Reactivity and flux calculations using MCNP for heavy-water experiments in the ZED-2 critical facility using low-enriched uranium fuel bundles

Experiments were performed in the ZED-2 (Zero Energy Deuterium) critical facility at AECL Chalk River Laboratories using a 24-cm pitch square lattice of 52 channels of heavy-water-moderated ACR-LEU and CANFLEX-LEU 43-element low-enriched uranium fuel bundles. These fuel bundles were cooled with H 2O, air (void) or a checkerboard pattern of H2O and air coolants. MCNP was used to calculate the reactivity and global flux distributions, which were compared with experimental measurements. Calculations demonstrated a small positive bias in the MCNP predictions of coolant void reactivity. MCNP predictions of axial and radial flux distributions agreed with experimental measurements within 2%. This study helps quantify the agreement between calculation and measurement for MCNP, which is one of the codes used in the analysis of the ACR-1000 reactor. Results demonstrate good agreement in code predictions for flux distributions and reactivity calculations. This is one component in the validation of MCNP. The extension of these MCNP results, compared against ZED-2 experiments, to the design and operating conditions of the ACR-1000 will require the use of extension methods.