Tort solutions to the three-dimensional MOX benchmark, 3-D Extension C5G7MOX

Solutions to the OECD/NEA three-dimensional fuel assembly benchmark problem, C5G7MOX, obtained using the discrete-ordinates neutron transport code TORT are presented. The accuracy and convergence of the effective multiplication factor and maximum pin power are examined while varying the fidelity of the geometric model and the order of the angular quadrature, specifically the Square Legendre–Chebychev quadrature. The calculated value of the effective multiplication factor is shown to converge asymptotically as the order of the quadrature is increased. The behavior of that asymptotic limit of keff with decreasing computational cell size and increasing staircase resolution of the curved rod-moderator is less converged. Moreover, rapidly increasing computational cost with geometric configuration refinement prevented us from achieving asymptotic convergence with the spatial approximation. The maximum pin power results are generally shown to asymptotically converge to within the statistical error of the reference solution for the problem slices where control rods are not present. For the zones that contain control rods, the solution does not appear to be tightly converged for the meshes and quadrature orders employed.