“This license marks a turning point, not just for Clean Core but for the US-India civil nuclear partnership,” says Mehul Shah, the company's chief executive and founder. “It places thorium at the center of the global energy transformation.”
Thorium has long been seen as a good alternative to uranium because it’s more abundant, produces both smaller amounts of long-lived radioactive waste and fewer byproducts with centuries-long half-lives, and reduces the risk that materials from the fuel cycle will be diverted into weapons manufacturing.
But at least some uranium fuel is needed to make thorium atoms split, making it an imperfect replacement. It’s also less well suited for use in the light-water reactors that power the vast majority of commercial nuclear plants worldwide. And in any case, the complex, highly regulated nuclear industry is extremely resistant to change.
For India, which has scant uranium reserves but abundant deposits of thorium, the latter metal has been part of a long-term strategy for reducing dependence on imported fuels. The nation started negotiating a nuclear export treaty with the US in the early 2000s, and a 123 Agreement—a special, Senate-approved treaty the US requires with another country before sending it any civilian nuclear products—was approved in 2008.
A new approach
While most thorium advocates have envisioned new reactors designed to run on this fuel, which would mean rebuilding the nuclear industry from the ground up, Shah and his team took a different approach. Clean Core created a new type of fuel that blends thorium with a more concentrated type of uranium called HALEU (high-assay low-enriched uranium). This blended fuel can be used in India’s pressurized heavy-water reactors, which make up the bulk of the country’s existing fleet and many of the new units under development now.
Thorium isn’t a fissile material itself, meaning its atoms aren’t inherently unstable enough for an extra neutron to easily split the nuclei and release energy. But the metal has what’s known as “fertile properties,” meaning it can absorb neutrons and transform into the fissile material uranium-233. Uranium-233 produces fewer long-lived radioactive isotopes than the uranium-235 that makes up the fissionable part of traditional fuel pellets. Most commercial reactors run on low-enriched uranium, which is about 5% U-235. When the fuel is spent, roughly 95% of the energy potential is left in the metal. And what remains is a highly toxic cocktail of long-lived radioactive isotopes such as cesium-137 and plutonium-239, which keep the waste dangerous for tens of thousands of years. Another concern is that the plutonium could be extracted for use in weapons.
Enriched up to 20%, HALEU allows reactors to extract more of the available energy and thus reduce the volume of waste. Clean Core’s fuel goes further: The HALEU provides the initial spark to ignite fertile thorium and triggers a reaction that can burn much hotter and utilize the vast majority of the material in the core, as a study published last year in the journal Nuclear Engineering and Design showed.