An Alternative to Gasoline: Synthetic Fuels from Nuclear Hydrogen and Captured CO[subscript 2]

Abstract

The motivation for this study stems from two concerns. The first is that carbon dioxide from fossil fuel combustion is the largest single human contribution to global warming. The use of nuclear power to produce hydrogen on a global scale for any of various possible end uses would reduce the net amount of carbon dioxide emitted into the atmosphere. The second concern is in regard to U.S. dependence on foreign oil. Over 58% of petroleum used by the US in 2002 was imported and most likely a higher fraction is being imported today. With the majority of this oil originating in highly volatile Middle Eastern countries, there is a potential threat to stability in the US energy market. This study was conducted to determine the extent to which nuclear power can contribute to a transition in the transportation sector; away from an infrastructure that places the US at risk for depending largely on foreign oil and that makes it inevitable that large quantities of carbon dioxide will be emitted into the atmosphere. Several scenarios are reviewed in this study for using nuclear hydrogen in transportation, including: • Combining hydrogen with carbon dioxide captured from fossil fired plants to produce liquid fuel • Using nuclear power to aid in the recovery of oil from tar sands or shale oil Initially, a review of the literature pertaining to the potential contribution of nuclear power to hydrogen production is performed. Two approaches for producing hydrogen from water are found that have significant literature related to the subject. These cycles are High Temperature Steam Electrolysis and the Sulfur Iodine Cycle. The UT-3 cycle is also promising but does not seem to offer the same advantages with respect to energy efficiency. This work focuses on the High Temperature Steam Electrolysis option. A review of possible nuclear reactor concepts is also performed. Many advanced concepts have been proposed, a large number of which show potential in producing hydrogen. However, there are drawbacks to many of them for several reasons. The high temperatures needed eliminate some reactors while lack of operational experience eliminates others. Ultimately, the two concepts that are proposed for hydrogen production in the literature found are the High-Temperature Gas Cooled Reactor (HTGR), which uses Helium coolant, and a modified version of the Advanced Gas Reactor (AGR) using supercritical CO[subscript 2] as the coolant (S-AGR). The reactor concepts that are chosen for aiding production of oil from tar sands are the Advanced Candu Reactor (ACR-700), the Pebble Bed Modular Reactor (PBMR), and the Advanced Passive pressurized water reactor(AP600). A detailed study of how nuclear power can contribute to production of shale oil has not been performed. Therefore, the section dealing with this particular possibility is much less in depth and more speculative. However, some preliminary calculations are performed and presented in this report. Based on the reference year 2025 case, we find that the United States will need about 6.60 billion barrels of ethanol (EtOH) or 8.77 billion barrels of methanol (MeOH) in order to replace the conventional gasoline (CG) that will otherwise be used. About 39.4% of the CO[subscript 2] that is projected to be emitted from coal plants will need to be captured to produce this much EtOH and about 41.1% of the CO[subscript 2] will need to be captured to produce the needed MeOH. For production of EtOH, we estimate that there will need to be between 700 and 900 GWth of nuclear power to produce the needed hydrogen and energy to create this amount of EtOH. By the same token, it will take between 1000 and 1400 GWth of nuclear power to aid in production of the needed MeOH. In the same year – 2025 – the entire world will require 16.87 billion barrels of EtOH or 22.49 billion barrels of MeOH to replace the CG that will otherwise be used. This would require capture of 29.5% of total emitted CO[subscript 2] for production of EtOH or 28.4% for production of MeOH. This amount of hydrogen and the associated energy requirements will demand between 1800 and 2300 GWth to produce the needed EtOH or between 2550 and 3500 GWth to produce the needed MeOH. These numbers show that there is a very wide market for using nuclear power to aid in the production of alternative fuels to aid in the transition to the hydrogen economy. The large fraction of emitted CO[subscript 2] that need to be captured shows that a benefit of this process would be to significantly decrease the total greenhouse gas emissions. A total cycle analysis reveals that the total reduction in CO[subscript 2] emissions in the U.S. will be slightly more than 20% for either ethanol use or methanol use. A second benefit would be to decrease a nation’s dependence on imported petroleum. In conclusion, it is found that the concept of alternative liquid fuels produced from nuclear hydrogen and captured carbon dioxide is viable. There is abundant CO2 for use and the hydrogen can be produced with proven technology. There is also evidence that nuclear power can be utilized in the production of oil from sand and shale.