Modeling of computerized procedure execution with State Token Petri Net for formal verification of procedure flow

Abstract

Computerized procedure system (CPS) is one of the primary operating support systems in the digital main control room (MCR) of a nuclear power plant. CPS displays the procedure at computer screen in the form of a flow chart and displays plant operating information along with procedure instructions. It also supports the operator to make a decision by providing system decision with logic. Most importantly; CPS guides the operator to follow a procedure flow that is predefined when the computerized procedure (CP) is written. A procedure flow should be correct and reliable, as error would lead to operator misjudgment and inadequate control. As such, the procedure flow should be verified before being applied to the MCR. In this article, we present a model of CPS that enables formal verification based on Petri nets. The proposed State Token Petri Net also supports modeling of a procedure flow that has various interruptions by the operator according to the plant condition.