Experience in the use of the Monte-Carlo code based tracing algorithm and the volume fraction method in VVER radiation shielding calculations

Monte-Carlo code based tracing algorithm is applied for converting combinatorial presentation of the problem geometry and source to a bit-mapped one with local conservation both the mass of original materials and the source yield for every spatial cell of the mesh. To make this transformation the volume fractions (VF) of original materials and source by spatial cells of the user supplied mesh are calculated by the tracing algorithm and the VF method is applied by introducing additional mixtures for spatial cells, where a few original materials are included. The use of the tracing algorithm makes this procedure fast and efficient. Received geometry and source approximation on the mesh ensures some improvement in convergence with mesh refinement. It also requires only minor changes in SN transport codes, working with regular orthogonal meshes. Developed approach is tested in an example of VVER-1200 radiation shielding calculations. (authors)