Nuclear Energy Options for Hydrogen and Hydrogen-Based Liquid Fuels Production

Abstract

Nuclear energy can be used for hydrogen production through thermochemical or electrochemical processes for splitting water (and/or steam) into its elemental parts. The overall performance of alternative routes for using nuclear energy to supply the needed heat or electricity depends on the operating temperature, efficiency of the processes involved, complexity of the systems used and capital costs of the nuclear and hydrogen technologies. In this work, we assess the economics of possible technologies to produce hydrogen using nuclear energy. The purpose of this assessment is to identify the most attractive options for further research and development and eventual application to nuclear hydrogen production. Both thermochemical processes and electrolysis require high temperatures for good efficiency. Thus, hydrogen production is best accomplished using advanced reactors that are capable of reaching much higher temperatures than today's LWRs. At temperatures above 700 [degrees]C, the options range from using steam methane reforming in the short term to the much more involved chemical cycles or steam electrolysis in the long term. The helium cooled graphite moderated reactors operating at temperatures above 850 [degrees]C have often been proposed for such purposes. However, we find the high temperature steam electrolysis process coupled to a supercritical CO[subscript 2] gas turbine cycle, possibly in a direct cycle Supercritical Advanced Gas Reactor, as more promising than other technology options. At 650 to 750[degrees]C of reactor outlet/turbine inlet/process temperatures, this technology can achieve 52 to 56% overall efficiency in converting nuclear thermal energy into energy content of hydrogen, respectively. In this work, we also evaluate the technical and economical viability of liquid fuel synthesis using nuclear hydrogen. The liquid fuel can be used in the existing mature infrastructure for transportation and combustion of liquid fuels before large scale hydrogen infrastructure becomes widely established. We propose that CO2 captured from coal plant emissions and nuclear hydrogen be the feedstock to the synthesis process. The cost of this approach would be independent of the natural gas feedstock and may prove market competitive in the near future. Considering the production cost of hydrogen, the thermochemical Sulfur-Iodide cycle coupled to the helium cooled Modular High temperature Reactor (MHR) is found to be also attractive at temperatures above 850 [degrees]C, based on the plant cost and the process efficiency estimates by the designer company. In our work, the cost of production is estimated to fall between $1.13 and 2.37/kg-H2. This range reflects the uncertainties about the operating conditions and cost of the technology in the future.