A Presentation of the OPTEX Reflector Model

We investigate the OPTEX reflector model for obtaining few-group reflector parameters consistent with a reference power distribution in the core. The reference power distribution is obtained using a 142 872-region calculation defined over a two-dimensional eighth-of-core pressurized water reactor (PWR) and performed with the method of characteristics. The OPTEX method is based on generalized perturbation theory and uses an optimization algorithm known as parametric linear complementarity pivoting. The proposed model leads to few-group diffusion coefficients or P₁-weighted macroscopic total cross sections that can be used to represent the reflector in full-core calculations. These few-group parameters can be spatially heterogeneous in order to correctly represent steel baffles and thermal shields present in modern PWRs. The optimal reflector parameters are compared with those obtained with a flux-volume weighting of the reflector cross sections recovered from the reference calculation. Important improvements in full-core power distribution are observed when the optimal parameters are used.