In modern light-water reactors the fuel rods typically spend 3 operational cycles (about 6 years) inside the reactor, generally until about 3% of the uranium has been used. Afterwards, they will be moved to a spent fuel pool which provides cooling for the thermal heat and shielding for ionizing radiation. Depending largely upon burnup efficiency, after about 5 years in a spent fuel pool the spent fuel is radioactively and thermally cool enough to be moved to dry storage casks or reprocessed.