Improvement in modelling ZED-2 critical experiments using WIMS-AECL/RFSP

The ZED-2 experiments were used for the validation of the WIMSAECL/ RFSP code suite. Two RFSP models (using the cross-sections provided by the WIMS-AECL lattice code) were constructed; one model used for calculations of regions just up to the critical heights, while the other model simulated explicitly the unmoderated region (called Improved Model herein). Results of the comparison between these two models, in terms of the biases in k_eff and reaction rates distribution, are presented. The Improved Model is more accurate in calculating both k_eff and flux distribution. Further studies are suggested to assess the validity of the diffusion theory at the interface between the moderated and unmoderated regions in the core.