If the recent events in Japan were a movie, we'd say that the plot was too outlandishly catastrophic to be true--first an earthquake, then a tsunami, then a nuclear accident. Watching footage of entire neighborhoods being shoveled inland by roiling water, and knowing that those buildings and vehicles contained people, was horrifying.
But while the citizens of Japan continue to struggle with their own personal hell, many of us who live elsewhere are already beginning to ask "what if?" Any nation that sits in an active seismic zone, as Japan does, cannot avoid quakes and tsunamis. But what about the damaged reactors? Are we now going to have to abandon nuclear power as an alternative to fossil fuels? And more importantly, what if a safer kind of reactor had been in place when the quake and tsunami struck?
I put that question to Kirk Sorensen, my go-to guy for information about alternative forms of nuclear power and the web host of EnergyFromThorium.com. What, if anything, might have happened if liquid-fluoride thorium reactors, or LFTRs (pronounced "lifters") had been used instead of regular uranium-based light-water reactors?
"Short answer," he explains, "My personal guess is that there would have been no concern at all about them after the quake."
That's partly because LFTRs don't run at high pressure like normal water-cooled plants do, and also because they have more reliable ways of controlling the nuclear inferno that continues to burn inside most reactors after they shut down. "A major problem at Fukushima was that the tsunami knocked out the emergency power system that was supposed to pump water through the plant to keep it cool," Sorensen says. In contrast, safer LFTR designs automatically shut themselves down even if emergency power is lost.
The harsh reactions in the Fukushima Daiichi complex blasted the surrounding water coolant and generated a pressure-cooker of flammable hydrogen gas, which eventually exploded. No such problem with LFTRs, it seems. "They run at low pressures and they have no water in the core itself, only stable molten salts," Sorenson says, "so there's no risk of radioactive steam explosions."
Also on the list of pluses of these so-called "green nukes" is the relatively benign nature of their wastes, the abundance of thorium worldwide, and the unsuitability of their contents for bomb-making. Nonetheless, no energy source is completely safe--even hydro dams sometimes collapse--and experts who design protective shield walls to house LFTR systems face a serious dilemma. What kinds of accidents should they be built to withstand? To survive an earthquake, for example, flexibility is key. But what about an aircraft collision (think terrorism). In that case, the barrier should be as rigidly resistant to impact as possible.
For an engineer like Sorensen, problems such as this are interesting puzzles begging to be solved. When I asked him what the safest possible design for a reactor might be, he quickly dreamed up a radical-sounding idea. "Small, water-tight LFTRs loosely tethered to the ocean floor would be immune to earthquakes, waves, and air attacks," he said. When I chuckled at the notion of a floating Three Mile Island, he pointed out that these would rest far below the surface, and added that more reactors have been used inside submarines than on land.
"Powerful submersible LFTRs could generate as much electricity as larger, land-based reactors do," he says. "They could be spread along a suitable coastline, with high-voltage power lines running offshore to connect with them. If there had been several LFTRs in submersibles when the Japanese earthquake struck, I suspect they would have survived the tsunami and might be powering the grid right now, helping to get the country back on its feet."
OK, but what's a "suitable coastline?" Wouldn't the next tsunami or typhoon simply smash a LFTR-sub and hurl it ashore, trailing a spaghetti tangle of sizzling cables behind it? I turned to my go-to guy for oceanography, Larry Cahoon at the University of North Carolina-Wilmington, for answers.
His verdict was that shallow-water coasts probably wouldn't work. "I've seen total bottom disturbance in 100 feet of water from a mere category 1 storm, and tsunamis create very strong lateral currents near shore. You'd also have to create a no-traffic zone, as Murphy’s Law for Boats states that two man-made objects on the sea will inevitably collide. But the ultimate problem is that when the danger is greatest you have the least control," he explains. "On land you can get in and out of a plant no matter what; at sea you have no chance once it gets rough. The Navy does run reactors on aircraft carriers and subs. but they send their ships out to sea when a big storm threatens, meaning shore power would be cut. I do like thorium reactors, though. Too bad if this disaster taints all things nuclear."
I don't know how realistic Sorenson's daydreams of a safe nuke future are, though they sound reasonable (at least for deep-water settings) and I've heard similar things from other experts, as well. Of course, even experts can be mistaken. Just this January, the World Nuclear Association updated an online report titled "Nuclear Power Plants and Earthquakes." The first line read "Japanese, and most other, nuclear plants are designed to withstand earthquakes, and in the event of major earth movement, to shut down safely," and later passages described in reassuring detail how Japan's nukes have weathered numerous quakes measuring up to 7.2 on the Richter scale. Two months later, a magnitude 9 quake has now teamed up with a tsunami, and that report doesn't seem so comforting any more.
But risk is a fact of life, and there's much at stake in our increasingly urgent quest for alternative energy sources. Failure to switch to non-fossil fuels during this century could trigger a global super-greenhouse lasting hundreds of thousands of years, and running out of affordable petroleum would be no picnic either. Simply put, I hope that we can still give LFTRs a chance to prove themselves. If the tragedy in Japan makes us toss them aside now, then its aftershocks may echo even more profoundly around the world and far into the deep future.
Curt Stager is an ecologist, paleoclimatologist, and science journalist with a Ph.D. in biology and geology from Duke University. His new book is DEEP FUTURE: The Next 100,000 Years of Life on Earth (St. Martin's Press, March 2011).
Read more coverage of the Japan earthquake.