1 Exergy analysis of a system using a chemical heat pump to link a supercritical water-cooled nuclear reactor and a thermochemical water splitting cycle Mikhail Granovskii, Ibrahim Dincer* , Marc A. Rosen and Igor Pioro 1 Faculty of Engineering and Applied Science, University of Ontario Institute of Technology 1 School of Energy Systems and Nuclear Science, University of Ontario Institute of Technology 2000 Simcoe Street North, Oshawa, Ontario, Canada, L1H 7K4 E-mails: mikhail.granovskiy@uoit.ca; ibrahim.dincer@uoit.ca; marc.rosen@uoit.ca; igor.pioro@uoit.ca * Corresponding Author Abstract Increases in the power generation efficiency of nuclear plants are mainly limited by the permissible temperatures in nuclear reactors and the corresponding temperatures and pressures of the coolants. Coolant parameters are limited by the corrosion rates of materials and nuclear- reactor safety constraints. The advanced construction materials for the next generation of CANDU reactors, which employ supercritical water/steam as a coolant and heat carrier, permit improved operating parameters (outlet temperatures up to 625 o C and pressures of about 25 MPa). An increase in the temperature of supercritical water allows it to be utilized in thermochemical water decomposition cycles to produce hydrogen. These methods are considered by many to be among the most efficient ways to produce hydrogen from water and to have advantages over traditional low-temperature water electrolysis. However, even lower temperature water splitting cycles (Cu-Cl, UT-3, etc.) require a heat supply at temperatures higher than 550-600°C. A sufficient increase in the outlet water/steam temperature from the nuclear reactor for a thermochemical water splitting cycle, without jeopardizing nuclear reactor safety, might be effectively achieved with a heat pump, which increases the temperature of the steam. A high-temperature chemical heat pump, which employs the reversible catalytic methane conversion reaction is proposed. The reaction shift from exothermic to endothermic and back is achieved by changing the steam concentration in the reaction mixture. This heat pump, coupled with the second steam cycle of a supercritical water (SCW) nuclear power plant on one side and a thermochemical water splitting cycle on the other, increases the temperature of the “nuclear” superheated steam and, consequently, the quality of heat transfer into the water splitting cycle. A comparative preliminary thermodynamic analysis is conducted of the combined system comprising a SCW nuclear power plant and a chemical heat pump, which provides high- temperature heat to a thermochemical water splitting cycle for hydrogen production. It is concluded that the proposed chemical heat pump permits the utilization efficiency of nuclear energy to be improved by at least by 2% without jeopardizing nuclear reactor safety. The influence of the steam/methane ratio in the heat pump working medium on the efficiency of the pump is investigated. Based on this analysis, further research appears to be merited on the proposed design of a nuclear power generation plant combined with a chemical heat pump, and implementation in appropriate applications seems worthwhile. Keywords: Nuclear energy, supercritical water, exergy, chemical heat pump, hydrogen, thermodynamics.