Experimental investigations into the rocking response of graphite-block assemblies in a HTGR core under horizontal earthquake shaking

This paper presents earthquake simulator experiments of graphite block assemblies that are representative of the core of a horizontal compact high temperature gas reactor (HC-HTGR). The reactor core consists of vertically stacked prismatic graphite blocks, connected via shear keys. The columns of blocks are separated by finite gaps in both the transverse and longitudinal directions to accommodate fabrication and installation tolerances, and swelling of graphite. The dynamic response of the graphite core is governed by a combination of factors, including rigid body rocking of blocks, friction and clearances within shear keys, kinematic constraints, design and manufacturing tolerances, uplift and disengagement, and impacts between adjacent columns of blocks. Characterizing these effects involves: (a) understanding the rocking dynamics of standalone columns of blocks without considerations of impact, which is the focus of this paper, and (b) evaluating the impact dynamics between closely spaced columns. This paper presents results of and observations from a series of vibration and seismic experiments conducted at the University at Buffalo. The tests include quasi-static loading to evaluate rocking initiation and progression across various block interfaces, harmonic excitation to assess frequency-dependent rocking behavior of standalone columns of blocks, free vibration measurements to investigate oscillatory and damping characteristics across varying column geometries (e.g., stack height, rocking axis), and seismic simulations of individual columns and as well as 2D wall assemblies using representative ground motions. Rigid-body responses of the blocks were measured using a high-precision optical tracking system, generating data that provide valuable insights into their dynamic (and rocking) characteristics, and a robust technical basis to support the development and validation of numerical models.