The present invention provides a reactor, which includes: a unitary shell assembly having an inlet and an outlet; a flow path extending within the shell assembly from the inlet to the outlet, the flow path having a steam reformer section with a first catalyst and a water gas shift reactor section with a second catalyst, the steam reformer section being located upstream of the water gas shift reactor section; a heating section within the shell assembly and configured to heat the steam reformer section; and a cooling section within the shell assembly and configured to cool the water gas shift reactor section. The present invention also provides a simplified hydrogen production system, which includes the catalytic steam reforming and subsequent high temperature water gas shift of low-sulfur (<100 ppm by mass) hydrocarbon fuels followed by hydrogen purification through the pressure swing adsorption (PSA). The integrated reactor offers significant advantages such as lower heat loss, lower parts count, lower thermal mass, and greater safety than the many separate components employed in conventional and is especially well-suited to applications where less than 15,000 standard cubic feet per hour of hydrogen are required. The improved system also may be started, operated and shut down more simply and quickly than what is currently possible in conventional systems. The improved system preferably employs active temperature control for added safety of operation. The hydrogen product is of high purity, and the system may be optionally operated with a feedback control loop for added purity.