In just a few months, three emerging companies have pushed their small and advanced reactor projects into the hands of France’s nuclear watchdog, signalling a rare moment of momentum for a sector that has spent years on the defensive.
Three challengers, one regulator: a new phase for French nuclear
Since late 2025, France’s nuclear industry has slipped into a different gear. New names are joining the traditional giants, and they are no longer just talking about concepts. They are putting formal dossiers in front of the Autorité de sûreté nucléaire et de radioprotection (ASNR), the national safety and radiation protection authority created from the merger of earlier regulators.
Three companies stand out: newcleo, Stellaria and Jimmy Energy. Each is developing a different type of small or advanced modular reactor, aimed at distinct markets and timelines. Yet they now share a common reality: direct scrutiny from one of the toughest nuclear regulators in Europe.
The arrival of three advanced reactor projects on the ASNR’s desk marks the clearest sign in years that French nuclear ambitions are shifting from speeches to blueprints.
Two of the firms, Stellaria and Jimmy Energy, have already applied for a “Demande d’Autorisation de Création” (DAC). This is not a casual step. Once granted, it turns a company into a full nuclear operator, with a fixed design and full legal responsibility for safety across the plant’s lifetime.
The third player, newcleo, has chosen a slightly different route. It has submitted a detailed nuclear safety programme for its lead‑cooled fast reactor, ahead of a full construction request. The move opens a structured technical dialogue with the ASNR while the design still has some flexibility.
Newcleo bets on lead‑cooled fast reactors and recycled fuel
A start‑up with unusually deep pockets
Newcleo, founded in 2021 by Italian nuclear physicist and former CERN researcher Stefano Buono, has set itself an ambitious target: revive fast reactors, but in a form that can meet twenty‑first‑century regulatory and societal expectations.
The start‑up is technically Franco‑Italian but headquartered in Paris. It has raised more than €500 million from private European investors since launch, an unusually large war chest for a young civil nuclear company.
This funding supports parallel efforts: design of its LFR‑AS‑30 and larger LFR‑AS‑200 lead‑cooled fast reactors, a fuel manufacturing plant, and an extensive experimental programme in Italy. The goal is to file a DAC in France by 2027 and have a first modular reactor operating around 2031 at the Chinon site, subject to public debate and regulatory green lights.
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Why lead and fast neutrons matter
Newcleo’s design belongs to the so‑called Generation IV family. The core uses fast neutrons, while liquid lead serves as coolant instead of water.
- The lead operates at atmospheric pressure, reducing the risk of high‑pressure failures.
- Its very high boiling point allows wide safety margins on temperature.
- Its thermal inertia supports passive cooling strategies if active systems fail.
These features shape the safety case now under review. The dossier sent to the ASNR details how the reactor behaves under normal operation, during transients such as sudden shutdowns, and in degraded conditions. It also examines how heat is removed after shutdown and how the core remains controllable and confined during extreme scenarios.
At the heart of the newcleo project lies a double promise: steady low‑carbon power and a way to cut the burden of long‑lived nuclear waste.
A reactor designed around advanced fuel
Newcleo’s approach ties the reactor closely to its fuel cycle. In late 2024, it submitted a separate safety programme for a plant that will manufacture advanced fuel, including MOX and recycled materials from existing spent fuel.
The company has already secured local backing for part of that plan. The département of Aube has approved the sale of land for a MOX fuel plant worth about €1.8 billion, which could create around 1,700 direct jobs. That facility would feed the lead‑cooled reactors and support a strategy of multi‑recycling: using certain high‑level waste streams as input, rather than leaving them in long‑term storage.
Regulators are examining reactor and fuel together, rather than as isolated pieces. This joint view will shape the final safety opinion sent to the relevant ministry before any construction licence is granted.
Data first: experiments in Italy and the PRECURSOR mock‑up
Newcleo is leaning heavily on experimental data rather than pure simulation. At the ENEA Brasimone Research Center in Italy, 16 research installations are in operation or being built. They test fluid dynamics, materials and thermal behaviour under conditions similar to the planned reactor.
On top of that, the company is building PRECURSOR, a full‑scale but non‑nuclear mock‑up rated at 10 MW thermal, delivering roughly 3 MW of electricity. It contains no nuclear fuel and no fast neutron flux. The aim is to observe in practice how pumps, heat exchangers, control systems and power conversion behave before any radioactive fuel is loaded in a real plant.
Results from Brasimone and PRECURSOR will feed back into the safety case, tightening model uncertainties and giving regulators concrete evidence rather than purely theoretical claims.
