In this work, a formal requirement analysis method for Nuclear Power Plant (NPP) I&C systems is suggested. This method uses Unified Modeling Language (UML) for modeling systems visually and Software Cost Reduction (SCR) for checking the system models formally. Since object-oriented methods enable us to analyze problems in terms of the objects in a real system, the UML models are useful for understanding the problems and communicating with people involved in a project. In order to analyze problems more formally, SCR is used and the UML models are converted into the SCR tabular notations. T his work tries to acquire the flow-through from UML models to SCR specifications by suggesting additional syntactic extensions for UML notation and a converting procedure in this work. The proposed method has been applied to the Dynamic Safety System (DSS) and the Inadequate Core Cooling Monitor ing System (ICCMS). Through these applications, some errors have been detected in the existing system requirements.
Furthermore, through the comparison of our proposed method with the conventional inspection, we conclude that our method can complement the limitations of the inspection, which has lack of detectability. The potential errors like completeness, consistency, and logical errors of requirement, were scarcely detected through the conventional software inspection. These limitations can be more serious in safety critical systems such as nuclear pow er plants. Therefore, formal requirement analysis methods are strongly recommended in the requirement engineering.