According to Surveillance Requirement SR3.0.3 in Technical Specifications, if it is discovered that a surveillance was not performed within its specified frequency, then compliance with the requirement to declare the LCO not met may be delayed, from the time of discovery, up to 24 h or up to the limit of the specified frequency, whichever is greater. This delay period is permitted to allow performance of the surveillance. The delay period is only applicable when there is a reasonable expectation the surveillance will be met when performed. A risk evaluation shall be performed for any surveillance delayed >24 h and the risk impact shall be managed. In this paper, by identifying the missed test, determining the delay time, performing risk analysis for the missed test with a delay time >24 h, developing risk assessment and risk management processes, we provide specific and executable risk assessment methods, so as to avoid the unit conversion mode caused by the immediate announcement of unavailability, and increase the flexibility of production activities in the nuclear power plant.