approximately 30 MW of mechanical output for 155 MW thermal power (see below). Other options include units featuring long-life, pre-manufactured cores, that do not require refueling for many years. The lead-cooled fast reactor battery is a small turnkey-type power plant using cassette cores running on a closed fuel cycle with 15 to 20 years' refuelling interval, or entirely replaceable reactor modules. It is designed for generation of electricity on small grids (and other resources, including hydrogen and potable water). Advantages of lead in fast reactors The use of lead as a coolant has several advantages if compared to other methods for reactor cooling. Molten lead does not significantly moderate neutrons. Moderation occurs when neutrons are slowed down by repeated collisions with a medium. When the neutron collides with atoms that are much heavier than itself, almost no energy is lost in the process. Thus, the neutrons are not slowed down by lead, which ensures that the neutrons keep their high energy. This is similar to other fast reactor concepts, including the molten liquid sodium designs. Molten lead acts as a reflector for neutrons. Neutrons escaping the core of the reactor are to some extent directed back into the core, which allows a better neutron economy. This in turn enables more spacing between the fuel elements in the reactor, allowing better heat removal by the lead coolant. Lead undergoes almost no activation by neutrons. Thus, virtually no radioactive elements are created by absorption of neutrons by the lead. This is in contrast to the lead-bismuth eutectic which was used in other fast designs, including in Russian submarines. The bismuth in this mixture (which has a lower melting point, 123.5 °C, than that of pure lead) is activated to some degree to 210Po, Polonium-210, which is an alpha emitter. Although virtually no neutrons are absorbed by the lead, lead is very effective at absorbing gamma rays and other ionizing radiation. This ensures that radiation fields outside the reactor are extremely low. In contrast to molten sodium metal, another relatively popular coolant that is used in fast reactors, lead does not have issues with flammability (although the combustion of sodium in air is a mild reaction, not to be confused with the violent reaction between sodium and water), and will solidify from a leak. The very wide temperature range at which lead remains liquid (more than 1400 K or °C) implies that any