The digitalization of nuclear facilities has brought many benefits,including high performance and convenient maintainability,in terms of facility operation.However,cyber accidents accompanied by the use of digital technologies have increased,and cyber security has been one of the most important issues in the nuclear industry area.Several guidelines have been published for nuclear power plants,but it is difficult to apply all requirements within the guidelines to research reactor facilities because the characteristics in terms of facility scale,purpose,and system design,are different from those of power plants.To address this emerging topic,this paper introduces system lifecycle processes for cyber security in a research reactor facility.It addresses the integration of activities for securing systems and guarding a facility safely using the practices at a research reactor facility. The digitalization of nuclear facilities has brought many benefits, including high performance and convenient maintainability, in terms of facility operation. Host, cyber accidents accompanied by the use of digital technologies have increased, and cyber security has been one of the most important issues in the The nuclear industry area. The guidelines have been published for nuclear power plants, but it is difficult to apply all requirements within the guidelines to research reactor facilities because the characteristics in terms of facility scale, purpose, and system design, are different from those of power plants.To address this emerging topic, this paper introduces system lifecycle processes for cyber security in a research reactor facility. It addresses the integration of activities for securing systems and guarding a facility safely using the practices at a research reactor facility.