A new risk monitor system is under development which can be applied not only to prevent severe accident in daily operation but also to serve as to mitigate the radiological hazard just after severe accident happens and long term management of post-severe accident consequences. The fundamental method for the new risk monitor system is first given on how to configure the Plant Defense in-Depth (DiD) Risk Monitor by object-oriented software system based on functional modeling approach. In this paper, software system for the plant DiD risk monitor is newly developed by object oriented method utilizing Unified Modeling Language (UML).Usage of the developed DiD risk monitor is also introduced by showing examples for LOCA case of AP1000.
