An experiment was performed to study the dynamic control of a reactor by hydrogen transport and to demonstrate its load-following capabilities. The system is based on the mass transport of hydrogen between two ZrHX beds—one UO2 fueled, the other unfueled. The in-core hydrogen concentration controls the reactivity, and the resulting changes in reactor flux control the heat input into the in-core UO2-fueled bed. In turn, the in-core hydrogen concentration is controlled by changes in temperature differences between the in-core and out-of-core beds. Within analytical design constraints set by experimental and safety requirements, calculated ranges of parameters established design specifications. Preliminary validation measurements included reactor stability and temperature coefficient, experimental system stability and temperature coefficient, and in-core hydrogen worth. Comparison showed that hydrogen mass transport contributed 73% of the effectiveness of hydrogen reactivity control while temperature contributed only 27%. All experimental transient responses to step changes in thermal load exhibited analytically predicted damped oscillatory behavior. Reactor startup, shutdown, and response to reactivity changes were demonstrated. This experiment verified that hydrogen reactivity control, a mechanically passive device, is an effective, self-regulating mechanism for controlling a nuclear reactor.