A fuel assembly for a boiling water reactor comprises a bottom tie plate, a top tie plate, and a first and a second group of vertical fuel rods, each including a column of fuel pellets surrounded by a cladding tube. The second group of fuel rods has a shorter active length than the first group of fuel rods. Both the first and the second group of fuel rods extend between the bottom tie plate and the top tie plate. The second group of fuel rods comprises a fission gas plenum surrounded by a plenum tube arranged above the cladding tube. The main part of the plenum tube has a cross-section area which is smaller than the cross-section area of the cladding tube.