Hydrogen has captured the imagination of the technical community recently, with visions of improved energy security, reduced global warming, improved energy efficiency and reduced air pollution as potential benefits. A significant "Hydrogen Economy" is predicted that will reduce dependence on petroleum imports, and reduce pollution and greenhouse gas emissions. Such a hydrogen economy will need significant new sources of hydrogen. Virtually all our current hydrogen is produced from natural gas and is equivalent to 48 GW(t). Replacing this growing demand with a non-fossil, non-greenhouse gas emitting source represents a huge potential market for fusion.
Hydrogen could potentially be produced from water using fusion energy by direct interaction of fusion products (charged particles, neutrons and gammas), and by electrolytic or thermochemical means. Significant effort was devoted to study of these possibilities in the 1970-80s. It is instructive to review these earlier studies today as interest in production of hydrogen is revived. Investigations into direct use of fusion products for radiolysis and "hot spot" chemistry found it was difficult to get much of the fusion energy into the reaction channels of interest. Use of fusion energy in heat-driven processes was more promising. Fusion blankets could give much higher temperatures than are possible from fission heat sources. Studies of high temperature electrolysis and thermochemical water splitting using this high temperature heat were promising. The requirement that fusion blankets breed tritium raises challenges, as the tolerance for tritium in the product hydrogen is extraordinarily low. Use of multiple coolant streams, multiple containment barriers and separate breeding and high temperature zones were proposed that appear to successfully address these concerns, but add complication. Fusion does have the potential to support the Hydrogen Economy as well as electricity production as long as care is given to maximizing the benefits and minimizing the liabilities inherent to fusion energy.
