The HTR-PM (High Temperature Reactor Pebble bed Module) reactor core consists of assemblies that include graphite bricks, carbon bricks and keys/dowels. The double-layer structure, which is composed of two layers of bricks connected by keys and dowels, is the basic load-bearing unit of the graphite internals. A series of seismic experiments have been carried out to study the dynamic characteristic of this multi-body structure. As a part of them, the present study aimed to evaluate the nonlinear dynamic response of a full-size graphite/carbon unit and investigate the integrity of this assembly.

Dynamic excitations were applied at the bottom of the double-layer structure. The experimental random-motion excitation ranged from 0.2g to 0.75g. The sine-sweep excitation frequency band ranged from 5–100Hz, sweep rate was 1oct/min, with acceleration magnitudes of 0.3g and 0.5g. The sine beat wave excitation frequencies were 5Hz, 10Hz, 20Hz and 40Hz with acceleration of 0.5g. Response data of acceleration and displacement at certain points on bricks were measured. PSD curves and displacement time-histories were acquired. Results indicated that the fundamental frequency of the assembly is 42∼49Hz and the damping rate is 4.9%. The dynamic response of the assembly exhibited as an integrated component only when the excitation is lower than 0.35g.

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