Lead-cooled fast reactor

Molten lead or lead-bismuth eutectic can be used as the primary coolant in a nuclear reactor, because lead and bismuth have low neutron absorption and relatively low melting points. Neutrons are slowed less by interaction with these heavy nuclei, (thus not being neutron moderators) and therefore help make this type of reactor a fast-neutron reactor. The coolant does however serve as a neutron reflector, returning some escaping neutrons to the core.

The concept is generally very similar to sodium-cooled fast reactor, and most liquid-metal reactors have used sodium instead of lead. Few lead-cooled reactors have been constructed, including some Soviet nuclear submarine reactors in the 1970s, but a number of proposed new nuclear reactor designs are lead-cooled. Some designs are claimed to be able to circulate the primary coolant via convection without requiring pumps, at least in emergency shutdown conditions.

The Gen IV lead-cooled fast reactor is a nuclear reactor that features a fast neutron spectrum, molten lead or lead-bismuth eutectic coolant. Options include a range of plant ratings, including a number of 50 to 150 MWe (megawatts electric) units featuring long-life, pre-manufactured cores. Plans include modular arrangements rated at 300 to 400 MWe, and a large monolithic plant rated at 1,200 MWe. The fuel is metal or nitride-based containing fertile uranium and transuranics. A smaller capacity LFR such as SSTAR can be cooled by natural convection, larger proposals such as ELSY use forced circulation in normal power operation, but with natural circulation emergency cooling. The reactor outlet coolant temperature is typically in the range of 500 to 600 °C, possibly ranging over 800 °C with advanced materials for later designs. Temperatures higher than 800 °C are high enough to support thermochemical production of hydrogen.

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