The majority of hydrogen comes from natural gas, produced in a process called Steam Methane Reforming. Even though this process is relatively cheap, it has the downside of producing significant amounts of the greenhouse gas carbon dioxide. Alternatively, hydrogen can be made by splitting water, a process that requires electricity for electrolysis and therefore another energy source, as well as large supplies of water. There is an ongoing desire for low-carbon electricity, clean hydrogen for industry (e.g. steel manufacturing, fertiliser manufacturing and heavy transport), and greater freshwater supplies, particularly in water-stressed regions.

In this work, the researchers investigate how a small nuclear reactor can be used to produce all three: hydrogen, clean electricity, and freshwater through seawater desalination. A small modular reactor produces 200 MW of thermal power. The heat creates steam that drives turbines and generates electricity. Part of the steam is diverted to a process called High-Temperature Steam Electrolysis, which splits water into hydrogen and oxygen. Because the steam is already hot, less electricity is needed than in conventional electrolysis. After the hydrogen production process, the steam is cooler but still contains useful heat, which is then used in a desalination plant to convert seawater into freshwater.

The integrated system was able to simultaneously produce around 90 MW of electricity, 0.6 kg/s of hydrogen (~52 tonnes/day), and 612 m³/day of freshwater from a single reactor module. By reusing waste heat from hydrogen production to drive desalination, the overall energy utilisation increased from 48% for electricity generation alone to 53% in the full tri-generation system.

The researchers evaluated two operating modes: a self-sufficient option, where desalinated water is used internally for hydrogen production, and a market-led option, where freshwater is sold externally. The market-led scenario achieved lower hydrogen production costs ($2.93-3.19/kg compared with $3.49-3.88/kg for the self-sufficient scenario) due to the additional revenue from water sales.

Overall, the study demonstrates that a small modular nuclear reactor could be used to produce clean electricity, hydrogen, and freshwater, offering an efficient and potentially attractive solution for water scarce regions seeking low carbon energy and industrial hydrogen supplies.

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Energy storage in long-term system models: a review of considerations, best practices, and research needs by John Bistline et al. (2020)