Leakage reconstruction method for 2D/1D fusion transport calculations

The 2D/1D fusion method (2D/1D method) is becoming a standard transport method for whole-core calculations, which reduces the group condense and assembly homogenization approximations in the conventional two-step reactor physics calculations. In most 2D/1D codes, a pin is chosen as a 1D calculation domain, which assumes that the axial leakage of the pin is flat on top/bottom surfaces. Similar to the axial leakage, the radial leakage of every 2D plane also introduces several approximations along axial direction for the 1D calculation. This paper studied the error introduced by both axial and radial leakages, and proposed a leakage reconstruction method according to the error analysis for the 2D/1D fusion method, in which MOC is applied to the radial 2D calculation and the Sn diamond difference method is used for the axial 1D calculation. Several cases are tested to show the performance of this leakage reconstruction method especially when the leakage term is significant.