Using x-ray emission spectroscopy and absorption spectroscopy, it has been possible to directly access the states in the unoccupied conduction bands that are involved with $5f$ and $6d$ covalency in oxidized uranium. By varying the oxidizing agent, the degree of $5f$ covalency can be manipulated and monitored, clearly and irrevocably establishing the importance of $5f$ covalency in the electronic structure of the key nuclear fuel, uranium dioxide.