The introduction of soft controls into the main control room may provide a more convenient environment for operations, but also may introduce new types of human errors and new risks into the nuclear power plants. In this paper, taking the Chemical and Volume Control System (CVCS) at pressurized water reactor nuclear power plant as an example, the task analysis of operating procedures for starting the CVCS under a normal shut-down operation condition, the potential failure modes during operators executing each step of operating procedures and the dependency analysis of sub-tasks are presented. Furthermore, the sensitivity analyses are conducted for identifying probability importance and critical importance of each model parameter. The countermeasures for preventing and reducing the human errors of soft controls are discussed.

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