Lead-Cooled Fast Reactors (LFRs) use liquid lead or lead-bismuth eutectic (LBE) as the primary coolant, operating in the fast neutron spectrum at near-atmospheric pressure. Lead offers several compelling advantages as a reactor coolant: an extremely high boiling point exceeding 1,700 degrees Celsius (providing enormous thermal margin above operating temperatures), chemical inertness with air and water (unlike sodium, which reacts violently with both), excellent natural circulation properties, and the ability to shield against gamma radiation. These properties eliminate the risk of coolant boiling accidents and energetic chemical reactions that require mitigation in sodium-cooled and water-cooled designs. Russia has the most extensive LFR operating experience, having deployed lead-bismuth-cooled reactors in Alfa-class submarines since the 1970s.
Newcleo, originally headquartered in the UK and now based in Paris, is the most advanced Western LFR developer. Their LFR-AS-200 (200 MWe) was accepted into the UK's Generic Design Assessment in June 2025 as the first advanced modular reactor in the UK GDA process, though the UK program was subsequently suspended. Newcleo relocated to France in 2025 after the UK decided to immobilize its plutonium stockpile rather than make it available for MOX fuel production, which is central to Newcleo's fuel strategy. The company is building a non-nuclear PRECURSOR prototype in Italy, with completion targeted by end of 2026 and commissioning in early 2027. Newcleo has raised over $755 million since 2021, with $125 million in 2025 alone, from investors including the CERN pension fund, Danieli, and Cementir.
Blykalla of Sweden is developing the SEALER (Swedish Advanced Lead Reactor) in both a 55 MWe commercial variant (SEALER-55) and a smaller SEALER-E configuration. Blykalla has raised $50 million for industrialization and completed Phase 1 construction of a test facility at the Oskarshamn nuclear power plant site, with testing underway since Q3 2025. SEALER-One targets first criticality in 2029 at Oskarshamn, with commercial units planned for the early 2030s. Westinghouse is also developing a lead-cooled fast reactor design, with eight test facilities operational in the UK since 2023 under the UK AMR Phase 2 program. The Westinghouse LFR features air-cooled power conversion and atmospheric-pressure operation, with a near-term reduced-scale demonstration planned as a stepping stone to a commercial plant optimized at approximately 450 MWe.