<p>Liquid-containing structures, including steam generators, water-cooling systems, in-containment refueling water storage tanks, suppression tanks, and tritiated water storage facilities, are integral components of nuclear reactor systems and are crucial for ensuring operational safety and stability. Traditional seismic analysis methods often struggle to accurately predict the dynamic behavior of such structures, particularly under transient events such as earthquakes. This paper presents a comprehensive study that applies the hybrid Eulerian–Lagrangian method to analyze fluid–structure interactions within these structures. The efficacy of this method for capturing the complex dynamics induced by liquid movement is demonstrated through simulations conducted primarily in a vertical storage tank. A comparative analysis with traditional response-spectrum analysis methods underscores the limitations of conventional approaches, particularly in terms of accounting for nonlinear free-surface motions and dynamic velocity distributions. The structural response of the tank containing liquid calculated using the hybrid Eulerian–Lagrangian method is approximately twice that calculated using the response-spectrum method, whereas in the case of a tank without liquid, the response is the same. Additionally, a high dynamic stress distribution exists near the liquid level of the structure. This study addresses the intricate interplay between structural components and fluid dynamics, thereby extrapolating insights from tanks to enhance safety protocols and design considerations for future nuclear devices.</p>