The planar Method of Characteristic (MOC) solution based direct whole core calculation method is stabilized and extended by employing an axial one-dimensional (1D) MOC solver with several augmentations. In order to resolve the inherent instabilities involved in the coarse mesh finite difference formulation employing a nodal simplified P3 (SP3) axial solver, the factors causing negative fluxes are identified and eliminated. The augmentations consist of (1) a subgrid scheme, (2) transverse leakage splitting, and (3) PL scattering and limited transport correction that are selectively applied depending on regional characteristics. Axial domain decomposition is employed for parallel solution of 1D MOC. Various core calculation results demonstrate that the augmented 1D MOC solver considerably enhances stability while retaining comparable accuracy with the SP3 nodal kernel and not causing significant computational overhead.