Best compromise multi-objective optimization of testing interval in an NPP’s emergency power supply system considering the ageing effects

This paper deals with the multi-objective optimization of an Emergency Power Supply System (EPSS) in a Nuclear Power Plant (NPP). Two objective functions are considered namely: the maximization of the EPSS reliability and the minimization of the testing cost of two Emergency Diesel Generators (EDGs) considering the Testing Interval (TI) as the control variable of the optimization problem. For doing so, a coupling between the fault tree analysis method (FTA) and the multi-objective optimization is performed. Furthermore, to be more realistic, the effect of ageing is considered. Seven case studies are considered for comparison purpose. An improved version of NSGA-II is proposed considering the integer model of the control variables and the identification of the best compromise solution from the Pareto front. For validation purposes, the boundaries solutions of the Pareto front are compared with those of the mono-objective optimization. The obtained results show clearly that the EPSS aging decreases its reliability. This last can be enhanced by decreasing the testing interval but with additional cost. In addition, the obtained Pareto front provides a set of optimal solutions that can be selected according to the reliability and cost values.