Study on core and fuel specifications aiming at short doubling time

In the JNC design of the reference core of a commercial fast breeder reactor, priority is placed on high-burnup fuel and long-cycle operation leading to a low fuel cycle cost. Less attention is paid to the breeding characteristics, given the present situation of plutonium demand and supply. However, after about 2030, a rapid growth of fast breeder reactors is expected and the need for plutonium breeding is likely to arise. Therefore, we have studied feasibility of meeting a future demand for short doubling time, only by modifying the fuel assembly specifications of the reference core, when required after the commencement of the commercial plant operation. The survey has been made on a variety of modifications starting from the reference two-region homogeneous core under a fixed condition of average discharge fuel burnup of 150 GWd/t. The study shows that an effective way to shorten the doubling time is a combination of modifications such as decreasing the core height and the gas plenum length, increasing the axial blanket thickness, increasing the number of fuel pins per assembly and shortening the period of the cycle operation. On the basis of the survey, the 397-pin core has been chosen as a suitable candidate for short doubling time and the core characteristics have been evaluated. In addition, a study has been made on axial heterogeneous core configurations, revealing that the doubling times are about the same as that of the homogeneous core. This study shows that the complex inventory doubling time of the commercial plant can be shortened to about 30 years, only by modifying the fuel assembly specifications. (author)