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Sodium-cooled fast reactor
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Sodium-cooled fast reactor
A sodium-cooled fast reactor (SFR) is a fast neutron reactor cooled by liquid sodium. The use of sodium as a coolant enables high power density and low-pressure operation. Such reactors are capable of burning up transuranic waste products in the spent fuel of light-water reactors, significantly reducing the quantity and lifetime of radioactive waste. Some SFR designs are breeder reactors, and can produce more fissile nuclear fuel than they consume.
More than 20 SFRs have been operated globally, starting with EBR-I in 1950, and several commercial plants have been constructed starting with Fermi 1. As of 2026, China, Russia, and India have operational sodium-cooled fast reactors. The SFR was one of the six technologies selected by the Generation IV International Forum in 2003 for further development. The ability of the SFR to burn transuranic waste and close the nuclear fuel cycle were highlighted as particularly desirable features. Several SFR reactors are under construction as of 2026, including a CFR-600 in China and the Natrium and Aurora reactors in the United States.
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.
The first commercial SFR, and first commercial breeder reactor, was the 66 MWe Fermi 1 reactor built in 1963 under the Power Reactor Demonstration Program. This reactor was based on the design of EBR-I, and experienced a similar partial meltdown in 1966. Fermi 1 was shutdown for repairs until 1970, after which it operated until 1972.
In the 1960s, the US AEC embarked on a significant program to build commercial liquid metal-cooled fast breeder reactors, eventually being declared the country's highest-priority energy program in 1969. This program culminated in the Clinch River Breeder Reactor Project (CRBRP), which aimed to build a 300 MWe demonstration SFR. The CRBRP experienced significant delays, and became the center of a large political battle of the future of nuclear energy leading to its cancellation in 1983. This decision effectively ended breeder research in the United States.
Following the cancellation of the CRBRP, the US program was refocused on the concept of an Integral Fast Reactor (IFR), an inherently safe SFR that would incorporate on-site fuel reprocessing to close the nuclear fuel cycle. EBR-II was used to investigate the inherent safety characteristics of SFRs as part of the IFR program, and successfully demonstrated safe removal of decay heat via natural circulation in the sodium coolant. However, the IFR program was terminated in 1994 by the Clinton Administration before a demonstration plant could be constructed, and EBR-II was shut down as well.
France constructed the Phénix demonstration SFR in 1973, and the larger commercial Superphénix in 1985. Superphénix was the largest SFR ever constructed, at 1242 MWe. It experienced technical issues and significant political opposition, and was closed in 1998 for political reasons. The closure of Superphénix led to the refocusing of the French nuclear program to light-water reactors instead of fast breeders. Germany constructed the 327 MW SNR-300 fast breeder reactor in 1985, however it suffered significant political backlash and was never taken online. The reactor was officially cancelled in 1991.
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Sodium-cooled fast reactor
A sodium-cooled fast reactor (SFR) is a fast neutron reactor cooled by liquid sodium. The use of sodium as a coolant enables high power density and low-pressure operation. Such reactors are capable of burning up transuranic waste products in the spent fuel of light-water reactors, significantly reducing the quantity and lifetime of radioactive waste. Some SFR designs are breeder reactors, and can produce more fissile nuclear fuel than they consume.
More than 20 SFRs have been operated globally, starting with EBR-I in 1950, and several commercial plants have been constructed starting with Fermi 1. As of 2026, China, Russia, and India have operational sodium-cooled fast reactors. The SFR was one of the six technologies selected by the Generation IV International Forum in 2003 for further development. The ability of the SFR to burn transuranic waste and close the nuclear fuel cycle were highlighted as particularly desirable features. Several SFR reactors are under construction as of 2026, including a CFR-600 in China and the Natrium and Aurora reactors in the United States.
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.
The first commercial SFR, and first commercial breeder reactor, was the 66 MWe Fermi 1 reactor built in 1963 under the Power Reactor Demonstration Program. This reactor was based on the design of EBR-I, and experienced a similar partial meltdown in 1966. Fermi 1 was shutdown for repairs until 1970, after which it operated until 1972.
In the 1960s, the US AEC embarked on a significant program to build commercial liquid metal-cooled fast breeder reactors, eventually being declared the country's highest-priority energy program in 1969. This program culminated in the Clinch River Breeder Reactor Project (CRBRP), which aimed to build a 300 MWe demonstration SFR. The CRBRP experienced significant delays, and became the center of a large political battle of the future of nuclear energy leading to its cancellation in 1983. This decision effectively ended breeder research in the United States.
Following the cancellation of the CRBRP, the US program was refocused on the concept of an Integral Fast Reactor (IFR), an inherently safe SFR that would incorporate on-site fuel reprocessing to close the nuclear fuel cycle. EBR-II was used to investigate the inherent safety characteristics of SFRs as part of the IFR program, and successfully demonstrated safe removal of decay heat via natural circulation in the sodium coolant. However, the IFR program was terminated in 1994 by the Clinton Administration before a demonstration plant could be constructed, and EBR-II was shut down as well.
France constructed the Phénix demonstration SFR in 1973, and the larger commercial Superphénix in 1985. Superphénix was the largest SFR ever constructed, at 1242 MWe. It experienced technical issues and significant political opposition, and was closed in 1998 for political reasons. The closure of Superphénix led to the refocusing of the French nuclear program to light-water reactors instead of fast breeders. Germany constructed the 327 MW SNR-300 fast breeder reactor in 1985, however it suffered significant political backlash and was never taken online. The reactor was officially cancelled in 1991.
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