SMRs & ADVANCED REACTORS | STELLARIA’S MSR
Renewable fission at industrial scale
Industrial energy demand is undergoing a massive transformation. Data centres, AI clusters, and large-scale hydrogen production are just some of the drivers placing unprecedented pressure on
already-strained electrical grids. To avoid pushing the dream of cheap, abundant, and available power almost into the realms of fantasy means new technology – on-demand, localised, cheap, and renewable. Step forward Stellaria.
AS ELECTRICITY SYSTEMS ACCUMULATE EVER higher shares of variable renewables, the structural need for dispatchable capacity becomes more pronounced. The difficulty, argues Nicolas Breyton, CEO of reactor company Stellaria, is that the fixed cost of maintaining a dispatchable fleet large enough to cover prolonged periods without sun or wind now dominates system economics. “The fixed cost is 80% of the price of the power,” he tells NEI, noting that utilities must size firm capacity for worst-case conditions, regardless of how often those conditions occur. Industrial users increasingly find themselves unable to secure around-the- clock power at predictable prices, pushing some operators toward self-sufficient energy solutions. For Stellaria these conditions frame specific technical requirements: a source of on-demand power that is local, high-temperature, dispatchable, and capable of long-term autonomous operation with minimal fuel logistics. The answer, Breyton concludes, is a fast spectrum reactor. He explains: “The only way to do that is renewable fission,” he say, noting that by ‘renewable’ he means a closed fuel cycle in which
fertile isotopes – primarily uranium 238 – are continuously converted to fissile plutonium 239 within the molten-salt core of a fast reactor. Breyton explains: “Molten salt reactors are very interesting because they can close the cycle and can also burn minor actinides which are the most difficult long life high activity waste that one has.” While the idea is not new – fast reactors have been studied and built for decades - Breyton points out that past programmes were hindered not by physics but by engineering economics. “We were lacking consistency,” he said of historical fast reactor efforts. “The main reason is that commercially it’s not viable.” Sodium- and lead-cooled reactors rely on solid pins within their fuel assemblies, but the inherent heterogeneity of solid fuel leads to problems in fast-spectrum conditions. “They accumulate plutonium outside the solid bar and they destroy fissile atoms inside,” Breyton explains. After roughly three years, assemblies must be removed and reprocessed. “Reprocessing takes 15 years, and it’s quite expensive, above the price of the reactor,” he says. While fast reactors offer an appealing
Above: The core of the Stellaria design is a fission region containing a mixture of fertile and fissile chlorides — primarily UCl₃ and PuCl₃ — dissolved in a purified sodium-chloride-based carrier salt
34 | December 2025 |
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