Overlapping Local/Global Iteration Framework for Whole-Core Transport Solution

In current practice of nuclear reactor design analysis, the whole-core diffusion nodal method is used in which nodal parameters are provided by a single-assembly lattice physics calculation with the zero net current boundary condition. Thus, the whole-core solution is not transport, because the interassembly transport effect is not incorporated. In this paper, the overlapping local/global iteration framework that removes the limitation of the current method is described. It consists of two-level iterative computations: half-assembly overlapping local problems embedded in a global problem. The local problem can employ heterogeneous fine-group deterministic or continuous-energy stochastic (Monte Carlo) transport methods, while the global problem is a homogenized coarse-group transport-equivalent model based on partial current-based coarse-mesh finite difference methodology. The method is tested on several highly heterogeneous multislab problems and a two-dimensional small core problem, with encouraging results.