Dortorest: A coupled transport-depletion code system for LWR fuel assembly burnup calculations

The well-known Discrete Ordinates code DORT has been implemented into the fuel assembly and nuclide inventory code system KENOREST, which in turn comprises the Monte-Carlo code KENO for stochastic transport and the fuel inventory code OREST for microscopic depletion. In this framework, DORT acts as an alternative, deterministic 2D-transport code for solving the neutron transport equation for fuel lattice geometries. A special modeling option for fuel rod arrays and a dedicated cross section collapsing and homogenization module have been added to DORT and extensively benchmarked for fresh fuel states. By coupling DORT and OREST, a new lattice code system DORTOREST has been conceived, thus facilitating the usage of DORT for depletion of LWR fuel assemblies. First comparisons between the stochastic KENOREST and the deterministic DORTOREST system indicate good agreement in eigenvalues, pin powers and nuclide inventory over the entire fuel depletion range. By means of a quadratic flux extrapolation algorithm, the expensive DORT transport calculations have also been substantially accelerated. (authors)