MIT conducted a study, An Alternative to Gasoline: Synthetic Fuels from Nuclear Hydrogen and Captured CO2, to determine the extent to which nuclear power can contribute to a transition in the transportation sector.
The study concluded 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.
Combining hydrogen with carbon dioxide captured from fossil fired plants to produce liquid fuel, either ethanol or methanol, is a way of producing fuels that could be used with little modification in the production of vehicles, requires few changes in the infrastructure for distributing fuels and is complementary to the production of ethanol from biosources.
A total cycle analysis revealed that the total reduction in CO2 emissions will be slightly more than 12% for either ethanol use or methanol use. A second benefit would be to decrease a nation’s dependence on imported petroleum.
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.
After reviewing the available technologies the study chose High Temperature Steam Electrolysis option for making hydrogen and the High-Temperature Gas Cooled Reactor (HTGR), which uses Helium coolant or a modified version of the Advanced Gas Reactor (AGR) using supercritical CO2 as the coolant (S-AGR) as the nuclear technologies of choice.
Based on the reference year 2025 case, they found that the United States will 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 43.1% of the CO2 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 CO2 will need to be captured to produce the needed MeOH. For production of EtOH, they 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 CO2 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 CO2 that need to be captured shows that a benefit of this process would be to significantly decrease the total greenhouse gas emissions.