[en] To achieve the reasonable and effective maintenance of nuclear power plants, it is essential to optimize the aging management from the viewpoints of both safety and efficiency. We propose a maintenance-scheduling model that minimizes the cost of maintenance activities while ensuring the reliability of safety-critical functions. In this study, we formulate the maintenance-scheduling problem as a mathematical programming model and consider that the effective maintenance activity differs depending on the cause of the latent failure. Computing maintenance activity schedules for a single component and all the components of a safety-critical function, we verify that the proposed model provides the optimal schedule. The proposed model enables us to quantitatively evaluate the impact of the allowable unreliability value of a function of interest on the schedule and thereby the tradeoff between the reliability of safety-critical functions and the maintenance cost. (author)