[en] It is required to select an optimal decommissioning scenario by evaluating its characteristics since there are various kinds of decommissioning options of nuclear facilities which ceased operation. A methodology was studied on evaluation of an optimal scenario from the viewpoints of radiological risk reduction and easiness of work activities together with preparing several scenarios based on the IAEA proposal options (immediate and deferred dismantlings, and entombment). In this study, the basic decommissioning work activities are classified into facility dismantlement, site remediation and waste management, then these are further disassembled to be small categories by using hierarchically form. The computer system was developed to build hierarchically decommissioning work activities on a computer screen, then the scenarios are compared by using the analytical hierarchy process. The developed system was applied to the evaluation of decommissioning scenarios of Fukushima-Daiichi nuclear power plant of Tokyo Electric Power Company as a case study. It was cleared that the facility entombment option scored the highest value of relative importance from the viewpoint of radiological risk reduction; otherwise the safe enclosure (deferred dismantling) was scored the highest value if the easiness of work activity was taken as evaluation viewpoint. (author)