Axial 3D effect on modeling a heterogeneous core

To assess the need of next generation method (NGM) for analyzing heterogeneous cores, a mini-core with 6 × 6 boiling water reactor (BWR) bundles is proposed as a benchmark problem. It is found that the traditional method based on reflective single bundle homogenization leads to very large errors even for a sliced 2D core analysis. For the 3D case there is very strong axial interface effect on fine mesh scale that has nothing to do with axial homogenization and cannot be captured by the traditional coarse mesh nodal method with radial pin power reconstruction. A single bundle 3D homogenization and pin power reconstruction model is proposed to couple with coarse mesh nodal method such that the detailed 3D effect of the reference solution can be reproduced accurately.