High temperature options for nuclear generation of hydrogen on a commercial basis are several years in the future. Thermo-chemical water splitting has been proven to be technically feasible on a non-integrated, laboratory scale. High temperature electrolysis using the solid oxide fuel cell material set has also been proven to be feasible at a small scale. It is expected that these technologies will continue to be researched and those results will be available for integration into advanced concepts for production of hydrogen for commercial use by synthetic fuels, fuel cells, and military applications.
Thermo-chemical cycles produce hydrogen through a series of chemical reactions where the net result is the production of hydrogen and oxygen from water at much lower temperatures than direct thermal decomposition. Energy is supplied as heat in the temperature range necessary to drive the endothermic reactions, generally 750 to 1000°C or higher. All process chemicals in the system are fully recycled. Thermo-chemical cycles are considered promising options for hydrogen production because of the potential for high efficiencies and economic scaling to large capacities. Thermo-chemical cycles are generally considered to have potential for lower costs than conventional electrolysis of water, because the production of hydrogen by electrolysis requires conversion of heat to electricity prior to hydrogen production, whereas thermo-chemical cycles produce hydrogen directly from thermal and chemical energy. Chemical plant economics-of-scale (such as thermo-chemical processes) have historically been favorable compared to the more modular electrolysis processes. Finally, the status of thermo-chemical cycle technology is relatively immature, and there is significant potential for improvement with further research. The focus of thermo-chemical research will be on the demonstration of the key processes and systems interface technologies for the "baseline" sulfur iodine cycle.
High-Temperature Electrolysis (HTE)
High-temperature electrolytic water-splitting supported by nuclear process heat and electricity has the potential to produce H 2 with a system efficiency of the hydrocarbon and the thermo-chemical processes. This can be done without the corrosive conditions of thermo-chemical processes and without the fossil fuel consumption and greenhouse gas emissions associated with hydrocarbon processes. Specifically, a high-temperature advanced nuclear reactor coupled with a high-efficiency, high-temperature electrolyzer could achieve a thermal-to-hydrogen conversion efficiency of 45 to 55%.