A French rehearsal for global ambitions
For Buono and his team, the French process is more than a national hurdle. The ASNR has a reputation for demanding evidence and detailed justification. If newcleo can secure approval here, it gains a template it can present to other regulators in Europe and beyond.
In parallel, France’s National Commission for Public Debate (CNDP) will organise a mandatory public consultation on the project in 2026. That process will test not just the technical design, but also the company’s ability to address public concerns over safety, waste and local impacts.
Stellaria and Jimmy: two very different paths to “small” nuclear
Three reactors, three strategies
While newcleo plays a long game with fast reactors and fuel recycling, Stellaria and Jimmy Energy target quicker or more targeted industrial uses. All three operate in the SMR or AMR space, yet their technologies and markets differ sharply.
| Company | Reactor name | Technology | Coolant | Approximate power | Main use | Timeline |
|---|---|---|---|---|---|---|
| Stellaria | Alvin | Fast reactor | Molten salts | Dozens of MW | Electricity and industrial heat | Prototype around 2030 |
| Jimmy Energy | JIMMY | Micro‑reactor | Helium gas | Few MW thermal | Low‑carbon process heat | Progressive rollout late 2020s |
| newcleo | LFR‑AS‑30 / 200 | Fast reactor | Liquid lead | 30 MW then 200 MW | Grid power and fuel recycling | Early 2030s |
Stellaria’s Alvin uses molten salt as coolant, operating at high temperature without high‑pressure water circuits. The chemistry of the salts forms part of the safety concept, helping control fission products and heat transfer.
Jimmy Energy’s reactor goes the opposite way: small, gas‑cooled and focused almost entirely on industrial heat. The idea is to slot compact units next to factories, where they can replace fossil‑fuel boilers and cut emissions without touching the power grid.
French SMR developers are not chasing a single “one size fits all” design; they are carving up different slices of the energy market, from factory boilers to baseload power.
What this “golden age” really means for France
From grand projects to diversified nuclear uses
For decades, French nuclear power meant huge standardised reactors feeding the national grid. The new wave looks more diversified. Some projects still target grid electricity. Others see nuclear as a tool for industrial heat, hydrogen production or even maritime propulsion, as the UK is actively considering.
This shift fits a broader EU challenge: decarbonise heavy industry, not just electricity. High‑temperature nuclear heat could substitute gas in sectors such as chemicals, steel or cement. Small reactors placed on or near industrial sites could provide steady heat with a much smaller footprint than large power stations.
Risks, trade‑offs and regulatory pressure
None of this comes without risk. Advanced reactors rely on coolants and materials that have seen far less operational experience than conventional water‑cooled designs. Lead can corrode structural metals; molten salts demand tight control of chemistry; gas‑cooled systems need meticulous design to avoid hot spots.
The ASNR’s role is to stress‑test these promises. That means asking for long‑term corrosion data, credible emergency cooling strategies and clear plans for waste handling, including novel fuel types. Companies must show not only that normal operation is safe, but also that rare accidents remain controllable.
Developers also face financial and reputational hazards. Timelines can slip as test results come in or public opposition rises. A single high‑profile failure could taint the entire SMR category in the eyes of investors and local communities.
Key concepts behind the headlines
What is a DAC and why does it matter?
The “Demande d’Autorisation de Création” is the formal birth certificate of a French nuclear installation. To submit one, a company must freeze its design, deliver a complete safety demonstration, assess environmental impacts and outline waste management strategies.
Once submitted, the file triggers in‑depth review by the ASNR, consultations with other state bodies and, for major projects, a structured public debate. Approval does not mean a plant starts tomorrow, but it signals that the concept has passed a significant legal and technical threshold.
Fast reactors, SMRs and public perception
Terms like “fast reactor” or “SMR” can sound exotic, even intimidating. In simple terms, a fast reactor uses higher‑energy neutrons that can fission not only traditional uranium fuel but also some components of long‑lived waste. An SMR is a smaller‑than‑usual reactor, often designed for factory‑style manufacturing and transport by road or ship.
Supporters argue that fast reactors and SMRs can reduce waste, improve safety margins and cut construction risk by repeating standard modules. Critics point to proliferation concerns, unresolved waste questions and the risk of overpromising on cost or schedule.
France’s new “golden age” sits at that intersection: high hopes, demanding regulators, significant money on the table, and a public that remembers past nuclear debates. Whether these three companies succeed or not, their push through the regulator’s front door marks a clear turn in the country’s energy story.
Originally posted 2026-03-12 20:45:49.