Oxide Chemistry in SFRs
Among the six Generation IV nuclear reactors retained by the Generation IV International Forum, the Sodium-cooled Fast Reactor (SFR) and Lead-cooled Fast Reactor (LFR) are one of the most advanced concepts. The reference fuel for these reactors in Europe is a mixed uranium-plutonium fuel (U,Pu)O2. SFRs use liquid sodium metal as a coolant, which shows a high boiling point (883oC), a high heat capacity, and a good thermal conductivity preventing overheating. These characteristics allow higher power density and efficiency compared to the second generation Light Water Reactor systems. Some drawbacks exist with this design, however, in particular due to the reactivity of sodium with water and air. LFRs rely on a lead or lead-bismuth eutectic coolant. Lead has relatively low melting point, and a high margin to boiling (1749oC). Compared to sodium, lead coolant is far more inert when it comes in contact with air or water. Both SFRs and LFRs operate at ambient pressure, and their coolants allow operation with a fast neutron spectrum.