A study on the seismic test of a planar model of the gas-cooled microreactor

This study examines the seismic behavior of a horizontal layout graphite core model for gas-cooled microreactors, with a focus on the impact of preload variations on structural dynamics and safety. A 1:1 scale partial planar model replicating the discrete graphite brick assembly was designed to respond to in-plane seismic responses. Experimental methods integrated contact-based accelerometers and non-contact digital image correlation to capture multi-point displacement and acceleration data. Three preload levels (15 kN, 10 kN, 5 kN) were applied via lateral metal restraints to evaluate their effects on stiffness, damping, and frequency characteristics. Sine-sweep tests demonstrated that lower preloads increased damping ratios (up to 27%) and natural frequencies (5 Hz at 5 kN vs. 4 Hz at 15 kN), attributed to lateral contact with side restraints and internal friction among loosened bricks. Furthermore, finite element analysis demonstrates that larger gaps lead to lower structural frequencies, thereby confirming that structural stiffness is correlated with lateral support. Seismic tests using 0.3g zero-period acceleration inputs validated structural integrity: control rod channel displacements remained within a 1 cm radius, ensuring safe shutdown capability. This work highlights the non-linear relationship between preload, lateral constraints, and dynamic behavior, with higher preloads reducing stiffness by increasing gaps. The results advance safety assessments for microreactors and offer practical insights for mitigating risks in next-generation nuclear systems.