Lead-bismuth eutectic

Lead-Bismuth Eutectic or LBE is a eutectic alloy of lead (44.5%) and bismuth (55.5%) used as a coolant in some nuclear reactors, and is a proposed coolant for the lead-cooled fast reactor, part of the Generation IV reactor initiative. It has a melting point of 123.5 °C/255.3 °F (pure lead melts at 327 °C/621 °F, pure bismuth at 271 °C/520 °F) and a boiling point of 1,670 °C/3,038 °F.

Lead-bismuth alloys with between 30% and 75% bismuth all have melting points below 200 °C/392 °F. Alloys with between 48% and 63% bismuth have melting points below 150 °C/302 °F. While lead expands slightly on melting and bismuth contracts slightly on melting, LBE has negligible change in volume on melting.

The Soviet Alfa-class submarines used LBE as a coolant for their nuclear reactors throughout the Cold War.

The Russians are the acknowledged experts in lead-bismuth cooled reactors, with EDO "Gidropress" (the Russian developers of the VVER-type LWRs) having special expertise in their development. The SVBR-75/100, a modern design of this type, is one example of the extensive Russian experience with this technology.

Gen4 Energy (formerly Hyperion Power Generation), a United States firm connected with Los Alamos National Laboratory, announced plans in 2008 to design and deploy a uranium nitride fueled small modular reactor cooled by lead-bismuth eutectic for commercial power generation, district heating, and desalinization. The proposed reactor, called the Gen4 Module, will be a 70 MWth reactor of the sealed modular type, factory assembled and transported to site for installation, and transported back to factory for refueling.

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