Dynamic response simulation of step reactivity for TRIGA research reactor based on Modelica

<bold>Background</bold>Simulating reactors is crucial for meeting the reactor teaching and research needs of ordinary universities. The TRIGA (Training, Research, Isotopes, General Atomic) research reactor is inherently safe and widely used in teaching, research, and isotope production.<bold>Purpose</bold>This study aims to construct a simplified multi-physics dynamic model suitable for TRIGA research reactors' simulation analysis using Modelica technology, so as to provide support for reactor teaching and research.<bold>Methods</bold>In this study, on the OpenModelica platform, Modelica technology was used to construct point reactor neutron kinetics model, Xenon and Samarium poisoning model, temperature feedback model, and aggregate parameter thermal dynamic model. By simulating the pulse startup and emergency shutdown processes with large step reactivity disturbances and the power regulation process with small step reactivity disturbances, the key dynamic response results such as the main pulse parameters, Xenon and Samarium concentrations, and power changes were obtained.<bold>Results</bold>The results show that the pulse peak power varies with the introduced reactivity during the pulse startup process, and the simulated and experimental values are in the same trend and close to each other. For the pulse release energy and pulse half-height width, the deviations are small when the introduced reactivity is large, but large when the introduced reactivity is small. During the emergency shutdown, due to the introduction of negative reactivity, the concentration of ¹⁴⁹Sm increases and gradually tends to the theoretical stable value. The concentration of ¹³⁵Xe increases and then decreases, and its maximum concentration is consistent with the theoretical prediction. In the process of power regulation, by introducing positive reactivity, the power first increases to the peak value, and then gradually decreases and stabilizes at the new power level. The simulation results have the same trend with the experimental results and are in good agreement.<bold>Conclusions</bold>The consistency of the simulation results with the experimental or theoretical values verifies the accuracy and reliability of the simulation model proposed in this study, indicating that the model can accurately reflect the basic dynamic physical laws of the TRIGA research reactor, which provides a strong support for reactor teaching and scientific research.