Numerical Simulations of Rocking, Keyed Graphite Blocks in the Core of a High-Temperature Gas Reactor

This paper presents the numerical modeling and dynamic analysis of graphite block assemblies designed for the core of a horizontal compact high-temperature gas reactor (HC-HTGR). The reactor core is composed of prismatic graphite blocks stacked in columns using shear keys. Under earthquake shaking, the dynamic response of a column of blocks is influenced by multiple factors, including rigid-body rocking of the blocks, graphite-to-graphite friction, horizontal and vertical clearances around the shear keys, energy dissipation at contact points, kinematic constraints, and block uplift and disengagement. These effects were characterized through vibration and seismic tests conducted on standalone columns of keyed graphite blocks at the University at Buffalo. The resulting data provided critical insights into their rocking behavior, supporting the development and validation of numerical models for the seismic analysis of these graphite assemblies, as described in this paper. These models are developed using the commercial finite element software package LS-DYNA, with damping and contact parameters calibrated using the test data. The utility of the models is evaluated under a range of harmonic and earthquake inputs. The peak column displacements and block rotations are predicted to within $\pm$20% of the experimental measurements, with close agreement in transient response histories across columns of varying heights and shaking directions. Parametric studies are conducted to examine the sensitivity of columns’ dynamic response to factors that are challenging to assess experimentally, such as variations in the graphite-to-graphite coefficient of friction, machining tolerances, block alignment, and installation imperfections. The outcomes presented herein directly support the design of the HC-HTGR core and offer valuable insights for reactor developers more broadly.