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DATE News (chronologically)
04/22/09
automotive
Researchers come up with way to destroy 99% of nuclear waste
In a twist on the proverb “Set a thief to catch a thief,” physicists at the University of Texas at Austin have designed a system to facilitate the disposal of spent nuclear fuel that combines nuclear fission with fusion. The hybrid system will destroy 99% of the spent fuel, and the waste that remains will be less toxic than the spent fuel now accumulating in storage at nuclear powerplants around the country, the researchers say.

Physicists at The University of Texas at Austin have designed a new system that, when fully developed, would use fusion to eliminate most of the transuranic waste produced by nuclear power plants.

The invention could help combat global warming by making nuclear power cleaner and thus a more viable replacement of carbon-heavy energy sources, such as coal.

"We have created a way to use fusion to relatively inexpensively destroy the waste from nuclear fission," says Mike Kotschenreuther, senior research scientist with the Institute for Fusion Studies (IFS) and Department of Physics. "Our waste destruction system, we believe, will allow nuclear power-a low carbon source of energy-to take its place in helping us combat global warming."

Note that they do not need to solve the (also very hard) problem of how to design a fusion reactor that produces energy. They've come up with a much more partial solution to the fusion problem - just good enough to generate lots of neutrons. Even the (politically blocked) Yucca Mountain nuclear waste storage site in Nevada isn't big enough to store waste beyond what will exist by 2010.

Toxic nuclear waste is stored at sites around the U.S. Debate surrounds the construction of a large-scale geological storage site at Yucca Mountain in Nevada, which many maintain is costly and dangerous. The storage capacity of Yucca Mountain, which is not expected to open until 2020, is set at 77,000 tons. The amount of nuclear waste generated by the U.S. will exceed this amount by 2010.

The physicists' new invention could drastically decrease the need for any additional or expanded geological repositories.

"Most people cite nuclear waste as the main reason they oppose nuclear fission as a source of power," says Swadesh Mahajan, senior research scientist.

Once this solution matures and becomes constructible the debate over nuclear power will change. Opponents of nuclear fission power who oppose it on the grounds of waste disposal will need to move on to other reasons to oppose it. What will become their next favorite reason to oppose it?

The key to their proposal is a way to generate lots of neutrons (that can bombard and convert nuclear waste into safer elements) without solving the much harder problem of making a power-generating fusion reactor.

The scientists propose destroying the waste using a fusion-fission hybrid reactor, the centerpiece of which is a high power Compact Fusion Neutron Source (CFNS) made possible by a crucial invention.

The CFNS would provide abundant neutrons through fusion to a surrounding fission blanket that uses transuranic waste as nuclear fuel. The fusion-produced neutrons augment the fission reaction, imparting efficiency and stability to the waste incineration process.

The neutron generator would be very small. Small sounds cheap to me.

One hybrid would be needed to destroy the waste produced by 10 to 15 LWRs.

The process would ultimately reduce the transuranic waste from the original fission reactors by up to 99 percent. Burning that waste also produces energy.

The CFNS is designed to be no larger than a small room, and much fewer of the devices would be needed compared to other schemes that are being investigated for similar processes. In combination with the substantial decrease in the need for geological storage, the CFNS-enabled waste-destruction system would be much cheaper and faster than other routes, say the scientists.

The key breakthrough was the development of a device that can handle a large amount of heat and particle fluxes.

The CFNS is based on a tokomak, which is a machine with a "magnetic bottle" that is highly successful in confining high temperature (more than 100 million degrees Celsius) fusion plasmas for sufficiently long times.

The crucial invention that would pave the way for a CFNS is called the Super X Divertor. The Super X Divertor is designed to handle the enormous heat and particle fluxes peculiar to compact devices; it would enable the CFNS to safely produce large amounts of neutrons without destroying the system.

"The intense heat generated in a nuclear fusion device can literally destroy the walls of the machine," says research scientist Valanju, "and that is the thing that has been holding back a highly compact source of nuclear fusion."

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