Resonance overlap effect on effective cross section in unresolved resonance region

The effect of resonance overlap on the effective cross section was studied in the unresolved resonance region. The sequential overlap between resonances belonging to the same sequence of an isotope was studied by a method that approaches Method A at higher energies and Method B at lower energies. The accidental overlap effect between different sequences was studied in reference to factors for overlap correction and flux correction. Numerical studies indicate that in large fast reactors, when an average is taken over the distribution of level spacing, a greater influence is provided on the effective cross section by the sequential as compared with the accidental overlap.