They dream to 'reinvent' nuclear power

Physicists have spent billions of dollars and half of a century trying to build a contraption that can create a sustained fusion reaction, where fusion is sparked and is then powerful enough to produce enough energy to perpetuate more fusion reactions.

They call this dream 'burn'. Scientists at the National Ignition Facility think they may achieve burn next year. Scientists at the University of Texas ask, Why bother?

"In the near term, there is nothing that can deliver what we need quickly enough," says Swadesh Mahajan, a research professor at the University of Texas. "We need something not in 20 years, but tomorrow."

Mahajan, along with colleagues Michael Kotschenreuther, Prashant Valanju and Erich Schneider, has described an idea for a fusion fission hybrid reactor that they think could be up and running sooner than a similar project, called LIFE, proposed by NIF scientists.

Both LIFE and the University of Texas proposal are schemes to surround a fusion reactor with a nuclear fission reactor. The idea is to use the neutrons produced by fusion to burn up nuclear waste created by traditional nuclear reactors and produce clean, carbon-free energy.

The LIFE plans employ so-called inertial-confinement fusion, in which lasers crush a pellet of frozen hydrogen with such force that the hydrogen nuclei fuse into helium, releasing energy. While the NIF lasers do have a reasonable chance of achieving fusion burn, the technical hurdles in front of turning this technology into an energy source are extraordinarily high.

The University of Texas plan uses a more traditional approach to fusion. It would use magnets to confine and pressurize a hot plasma of hydrogen nuclei circulating in a tube shaped like a doughnut. Achieving burn this way is a distant hope--an international project now under way in France, called ITER, is spending $16 billion with hopes of just getting close.

But the Texas proposal doesn't require a sustained burn; it just requires those neutrons produced by the fusion reactions that are sparked by energy added to the system. They call their fusion reactor a "compact fusion neutron source."

"The physics requirements of our machine are very modest," says Mahajan. "They are being demonstrated every day (at experimental fusion reactors around the globe)."

Their plan does not need superconducting magnets to confine the plasma, which contributes to the huge cost of ITER. They do, however, need the so-called fusion "pulse" to last many times longer than the 1,000 seconds or so current fusion reactors have reached. They need it to last days or weeks, and this will take some doing.

Part of what gives researchers hope for their system is a new invention, with a name straight out of comic books, that will at least be able to handle the results of these long pulses. The device, called a Super-X Diverter, is able to exhaust from the system the tremendous accumulation of heat and particles produced by the long pulses.

The neutrons produced are then sent through a blanket of lead, where they are slowed down and multiplied. The neutrons will then be numerous enough, and they will travel at the ideal speed to turn nuclear waste into nuclear fuel.

"We are going to burn crud that no one else is willing to," says Mahajan. He says that only one of his reactors would be required to dispose of the waste of 15 current nuclear reactors.

He calculates that if, like the US, the world eventually produced 20 per cent of its power with nuclear reactors, 100 storage centers like the proposed Yucca Mountain site would be needed to handle the waste. The University of Texas reactors would reduce that number to five.

This way, Mahajan says, we can dramatically increase carbon-free nuclear power generation without creating more waste than we can handle.

His reactor would produce a total of about 1,000 megawatts of power, but 30 per cent would be siphoned off to keep the fusion reactions going. The total reactor would be not very efficient, then--not to mention expensive. But it might ultimately prove to be cheaper, more efficient and safer than building 100 Yucca Mountains.

"If I told anyone this is my scheme to produce power, they would say go fly a kite," he says. "But I am getting rid of a big mess and making some power that we can sell."