Fuel assembly

A cladding tube, a spacer and a channel box contain 1 to 2% of tin, 0.20 to 0.35% of iron and 0.03 to 0.16% of nickel by weight, and the substantial balance of zirconium. The solid solubilizing amount of iron and nickel is greater on the outer surface than on the inner surface of the cladding tube, and the orientation rate (Fr value) crystallization direction (0001) of the channel box in the direction of plate thickness is 0.25 to 0.50. In such a fuel assembly, only the fuel rod is elongated by irradiation growth, while the length of the channel box and a water rod remains unchanged. The elongation of the fuel rod is eliminated by protruding an upper end plug of the fuel rod from an upper tie plate. (T.M.)