Cross section methods for evaluation of clustered burnable absorbers for the combustion engineering fuel lattice type

A method for generating transport-equivalent cross-sections for a strong, depletable absorber with a complex geometry is described. The method is used to develop cross-sections to be applied in diffusion theory analysis of reactor cores employing the Clustered Burnable Absorber, a new burnable absorber concept for the large guide tube design in a Combustion Engineering fuel lattice. The absorber is modelled using the Monte Carlo KENO code, and reaction rate ratios of the neutron absorptions in the absorber to the absorptions in the fuel are calculated. These reaction rate ratios are then used as the searched variable in a diffusion theory code to generate transport-equivalent cross-sections for the absorber. The KENO-calculated fluxes are used to deplete the absorber, and the process is repeated for various absorber concentrations