium, iodine, krypton.

KASE:
In other words, address the hardest-to-control radioactive gases before they complicate later steps.

MARTIN:

If we can take care of that in one space and in one process, that simplifies some of the things and reduces the amount of waste and processing that we need later on.

MORGAN:

Researchers are also looking at whether some of the material in used fuel could serve a second purpose.

MARTIN:

We're also looking at not just the uranium piece of this, what we can make energy with, but whether there's any medical isotopes that we could pull out at the same time, so that it becomes more cost effective.

KASE: So, instead of viewing used fuel strictly as a liability, it may also contain materials that have real economic value.

MORGAN:
But identifying value in the fuel is only part of the equation.

KASE:
The harder part is figuring out how to do it reliably, safely, and at scale.

MARTIN:

It's always been a strength of Oak Ridge to take a bench scale process and make it something that you can run at an industrial scale. And that's one of the things that we're trying to do.

MORGAN:
Whether fuel is recycled or not, some material will always require long-term disposal.

MARTIN:

There are benefits from that, from the point of view that we're not sending as much waste into a repository straight away. Ultimately, at some point you have to get rid of all of it.

KASE:
In the United States, used nuclear fuel is currently stored safely at reactor sites in pools and dry casks.

MORGAN:
Several countries are moving forward with deep geologic repositories - isolating waste in stable rock formations far underground.

KASE:
In the U.S., that long-term pathway is still evolving.

MORGAN:
Which means decisions about fuel design and recycling today have to account for disposal realities that may look different decades from now.

KASE:
So when Leigh talks about an "integrated fuel cycle," he's not just talking about recycling.

MORGAN:
He's talking about managing fuel responsibly from beginning to end.

KASE:
Across different reactor types, different fuels, and different futures.

MARTIN:

How do we integrate these new reactor designs and these new reactor fuels into an existing fuel cycle system that ultimately ends up in some kind of long-term disposal?

MORGAN:
That question doesn't have a single answer.

KASE:
But it does define the work.

MORGAN:
And it explains why the back end of the fuel cycle is just as important as the front.

MUSIC TRANSITION

MORGAN:
For decades, the nuclear fuel cycle has largely been shaped by governments and national laboratories.

KASE:
But now, private companies are starting to invest directly in fuel-cycle infrastructure.

MORGAN:
One of those companies is Oklo - a nuclear startup established in 2013.

KASE:
And what's interesting is they're not just building reactors.

MORGAN:
They're building the fuel strategy around those reactors at the same time.

KASE:
Oklo has announced plans for a fuel recycling facility as part of a larger advanced fuel center in Tennessee - a move that signals growing industry confidence in integrating the fuel cycle.

MORGAN:
To understand why companies like Oklo are engaging in the fuel cycle, we spoke with Ed Petit de Mange, Vice President of Recycling at Oklo.

PETIT DE MANGE:

We are building advanced fission reactors using a business model of supplying power as a service to our customers. This is distinctly different from some other companies in the space that may design a reactor or deliver a reactor to a utility, whereas Oklo is taking the approach of being an independent power producer. To do that we end up owning really all the aspects of the value chain, one of which is fuel.

KASE:
That's a pretty big distinction.

MORGAN:
Instead of selling a reactor and stepping away, they're saying: we own the fuel, we control the supply chain.

KASE:
Which makes fuel not just a technical question - but a business one.

MORGAN:
And that changes the incentives.

PETIT DE MANGE:

Rather than treating fuel supply as a separate upstream challenge, we're integrating that. So we're integrating fuel supply and fuel fabrication into a cohesive system.

We could use fresh HALEU. We can use recycled fuel, whether that's the fuel from existing light water reactors or for example our first core will actually use material that has already been recycled by the Department of Energy.

KASE: In other words, they can use newly produced fuel - or recycled material from existing reactors.

PETIT DE MANGE:

The fuel for our first core at our INL plant will actually be coming from fuel that the DOE has recycled from the EBR-II reactor and then downblended it. So it's actually it's pretty elegant because our reactor design really builds off the heritage of that EBR-II design that operated really successfully for 30 years, and the fact that we're fueling our first reactor with its used fuel is really… I find that to be really elegant.

MORGAN:
EBR-II stands for Experimental Breeder Reactor Two.

KASE:
It operated at Idaho National Laboratory from the 1960s through the 1990s and was one of the most important fast reactor experiments in U.S. history.

MORGAN:
Most commercial reactors today are what's called thermal reactors - they slow neutrons down to sustain the reaction.

