Control rod drop dynamic analysis in the TMSR – SF1 based on numerical simulation and experiment

•The rod drop dynamic of the TMSR – SF1 is investigated by experimental and theoretic analysis.•The efficiency of the driving mechanism is deduced as a relationship with the rod dropping velocity.•The calculated rod drop time is satisfied with the limiting fast drop time of the TMSR – SF1.•A hydraulic buffer is designed to alleviate the dropping shock in the scram. The scram function renders the core subcritical in response to plant upsets, which is realized by fast drop of the control rods. In the solid fuel (SF) thorium molten salt reactor system (TMSR), denoted as the TMSR – SF1 project, the drop time of the rod is obviously affected by the driving mechanical drag and the hydraulic resistance of the liquid environment. An inner-house code is developed to analyze the rod drop in the TMSR – SF1. In the code, the total transmission efficiency of the driving mechanism is deduced as a relationship with dropping velocity of the rod. With the experimental and theoretic analysis, the motion process of the rod drop is simulated in this study. And it turns out that the drop time in the molten salt is satisfied with the limiting drop time in the TMSR – SF1. In addition, a hydraulic buffer is designed to alleviate the dropping shock from the scram and the calculation results are presented in the paper as well.