A Multi-Objective Optimization Method for Reactor Coolant Pump Operation and Maintenance Under Multiple Operational Constraints

Floating nuclear power plants (FNPPs) must remain in service in island mode for extended periods, placing stringent demands on the availability of the reactor coolant pump (RCP). Conventional strategies rely on fixed intervals and prioritize safety over cost. In existing studies, the failure rate is prescribed as a function of calendar time and degradation is represented by a discrete grade, so the maintenance interval cannot respond to the equipment condition. Occupational exposure is evaluated only after the plan has been determined rather than co-optimized with unavailability and cost. This study proposes a prognostics-informed multi-objective optimization framework for RCP maintenance. The predicted remaining useful life (RUL) is mapped onto the time-dependent failure rate, so the unavailability of each minimal cut set depends on the equipment condition, and the maintenance interval becomes state-dependent and revised with the prognosis. Radiation exposure time joins unavailability and cost in the objective vector, and a compromise solution is selected from the NSGA-II Pareto set using a sensitivity index. Validated against operational data from 40 RCPs totaling approximately 5 reactor-years, the optimized strategy reduces unavailability, maintenance cost and radiation exposure time by 50.0%, 41.5% and 48.1%, respectively. As the RUL decreases, a fixed-interval strategy departs from the Pareto front, so the plan must be updated with the prognosis to remain near-optimal.