Should We Believe The Thorium Hype?

by Bradford Plumer | January 5, 2010

Has any element on the periodic table gotten better press lately than thorium? (Okay, maybe lithium, what with all the fuss over electric-car batteries.) The December issue of Wired has a long feature by Richard Martin on why good old Th could be a miracle fuel for nuclear power. Here's why it beats uranium, for starters:

Uranium is currently the actinide of choice for the [nuclear] industry, used (sometimes with a little plutonium) in 100 percent of the world’s commercial reactors. But it’s a problematic fuel. In most reactors, sustaining a chain reaction requires extremely rare uranium-235, which must be purified, or enriched, from far more common U-238.

The reactors also leave behind plutonium-239, itself radioactive (and useful to technologically sophisticated organizations bent on making bombs). And conventional uranium-fueled reactors require lots of engineering, including neutron-absorbing control rods to damp the reaction and gargantuan pressurized vessels to move water through the reactor core. If something goes kerflooey, the surrounding countryside gets blanketed with radioactivity (think Chernobyl). Even if things go well, toxic waste is left over.

When he took over as head of Oak Ridge in 1955, Alvin Weinberg realized that thorium by itself could start to solve these problems. It’s abundant—the US has at least 175,000 tons of the stuff—and doesn’t require costly processing. It is also extraordinarily efficient as a nuclear fuel. As it decays in a reactor core, its byproducts produce more neutrons per collision than conventional fuel. The more neutrons per collision, the more energy generated, the less total fuel consumed, and the less radioactive nastiness left behind.

Okay, so it's cheap and plentiful, coughs up less waste (and what waste does remain is far less nasty), and it's hard to make a weapon out of the byproducts. But if thorium reactors are so swell, uh, why don't we have any? Martin argues that it's partly an accident of history. In 1965, Weinberg built a working prototype molten-salt reactor, but the U.S. government preferred uranium reactors because it wanted the leftover plutonium to make bombs. And after Weinberg was ousted from Oak Ridge in 1973, thorium research withered away.

The rest gets blamed on path dependency. Nowadays, U.S. power companies seem to feel more at ease with the light-water reactors they've been running for decades. Even if thorium reactors could prove 50 percent more efficient than their uranium counterparts, utilities aren't keen on plunking down big bucks to build (and learn how to operate) a radically new reactor design. They're having a hard enough time getting old-fashioned reactors off the ground as is.

So that leaves a few options for thorium. A developing country that's not quite as invested in uranium could lead the charge: India and China both have very active thorium-research programs. Or we could mix thorium in with the fuel rods in existing reactors, known as a "seed-and-blanket" approach. You get less waste and fewer proliferation risks. But this is hard to pull off—as The New York Times reported in October, one method would require "a proton accelerator 10 times more power intense than anything that has been produced to date."

Still, thorium is starting to attract attention from Congress. Orrin Hatch and Harry Reid have been pitching legislation to put the fuel at the center of federal nuke research. The fact that the Yucca Mountain waste repository has been effectively shuttered seems to mean thorium's getting a second look. But it's not clear whether thorium reactors could out-compete all the other neat-sounding clean-energy gizmos on offer. So why not just slap a price on carbon, clear away some of the inefficient regulations in our power sector, and find out for sure?

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