Atomic Show #313 – Stefano Buono, Founder and CEO of Newcleo
Stefano Buono is a physicist and the successful founder of Advanced Accelerator Applications, a multibillion dollar company that pioneered the use of several therapeutic medical isotopes. After making several people very rich, including himself, he sold the medical isotope business and returned to his early 1990s field of study – nuclear fission reactors using molten lead as a coolant.
About two years ago, Stefano Buono and some of his colleagues and associates founded newcleo, a company with Italian roots based in the UK. Last year, newcleo ran two successful rounds of start-up funding that netted the company a total of €400 M. After passing through several important milestones, it is raising a subsequent round with a target of €1 B for continued development and for a state-of-the-art fuel manufacturing plant.
Dr. Buono visited the Atomic Show to share his insights on the paths to success as an entrepreneur in a deeply technical and undervalued field and on the role that timing – both planned and fortunate – plays in business success. He is convinced that it is a good time to be building a nuclear fission energy company.

Lead cooling for reactors has a long history with some demonstrated success. In the 1970s and 1980s, the Soviet Union operated a class of submarines called the Alfa class, which were famously the fastest and deepest diving submarines in the world at the time. Seven subs were completed and operated with both impressive performance and technical issues that limited their reliability and service life.
The reactors in those submarines were metal cooled thermal reactors using lead-bismuth eutectic for cooling and beryllium for moderation.
The collapse of the Soviet Union and subsequent economic conditions halted most lead cooled reactor development in Russia, but it resulted in a diaspora of Soviet scientists and engineers that stimulated research and development of the technology in Europe, especially in Italy and Sweden.
For several reasons, the lead cooled reactor community moved from lead-bismuth towards pure lead and away from beryllium moderation.
Compared to water, lead is virtually invisible to neutrons, letting fission neutrons remain in the fast spectrum. Fast neutrons will fission all actinide materials, allowing reactors to advantageously consume the long-lived components of used nuclear fuel and to breed new fuel from fertile materials like Uranium 238.
Lead remains in liquid form at temperatures far above reactor operating temperatures, eliminating the need to pressurize the coolant system. Compared to sodium, the molten metal that has been used more frequently by reactor designers, lead is not subject to explosive or flammable reactions if it comes in contact with water or air. Though sodium-cooled reactor designers have devised ways to ensure safe use of their chosen fuel, the techniques require additional systems and components that add cost.

One disadvantage of lead has limited its attractiveness as a coolant. At the temperatures of interest for a reactor, corrosion rates in contact with stainless steel can cause operational problems. For the Alfa class submarines, corrosion products created some clogging issues – mainly in small diameter piping like that found in steam generators.
newcleo, Stefano’s company, is taking advantage of research and development conducted during the 40+ years since the Alfa’s were designed and operated. That research and testing has proven several different techniques that can be used to limit the effects of corrosion and that also offer the opportunity for future improvements that will enable even higher operating temperatures in subsequent reactor models.
During Atomic Show #313, we talked about advantages and challenges of lead cooling, the use of mixed oxide (MOX) fuel, the company’s phased technology development program, its licensing strategy, its options for initial deployment and the reasons that now is a great time to be developing nuclear fission power systems in Europe.
This show should provide plenty of food for thought. Please participate in the discussion using the comment features here.
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Fascinating episode, thanks
Lead coolant is not free from challenges; obviously the Russians found adequate or reasonable solutions to the flow accelerated corrosion in ferrous piping (alumina forming alloys). I seem to remember managing slag was also challenging and complex, and that a lot of that oxide came from the pipe walls. A young Westinghouse engineer was exuberantly describing their lead-cooled concept, which emerged from in-house phenomenological identification and ranking efforts, at a dog and pony show last year. He claimed it was the most economical solution – lowest cost of operations. While figuring out the details of how to manage the fuel cycle in such a system would be a fun 25-year ride to the end of my career, I just don’t see where the savings would manifest. It sounds like typical academic reactor thinking. Fast reactors like BN600, BN800 and these lead-cooled types need regular (annual, semi-annual for BN600) outages to DE-FUEL when they operate with breeding ratio > unity. I’m 100% certain these spatially well-coupled cores aren’t suited to refueling while underway, based my own experience attempting to manage single assembly asymmetries in cores with a lot more feedback (PWRs). I give all the gen4 reactors a grade of “meh”. They’re certainly going to cost a lot, at least initially. They’re certainly going to have radiation protection challenges. They’re certainly going to have teething problems, and they don’t really improve any parameter my company would be interested in as an operator. They’re just different. The fuel isn’t scarce; we don’t need breeders.
In my opinion, LWR’s are the problem, not the solution. They have by far the lowest thermal efficiency of any power generation system on the planet and are obscenely wasteful of nuclear fuel. Gen4 designs address all of these issues. The breed and burn/travelling wave core setup enabled by fast reactors is a no-brainer for game-changing reductions in refueling outages, to say nothing of the fuel utilization and waste management benefits. The VHTR and GCFR have the potential for net efficiencies far in excess of 50% along with massive reductions in balance of plant. Of course there are material challenges but there are no technological show-stoppers, only a lack of will. As far as high FOAK costs go, LWR’s had to deal with those as well. LWR’s have served us well during the long periods of innovation stagnation and anti-nuclear sentiment, and sustaining the current fleet makes sense, but when it comes to new builds, their fundamental shortcomings are no longer justifiable.
I’m not an engineer, but I think that lead cooling combined with Moltex’s molten salt fuel in fuel pins might just be the ultimate approach to making a small reactor that produces lots of cheap electricity/heat.
I understand why they are using MOX, you can actually buy and use it today. Using it rather than molten salt fuel is one less risk on the path to getting to a viable first reactor in operation.
One question I have is – would lead cooling be better than molten salt cooling for getting higher output temperatures for hydrogen/chemical fuel production?
One advantage of MOX fuel is that bad agents cannot use it to breed pure Pu239. Fresh MOX fuel already has a high content of denaturing Pu240, its ratio only increasing with burn up.