Hydrogen production using high temperature nuclear reactors: Efficiency analysis of a combined cycle

• Nuclear power plants may reach an efficiency of around 50%.
• The CCGT cycle presented has potential to improve the efficiency.
• Modern plants co-produce electrical energy, fuel and process heat.

The high temperature nuclear reactor provides a new way to produce hydrogen with high efficiency. In the present work, the feasibility of using a VHTR for both electricity generation and hydrogen production is analyzed. The nuclear reactor is combined with a gas turbine, a steam turbine and a system for the delivery heat for high-, medium- and low-temperature processes. Industrial-scale hydrogen production via thermochemical water decomposition is considered, using high- and medium-temperature processes. Specifically, sulphur-iodine (SI) and copper-chlorine (CuCl) thermochemical cycles are examined. These water splitting cycles permit the conversion of water into hydrogen and oxygen at much lower temperatures than the direct thermal decomposition of water. Both cycles are considered promising routes for continuous, efficient, large-scale and environmentally benign hydrogen production without CO2 emissions. The results show that the combination of a high temperature helium reactor, with a combined cycle for electric power generation and hydrogen production, may reach an efficiency of around 50%. The power plant cycle analyzed in the present paper is complex and it is difficult to determine conditions under which all target objectives are fulfilled: high thermodynamic efficiency for combined production of electricity and high-temperature heat which can be used to produce hydrogen.