STUDIES ON EFFECTS OF WIRE WRAPPED ROD BUNDLES ON THERMAL HYDRAULICS PERFORMANCE

Abstract

This thesis investigates the thermal hydraulics and optimization of wire wrapped spacers in 2×2 heated rod bundles operating under supercritical circumstances. The main objective was to improve the performance of Supercritical Water Reactors (SCWRs). There is crucial significance of nuclear power in attaining carbon neutrality and reducing the impact of global warming. Previous studies examine nuclear energy as a viable and dependable source of power, emphasizing the potential of SCWRs as a feasible substitute for traditional reactor designs. The studies emphasize the importance of doing advanced thermal hydraulic analysis and optimization in order to improve reactor performance. It also provides the rationale for the research. Many previous research conducted on SCWRs, including both experimental and numerical investigations. The study explores the heat transport characteristics of supercritical water, evaluates the effectiveness of different spacer designs, and highlights areas where our understanding is lacking. The literature assessment compiles important discoveries from prior research, emphasizing the need for thorough examination of wire spacer arrangements and their influence on thermal hydraulics. The computer modelling techniques employed in the investigation, includes geometry preparation, mesh production, and the governing equations for the simulations. A user defined function for each thermo-physical property of supercritical water at the operating condition was made and interpreted in the Fluent software. The boundary and operating conditions, the solver and solution methods, and the verification of the CFD model using grid independence tests and validation has been described. A novel optimization framework has been presented, which integrates Taguchi design, Radial Basis Function (RBF) surrogate modelling, and the Non-Dominated Sorting Genetic Algorithm II (NSGA-II). An analysis of the thermal hydraulic characteristics of 2×2 rod bundles with wire wrapped spacers operating at supercritical conditions was conducted. The analysis investigates fluctuations in axial velocity, velocity vectors, pressure distribution, and temperature distribution. The study contrasts traditional helical wire wrap configurations which is in clockwise direction with novel pattern geometries which wraps wire in clockwise and anti-clockwise direction, emphasizing the advantages of improved coolant mixing and decreased high-temperature areas in the new patterns by 8.5°C. The study examines the differences between straight and helical wire spacers, highlighting the enhanced swirl and turbulence properties of helical wires, despite the presence of a greater pressure drop. The design optimization of wire spacers with varying wire diameter and varying pitch of wrapping by utilizing the RBF surrogate model and NSGA-II optimization v technique was done. The optimization technique was used to achieve a balance between the heat transfer factor and the pressure drop factor. The optimization framework uses the Taguchi approach for selecting sample points, applies RBF surrogate modelling to create a response surface, and employs NSGA-II for global optimization. The Pareto front analysis offers extremely helpful insights into the ideal ranges for pressure drop factor (ranging from 5.051 to 8.082) and heat transfer factor (ranging from 1.05 to 1.087). The potential areas for future research of this study may be, extended design parameters, conducting transient flow and temperature studies, implementing real time optimization, validating through experiments, and integrating with reactor core design. There are the societal implications of the study, emphasizing its contributions to energy security, environmental sustainability, economic growth, technical safety, and contribution to global energy goals.