[en] In a reprocessing method including a decladding step for spent fuel rods and a refining step for pellets, a cladding tubes of a spent fuel rod is partially removed, thereafter, the fuel rod is heated in an oxidative atmosphere for 1 to 100 hours, to remove the clads. Then, the pellets are heated in an reducing and an oxidative atmospheres alternately by a plurality of times at 500 to 800degC. Since the cladding tube is thus partially removed and heated under exposure to the oxidative atmosphere, UO₂ is entirely subjected to phase transformation into U₃O₈ in the fuel pellet to expand the cladding tube and, accordingly, circumferential distortion of the cladding tube is increased, the cladding tube is certainly burst and easily removed. Further, since the UO₂ pellet undergoes repeating oxidative and reducing reactions alternately at about 500degC, to cause phase transformation between UO₂ and U₃O₈, expansion and shrinkage for the volume of the pellet are repeated, which promotes the grain refinement and shortens the dissolving time. (T.M.)