Design of a Small Modular Nuclear Reactor with dual cooled annular fuel and investigation of the fuel inner radius effect on the power peaking factor and natural circulation parameters

Abstract

Recently, a kind of fuel called “dual-cooled annular fuel” is used in the nuclear reactors, which allows the coolant to flow from the inside and outside of the fuel rod and finally causes a substantial increase in power density. The dual-cooled annular fuel rod has both inner and outer coolant channels. Also, Small Modular Reactors (SMRs) are the innovative design of nuclear reactors making remarkable interest during recent years. Since there is not enough available operating experience on SMRs, it might be possible to initiate extensive investigations on these types of reactors for the purpose of improving the current performance level of these systems, significantly.In this paper, for the first time, the core of a Small Modular Reactor (SMR) is designed based on the use of internally and externally cooled annular fuels. And then, neutronics and natural circulation parameters of this type of reactor are analyzed. For this purpose, at the first, the dual-cooled annular fuel under clean and cold conditions is modeled for the different inner clad diameter with same distance gap to gap of fuel rod and effective multiplication factor has been calculated. Then, these annular fuels under full power conditions are modeled for each inner clad diameter and power peaking factor has been calculated. Finally, natural circulation parameters calculations are performed for a simulated fuel rod in the hot channel using computational fluid dynamics simulation codes. These calculations are compared with a conventional NuScale reactor that does not use this kind of fuel. One of the most prominent of its advantages is the ability to moderate more of the neutrons in the reactor core with this type of fuel, which can increase the core effective multiplication, reduce total power peaking factor and improve natural circulation parameters. Increasing of the effective multiplication coefficient at cold and clean condition leads to increase the excess reactivity of the core which increases the operation cycle without refueling and it is useful from fuel management view-point. Also, it was found that by increasing the inner radius by more than 0.5 (cm), the power peaking factor increases, which is due to the more increasing of the pitch lattice relative to the mean free-path and excessive reduction of the mean power-density in the core and, also, increasing the flux gradient.