Nuclear reactors are receiving renewed interest in the United States for generation of electric power to help meet future energy requirements. Modular helium reactors (MHRs), a type of high-temperature gas-cooled reactor (HTGR), have high potential for satisfying the need for new energy generation capacity. They can be used to drive Brayton-cycle energy-conversion systems to produce electricity at high efficiency and low cost. Moreover, they can be used for efficient, cost-effective production of hydrogen that would enable further development of a hydrogen energy economy.