Dynamic characteristics identification of two graphite bricks in molten salt reactor considering fluid-structure interaction

Graphite core plays a very important role in thorium molten salt reactor (TMSR) served as a reflector, a moderator as well as a structural material. The whole graphite core is submerged in molten salt during operation and consists of a large number of graphite bricks interconnected with keys and dowels. The molten salt as a fluid will affect the dynamic behavior of the graphite core. This phenomenon is called fluid-structure interaction (FSI). In order to maintain the integrity of the graphite core under a seismic event, it is essential to predict dynamic characteristics of the graphite bricks affected by FSI. In this paper a 1/4 scaled-down test model derived from similarity analysis will be presented. The nonlinear response of the graphite brick under the excitation of the sinusoidal harmonic is regarded as a single degree of freedom system. The dynamic characteristics of added mass and added damping can be obtained by fitting the time history of models' displacement subjected to simple harmonic motion. The experimental results shown that the added mass and the added damping are strongly dependent on the gap size between two bricks. Furthermore, a three-dimensional finite element model has been derived for the dynamic analysis of two graphite bricks with molten salt and the modelling parameters are obtained from the experiment. We found that the results from the numerical method are in good agreement with the experiment.