Improvement of the fuel assembly heterogeneity analysis model of Mc2-2 code using an analytic method of resonance escape cross sections

The MC2-2 code models a single fuel rod. The shadowing effect due to the lattice geometry of fuel rods is considered using the Bell factor together with the Dancoff correction to evaluate the heterogeneity of a fuel assembly. This model requires a pre-calculated Bell factor of the considered assembly and is inappropriate in representing the effect of other structural materials in the fuel assembly such as a duct. To overcome this drawback the annular model of the fuel assembly is proposed and an analytic method accounting for resonance escape is applied to the model. To evaluate the validity of the fuel assembly model, a criticality calculation was performed using MC2 -2/ONEDANT and heterogeneity effect is compared with that of MCNP. The results obtained show that the improved MC2-2 herein can represent the heterogeneity of a fuel assembly more accurately than the original one