Microfusion Breeder

 or MF breeder is a type of ammunition in Fallout: New Vegas.

Characteristics
A specially designed kind of energy cell that is unique in that it is not a physical object that can be gathered like other ammunition. Found only in Recharger weapons, these energy cells replenish their reserves over time, essentially providing infinite ammo.

Used in

 * Recharger rifle
 * Recharger pistol

Appearances
Microfusion breeder ammo only appears in Fallout: New Vegas.

Behind the scenes
From the name it is likely to be associated with breeder reactors, which are a type of nuclear fission reactor that is able to produce more fissile material than it uses.