Abstract: The present invention includes a nuclear fission reactor apparatus comprising a core open to an atmosphere containing a hydrogen or a hydrogen isotope material, said core consisting essentially of a powdered fissile metal hydride material that remains entirely within said core; a plurality of trays outside said core that store a non-fissile material thereon wherein said non-fissile material absorbs and desorbs said hydrogen isotope material based on said core's temperature; a means for heating and cooling said plurality of trays; and a means for extracting energy produced in said core.