A precise method for estimating residual radioactivity and decommissioning cost is indispensable when deciding whether to adopt low-activation material. For this precise estimation, accurate estimation of both the thermal neutron flux and the activation cross section of the structural material is necessary. We developed a new groupwise cross-section library that has ten thermal groups for SN transport calculation and activation calculation. These libraries are tested and used for advanced boiling water reactor (ABWR) and advanced pressurized water reactor (APWR) activation analyses.