The Fuel Rod (Uranium) is an item added by IndustrialCraft 2. It is used as the standard fuel for the Nuclear Reactor. It outputs at minimum 5 EU/t, though the more fuel rods next to each other the more energy it produces. More information about this can be found here. It is available in Dual and Quad rod variants, which act like 2 and 4 fuel rods next to each other, respectively.
A Uranium Fuel Rod lasts for 20,000 seconds while producing power, and produces a base rate of 5EU/t, multiplied by the efficiency of the Fuel Rod. The efficiency of a fuel rod is increased for each additional fuel rod (or 'Reflector') in a cardinally adjacent slot. The heat output however goes up exponentially making it increasingly difficult to design a reactor that can stay cool.