KASE:
A fast reactor does the opposite. It keeps neutrons moving at high energy, which changes how the fuel behaves and what materials it can use.

MORGAN:
Some fast reactors were designed as "breeder reactors," meaning they could create more usable fuel from certain materials as they operated.

KASE:
EBR-II was part of that fast reactor program, and it helped demonstrate metallic fuel - the same type of fuel Oklo is using today.

MORGAN:
So when Ed says they're fueling their first reactor with recycled material from EBR-II, he's talking about continuing a technological lineage that's been tested before.

KASE:
It's almost poetic. The next generation running on the last generation's fuel.

MORGAN:
And it reinforces something we've heard throughout this series - nuclear innovation isn't starting from scratch.

KASE:
It's building on decades of work.

MORGAN:
But the type of recycling Oklo is proposing isn't exactly the same as the traditional PUREX process we just talked about.

PETIT DE MANGE:

The type of recycling that we'll be deploying in Oak Ridge falls into a category of technology usually called pyroprocessing. So this is distinctly different from used fuel reprocessing as it has been deployed going back to the Manhattan Project and coming out of the Cold War weapons program. Those were all aqueous based processes and that's similar to what is done now in France, as well as in other countries.

With pyroprocessing, it is quite a bit different in that it's a dry process, so it doesn't use aqueous solutions. It allows for a lower hazard facility, a smaller facility. So there are definitely some benefits there.

MORGAN:
Smaller facility. Lower hazard profile. Different regulatory posture.

KASE:
Which also makes sense for a commercial company trying to build something first-of-a-kind in the U.S.

PETIT DE MANGE:

The facility that we're going to deploy in Oak Ridge is really a campus. We have selected a site in what used to be called the K-25 site. A campus where we have an anchor operation of used fuel recycling, but we also have a co-sited fuel fabrication plant where we can take the output from recycling and immediately form that into fuel for our reactors.

One is recovery of radioisotopes which are used for industrial, medical and defense purposes and some of these radioisotopes are really only present in used nuclear fuel.

MORGAN:
So this isn't just a recycling plant.

KASE:
It's recycling, fabrication, potentially isotope recovery - all in one place.

MORGAN:
So why did Oklo decide to site its facility in Oak Ridge?

PETIT DE MANGE:

Oak Ridge obviously has a long legacy of successful nuclear operations. Huge amount of engineering expertise, supporting infrastructure, other businesses in the area - all that just combined to make it the natural location for a technically rigorous new recycling project.

Really just what I'll call like a really strong nuclear workforce and a community that is just very knowledgeable about nuclear.

MORGAN:
That's a theme we heard in our last episode too.

KASE:
Oak Ridge isn't just history - it's infrastructure, expertise, and community.

MORGAN:
And if this project moves forward, it would represent something the U.S. hasn't seen in decades.

PETIT DE MANGE:

This is really a watershed moment in terms of the fuel cycle for the US. There hasn't been a commercial undertaking really since the 1970s.

We bring somewhat of a different approach to it in that this is a commercial activity and we're very motivated to hit milestones, to do this economically and to keep the project moving ahead.

KASE:
That commercial motivation is different from the government-led efforts of the past.

MORGAN:
It also introduces pressure - timelines, economics, market expectations.

KASE:
Which makes this moment feel bigger than just one facility.

PETIT DE MANGE:

I have never seen more enthusiasm across the board and just so much excitement. I think we have woken up a bit as a nation and realized the connection between energy security and national security and economic success and nuclear needs to play a big part of that.

The key common thread in all that is they all need fuel.

MUSIC TRANSITION

KASE:
If there's one thing this conversation makes clear, it's that the fuel cycle isn't just a technical detail.

MORGAN:
It's a system - connecting reactor design, chemistry, economics, and long-term stewardship.

KASE:
The nuclear fuel cycle may not be the most visible part of nuclear energy.

MORGAN:
But it may be the most consequential.

KASE:
Because how we design, use, recycle, and ultimately manage fuel shapes the future of nuclear. If nuclear energy is going to scale…

MORGAN:
…the fuel cycle has to scale with it.

KASE:
That's why the work happening at Oak Ridge - and beyond - matters.

MUSIC

MORGAN: Thanks for listening to the latest episode of our nuclear miniseries.

KASE:
In our next episode, we'll look beyond fission - and into what's new in fusion.

MORGAN: Until next time!

MUSIC OUTRO