A sodium-cooled fast reactor (SFR) is a fast neutron reactor cooled by liquid sodium. It offers several advantages over light-water reactors (LWRs), including high thermal efficiency and power density. A fast spectrum allows SFRs to destroy transuranic waste products in the spent fuel of LWRs, significantly reducing the quantity and lifetime of radioactive waste. The primary disadvantage is sodium's chemical reactivity, which requires special precautions to prevent and suppress fires. An SFR uses liquid metallic sodium to carry heat from the reactor core. Sodium's low melting point and high boiling point allow a sodium-cooled reactor to operate at high temperature while remaining at atmospheric pressure. The elimination of pressurized coolant effectively eliminates the risk of a loss-of-coolant accident, while the higher-temperature operation provides better thermal efficiency than light-water reactors. There are two main design approaches to sodium-cooled fast reactors. In pool-type reactors, the intermediate heat exchanger is contained within the reactor vessel, whereas in loop-type reactors, it is located outside the reactor vessel. As fast-neutron reactors, sodium-cooled fast reactors require nuclear fuel with a higher enrichment to attain criticality than thermal reactors like LWRs. Some SFR designs are breeder reactors, and can produce more fissile plutonium fuel than they consume. However, concerns over the proliferation risk of plutonium fuel are a significant obstacle to the deployment of fast reactors, including SFRs. The first SFR, and the first nuclear reactor to generate electricity, was the Experimental Breeder Reactor I (EBR-I), which achieved criticality in 1950. Following the success of EBR-I, several additional experimental SFRs were constructed in the United Kingdom, Japan, and France, and a larger prototype in the US. More than 20 SFRs have been operated globally since 1950. Commercial SFRs have been in operation since 1963 with Fermi 1, and several commercial SFRs are under construction as of 2026, including a CFR-600 in China and the Natrium and Aurora reactors in the United States.
History The concept of a fast-neutron reactor cooled by liquid metal was first demonstrated at Los Alamos with the construction of the Clementine reactor in 1946. The first nuclear reactor to generate electricity was the Experimental Breeder Reactor I (EBR-I), which achieved criticality in 1950. EBR-I was a 0.2 MWe fast reactor cooled by liquid sodium-potassium alloy, and demonstrated the concept of nuclear breeding. It also established sodium as the coolant of choice for fast reactors. However, the reactor experienced a partial meltdown in 1955, which required the core to be removed and replaced. Following the success of EBR-I, several additional experimental SFRs were constructed. The United Kingdom Atomic Energy Authority built the Dounreay Fast Reactor (DFR), which achieved criticality in 1962, while the US Atomic Energy Commission (AEC) built a larger 20 MWe prototype SFR, the Experimental Breeder Reactor II (EBR-II). EBR-II is considered the most successful US fast reactor, and demonstrated the feasibility of an SFR power plant. The DFR, as well as the French Rapsodie and Japanese Jōyō test reactors all served as prototypes for larger commercial plants.
Commercial SFRs
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