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Unformatted text preview: TRAVELLING WAVE REACTOR
In this conceptual reactor design, highly enriched U235 or Pu239 fuel propagates a fission wave
preceded by a breeding wave into fresh depleted uranium fuel in hexagonal pillars sitting in a liquid metal
sodium coolant, turning it into spent fuel. The fission gases accumulate in the space above the assembly.
The heat generated is extracted by the sodium coolant using the columnar cooling pumps.
The travelling wave concept dates back to the early 1990s, but a working design has only emerged
around 2009 by Intellectual Ventures which patented the design . Commercial units are expected to be
operational by 2020. Fig.1: Schematic of Travelling Wave Reactor, TWR. Highly enriched U235 or Pu239 fuel propagates
a fission wave (red) preceded by a breeding wave (yellow) into unused depleted uranium (green) in
hexagonal pillars sitting in a liquid metal sodium coolant, turning it into spent fuel (black). The
fission gases accumulate in the space above the assembly. The heat generated is extracted by the
sodium coolant using the columnar cooling pumps. Source: Technology Review.
DESCRIPTION The fuel is an initial loading of highly enriched U235 or Pu239 that creates a fission wave that breeds
further Pu239 in a propagating wave into the depleted uranium containing about 0.25 percent U235
compared with the 0.72 percent content in natural uranium. The active region, of less than a meter in
thickness, moves along the reactor core breeding new Pu239 from the depleted uranium in front of it.
The end products are residual unburnt depleted U238, fission products and the actinide elements
Np, Pu, Am, and Cm.
The produced actinides can be later recycled and burnt in the same configuration. If these are
burnt, the remaining fission products take from 300-500 years to decay to the same level of activity as the
natural uranium that was mined from its ore deposit in the first place.
The fuel would be stored under water for about 5-10 years to allow its activity to decay. It would
be then recycled to extract any Pu to use as fuel, and the fission products for disposal.
Terrapower’s John Gilleland describes the potential advantages of the concept as:
1. The uranium isotope that is food for the new nuclear reactors does not have to be enriched, which
means it is less likely to be used in atomic weapons.
2. The fission reaction in the new process burns through the nuclear waste slowly, which makes the
process safer. One supply of spent uranium could burn for 60 years.
3. The process creates a large amount of energy from relatively small amounts of uranium, which is
important as global supplies run short.
4. The process generates uranium that can be burned again to create "effectively an infinite fuel supply."
Since the concept breeds its own fuel, it theoretically can operate for 20-200 years without
refueling. The main limitation would be the material properties that can withstand the operating
The concept falls under the category of battery reactors which do not separate the bred fuel and
hence eliminate proliferation concerns since the fuel can only be recycled in a fully safeguarded site.
Critics suggest that the technology is misguided, naïve and expensive. Supporters identify it as
part of the new enthusiasm that is a part of the “nuclear renaissance.”
A privately funded research company, TerraPower in Belleview, Washington with investment
support from Microsoft’s founder Bill Gates, is developing the concept. At a TED (Technology,
Entertainment, Design) conference in Long Beach, California he identified energy innovation as: “To
prevent famine, poverty and the hardship that will come with global climate change we need ‘energy
miracles’.” He encouraged optimism, along with heavier investment in solar, wind, battery and nuclear
technologies. “We have to drive full speed and get a miracle in a pretty tight timeline.” TED is a
nonprofit group dedicated to “ideas worth spreading.”
1. Matt Wald, “TR10: Travelling-Wave Reactor,” Technology Review, March/April, 2009. ...
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This note was uploaded on 06/16/2010 for the course NPRE 402 taught by Professor Ragheb during the Spring '08 term at University of Illinois at Urbana–Champaign.
- Spring '08