As compared to sodium-based liquid metal coolants such as liquid sodium or NaK, lead-based coolants have significantly higher boiling points, meaning a reactor can be operated without risk of coolant boiling at much higher temperatures. This improves thermal efficiency and could potentially allow hydrogen production through thermochemical processes.
Lead and LBE also do not react readily with water or air, in contrast to sodium and NaK which ignite spontaneously in air and react explosively with water. This means that lead- or LBE-cooled reactors, unlike sodium-cooled designs, would not need an intermediate coolant loop, which reduces the capital investment required for a plant.
Both lead and bismuth are also an excellent radiation shield, absorbing gamma radiation while simultaneously being virtually transparent to neutrons. In contrast, sodium forms the potent gamma emitter sodium-24 (half-life 15 hours) following intense neutron radiation, requiring a large radiation shield for the primary cooling loop.
As heavy nuclei, lead and bismuth can be used as spallation targets for non-fission neutron production, as in accelerator transmutation of waste (see energy amplifier).
Both lead-based and sodium-based coolants have the advantage of relatively high boiling points as compared to water, meaning it is not necessary to pressurise the reactor even at high temperatures. This improves safety as it reduces the probability of a loss of coolant accident (LOCA), and allows for passively safe designs. The thermodynamic cycle (Carnot cycle) is also more efficient with a larger difference of temperature. However, a disadvantage of higher temperatures is also the higher corrosion rate of metallic structural components in LBE due to their increased solubility in liquid LBE with temperature (formation of amalgam) and to liquid metal embrittlement.