This study aims to optimize the orifice diameter to reduce pressure hunting in the pilot valves of positioners used in nuclear power plant control systems. Computational Fluid Dynamics (CFD) analysis using ANSYS CFX was conducted to create 3D models with varying orifice diameters (1 mm, 1.5 mm, 2 mm, 2.5 mm, and 3 mm). To enhance the accuracy of the analysis, boundary layer meshing techniques (Inflation) were applied, and the SST k-ω turbulence model was employed. The analysis of pressure variation and pressure hunting over time revealed that larger orifice diameters resulted in reduced pressure hunting, with a 3 mm orifice diameter achieving 0% pressure hunting. Additionally, it was observed that larger orifice radii slightly increased the average outlet pressure. Based on the findings, a 3 mm orifice diameter is recommended to effectively mitigate pressure hunting in pilot valves, contributing to improved system stability in nuclear power plants. Future studies will explore the design of slanted orifices to further analyze fluid flow characteristics.

The reliability of control valves is critical in nuclear power plants to ensure precise fluid regulation and prevent risks associated with overheating or decreased efficiency. Recently, the supply of imported control valves used in these plants has been discontinued, making the development of domestic alternatives an urgent necessity. This study focuses on the design of an orifice in the pilot valve pipe of a positioner to reduce hunting, a key issue that compromises control stability. Fluid analysis was conducted using ANSYS CFX to investigate the fluid behavior in the pipe with the orifice. The analysis methods included enhanced meshing techniques, turbulence models, and residual values to improve convergence and accuracy. To meet the operational requirements of nuclear power plants (outlet pressure: 3.2 bar, inlet pressure: 7 bar), the inlet fluid velocity was determined. The pressure and pressure hunting were analyzed. Results showed that the selected inlet velocity satisfied the operational conditions, and pressure hunting values were measured and analyzed. The findings provide a basis for further optimizing orifice shapes to achieve the target pressure hunting value of 0.5%.

The domestic shipbuilding industry is building high-value-added ships such as LNG and LPG, and the demand for natural gas, a clean energy source, is continuously increasing. Climate change, such as global warming, is occurring due to rising oil prices and excessive use of fossil fuels. To protect their homes from the changing environment, 121 countries announced intensive climate target policies to reduce carbon emissions to 0% by 2050. In this study, modeling and design were performed using SUS410 and SUS304L about the operating part of the Pilot valve based on the physical properties of the aluminum alloy used in the Pilot valve, a component of the gas pressure Regulating valve for LNG ships. Numerical We want to develop the optimal Pilot valve by comparing and analyzing the results using ANSYS, an analysis simulation program.