Conceptual design of nuclear systems for hydrogen production

Abstract

Demand for hydrogen in the transportation energy sector is expected to keep growing in the coming decades; in the short term for refining heavy oils and in the long term for powering fuel cells. However, hydrogen cannot be harvested from natural sources like other fuels, it must be industrially produced. In the United States, the vast majority of hydrogen is produced today by reforming methane, a carbon-based fuel. Due to environmental and fuel source concerns, non-carbon alternatives for producing hydrogen from water are being explored using different combinations of thermal, chemical, and electrical energy. This work explores some of the non-carbon alternatives, specifically using a nuclear reactor for providing heat and electricity for high temperature steam electrolysis and a hybrid electrolysis-chemical sulfur cycle. Also addressed is the sensitivity of production and efficiency of these cycles to process conditions. For a desired hydrogen distribution pressure of 3MPa, high system pressures increase the efficiency of high temperature steam electrolysis because of the decreased post-cycle compression energy requirements. High system pressures for the hybrid sulfur cycle, however, decrease the equilibrium thermal acid decomposition necessary to the process. High temperature steam electrolysis may also be used to provide variable hydrogen production when coupled with an electricity generation system. Increased hydrogen production decreases the efficiency of the electricity production, because of the high enthalpy removed from the reactor system. Both approaches are also analyzed for their sensitivity to incomplete reactions within the process loop.