Hi!
If an empty Fueld Rod (x64) and Enriched Uranium Nuclear Fuel (x64) are placed in the machine input slots, there will be 64 filled Fueld Rods in the output slot. It is right.
If you don't take them out of the output slot, and repeat the operation, the machine will continue to fill the rods somewhere inside themselves instead nothing. You can pick them up just by breaking the machine.