Sodium-Cooled Fast Reactor

A sodium-cooled fast reactor, or SFR, is a fast neutron reactor cooled by liquid sodium, offering higher thermal efficiency and power density than light-water reactors and, because its fast neutron spectrum can destroy transuranic waste products from spent light-water fuel, a way to significantly cut the quantity and lifetime of radioactive waste; its main drawback is sodium's chemical reactivity, which requires special precautions against fire. Sodium's low melting point and high boiling point let an SFR operate at high temperature while its coolant stays at atmospheric pressure, eliminating the risk of a loss-of-coolant accident that comes with a pressurized system while improving thermal efficiency over light-water designs. Two main design approaches exist: pool-type reactors, which house the intermediate heat exchanger inside the reactor vessel, and loop-type reactors, which place it outside. As fast-neutron reactors, SFRs need more highly enriched fuel to reach criticality than thermal reactors do, and some SFR designs are breeder reactors able to produce more fissile plutonium than they consume, though proliferation concerns over that plutonium remain a significant obstacle to wider deployment. The first SFR, and the first nuclear reactor of any kind to generate electricity, was the Experimental Breeder Reactor I, which achieved criticality in 1950; more than 20 SFRs have operated worldwide since, and commercial SFR generation has run since Fermi 1 began operating in 1963.