Solution of the C5G7 3-D extension benchmark by the SN code TORT

The 3-D multigroup discrete ordinates transport code TORT is applied to solve the 3-D extension of the C5G7 MOX fuel assembly benchmark. In the present paper, our calculation models for the three control rod configurations are described in detail, including the meshing of the circular pin cells within the rectangular geometry. The calculations are repeated for different mesh sizes and quadrature orders in order to obtain estimates for the sensitivity of the results on these modelling features. With respect to keff, our TORT solutions agree to within 0.3% with the corresponding Monte Carlo reference values. Concerning the pin-wise fission rate distributions, the maximum errors do not exceed 1.2%. The maximum pin-wise fission rate errors decrease with increasing quadrature order and meshes per pin cell. It is found that there is a stronger dependence on the spatial than on the angular variable. Investigations of the axial fluxes and fission rates along with control rods and neighbouring fuel rods reveal the influence of the control rods, causing flux depressions depending on the control rod insertion depth.