Development of Two-Group Drift-Flux and Interfacial Area Models for Two-Phase Flows in Tight-Lattice Fuel Bundle of Advanced Nuclear Reactors

Description

Thermal power generation burns fossil fuels such as coal, oil, and natural gas and uses their thermal energy to generate electricity, which emits carbon dioxide in the process. On the other hand, nuclear power generation uses the heat generated when uranium fuel undergoes nuclear fission to generate electricity. It does not emit carbon dioxide during the power generation process, just like solar and wind power generation. Nuclear power generation is one of the best approaches for power generation in terms of preventing global warming.One of the challenges in nuclear power generation is the accumulation of transuranium elements (TRU) as a byproduct of burning uranium fuel. It takes about 100,000 years for the radio-toxicity of nuclear waste containing TRU to decay to the same level as that of uranium ore, which is a natural resource. (Radio-toxicity is an index of radiation intensity weighted by the effect of each radioactive isotope on the human body.) An advanced nuclear reactor concept that uses a tight-lattice fuel bundle has been proposed to solve this problem. The tight-lattice fuel bundle design increases the neutron energy in the reactor core, thereby decreasing the amount of TRU for the same level of power generation.Coolant channels between fuel rods are narrowed to reduce the volume fraction of coolant in the core. Additionally, by utilizing the characteristics of boiling water reactors, in which the coolant water boils to steam and the density of hydrogen nuclei decreases, calculations show that even in light water reactors, neutron energy can be increased, and plutonium breeding is possible.Design and licensing processes require extensive numerical simulations of gas and liquid dynamic behaviors in the tight-lattice core fuel bundle, which directly impact the nuclear reactor safety and performance. Numerical simulation codes are based on theoretically derived mass, momentum, and energy conservation equations. Constitutive equations need to match the number of variables with the number of equations in the simulation codes. Constitutive equations are used to estimate two-phase flow parameters, which cannot be determined purely theoretically. The accuracy and robustness of constitutive equations significantly impact the fidelity of numerical simulation capability.The proposed project aims at developing key constitutive equations: the two-group drift-flux model and the interfacial area model for a tight-lattice fuel bundle in a square channel box. The developed models will substantially improve the fidelity of numerical simulation codes, which significantly contributes to safe and economical nuclear reactor design.