Austria’s Emerald Horizon is developing particle accelerator technology that can be used to generate nuclear power from thorium, a process the company says is cheaper and safer than current solutions. Power is generated by a machine the size of a shipping container, which can be mass-produced and used almost anywhere. Potential end users include industrial sites, data centers, ships, locations without access to electrical power, and military bases and other places that require energy security.
The company’s Accelerator Driven Energy Source (ADES) technology was recently nominated for the Earthshot 2025 prize, a global environmental award.
“We are combining the world of particle accelerators and the world of nuclear reactors to put in place a cheaper, safer, highly reliable source of energy that is available 24/7,” says co-founder Dr. Mario J. Mueller, Emerald Horizon’s Chief Technology Officer. “Our approach is smaller, smarter and greener.”
Unlike most small modular reactors (SMRs) Emerald Horizon’s particle accelerator does not depend on a chain reaction that involves splitting uranium into two parts to achieve exponential growth of energy. The Austrian startup instead relies on the release of energy from thorium by controlling the power of a particle beam. “The more particles released, the more energy we can release,” says Mueller, a physicist who earned his PhD at CERN. This approach avoids the risk of explosions that plague traditional nuclear reactors, he says.
Using thorium, a silvery, slightly radioactive metal commonly found in igneous rocks and heavy mineral sands, instead of uranium reduces the amount of radioactive waste, says Mueller, making thorium-fueled reactors more environmentally friendly than their uranium counterparts.
Cost is another advantage. France’s new Flamanville European Pressurized Reactor plant in Normandy, which cost €13.2 billion, is expected to produce 1.6 gigawatts of electric power over 50 years, at a price of 16 euro cents per kilowatt hour. Mueller says Emerald Horizon’s plants are expected to produce energy at a cost of less than one euro center per kilowatt hour.
The cost differential is due to the fact that traditional nuclear plans convert only 3% of costly uranium into energy, says Mueller. Some 97% ends up as nuclear waste. He says that by using Emerald Horizon’s particle accelerator 80% of thorium can be transformed into energy due to the efficiency of the burn rate.
This factor, along with the modular nature of Emerald Horizon’s approach, makes it both cost effective and scalable, Mueller says. Each of the Austrian startup’s 40-foot units are expected to produce 25 megawatts of thermal power and it will be easy to add additional units, depending on the use case, he says.
Emerald Horizon will not sell the units. It plans to sell energy-as-a-service, he says, and compete with the some 80 existing SMR companies as well as larger traditional nuclear power plants.
The company, which was founded in 2019, has raised €300 million for the prototype and additional money for the transition to a serial production. It expects to have a prototype ready in 2029 and start producing its first units in 2032.
Using thorium for energy production is not without challenges. Thorium-232, is more abundant than the commonly used isotope in nuclear fuel, uranium-235, but it isn’t directly fissile–it can’t undergo fission, the splitting of atomic nuclei that produces energy. It must first be transmuted into fissile uranium-233, which Emerald Horizon achieves with an internal, integrated process of its ADES technology.
An enormous amount of thorium has been brought to the surface during mining operations but set aside as it was thought to have had little value. That is changing. “Any place we have gone to source thorium the Chinese had already been there,” says Mueller. “That tells us that we are on to something.”
In 2018, China started the erection of a thorium-based molten-salt reactor (TMSR-LF1) in the Gobi Desert. The 2-megawatt reactor project, managed by the Chinese Academy of Sciences’ achieved its first energy release in August 2021. Since then Shanghai Institute of Applied Physics (SINAP), announced a commercial 373 MWth Molten Salt Reactor (nuclear fission reactors in which either the fuel and/or the coolant is a molten salt) by 2030, according to an environmental-impact report released by the Academy
China’s efforts put it at the forefront of both thorium-based fuel breeding and molten-salt reactors. Several companies elsewhere in the world are developing plans for this kind of fuel or reactor, but none has yet operated one, according to the Institute of Electrical and Electronics Engineers (IEEE).
The International Atomic Energy Agency estimates that there is about 6,000,000 tons of identified thorium available globally. “That is enough to last for 100,000 years,” says Mueller. “If we are able to use thorium as an energy source we won’t have an energy problem anymore.”
In addition to its ambitions in the energy sector Emerald Horizon is experimenting with another potential use for its technology: the medical field. It has a cooperation agreement with Boston-based Neutron Therapeutics, a Boston-area company that is using an accelerator-based neutron source for Boron Neutron Capture Therapy (BNCT), an alternative to traditional radiotherapy and proton therapy, with the ability to deliver targeted radiation to cancer cells while sparing surrounding healthy tissue.
Emerald Horizon’s Accelerator-Driven Energy Systems (ADES) and Boron Neutron Capture Therapy (BNCT) both rely on high-intensity neutron sources, with ADES using neutrons for energy generation and BNCT utilizing epithermal neutrons for targeted cancer treatment. “Cooperation in R&D makes sense,” says Mueller, “because advancements in neutron moderation, beam optimization, and accelerator efficiency can enhance both fields—improving neutron flux control for ADES while refining neutron delivery and spectral shaping for BNCT, leading to more effective and efficient systems in energy and medicine.”
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