LLNL and Ampera launch THUNDER project to develop thorium-based TRISO nuclear fuel

Lawrence Livermore National Laboratory and nuclear fuel startup Ampera have joined forces to develop a new kind of TRISO fuel—one built around thorium instead of conventional uranium. Their collaboration runs under the project name THUNDER, short for Thorium Unimodal Droplet Ejection for Reactors.

At the core of the effort is a straightforward but meaningful swap: replacing uranium kernels with thorium-232 kernels as the basic building block of TRISO fuel.

LLNL and Ampera formalize partnership under the THUNDER project

Lawrence Livermore National Laboratory is one of the most advanced research institutions in the US, and its decision to partner with Ampera signals a serious commitment to exploring alternative nuclear fuel cycles. The two organizations have formalized their work through a strategic partnership agreement, organized under the THUNDER project—Thorium Unimodal Droplet Ejection for Reactors.

LLNL and Ampera are evaluating and optimizing this process specifically to produce thorium-232 kernels that meet the strict geometric standards TRISO fuel requires.

The project name itself reveals quite a bit about the technical approach. “Unimodal Droplet Ejection” refers to the manufacturing method at the center of the effort: using liquid metal–jetting technology to produce thorium kernels that are consistent, spherical, and tightly controlled in size.

Ampera brings the proprietary fuel concept. LLNL brings the research infrastructure and scientific expertise to evaluate, refine, and validate it. Together, they’re working to move thorium-based TRISO fuel from concept toward something that can actually be demonstrated at scale.

Why thorium instead of uranium: The rationale behind THUNDER

Standard TRISO fuel uses uranium as the kernel—the dense, fuel material core sitting at the center of each particle. THUNDER flips that assumption, substituting thorium-232 as the kernel material.

Thorium-232 is more abundant in nature than uranium, which is a meaningful advantage for long-term fuel supply. But the case for thorium goes further: it produces less long-lived radioactive waste compared to uranium-based fuel cycles—a significant consideration as the nuclear industry works through waste storage and disposal challenges.

The manufacturing side, though, is tricky. Thorium kernels need to be highly uniform and spherical to perform properly inside a TRISO particle. Any inconsistency in shape or size can compromise the surrounding protective layers, affecting both safety and performance. That’s where the liquid metal–jetting technology comes in. LLNL and Ampera are evaluating and optimizing this process specifically to produce thorium-232 kernels that meet the strict geometric standards TRISO fuel requires. Getting the kernels right isn’t a minor detail—it’s foundational to everything else the project is trying to achieve.

Projected outcomes: From kernel production to reactor-ready fuel

The THUNDER project isn’t just about making thorium kernels. It’s about proving those kernels can become finished, functional TRISO fuel—and that the process can work at production scale, not just in a lab.

Once the liquid metal–jetting process produces thorium-232 kernels, those kernels go through further processing to become complete TRISO particles, with all the ceramic and carbon layers applied around them. That downstream processing is part of what the partnership aims to demonstrate. The core question is technical feasibility: can thorium-based TRISO be manufactured consistently, and can it meet the performance and safety requirements that advanced reactors demand?

If the project succeeds, the implications extend well beyond Ampera and LLNL. The US advanced reactor sector is actively developing a range of new reactor concepts, many of which rely on TRISO fuel. Adding thorium-based variants alongside conventional uranium-based TRISO could meaningfully diversify the domestic nuclear fuel supply chain, reducing dependence on any single fuel type or source.

What TRISO fuel is and why it matters for advanced nuclear reactors

TRISO stands for Tristructural Isotropic. It’s a fuel form where the nuclear material—the kernel—is encapsulated in multiple layers of ceramic and carbon materials that act as a built-in containment system, trapping fission products and preventing them from escaping even under extreme conditions.

That design makes TRISO one of the most robust fuel forms available for advanced reactor applications. It’s particularly well-suited to high-temperature gas-cooled reactors, which operate at temperatures that would compromise conventional fuel assemblies. Several US advanced reactor developers are already building their designs around it.

Each TRISO particle is essentially its own miniature containment vessel—a feature that carries real weight in reactor designs prioritizing passive safety, where systems must stay stable under accident conditions without active intervention. The multi-layer structure is what makes that possible.

Introducing thorium-232 as an alternative kernel material doesn’t change the fundamental TRISO architecture. The protective layers stay the same. What changes is what sits at the center—and by extension, the waste profile and the resource base feeding the fuel cycle.

The key takeaways from the THUNDER project are fairly clear. Lawrence Livermore National Laboratory and Ampera have entered a formal strategic partnership to develop thorium-based TRISO fuel, centering their work on liquid metal–jetting technology to produce uniform thorium-232 kernels. The project aims to demonstrate both technical and production feasibility. Should it succeed, a thorium-based option could be added to the fuel choices available for the next generation of US advanced reactors—broadening the supply chain and expanding the possibilities for how those reactors get powered.

Kelly Lippke

Kelly is an experienced writer with 15 years of experience exploring the big stories that shape our world, from tech breakthroughs and space exploration to climate, energy, and the fascinating quirks of science. She has a talent for turning complex ideas into sharp, memorable insights that stay with readers long after they’ve finished reading.