The concept of the traveling wave reactor (TWR) was first proposed in 1958 at a International Atomic Energy meeting.  The concept essentially involved the idea that a reactor could be designed to create and consume (i.e. "breed-and-burn) its own fuel, given raw material. This "breed-and-burn" reactor concept caught the attention of Dr. Edward Teller; however, the concept remained largely ignored by the rest of the scientific community until recent years. 
In the past few years, TWR technology has gained the interest of not only the scientific community, but also the private sector. Leading the forefront of TWR research and development is Dr. Lowell Wood and his collaborators at Terrapower, a privately funded research company based in the U.S.  While currently TWRs exist only virtually, in Terrapower software, the concept is far enough along in development where a test version of the reactor could be built; Terrapower is in the process of seeking a customer and a host country for such a purpose. 
Unlike conventional reactors which use uranium-235 for fuel, TWRs largely rely on uranium-238, a byproduct of conventional nuclear reactors, for fuel (roughly 90 percent of fuel requirements) and only marginally rely on enriched uranium. [1,3] To utilize uranium-238, TWRs initially require a fission reaction involving the enriched uranium. This reaction then sets off a chain reaction which breeds fissible fuel, plutonium-239, from the remaining uranium-238. [1,3] The plutonium-239 subsequently undergoes fission; this provides energy output and the "breed-and-burn" cycle propagates through the life of the reactor. [1,3] Given certain assumptions about size and amount of fuel in a reactor, some scientists believe that TWRs may be able sustain energy production for decades without requiring refueling. 
With respect to physical parameters, the core of TerraPower's design is a cylinder, 10 feet wide and 13 feet long.  Regarding power production capacity, an individual TWR unit is expected provide about 500 MWe; this is in comparison to the 1,000 MWe plus designs of modern light-water reactors. 
TWR technology has several economic, environmental, and political advantages when compared to other nuclear reactor technologies. These advantages generally relate to the fueling characteristics of TWRs; as noted above, TWRs meet the majority of their fueling requirements with waste uranium and only marginally require enriched uranium.  Additionally, TWRs may be able to run for decades without refueling and fuel removal.  Because of these characteristics, TWRs in theory would incur lower fueling costs than conventional reactors. In addition to these economic advantages, the fueling characteristics of TWRs provide benefits related to environmental preservation and national security as well. TWRs can, to a significant extent, "recycle" waste uranium byproducts derived from the operation of conventional nuclear reactors; if TWRs were widely deployed and substituted for new light-water reactor constructions, there would be a reduced need for uranium mining, uranium enrichment, spent nuclear fuel reprocessing, and nuclear waste disposal. In theory, a reduced need for these processes would translate to reduction of society's impact on the environment, holding all other assumptions constant. Moreover, because uranium enrichment and spent fuel reprocessing are two significant sources of nuclear proliferation risk, a reduced need for these services and associated facilities would translate to a reduction in nuclear proliferation risk. 
Because no TWR facilities have yet been built, the actual economics of these reactors have yet to be realized. Additionally, the U.S. does not yet have a certification process for TWRs; as such, it may be a decade or more before a TWR test reactor could be built in the U.S.  With respect to safety concerns, like other breeder reactor designs, TWRs use liquid sodium as coolant; liquid sodium reacts strongly with air and water and thus poses a significant hazard. [1,3]
© Ahmed Sharif. 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.
 W.C. Sailor, "Creating the Ultimate Nuclear Reactor," Bulletin of the Atomic Scientists 66, No. 4, 23 (2010)
 R. A. Guth, "A Window Into the Nuclear Future," Wall Street Journal, 29 Feb 11.
 N. Jackson, "How It Works; Traveling-Wave Reactor," The Atlantic, 17 Nov 10.
 B. Richter, "Reducing Proliferation Risk," Issues in Science and Technology, Fall 2008, p. 45.