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| Fig. 1: Sodium fast reactor. (Source: Wikimedia Commons) |
Given the world's rising concerns about carbon emissions and fossil fuels, alternative sources of energy come under greater consideration and scrutiny. Nuclear energy is a low-carbon alternative to coal and natural gas; however, the use of nuclear power is not without its concerns. Fissile material is a finite resource, as only so much uranium exists in the Earth's crust. Notably, an alternative nuclear plant design, the so-called fast breeder reactor (FBR), as seen in Fig. 1, is emerging as a way to solve this problems.
Conventional nuclear reactors smash neutrons into uranium fuel rods, causing the atoms to split, releasing more neutrons and more energy. This chain reaction produces massive amounts of heat that is harvested via a coolant fluid, running a turbine. This is seriously inefficient as a mere fraction of the potential energy in uranium is turned into electricity, with the rest remaining in the form of plutonium and ejected as waste, yet still containing a significant amount of energy [1]
Fast breeder reactors resolve this issue. These machines allow repeated recycling of the spent fuel though the reactor, harvesting a greater fraction of energy. [2] In a conventional reactor, the speed of neutrons is slowed down to ensure that the chain reaction is sustainable, removing valuable kinetic energy. [3] Yet FBRs achieve a vastly higher level of energy. The best output of a reactor results from bombarding the fuel much faster. This higher energy level is achieved with concentrated liquid metals (such as sodium) as opposed to water. [2] With this intense reaction, almost all of the fissile potential of inactive U-238 atoms are able to be released as energy instead of being discarded. [3]
Fast breeder reactors offer solutions to several concerns regarding nuclear energy. Principally, FBRs address resource depletion. After an initial load of uranium, the design of the reactor keeps the neutron economy high enough to breed more fissile material, meaning that the fuel can be self-sustaining. [3]
Some may argue that FBRs address the issue of nuclear disposal in addition to resource depletion. It is true that already spent fuel rods may be reused for FBRs, and this is an attractive aspect as the United States has over 54,000 tons of nuclear fuel stored across the country. [4] However, over long timescales, the total amount of dangerous waste is proportional to the energy produced, so FBRs will have a minimal impact on this situation.
It should also be noted that fast breeding reactors are much more dangerous than conventional light water reactors. Light water design allows the core to shut down in the event of a coolant loss, but fast breeding reactors forgo this and adopt the use liquid metals in place of water, preventing moderation.
Since the 1950s, nine countries have developed FBRs, including the U.K, China, Russia, India, Japan, and the United States. [3] The U.S. has constructed two experimental fast breeder reactors: the Enrico Fermi Nuclear Generating Station that was shut down in 1972 due to licensing problems and the Clinch River Plant in Tennessee shut down in 1983. [1] It should be noted that the Clinch River Plant may have been influenced by the political field of nuclear technology, as the Three Mile Island accident had occurred around four years earlier.
One of the major barriers preventing the implementation of this technology is cost. It is hugely expensive to maintain a breeder reactor program as the price of these plants equates to roughly 25% more than a light water reactor. Therefore, many OECD countries have abandoned their programs after spending a collective $50 billion. [3] For example, the French Superphenix reactor simply couldn't compete economically with light water technology. It was shut down in 2009 due to the hemorrhaging costs of sodium leaks, fires, and reactivity incidents. [5] It was the last fast breeder reactor in Europe for electricity generation. Japan is now one of the only countries remaining with a strong outlook on their breeder reactor research, due to their fuel reprocessing program. [3]
Fast breeder reactors solve many problems associated with nuclear energy. The expense previously associated with FBRs unfortunately inhibited the full adoption of this technology, especially in the U.S. as support has dropped off post the Obama administration. [1] However, the planet's vocal demand for low-carbon alternatives provides an opportunity to revisit FBRs. Cost may potentially decrease in step with developing technological advancements, allowing FBR programs to regain momentum. This would be a worthwhile scientific and economic endeavor as FBRs provide a much-needed solution to the world's thirst for energy.
© Will Hooks. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. 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] T. B. Cochran, H. A. Feiveson, and F. von Hippel, "Fast Reactor Development in the United States," Sci. Global Secur. 17, 109 (2009).
[2] F. Pearce, "Are Fast-Breeder Reactors the Answer to Our Nuclear Waste Nightmare?," The Guardian, 30 Jul 12.
[3] T. B. Chchran et al., "Fast Breeder Reactor Programs: History and Status," International Panel on Fissile Materials, February 2010.
[4] J. Ahearne et al., "Consolidated Interim Storage of Commercial Spent Nuclear Fuel: A Technical and Programmatic Assessment," American Physics Society. February 2007.
[5] M. Schneider, "Fast Breeder Reactors in France," Sci. Global Secur. 17, 36 (2009).
