Abstract
Japan has been promoting its Pu utilization program based on the principle of not having excess Pu from the viewpoint of non-proliferation of nuclear weapons. On the other hand, by the end of 2020, Japan had 46.1 tons of separated plutonium, and the Rokkasho reprocessing plant, which will extract separated plutonium from spent nuclear fuel, is scheduled to start operation. Currently, there is a lack of ways for Pu consumption, and the practical way of Pu consumption is the use of MOX fuel in light water reactors. However, the conventional nuclear design of MOX fuel assemblies of light water reactors is mainly determined by focusing on the local peaking factor, and the Pu consumption has not been considered much. In this study, we focused on the Pu consumption in the MOX fuel assembly and obtained the fuel pin arrangement that maximizes the Pu consumption by changing the fuel pin arrangement and Pu composition using a genetic algorithm. Focusing only on the local peaking factor, the optimization was performed to obtain the fuel pin arrangement that minimizes the local peaking factor. As a result, it was found that fuel pins with high enrichment were placed in the fuel assembly where Pu consumption was maximized, except for the fuel pins adjacent to the uranium fuel where the thermal neutron influx has a large effect. In the arrangement that minimized the local peaking factor, the local peaking factor is suppressed to 1.1. From these results, it was confirmed that the optimization can increase the amount of Pu consumption.
