An analytical study to assess the influence of control rods on the seismic response of the core of large High Temperature Gas Cooled Reactors (HTGR) is reported. The study is part of an extensive experimental and analytical program concerned with demonstrating the safety and functionability of the control rods and reserve shutdown systems during and after seismic events. This program which is being conducted by General Atomic Company (GAC) under the sponsorship of the Energy Research and Development Administration (ERDA), includes seismic testing of a one-fifth scale full array model of the core including both the control rods and the reserve shutdown systems.