Patent Number: 
Section: claims

1. A control rod for a nuclear boiling water reactor, wherein the reactor comprises a plurality of fuel assemblies, elongated channel boxes forming outer casings of each fuel assembly and enclosing fuel rods, and a plurality of control rods which are configured to be insertable in respective control rod positions between the fuel assemblies, wherein the control rod has a longitudinal center axis and control rod blades, each control rod blade having a first and a second side and being substantially parallel to the longitudinal center axis, and wherein each control rod blade comprises an absorber material which extends along the longitudinal centre axis from a first absorber end to a second absorber end, a distance between the first absorber end and the second absorber end defining an active length of the control rod blade, wherein the control rod blades are provided with distance means on the first and second sides of the control rod blades, the distance means extending a distance of at least a third of the active length of the control rod blade, the distance means being configured to ensure a minimum distance between the control rod blade and the channel box, and to enable the control rod to easily slide along the channel box, wherein the distance means have the form of protrusions, each of which protrudes 0.5-2 mm from the sides of the control rod blades, wherein the distance means are press formed in, or welded onto, the control rod blades and form a homogeneous part of the control rod blades,wherein each of the protrusions comprises an elongated ridge and the ridges are provided along lines extending in parallel to the longitudinal center axis and distributed along a width of the first and second sides, radially out from the longitudinal center axis. 2. The control rod according to claim 1, wherein the distance means is distributed on the sides of the control rod blades. 3. The control rod according to claim 1, wherein the protrusions have a curved shape, the curved shape facilitating the sliding of the control rod along the channel box. 4. The control rod according to claim 3, wherein at least one protrusion is provided on an upper portion of the control rod blade and at least one protrusion is provided on a lower portion of the control rod blade. 5. The control rod according to claim 1, wherein the control rod is arranged to be inserted in the control rod position with the first absorber end first and wherein the ridges extend from the first absorber end on the first and the second sides of the control rod blades. 6. The control rod according to claim 5, wherein the ridges extend along the full active length on the first and the second sides of the control rod blades. 7. The control rod according to claim 1, wherein each protrusion comprises a spot-like protrusion. 8. The control rod according to claim 1, wherein the control rod comprises four control rod blades, the control rod blades being arranged to form a control rod having a cruciform cross section. 9. The control rod according to claim 1, wherein the control rod is made mainly of a first material which is different from the absorber material.