Europe has been turning uranium into energy for over half a century. In the process, the continent has amassed vast stockpiles of nuclear waste. This radioactive material can take millions of years to become safe, and no one really knows what to do with it.

Thorizon, a Franco-Dutch startup, has an idea: reuse the nuclear waste to generate new energy. The company is developing a small modular molten salt reactor (MSR) that runs on a mix of spent nuclear fuel and thorium, a radioactive metal with untapped potential. 

Thorizon aims to begin construction of its first reactor, Thorizon One, within five years. Once complete, the plant is expected to produce 100 megawatts of electricity — enough to power around 100,000 homes or a major data centre.

“We’re not just building a new type of reactor — we’re rethinking how we use the fuel we already have,” Thorizon’s CEO Kiki Leuwers told TNW. “Europe is sitting on a stockpile of valuable nuclear material. With the right technology, that waste becomes a resource.” 

When the radioactive uranium is used as fuel in a nuclear reactor, its atoms undergo fission, releasing heat. This heat is then used to produce steam, which spins a turbine to generate electricity. The radioactive waste produced in this process still retains around 90% of the uranium’s original energy.

Lauwers estimates that Europe’s stockpiles of nuclear waste could power the entire region for 40 years. In the US, scientists believe it could power their country for around 100 years.

Why aren’t we reusing nuclear waste?

Countries including the US, France, and Japan have long understood the potential of reusing spent nuclear fuel. In the 1960s and ‘70s many so-called fast reactors were built — advanced designs capable of extracting more energy from nuclear fuel and even “breeding” new fuel from waste. But in the decades that followed, most were phased out.

There were two key reasons: politics and economics. Fast reactors produce significant quantities of plutonium, the building block of atomic bombs. At the height of the Cold War, fears of nuclear proliferation prompted many countries, especially the US, to abandon efforts to recycle nuclear waste.

At the same time, global uranium supplies turned out to be far more abundant than expected. Discoveries of deposits in Australia, Canada, and Africa drove prices down, making it cheaper to mine fresh uranium than to invest in recycling infrastructure. Combined, these factors put radioactive recycling on ice.  

While France and Japan still reprocess some of their used fuel, most of the world’s nuclear waste today ends up in massive steel cylinders called dry casks — a temporary solution to a very, very long-term problem. Efforts to bury it deep underground for eternity — like Finland’s 500-metre-deep Onkalo repository — are making progress, but remain contentious and expensive.

Meanwhile, expanding nuclear power in Europe continues to be a thorny issue, but the tide may be turning. Faced with the twin crises of climate change and energy insecurity, countries including the UK and France are pushing to expand nuclear power capacity, especially in small modular reactors (SMRs). 

Whether nuclear energy gets its moment back in the sun or not, Europe still has a massive nuclear waste problem. One that Thorizon hopes to clean up.  

How will Thorizon’s plant work?

Thorizon’s MSR operates at high temperatures but low pressure, making it safer and more efficient. If something goes wrong, the salt solidifies and contains the radioactive material, limiting the risk of leaks or explosions. 

MSRs were first developed in the 1960s at the Oak Ridge National Laboratory in the US and showed great promise. But they never reached commercial viability, largely because housing the corrosive salts safely proved technically challenging and expensive.  

To counter this, Thorizon’s design uses a system of cartridges. Each massive steel cylinder is filled with molten salt and a mix of spent fuel from traditional reactors and fresh thorium — a radioactive material much more abundant than uranium and safer to handle. The idea is that these cylinders can simply be replaced once the radioactive part of the fuel has largely been depleted.

“The cartridge approach lets us isolate the most extreme conditions inside the reactor,” said Lauwers. “It’s modular, replaceable, and gives us a safe way to deal with radioactive materials.”

Thorizon spun out from the Netherlands’ nuclear research institute NRG in 2018. It now employs around 50 engineers split between Amsterdam and Lyon. The company says it has completed its conceptual design and is engaged in regulatory talks with Dutch, French, and Belgian authorities. 

Three pre-feasibility studies are underway for potential launch sites in France, the Netherlands, and Belgium. Industry partners, including Dutch manufacturing giant VDL, are helping prototype core components.  

By blending spent uranium fuel with thorium in a molten salt reactor, Thorizon aims to create a cleaner, more sustainable source of nuclear energy. It could turn a huge nuclear waste problem into a solution for Europe’s clean energy future. But the benefits won’t come cheap.    

Funding a nuclear waste renaissance 

So far, Thorizon has raised €42.5mn, including funding from the French government and Dutch bodies such as Invest-NL and the Brabant Startup Fonds. However, that’s just a fraction of the €750mn it says it needs to begin building its prototype reactor. 

The long timelines, strict regulations, and high upfront costs of nuclear startups typically make them a hard sell. “To bring the technology to life, public-private partnerships are crucial,” said Lauwers. “Some of the money being spent on burying nuclear waste could be instead diverted to reusing it.” 

Government backing will be crucial, she said, as will venture capital. However, the CEO said that being based in Europe may put the company at a disadvantage from a funding perspective. 

“In the US, relatively small teams have been able to scale much faster, obtain more private funding, and obtain their licenses,” she said. “Here in Europe, that can take longer.” 

TerraPower and X-Power are two examples. Each SMR startup has raised over $1bn to commercialise its technology. In Europe, by contrast, no tech companies have attracted a fraction of that funding.

However, if Thorizon manages to overcome the hurdles, it could hit three birds with one stone: cleaning up nuclear waste, reducing Europe’s reliance on fossil fuels, and supplying stable baseload power to homes and industries.