There are many types of risks, of which dominant one needs to be identified and quantitatively estimated for designing safe fusion reactor plant. A comprehensive safety evaluation methodology was devised for that purpose and a process code was programmed on the basis of the methodology. It was designed so as to be executable on an engineering work station, and simplified as much as possible to attain quick response. In addition, the code can provide clear understanding of the plant conditions and the calculational results by graphic display system. As a result, an extensive design survey was made possible through miscellaneous design options to find a reasonable fusion reactor model with respect to safety.