As a dynamic reliability methodology, current Event Sequence Diagram (ESD) framework becomes an important tool to model the dynamic situations. It has been employed in the risk analysis in nuclear and space industries. It has been proved that ESD can be helpful for the operators of nuclear power plant to understand the accident scenarios and monitor progress during accident evolution. Despite this, there are some limits for the ESD framework in the practical application, such as the icons in the ESD framework are inadequate, so many dynamic situations are difficulty or complicated to describe. As for nuclear power plant, this paper proposes to extend its current iconic system to simpler and better model the dynamic process. Based on current ESD icons, we have created many other icons to represent the dynamic situations of the system and the component according to the characteristics of nuclear power plant. Some complex situations and interactions in the operation and accident are expressed by only one or two icons, so the system dynamics and accident evolution can be clearly described and simply translated into ESD models. Then the loss-of-coolant accident is used as the example to show the application of extended icons. These new icons greatly reduce the size of ESD model, which is well for its building and quantitative analysis. Most of the extensional ESD icons are also suitable for complex systems in other research fields and the ESD methodology may become popular for dynamic reliability analysis in the industry application.

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