Thinking Tech

A meltdown-proof nuclear reactor may alleviate fears

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A "sub-critical" nuclear reactor design essentially allows for an off-switch.

Until this weekend, the nuclear industry was arguably in the midst of a resurgence.

As the terrifying memories of past disasters seemed to fade comfortably into the recesses of history books, many nations had started to explore nuclear energy as an greener alternative to fossil fuels. However, the 8.9 magnitude earthquake that struck Japan on Friday has set off a chain reaction of devastation that will likely lead to a widespread re-evaluation of planned facilities throughout the world.

And despite the outcome of Japan's efforts to prevent full-blown nuclear meltdown, the fallout over nuclear energy has already begun.

“This event may be a big dampener for our program,” Shreyans Kumar Jain, chairman of the Nuclear Power Corporation of India, told Bloomberg News. “We and the Department of Atomic Energy will definitely revisit the entire thing, including our new reactor plans, after we receive more information from Japan.”

In the U.S., it's still too soon to tell if the unfolding events on the other side of the Pacific has put into jeopardy President Obama's pledge to inject eight billion dollars into new nuclear construction projects. In an appearance on CBS's Face the Nation, Senator Joseph Lieberman suggested that America's nuclear energy ambitions will likely be put on hold, but cautioned against rushing to judgment.

“I think it calls on us here in the U.S., naturally, not to stop building nuclear power plants but to put the brakes on right now until we understand the ramifications of what’s happened in Japan,” Senator Joseph I. Lieberman on CBS’s “Face the Nation.”

But what rarely gets mentioned in these sorts of discussions are nuclear technologies under development that may someday lead to safer -- and possibly cleaner -- nuclear facilities.

For instance, the proposed pebble-bed nuclear reactor design encases enriched uranium fuel within tennis-ball-sized graphite spheres. Doing so allows the reactor to run at even higher temperatures temperatures (up to 1,600 °C) and cool down by way of a helium-gas coolant. A silicon carbide coating keeps the radioactive fission material of the spent fuel safely contained within the pebbles, even in the case of a core meltdown or when the coolant is lost.

South African power company Eskom had hoped to put into operation the world's first industrial pebble-bed nuclear reactor but abandoned the project as investors withdrew funding due to technical problems and soaring costs. China also has a prototype in the works.

To learn more about pebble-bed nuclear reactors, check out this very informative segment on 60 Minutes here. (Sorry, but I was unable to embed the video for you folks)

Another safe alternative involves swapping out uranium with a similar radioactive material known as Thorium. The naturally-occurring metal element has been researched as an alternative to uranium as early as the 1960’s right here in the U.S. at the Oak Ridge National Laboratory. The material alone can’t be used to sustain the chain reaction process known as nuclear fission, but can absorb slow neutrons to transform into U-233, an artificial version of uranium that is fissile.

Proponents of the technology often cite a whole host of reasons that makes thorium a more attractive fuel source than uranium. Some of the major advantages include:

  • Thorium is a lighter than uranium and leaves behind less radioactive waste. Also, the waste would only remain radioactive for 500 years whereas Uranium byproducts have toxic properties that last upwards of 10,000 years.
  • Unlike Uranium-fueled power plants, the thorium fission processes don't produce plutonium, a byproduct that has raised nuclear weapon proliferation concerns in the past.
  • Most scientific estimates suggest that Thorium is three to four times more abundant than uranium.

But more importantly, the fact that thorium undergoes an entirely different fuel cycle lends itself to nuclear reactor designs that are also safer.

One such system, known as Accelerator Driven System, does away with uranium and plutonium altogether. Originally proposed by Nobel laureate Carlos Rubbia, ADS initiates the fission process by using a particle accelerator that shoots protons at a lead target to cause it to release neutrons as a way of kick-starting the thorium fuel cycle.

This kind of "sub-critical" reactor design, which differs from other reactors in that it requires neutrons from an outside source, essentially allows for an off-switch. Turn off the particle accelerator and the fission process is brought to a whimpering halt.

"If the particle beam is switched off, it is impossible for the fuel to enter a chain reaction and cause a meltdown, like that at Chernobyl," said Reza Hashemi-Nezhad, a physicist at the University of Sydney who is developing a prototype that may eventually be scaled up.

The CERN European Organisation for Nuclear Research estimates that an ADS reactor system would be at least three times cheaper than coal and 4.8 times cheaper than natural gas, due to the long life of the reactor.

Still, some environmental groups, while acknowledging the benefits of thorium-based nuclear technology, advocated steering clear of nukes altogether and instead focusing on further developing renewable energy technologies of the non-radioactive variety.

According to a report on the Australian Broadcasting Corporation's website:

Australian Conservation Foundation president Ian Low says although thorium has advantages he says using thorium is like being run over by a diesel train rather than a steam train.

"It's true that the period of danger of radioactive waste from thorium reactors, if the design can be worked up and proven, would be hundreds of years rather than hundreds of thousands of years," he said.

"But we're still talking about very long lifetimes."

Mr Lowe says nuclear power is still a long way from becoming clean and green, even with thorium.

"If we spent as much as we spend every year on nuclear research on renewable energy, we wouldn't be talking about this issue," he said.

"We'd have had enough solar and wind and other forms of renewable energy to give us clean energy solutions for the entire future."

Video explaining thorium nuclear technology:

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Tuan Nguyen

Contributing Editor

Contributing Editor Tuan C. Nguyen is a freelance science journalist based in New York City. He has written for the U.S. News and World Report, Fox News, MSNBC, ABC News, AOL, Yahoo! News and LiveScience. Formerly, he was reporter and producer for the technology section of ABCNews.com. He holds degrees from the University of California Los Angeles and the City University of New York's Graduate School of Journalism. Follow him on Twitter. Disclosure