Development of the Hazard and Safety Assurance Evaluation Technology for Nuclear Safety Software

Based on the summary of the trends of regulatory body and technical standards for hazard analysis of nuclear safety software, the hazard method to be applied to each period of life cycle of safety software in nuclear power plant was derived, and we developed hazard analysis methodology coverage and hazard analysis technique template. We have proposed a new framework to remove the design phase FTA from the existing framework and to perform the STPA in the middle of the planning phase and the software requirement phase in the safety software hazard analysis applied to the safety system of nuclear power plant. This is because the purpose of STPA is to derive safe software requirements at the beginning stage of the system development. We have introduced a new framework that applies safety case to existing frameworks to achieve safety assurance with software verification and validation and hazard analysis to provide systematic evaluation techniques to determine if software defects are acceptable. The safety case is applied based on the qualified document of the Digital Reactor Protection System bi-stable logic/coincidence logic processor. The claim, which is a high-level objective that the system should satisfy, the argument that connects the claim and the evidence, and the verification and validation and the result of the hazard analysis are the evidence. Guidelines for the preparation and evaluation of safety case were developed. In the era of the Fourth Industrial Revolution, an intelligent information society symbolized by the cyber physical system and internet of things, software safety issues are becoming more and more important with cyber security. If the safety of the virtual world collapses, the safety of the real world will be seriously damaged. Therefore, it can be utilized as a base technology for software safety assurance of cyber physical system.