ASTRID (reactor)

ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration) was a proposal for a 600 MW sodium-cooled fast breeder reactor (Generation IV), proposed by the Commissariat à l'énergie atomique (CEA). It was to be built on the Marcoule Nuclear Site in France. It was the successor of the three French fast reactors Rapsodie, Phénix and Superphénix.

The main goals of ASTRID were the multi-recycling of plutonium, aiming at preserving natural uranium resources, minor actinide transmutation, aiming at reducing nuclear waste, and an enhanced safety comparable to Generation III reactors, such as the EPR. It was envisaged as a 600 MW industrial prototype connected to the grid. A commercial series of 1500 MW SFR reactors was planned to be deployed around 2050.^[1]

France had already built and operated several sodium-cooled fast reactors: Rapsodie,^[2] Phénix,^[3] and Superphénix.^[4] These earlier reactors informed lessons about fuel recycling, sodium coolant behavior, material stresses, and safety. The experience from these reactors shaped French expectations for a next-generation fast reactor.

In June 2006, France passed a law on the sustainable management of nuclear materials and waste. Under that law, ASTRID was formally initiated as part of a strategy to ensure long-term sustainability in nuclear energy. The legal act authorized the development of next-generation reactors and the management of long-lived nuclear waste and actinides.

By the end of 2009, the project became part of France’s "Investissements d’Avenir" (Investments for the Future) program. The government allocated approximately €650-€652 million for the project to cover the design phase up to a prototype. In September 2010, an agreement was signed between the French government and the CEA, formalizing the project structure. Industrial partners such as AREVA, EDF, and others were involved. Bouygues Construction was later engaged (2012) for engineering/civil works^[5]

During this period, detailed conceptual design work was undertaken. This included studies of reactor core design, fuel cycle scenarios, thermal hydraulics, safety features, structural materials (e.g. steel variants), and site selection (Marcoule was selected). The Japanese Atomic Energy Agency (JAEA) entered into cooperation with France around 2014 to help with certain design elements and safety / core component testing.

As the basic design phase progressed, several challenges emerged: cost escalations, complexity in fuel cycle and materials, changing regulatory requirements, and concerns about market competitiveness. In 2014-2015, the project schedule slipped, and initial estimates for commissioning (originally aimed for around 2020) were pushed back. In 2018, CEA proposed reducing the power of the prototype or changing the scope to a smaller reactor (e.g. around 100-200 MWe instead of full 600 MWe) to manage risk and cost. Also, Japan’s role began to decline, and joint development with Japan was paused.

In late 2018, a formal review (tied to France’s Multiannual Energy Program, “Programmation pluriannuelle de l’énergie”) concluded that while fast reactors remain an option, their industrial deployment was unlikely in the short to medium term. By August 2019, the French government announced that “the project to build a prototype reactor is not planned in the short or medium term”. Nearly €735-€738 million had been invested by that point (including funds from the Investments for the Future program). The coordination office was disbanded or reduced, and many teams were reassigned or reduced.

Even after the official suspension, research and cooperation continued in some areas. For example, the Implementing Arrangement with JAEA (Japan) handled joint safety, modeling, and accident scenario R&D, which operated until December 2019. Knowledge management became a major task: ASTRID studies, documentation, design data were gathered, archived, and methods evolved to preserve competencies. In March 2025, under France’s renewed nuclear policy, fast reactor technology was relaunched on a strategic level, with plans to begin building a demonstrator possibly around 2038 and operation target between 2045-2050.

ASTRID was designed as a pool-type sodium fast reactor. The reactor vessel housed the core, primary sodium pumps, and intermediate heat exchangers in a large sodium pool. This reduced external piping and leak risks compared with loop-type designs. Two secondary sodium circuits transferred heat to steam generators, isolating radioactive sodium from water/steam.^[6]

The planned core used MOX^[7] (mixed oxide) fuel, with uranium dioxide and recycled plutonium, and considered adding minor actinides for transmutation studies. The design applied axial and radial zoning with different enrichments in the inner and outer zones, optimizing neutron economy and power distribution. Studies reported enrichment values for various pre-conceptual designs, demonstrating heterogeneity in the core layout.

Liquid sodium was chosen as coolant for its high thermal conductivity and low vapor pressure. Sodium flowed from the reactor core to intermediate heat exchangers, transferring heat to secondary sodium loops, which in turn delivered energy to steam generators. This configuration limited the possibility of sodium–water contact in the primary system.

ASTRID aimed to demonstrate enhanced safety over earlier fast reactors. Planned features included:

- Multiple decay-heat removal systems (both active and passive).

- Diverse reactivity control devices and control rods.

- In-service inspection and repair capabilities, addressing a known weakness of sodium fast reactors.^[8]

- Advanced monitoring systems for neutron flux, sodium chemistry, and temperature.

Sodium is chemically reactive (burns in air, reacts with water) so there is risk of sodium fires or sodium‐water reactions. Any leak or breach could lead to dangerous scenarios and the cost of building and maintaining a fast reactor with all the safety systems is very high, especially given that uranium market prices have often been low, undermining the economics of breeder or recycler reactors.

High burn‐up of MOX‐fuel^[9] including plutonium and minor actinides introduces materials challenges (cladding, irradiation damage, corrosion, swelling) and requires advanced fuel fabrication and recycling infrastructure.

Meeting safety comparable to Generation III reactors (e.g. EPR^[10]) while being fast, sodium cooled, and using recycled fuel adds regulatory, inspection, oversight, and public acceptance hurdles.

Although ASTRID’s design aimed for a negative or near-zero sodium void coefficient, historically fast reactors have shown the risk of positive reactivity feedback if sodium boils or voids form. This could worsen accidents rather than stabilize them, and requires precise design margins and core configuration.

After cancellation in 2019, in March 2025 France relaunched a fast neutron reactor development program. The studies include possibly building a demonstrator around 2038, operation between 2045‐2050. There is focus on closing the fuel cycle, meaning better MOX fuel fabrication, reprocessing, handling minor actinides, reducing long‐lived waste. These are legacy goals from ASTRID. Research continues in collaboration (e.g. Japan and France) on reactor safety, materials testing, modeling and simulation of accident scenarios, and design of mitigation systems.[1]

By 2019, the ASTRID program had consumed hundreds of millions of euros in design and R&D. The French government suspended prototype construction, citing budget constraints and reduced urgency for plutonium multi-recycling given global uranium supplies. Research outputs and technical documentation were archived for future use.

As of 2025, France has not restarted ASTRID but continues research in fast neutron physics, safety methods, and fuel cycles. CEA and partners have emphasized the importance of knowledge preservation for potential long-term deployment.

• Nuclear power in France
• Nuclear power in Japan
• Phénix
• Superphénix
• Sodium-cooled fast reactor
• Generation IV reactor

• The ASTRID Technological Demonstrator