Leakage Correction Cross-Section for Axial Void Channels in the 2D/1D Method

A new leakage correction method is proposed to improve the accuracy and stability of 2D/1D transport calculations, especially for designs with large void channels. The approach introduces a leakage correction cross-section that increases neutron collisions in void regions, thereby correcting flux underestimation caused by the isotropic transverse leakage (TL) approximation in the 2D/1D method. This cross-section is numerically derived from a one-group fixed-source 3D cylindrical problem and expressed as a simple function of channel radius. The leakage cross-section ensures that scalar flux in void regions more closely matches 3D transport results. Verification with microreactor problems of varying void channel sizes demonstrates significant improvements in keff and axial power distribution, along with enhanced convergence stability and fewer required iterations compared to the standard 2D/1D method.