Methods and Devices Relating to a Nuclear Light Water Reactor of the Boiling Water Kind

A method of determining the R-factor for a bundle of nuclear fuel rods in a nuclear light water reactor of the boiling water reactor kind, which reactor comprises a plurality of bundles of nuclear fuel rods, wherein the fuel rods in the bundle are arranged side by side, at least substantially parallel to each other, and extend essentially in an axial direction, wherein said R-factor is a factor that accounts for the weighted local power influence on a fuel rod, including contributions from neighbouring fuel rods, the method being characterized by the fact that a local R-factor (Ri(z)) is determined for each fuel rod (i) in said bundle and for each of a plurality of levels (z) in said axial direction, wherein the individual axial heat generation profile for a certain fuel rod (i) is taken into account when determining the local R-factors (Ri(z)) for said fuel rod (i).