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BackgroundThe liquid-fueled molten salt reactor (MSR) is one of the Generation IV advanced reactor concepts, which has unique advantages in aspects of safety, economy and nonproliferation. However, in view of the special neutron dynamics and hydrodynamics of the liquid-fueled MSR, traditional system analysis codes for solid fuel reactors cannot be applied to liquid-fueled MSR directly without improvement.PurposeThis study aims to improve the applicability and accuracy of the RELAP5/Mod4.0 code in liquid-fueled MSR simulation.MethodsFirst of all, the RELAP5/Mod4.0 code was expanded by adding a 1-D delayed neutron precursor (DNP) transport model to the code, hence the DNP concentration was calculated by an algorithm using a second-order Godunov method. The DNP model was coupled with built-in point kinetics model and hydrodynamics model. Then the code was validated by experimental data of the molten salt reactor experiment (MSRE) at Oak Ridge National Laboratory (ORNL), USA. Four transient scenarios studied in the MSRE were reproduced, including pump startup, pump coast down, natural-convection circulation and reactivity perturbation transients.ResultsThe results show that the numerical results are in good agreement with the experimental results, and the model with second-order Godunov method can simulate the delayed neutron precursor transport well.ConclusionsThe modified RELAP5/Mod4.0 code is suitable for liquid-fueled MSR transient and safety analysis. It provides a better and more powerful tool for design and optimization of the liquid-fueled MSR.