the invention relates to the fault tree analysis system for a nuclear power plant with advanced boiling water reactor . the full digital instrument control system uses six different modes to simulate the transmission of the digital signals and the analog signals from the detection units . it is to develop the fault tree for various signal transmission modes to support the nuclear power plant in probabilistic risk assessment and meet requirements for simulated signal detection , transmission , logic operation and equipment actuation . thus , the digital instrument control flow process can fit into pra model and properly reflect its importance in risk assessment .