Upgrading of Waste Heat for Combined Power and Hydrogen Production With Nuclear Reactors

Abstract

This paper presents a new heat upgrading method that utilizes waste heat from nuclear reactors for thermochemical water splitting with a copper-chlorine (Cu–Cl) cycle. Through combined power, hydrogen, and oxygen generation, the exergy efficiency of a power plant can be significantly augmented. The heat rejected to the environment for moderator cooling, a relatively small amount of low pressure superheated steam and a small fraction of generated power, are extracted from the nuclear reactor and used to drive a Cu–Cl hydrogen plant. More specifically, the moderator heat transfer at ∼80°C is used as a source to a newly proposed vapor compression heat pump with a cascaded cycle, operating with retrograde fluids of cyclohexane (bottoming cycle) and biphenyl (topping supercritical cycle). Additionally, the heat pump uses as input the heat recovered from within the Cu–Cl cycle itself. This heat is recovered at two levels: ∼80–130°C and ∼250–485°C. This heat input is upgraded up to 600°C by work-to-heat conversion and then used to supply the endothermic water splitting process. The extracted steam is fed into the Cu–Cl cycle and split into hydrogen and oxygen as overall products. Electricity is partly used for an electrochemical process within the Cu–Cl cycle, and also partly for the heat pump compressors. This paper analyses the performance of the proposed heat pump and reports the exergy efficiency of the overall system. The proposed system is about 4% more efficient than generating electricity alone from the nuclear reactor.