Fast reactors do have some attractive features. They have better neutron economy and work better with plutonium. They can achieve breeding ratios comfortably above 1 with the U-Pu system. They produce less actinide waste since the chance of neutron capture not causing fission is lower, and can more effectively destroy actinide waste. Sodium-cooled fast reactors will operate at higher temperature than LWRs, enabling the salt thermal storage scheme they propose to use.

In large reactors, these features have not been enough to compensate for the disadvantages and sodium-cooled reactors have not been successful, coming in more expensive than light water reactors for a given power output. France, which had been developing fast reactors, has recently mothballed the effort with no plan to restart before 2050.

The main advantages of using a fast reactor are less nuclear waste and more energy for a given fuel input.

It can make more fuel than it uses. It needs enriched uranium at startup but then can convert regular uranium and/or thorium to usable fuel.