thermal excursions are absorbed without any pressure increase. In practice, the operational temperature will be kept at around -, mainly because of other material properties. As with all fast reactor designs, because of the high temperature and the high thermal inertia, passive cooling is possible in emergency situations. Thus, no electrical pumping is required, natural air convection is sufficient to remove residual heat after shutdown. To achieve this, reactor designs include dedicated passive heat removal systems, that requires no electrical power and no operator action. All fast reactor designs operate at substantial higher temperatures in the core than water cooled (and moderated) reactors. This allows a significantly higher thermodynamic efficiency in the steam generators. Thus, a larger portion of the nuclear energy is converted into electricity. More than 40% efficiency is achievable in real life, compared to around 30% in water cooled reactors. Similarly, as with all fast spectrum reactors, the coolant is not pressurized. This means that no pressure vessel is required, and the piping and ducts can be constructed with non-pressure resistant steel and alloys. Any leak in the primary coolant circuit will not be ejected at very high pressures. Lead has a high thermal conductivity (35 W/m.K) compared to that of water (0.58), which means that heat transport from the fuel elements to the coolant is effective. Instead of refueling, the whole core can be replaced after many years of operation. Such a reactor is suitable for countries that do not plan to build their own nuclear infrastructure. Lead's nuclear properties allow it to prevent a positive void coefficient, which is difficult to prevent in large sodium fast reactor cores. Lead does not react significantly with water or air, unlike sodium which burns readily in air and can explode in contact with water. This allows easier, cheaper and safer containment and heat exchanger/steam generator design. Disadvantages Lead and lead-bismuth are very dense, increasing the weight of the system therefore requiring more structural support and possibly seismic protection which increases building cost, although a more compact structure may be beneficial as well. While lead is cheap and abundant, bismuth is expensive and quite rare. A grid connected lead-bismuth reactor requires hundreds of tonnes of lead-bismuth depending on reactor size. Solidification of lead-bismuth solution renders the reactor inoperable. However, lead-bismuth eutectic has a comparatively low melting temperature of , making melting a relatively easily accomplished task. Lead has a