This reactor works with no fuel. It could change the future of fission.

Here’s what you’ll learn when you read this story:

• Designed by Newcleo, an Italian tech company looking for a more sustainable solution to nuclear reactors, the PRECURSOR reactor uses lead as a coolant and no actual fuel.
• Because lead has a ridiculously high boiling point, it’s almost impossible for the machine to overheat and trigger an explosion.
• While PRECURSOR will not be completed until the end of 2026, Newcleo will be using plutonium from a U.S. Cold War surplus to power its upcoming reactors.

Nuclear reactors can be an enormous hazard. The Chernobyl nuclear disaster is so famous that it almost goes without saying, and Japan was so shaken by the Fukushima Daiichi accident of 2011 that it shut down all nuclear power production and only lifted the ban in the last few years. One main reason for the danger of such meltdowns in traditional nuclear reactors is that they rely on water as a coolant, which can evaporate under extreme conditions, leaving the reactor core exposed and vulnerable to overheating. But PRECURSOR, a next-gen test reactor developed by Italian tech company Newcleo, uses lead as a coolant instead. There’s also nothing nuclear about PRECURSOR.

How can a reactor possibly operate without fuel and still call itself a reactor? When they developed the contraption known as PRECURSOR, the team at Newcleo figured that simulating the behavior of a nuclear reactor without actually using nuclear fission could provide the same results without risking another apocalyptic disaster. PRECURSOR mimics everything about fission reactors from their thermal physics down to their plumbing and size. Both PRECURSOR and the company’s upcoming fueled reactor will use lead for a coolant. The only difference is that PRECURSOR is much safer to test before moving on to a larger and more powerful fueled reactor because it uses electrical heaters—no fuel required.

“What makes [PRECURSOR] truly unique is that it will generate electricity using a turbine, the only component we didn't manufacture but just completed by our partner FINCANTIERI, making it potentially the only facility in the world to do such a complete demonstration of reactor functionalities,” said Stefano Buono, CEO and founder of Newcleo, said in a recent LinkedIn post.

When the empty reactor was lowered into place in the ENEA Brasimone Research Centre near Bologna, Italy, it weighed over 44,000 pounds (about 20 metric tons), and once filled with lead it will reach 35,353 pounds (115 metric tons). Melting a heavy metal to use as a coolant has its advantages. Because lead needs to be heated to an astronomical 3,170°F (1,743°C) to so much as start boiling, the reactor won’t need the extreme pressure that’s required when water, which only boils at 212°F (100°C), is used as a coolant, as in most fueled reactors. Heated lead is so dense it can also circulate on its own without needing an assist from pumps, but will easily solidify if there’s fuel leakage. Reactors that use fuel benefit from lead capturing fission byproducts such as iodine and cesium.

The absence of fuel means PRECURSOR will never be in danger of going supercritical when tested. Critical mass is the the minimum amount of fuel it takes for a reactor to keep a continuous nuclear chain reaction going, with the neutrons born from each fission reaction causing the same reaction in another atom. Reaching the supercritical threshold means the fuel has gone beyond the critical mass rate of fission reactions. Left unchecked, rapidly increasing reactions make nuclear fuel prone to igniting itself and triggering an explosion. But in PRECURSOR, the vessel that would otherwise hold fuel will be empty. Electrical heaters instead heat the molten lead in the space where fuel would have been, and the lead then transfers that heat to a steam generator that powers a turbine. PRECURSOR has an output of 10 thermal megawatts.

While PRECURSOR is still under construction and will be finished near the end of 2026, it’s still just a demonstration. Newcleo’s 30-megawatt LFR-AS-30 will be its first commercial reactor. Though LFR-AS-30 won’t be operational until 2031, Newcleo has partnered with Oklo, one of two nuclear tech companies that the U.S. Department of Energy chose for its Surplus Plutonium Utilization Program. The DOE will supply Oklo with some of the nearly 44,100 pounds (20 metric tons) of weapons-grade plutonium left over from the Cold War. Newcleo has also teamed up with Oklo and will use this plutonium for future nuclear plants, and the massive recycling plan is a definite improvement over being disposed of in New Mexico’s Waste Isolation Pilot Plant.

“Surplus plutonium was once viewed solely as a nuclear liability and a multi-billion-dollar financial drain on taxpayers—but it doesn’t have to remain one,” Josh Jarrel, Deputy Assistant Secretary for the Nuclear Fuel Cycle, recently said in a press release. “we are redirecting this Cold War legacy to serve as a vital energy asset, powering the next generation of American nuclear innovation.”