Sustainability by Combining Nuclear, Fossil, and Renewable Energy Sources Charles W. Forsberg

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Progress in Nuclear Energy xxx (2008) 1–9

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Progress in Nuclear Energy
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Sustainability by combining nuclear, fossil, and renewable energy sources Charles W. Forsberg*
Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Room 24-207a, 77 Massachusetts Avenue, Cambridge, MA 02139, United States

a b s t r a c t
Keywords: Sustainability Nuclear energy Liquid fuels Underground refining Peak electricity

The energy industries face two sustainability challenges: the need to avoid climate change and the need to replace traditional crude oil as the basis of our transport system. Radical changes in our energy system will be required to meet these challenges. These challenges may require tight coupling of different energy sources (nuclear, fossil, and renewable) to produce liquid fuels for transportation, match electricity production to electricity demand, and meet other energy needs. This implies a paradigm shift in which different energy sources are integrated together, rather than being considered separate entities that compete. Several examples of combined-energy systems are described. High-temperature nuclear heat may increase worldwide light crude oil resources by an order of magnitude while reducing greenhouse gas releases from the production of liquid fossil fuels. Nuclear–biomass liquid-fuels production systems could potentially meet world needs for liquid transport fuels. Nuclear–hydrogen peak power systems may enable renewable electricity sources to meet much of the world’s electric demand by providing electricity when the wind does not blow and the sun does not shine. Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction The two major energy challenges for the world are replacing crude oil and reducing greenhouse gas emissions. The world’s supply of light crude oil is limited and most of the remaining oil comes from politically unstable parts of the world. However, oil remains important. For example, in the United States oil provides 39% of the total energy demand. Two-thirds of that oil is used for transportation, the same fraction of oil that is imported. The other challenge is the increasing concentration of greenhouse gases in the atmosphere, particularly carbon dioxide. Carbon dioxide is the primary greenhouse gas that affects climate. After atmospheric carbon dioxide levels have increased, it takes millennia for these levels to return to normal. Equally important, carbon dioxide levels strongly impact the characteristics of the biosphere and geochemistry because atmospheric carbon dioxide concentrations control the planet’s average pH (acid–base concentrations). The world has three major energy sources: fossil fuels, renewables, and nuclear. Historically, these energy sources have been treated as competing energy resources for which economics and environmental constraints determine which energy source is used. Traditional strategies to address oil shortages or concerns about climate change assume that one energy source replaces another. However, the assumption that these are primarily competing

energy sources may be fundamentally incorrect. New constraints and new technologies suggest that in many cases these energy sources must be tightly coupled to meet society’s requirements. This paper examines this hypothesis with four examples. Two of the examples represent alternatives to replace the traditional production and refining of crude oil into liquid transport fuels; the other two exemplify possible future nuclear–renewable electrical systems.

2. Liquid-fuels production Major changes are occurring in liquid-fuels (gasoline, diesel, and jet fuel) production. Because of limited supplies of high-quality crude oil, heavier feedstocks (heavy oil, tar sands, shale oil, and coal) are being increasingly used to produce liquid fuels. However, the production of...
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