Patent ID: 8149981

Claim:
A method of determining the R-factor for a bundle of nuclear fuel rods in a nuclear boiling light water reactor, 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 a weighted local power influence on a fuel rod, including contributions from neighbouring fuel rods, the method comprising determining a local R-factor (R i (z)) for each fuel rod (i) in said bundle and for each of a plurality of levels (z) in said axial direction, wherein an individual axial heat generation profile for a certain fuel rod (i) is taken into account when determining the local R-factors (R i (z)) for said fuel rod (i), and determining a total R-factor (R z ) for each of said levels (z) for the whole bundle of fuel rods, wherein said total R-factor (R z ) at a level (z) is determined as a maximum of said local R-factors (R i (z)) at said level (z) in said bundle of nuclear fuel rods.