An apparatus and system for separating remaining powder of hulls includes a first remaining powder separating unit to be supplied with hulls of a spent nuclear fuel subjected to a high-temperature oxidation, and to include a first brush for separating remaining powder of the hulls; a hull alignment unit to be supplied with the hulls from the first remaining powder separating unit, and to align the hulls; a second remaining powder separating unit to be supplied with the aligned hulls from the hull alignment unit, and to include a second brush for separating remaining powder adhered on an inner peripheral surface of the hulls; and a third remaining powder separating unit to be supplied with the hulls from the second remaining powder separating unit, and to separate the remaining powder remaining on the inner/outer peripheral surface of the hulls by using air.