In 2010, the world consumed roughly 5 x 1020 joules of energy and just under 90% of that energy was derived from hydrocarbon (HC) based fossil fuels (petroleum, coal, and natural gas) while only about 5% was nuclear based. [1] Despite growing concerns about global warming and no end in sight for our hydrocarbon based economy, few people are talking seriously about a nuclear based economy. However ridiculous it may sound, I will spend the remainder of this paper examining the consequences of a nuclear fueled world.
Currently the world exhausts about 30 billion tonnes of CO2 into the atmosphere each year. This number is consistent with an elementary calculation that converts the world's HC based energy demand to CO2 production based off an average fuel energy density and carbon content. If our energy all came from nuclear power, such CO2 emissions and all of the ramifications they carry (primarily global warming) would cease to exist. Of course, this benefit is certainly not without cost.
Even at the present modest rates of production, the world's nuclear fleet produces 10,000 metric tonnes of high level nuclear waste each year. [2] While this number is certainly dwarfed by the mass of annual CO2 emissions, disposal and proper storage of nuclear waste is a much more serious problem. The half life of the various components of nuclear waste ranges from thousands of years to millions of years. For example, the half life of fissile Uranium-235 and Plutonium-239 is approximately 700 million and 24 thousand years respectively. This is problematic namely because it poses a health hazard on a timescale that cannot be properly evaluated. Ultimately, this makes the proposition of "safe" storage difficult to sell to anyone.
Secondly, there is simply not enough harvestable fissile material to sustain the world's energy demand for more than a few tens of years without moving to breeder reactors. For example, Wilson estimates that there is roughly 50 years left of known recoverable uranium to power nuclear plants at several times the current demand. [3] However, given that powering the world with nuclear energy would require a 20 fold increase in nuclear fuel, even utilizing more abundant Thorium-232 would result in a fuel shortage within 20-30 years. As a result, it is overwhelmingly clear that if nuclear power is to become a dominant and sustainable mechanism for powering the world, breeder reactors are a necessity.
Breeder reactors are an attractive mechanism for improving the fuel economy of nuclear power plants and reducing the amount of high level nuclear waste produced. For example a fast neutron reactor can produce more Pu-239 than it burns U-235. As a result, one can obtain roughly 100 times more energy from the same amount of fuel. Such reactors can also utilize Thorium-232. In addition, at the end of the fuel cycle the majority of the nuclear waste is composed of species with half-lives less than 30 years which is a much more manageable time scale to safely store such hazardous materials. [3] Unfortunately, the benefits of breeder reactors are often overshadowed by omnipresent concerns about the possibility for the plutonium to be diverted or stolen for use in nuclear weapons.
While nuclear power has the potential to meet the world's energy demand without emitting significant amounts of greenhouse gases, many still believe it is currently not a viable source of alternative energy. Conventional nuclear reactors produce large quantities of long-lived hazardous waste for which a permanent storage solution remains elusive. In addition, known reserves of both uranium and thorium are not large enough to fuel the world's energy demand without the use of breeder reactors which produce an enormous volume of plutonium when fueled with uranium.
© Chris Goldenstein. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "BP Statistical Review of World Energy 2011," British Petroleum, June 2011.
[2] B. K. Sovacool, Contesting the Future of Nuclear Power: A Critical Global Assessment of Atomic Energy (World Scientific, 2011), p. 141.
[3] R. Wilson, "The Changing Need for a Breeder Reactor," Nuclear Energy 39, 99 (2000).