On April 26, 1986, two powerful explosions tore through Unit 4 of the Chernobyl nuclear power plant, flipping the reactor’s giant 2,000-ton concrete lid into the air like a coin. White-hot chunks of the nuclear core rained down on adjacent buildings, setting fires and peppering the ground outside. Remnants of the core burned for 10 days, churning a thick plume of radioactive isotopes equivalent to 400 Hiroshima bombs high into the atmosphere.
Although Chernobyl contaminated half the planet with fallout, memory of the disaster had almost faded into obscurity when a tsunami swamped Japan’s Fukushima Daiichi power plant last year. At the time, many observers resurrected the specter of Chernobyl as a reassuring example of what wasn’t happening at Fukushima—a nuclear meltdown. We know now, though, that three of Fukushima’s reactors did melt down, spewing radioactive contamination over parts of Japan and into the sea.
Twenty-five years separate Chernobyl from Fukushima, but the occurrence of nuclear meltdowns is more frequent than this span suggests. The nuclear power industry measures safety trends in “reactor-years.” One reactor-year is equivalent to one nuclear reactor generating electricity for one year. The Nuclear Regulatory Commission’s safety goal for U.S. reactors is one incident in every 10,000 reactor-years. Thomas Cochran, a physicist and consultant for the Natural Resources Defense Council, calculates that the world’s fleet of light-water power reactors has racked up 11,500 reactor-years and counts five “partial core melt” accidents (“nuclear meltdown” is a term of art with no well-defined meaning) thus far worldwide. He credits Fukushima with three partial core melts. Three Mile Island and Greifswald, a plant in the former East Germany, account for the other two. (Chernobyl is not on the list because it was an old Soviet design used in only a handful of nuclear power plants in operation today.) “Historically, that means 1 percent of light-water reactors have had a partial core melt,” Cochran says. “One percent is a lot higher than one in every 10,000 reactor-years. What does that tell you about safety?”
In fact, the global rate is about five times the baseline goal of U.S. regulators. If the rate of partial core melts holds true for the 353 light-water reactors currently operating, we can expect a nuclear meltdown to occur every six years on average. From a historical perspective, Chernobyl isn’t just a curious artifact of the Cold War; it is one of the first events in a growing trend, and we are only now beginning to understand how to cope with its fallout.
While Japanese emergency workers fought to stabilize Fukushima’s overheated reactors, Ukrainian construction crews half a world away began an important new phase in Chernobyl’s protracted cleanup, bulldozing the contaminated soil around the steel-and-concrete tomb that encloses the scorched wreckage of Unit 4’s reactor building. The Shelter, as the tomb is known in Ukraine, was designed to last 15 years. More then a decade after that deadline, it still looms above the complex like a medieval fortress.
“It’s a house of cards,” said Eric Schmieman, a senior technical adviser for the Shelter Implementation Plan, the organization charged with maintaining the Shelter. Schmieman was standing outside SIP’s office building, located several hundred yards from the Shelter. He explained how Soviet engineers cobbled it together in just six months. The north wall is a stack of debris-filled concrete forms. The south wall consists of steel panels propped against girders. The steel plates that make up the roof are affixed by gravity alone. “They didn’t have a guy up there saying, ‘Move it another foot,’ ” Schmieman said. “It was all done by crane.”
Some 480,000 cubic yards of concrete and 7,300 tons of steel went into the Shelter, and it is held in place mostly by friction and luck. When Soviet workers finished building the Shelter, it was riddled with holes the size of picture windows. Leaking water corroded the steel support beams. A large crack was buckling the west wall. Birds flew in and out, spreading radioactive contamination. Ukraine inherited the crumbling Shelter after the Soviet Union broke up. By then it had become even more dangerously unstable, and Ukraine didn’t have the money or expertise to repair it.
The G7 nations agreed to fund a complete rehab of the Shelter in 1997. They chartered SIP to oversee dozens of projects: plugging holes in its walls, replacing its roof, stabilizing its west wall and ventilation stack, installing monitoring equipment, and so on. In essence, the Shelter had to be fixed up in order for it to be safely torn down. The costliest project to date, and the last in SIP’s mandate, is the New Safe Confinement, a $1.3-billion arch that will, if all goes well, completely seal off the Shelter from the environment. Schmieman, the principal member of the arch’s conceptual design team, has tackled complex engineering problems all over the world. But the arch, he said, is by far the most challenging project he’s ever worked on. Everything about the arch—its size, its purpose and the hazardous conditions under which it’s being built—is unprecedented. Now he grinned. “This is kind of like what working on the pyramids must have been for engineers back in Egyptian times.”single page
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.