The «CORNER» neutronics calculation code
The CORNER software is designed for high-fidelity deterministic neutronics calculations of fast reactors, namely: spatial and energy distribution of the angular neutron flux, the effective multiplication factor and efficiency of a single control rod and their groups.
The computation algorithm is based on the SN discrete ordinates method  and the PM approximation of scattering cross section and allows solving two types of stationary problems of neutron and gamma rays transport in three-dimensional hexagonal (HEXZ) geometry: Keff problems (homogeneous) and the source problems (inhomogeneous).
The software tool is developed in Fortran and has a modular structure. The main modules are: the module to prepare neutron constants in ANISN format; the geometric module, containing a description of the core’s loading map and fuel assembly types including their axial mesh and material composition; the module to prepare angular quadrature sets; the input data module containing the approximation and control parameters; the neutronics calculation module and the module to process calculation results.
The Directional Theta-Weighted (DTW) difference scheme  is built to approximate spatial dependence. It has advantages over the widely used DD (Diamond Difference) scheme in coarse-mesh problems.
Energy dependence is represented by the multigroup approximation. The CONSYST constants system with ABBN-93 library is used.
Discretization of the angular variable is carried out by introducing the angular quadrature set. There is an option of specifying a set of user’s quadratures.
An iterative process of solving is used, including external iterations over the fission source and internal iterations over the scattering source. Iterations stop by a condition imposed onto the accuracy or the number of iterations.
Сalculations of a BN-800 core problem were verified against the MMK Monte Carlo code .
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