These reactors are cooled by liquid sodium metal. Sodium is heavier than hydrogen, a fact that leads to the neutrons moving around at higher speeds (hence fast). These can use metal or oxide fuel, and burn a wide variety of fuels.
- Can breed its own fuel, effectively eliminating any concerns about uranium shortages (see what is a fast reactor?)
- Can burn its own waste
- Metallic fuel and excellent thermal properties of sodium allow for passively safe operation — the reactor will shut itself down safely without any backup-systems working (or people around), only relying on physics.
- Sodium coolant is reactive with air and water. Thus, leaks in the pipes results in sodium fires. These can be engineered around but are a major setback for these reactors.
- To fully burn waste, these require reprocessing facilities which can also be used for nuclear proliferation.
- The excess neutrons used to give the reactor its resource-utilization capabilities could clandestinely be used to make plutonium for weapons.