Abstract
Molten salt system is characterized by using molten salt as its working fluid and fissile dissolved in the molten salt. Unlike traditional solid fuel systems, molten salt expansion and circulation should be additionally considered. Since neutronics and thermal-hydraulic influence each other in the system, neutronics and thermal-hydraulic coupling analysis is a step to understand its characteristics. This study developed a coupling methodology to analysis a molten salt natural circulation loop and the Molten Salt Reactor Experiment (MSRE). This study used SCALE-CSAS6 as neutronics calculation code and FLUENT as thermal-hydraulic calculation code. Two self-developed codes, Neutronics and Thermal-hydraulic Coupling Code (NTC) and Coupling User Defined Functions (Coupling UDF), were used to automatically control the calculation and exchange data between SCALE-CSAS6 and FLUENT. This study has showing that it operated SCALE-CSAS6 and FLUENT correctly by reproducing the results in the references respectively. The self-developed codes were also applied to the case of Chuang's calculation which exchanged neutronics and thermal-hydraulic data manually. The corresponding results imply that NTC and Coupling UDF can operate correctly. The first case is startup analyses for the simple natural circulation loop. To make the calculation more physically realistic, this study built new models, considered negative reactivity feedback from thermal expansion, and moved the control rods to compensate the negative reactivity feedback. Via the analyses, my research obtained the temperature, velocity, and power distribution at the startup and stable operational state. The second case is MSRE transient simulation. It is necessary to take account of reactor dynamics when reactor power varies with time. Reactor dynamics and delayed neutron precursors movement reactivity loss codes were additionally developed. This study obtained similar results with the experimental data and thus proved that the coupling methodology is feasible.