Reduced order SP₃ core calculation based on Local/Global iterations using proper orthogonal decomposition

For an efficient heterogeneous neutron transport calculation, this study newly proposes a reduced order core calculation method by applying proper orthogonal decomposition (POD) to the simplified P₃ (SP₃) calculation with the local/global iterations. The fine mesh SP₃ calculation (local calculation) for each single assembly can be efficiently solved using POD, thanks to the matrix form-based SP₃ equation and the relatively small system of linear equations. By reconstructing the fine mesh distribution of neutron flux and partial neutron currents from the POD bases and the expansion coefficients estimated by the local calculation, the partial current-based coarse mesh finite difference (p-CMFD) calculation is applied to the coarse mesh calculation (global calculation). Using the global calculation results, each local boundary condition can be updated. These local and global calculations are iterated until convergence. Through a two-dimensional UO₂-MOX whole core calculation with different fuel loading patterns, the proposed method is verified in comparison with the reference result by the conventional fine mesh SP₃ calculation. The calculation results show that the proposed method accurately reconstructs the fine mesh distribution of neutron flux.