Hydrogen Production Using Nuclear Energy

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 depends on the operating temperature, energy efficiency of the processes involved, complexity of the systems used and capital costs of the nuclear and hydrogen technologies. In this work, the focus is on the economics of possible technologies to produce hydrogen using nuclear energy. The goal 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°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°C have often been proposed for such purposes. However, we find the high temperature steam electrolysis process coupled to a supercritical CO₂ gas turbine cycle, possibly in a direct cycle Supercritical Advanced Gas Reactor, very promising. At 650 to 750°C of reactor outlet/turbine inlet/process temperatures, this technology can achieve 52-56% overall efficiency in converting nuclear thermal energy into energy content of hydrogen, respectively.

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°C, based on the plant cost and the process efficiency estimates (above 45%) by the designer company GA. In our work, the cost of production is estimated to fall between $1.13 and $2.37/kg-H₂. This range is somewhat higher than the GA estimates and reflects the uncertainties about the operating conditions and cost of the technology in the future. However, if the natural gas prices are above $5/MBTU, the nuclear methods could become economically viable.

Future work will establish a thermohydraulic model for the electrolysis process to gain insights about the effects of pressure and temperature on the overall process efficiency.

Investigators : Dr. B. Yildiz, Profs. M. S. Kazimi, M. J. Driscoll and J. Tester.

Transition from Prescriptive to Risk-Informed Regulations in U.S.

Continuing its past work for the Tokyo Electric Power Company, Professors Kadak and Hansen are in the final stages of completing a Phase II of the study of US nuclear plants and their regulation. This Phase II study was aimed at understanding how the transition to a more risk informed regulatory process occurred in the US. Many key people from utilities, regulators and past and current Chairmen of the Nuclear Regulatory Commission were conducted to understand the process of transition and what lessons could be learned from this process. As Japan begins to look more favorably on risk information as a part of the regulatory process, this study should be quite timely in their deliberations.