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Hybrid fusion-fission reactors to run on nuclear 'sludge'

Most nuke waste actually useful fuel, say boffins

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At the end, the high-level waste needing to be stored would be one per cent of the original amount.

"We have created a way to use fusion to relatively inexpensively destroy the waste from nuclear fission," says Kotschenreuther.

There have long been plans to deal with nuclear wastes by neutron bombardment, of course, but these have normally centred on the use of normal fission-driven processes to provide the neutrons rather than fusion. Such "fast breeder" reactors have been built by many countries. However, waste processing has been only one of their goals - fast breeders have also been historically seen as a means of artificially creating fissionable fuel and/or weapons material, though this aim has lost relevance as it is expensive and troublesome compared to mining or waste-processing. (There turns out to be more uranium ore in the world than people thought back in World war Two.) Most commercial-scale fast breeder facilities worldwide have shut down in recent decades.

But Kotschenreuther seems to suggest that hybrid fusion/fission processing would be much cheaper, so much so as to be cheaper than simply storing wastes. He and his colleagues believe that one hybrid fusion-fission reactor could process the transuranic "sludge" output of ten to 15 LWRs. The special Super-X-Divertor tokamak cores of these facilities would be only the size of a small room, according to the scientists.

Mahajan, Kotschenreuther and their colleagues obviously look forward to the day when fusion reactors can produce abundant energy on their own, avoiding the need for scarce uranium. On that long-anticipated day, the human race's energy problems will largely be over - fusion, the same process that powers the sun, involves no carbon emissions, no troublesome wastes and no finite resources. The only fuel needed would be isotopes of hydrogen, the most common element in the universe, easily extracted from water.

But the advent of fusion power has been expected for a long time, and the human race needs to start getting off fossil fuels now.

"The hybrid we designed should be viewed as a bridge technology," says Mahajan. "Through the hybrid, we can bring fusion via neutrons to the service of the energy sector today. We can hopefully make a major contribution to the carbon-free mix dictated by the 2050 time scale set by global warming scientists."

The nuclear boffins say that research tokamak facilities in the UK and US are interested in testing out their Super X Divertor tech. Their research is published in the January issue of Fusion Engineering and Design. An abstract and DOI details can be viewed here. ®

Bootnote

*The normal method of getting an atom to "fission", or split into smaller ones, is to bang a flying neutron into it. The neutron comes from another unstable atom which has split on its own. In normal fission reactors, the neutron-split atoms then release more neutrons to split more atoms, so making the process self-sustaining.

In a weapon, by cramming together a lot of highly refined fission-y atoms very quickly using ordinary explosives, the process can be made to go runaway so fast that the lump of material has no time to melt or otherwise separate itself out and so reduce the intensity of the neutron hail as would normally happen. The result is a nuclear explosion.

No doubt most of you remember all this from school - sorry to waste your time.

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