© 2019 Elsevier B.V. A hybrid system combining nuclear energy from a high temperature gas reactor (HTGR) and renewable energy from solar and wind is investigated for its ability to compensate the characteristic effects of intermittent and perturbating performance of the renewable energy power generation to provide electric grid stability. The HTGR considered employs a direct cycle gas turbine for power generation while cogenerating heat for industrial use as such hydrogen production. The hybridization with renewable energy takes advantage of two intrinsic design features of the HTGR system, namely, the agile power maneuvering of the gas turbine and the existential massive capacity of heat in the reactor graphite core. The former, performed through a new proposal of using the inventory and bypass control devices already built in the gas turbine, is found to be effective and efficient to compensate for the intermittent power generation including hourly to daily variation of renewable energy. The reactor thermal power remains at constant full power while the heat output is increased or decreased subject to the need of reactor power generation. On the other hand, the massive heat capacity stored the HTGR graphite core is shown to be sufficient to compensate for the perturbating power generation of renewable energy on a time scale of seconds to minutes and up to about 20 percent of the rated power output of the nuclear plant. Similarly, no additional control devices, only a new proposal of using the existing devices, are required to perform this control operation. These findings demonstrate the technical and economic potential of the HTGR system to maintain the stability of a grid being incorporated with significant portfolios of renewable energy power generation.