The you don't have to refuel every 3 days like a conventional carrier. is based on fuel for the ship to run. But nuclear power doesn't fuel the planes that fly! Under high tempo operations, like those just experienced for the Afghanistan or Iraqi Freedom campaigns, a visit by the local AOE to pass more av-gas and ordnance is required regularly -whether or not the carrier needs fuel for its engines. Without the av-gas refueling every 5-6 days, the carrier becomes an overlarge dance floor!
A nuclear carrier might be able to transit from point A to point B without worrying about refueling - but then remember that the Carrier Battle Group has several Aegis Cruisers/Destroyers and other ships, that require regular refueling.
A nuclear carrier has several advanatages - primarily no high temperature exhaust plume that can affect the jets that are coming in for a landing. Also - no need for the exhaust stacks that occupy so much space up the "island".
But if you include the cost of the cut-up and disposal of the reactor compartment, the disposal costs of the nuclear fuel, the higher manpower costs for the engineering crew (including training and nuclear proficiency pay) the nuclear power ship has a life-cyle costs that is about 10% greater than for a comparable fossil fuel powered ship.
For submarines, where the amount of fuel that can be carried is limited, and the ability to conduct sustained operations undetected - nuclear power is a definite plus. There are many benefits without considering costs to justify using nuclear power. But for surface ships - the cost factor just isn't there!!
Mike -- former Nuc Submarine Officer