Brennstoffbündel mit Strömungskanal

A fuel assembly comprises a plurality of fuel rods (3) supported by an upper tie plate (7) and a lower tie plate (8) respectively at each of upper end portion and lower end portion, and a channel box (2, 2A) surrounding a bundle of the fuel rods (3) and the lower tie plate (8). The fuel assembly forms a natural uranium region at lower end portion of effective fuel length portion. A wall thickness at a lower thick wall region of the channel box (2, 2A) is thicker than the wall thickness at a region locating upward from the lower thick wall region and between corner portions of the channel box. Upper end of the lower thick wall region locates upward from upside of the lower tie plate and downward from upper end of the natural uranium region. A wall thickness at the corner portion of the channel box (2, 2A) is thicker than the wall thickness at middle portion of said wall between the corner positions at the region locating upward from the lower thick wall region. The fuel assembly is able to reduce stresses caused in the channel box (2, 2A) in an earthquake, and, is able to improve fuel economy.