An energy sector company, such as EDF, is dedicated to safeguarding the integrity of its power generation infrastructure and must therefore stringently manage the production quality of its components, with a particular focus on large-scale parts. At present, numerous components are produced through forging or casting. Nevertheless, EDF's innovation team is proactively investigating alternative manufacturing techniques to expand its procurement strategies. Given EDF's unique applications and industrial needs, one noteworthy alternative method for creating large components is Wire Arc Additive Manufacturing (WAAM). Numerical simulation is an essential instrument in the validation process of components produced via WAAM, especially in high-stakes industries like nuclear power. It is integrated throughout the component's entire lifecycle—from design and fabrication to post-processing—facilitating parameter optimization and bolstering traceability for EDF. Consequently, this approach guarantees adherence to technical and regulatory standards. The main goal of this investigation was to create a detailed model of an intricate austenitic stainless steel part consisting of around 1,200 weld beads. Following this, a comprehensive thermal numerical simulation was carried out. Through post-processing analyses, we were able to determine the temperatures achieved at the conclusion of each layer and pinpoint areas where sigma phase formation might occur. This study provided crucial insights into the thermal dynamics of the complex stainless steel component during the WAAM process. By identifying regions at risk of sigma phase formation, we can now optimize process parameters, make necessary design adjustments, and implement appropriate post-processing treatments. These steps are essential for reducing the risk of sigma phase precipitation and ensuring that the component maintains the desired material properties.