1) is cheaper to build and cheaper to operate than water reactors.
2) is passively safe. It uses a metallic fuel that expands when it overheats, causing the volume to increase which decreases the neutron density to the point where the reaction is shut down by the laws of nature without operator intervention! Loss of coolant poses no threat because the thermal currents of the liquid sodium are sufficient to stabilize the reactor.
3) can be operated in a mode where it uses as its fuel the spent fuel of the water reactors. By far the most lethal nuclear waste on the planet is the spent fuel which is produced in the United States at the rate of 6 tons a day. Currently our government policy is to store this waste for 30,000 years (Yucca Mountain). Electric rate payers are assessed one mill per kilowatt hour of power produced by nuclear reactors to deal with nothing but these spent fuel rods --- to the tune of more than $800 million per year!
http://www.dcia.com/ifr.html
