Fuel assembly for a nuclear boiling water reactor

A fuel assembly for a nuclear power boiling water reactor, comprising:

• a fuel channel extending in and defining a length direction of the fuel assembly and defining a central fuel channel axis extending in said length direction,
• fuel rods positioned such that they are surrounded by said fuel channel, each fuel rod having a central fuel rod axis extending substantially in said length direction,
• water channels positioned such that they are surrounded by said fuel channel, the water channels being configured and positioned for, during operation, allowing non-boiling water to flow through the water channels, each water channel having a central water channel axis extending substantially in said length direction,
• wherein said fuel rods comprise a first group of fuel rods and a second group of fuel rods,
• wherein each fuel rod in said first group is a so-called full length fuel rod which extends from a lower part of the fuel assembly to an upper part of the fuel assembly,
• wherein each fuel rod in said second group extends from said lower part of the fuel assembly and upwards, but does not reach as high up as said full length fuel rods,
• wherein the fuel assembly comprises at least 3 water channels, each of which has a cross-sectional area which is at least twice as large as the cross-sectional area of each one of said fuel rods, or, in case the fuel assembly has fuel rods of different cross-sectional areas, at least twice as large as the average cross-sectional area of the fuel rods,
• wherein said at least 3 water channels are positioned such that there is no further water channel, the central water channel axis of which is closer to the central fuel channel axis than the central water channel axis of each of said at least 3 water channels,
• wherein the fuel assembly comprises 3 or 4, but not more than 4, fuel rods which belong to said second group and which are positioned such that the central fuel rod axis of each of these 3 or 4 fuel rods is closer to the central fuel channel axis than any of the water channel axes of the water channels, wherein the fuel assembly comprises no more than 3 of said at least 3 water channels.