This paper describes a seismic test on a one-fifth scale HTGR graphite core model. The test program included: (a) a horizontal uniaxial excitation in two orthogonal directions at accelerations up to approximately 1.5 g; (b) sinusoidal, time history (El Centro, Taft, synthesized), excitations imposed on the model; (c) damping and resonance tests; and (d) variation in lateral restraint structure, soft and hard springs. The test program also included pendulum collision test of one-fifth scale and full-scale blocks, two-dimensional array tests, and instrumentation development in support of the final test. The purpose of the test was to: (a) study collision dynamics between graphite blocks; (b) employ data to aid in verifying model scaling laws; (c) investigate model dynamic behavior and response characteristics; (d) provide specific data on block relative displacement, acceleration and strain; and measure boundary support forces; (e) provide data for correlation with analytical models; and (f) provide preliminary design data.