Abstract: This paper describes the basic principles and methods of the significance determination process (SDP) at power condition, which was developed by the National Nuclear Safety Administration, and was used to analyze the significance and sensitivity of the failure of the pneumatic auxiliary feed pump (ASG004PO) in nuclear power plants. The result has indicated that the period of the recirculation flow test for the steam-driven auxiliary feed pump was too long, and the optimization proposal for this issue is to optimize the cycle of ASG004PO recirculation flow test to less than 34 days.