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.
1. "WHAT DOES THAT TELL YOU ABOUT SAFETY?"
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.
2. "A HOUSE OF CARDS"
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."
"This is kind of like what working on the pyramids must have been for engineers back in Egyptian times."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."
3. "THE BOGEYMAN IN EVERY EQUATION"
Dust, the most mobile and breathable of radioactive contaminants, is an ever-present threat at Chernobyl. Radiation-detection portals at the entrance to every building scan feet and hands for contaminated dust. Mop-wielding women swab floors around the clock. Tanker trucks patrol the arch's construction site, spraying water to keep dust from blowing around. And nobody pets the feral cats prowling the streets because their fur is dusted with the radioisotopes cesium-137, strontium-90 and plutonium-239.
Iodine-131 is another dangerous radioisotope released during nuclear accidents. It mimics ordinary iodine, collecting in thyroid glands and giving rise to thyroid cancers years down the road. But iodine-131 decays to safe levels within a few weeks. Cesium and strontium, which mimic potassium and calcium, two minerals critical to the function of healthy ecosystems, persist in the soil and water, in plants and animals, for decades. The radioactive "ground shine" that makes Geiger counters click faster in contaminated areas is mostly the product of cesium decay. Plutonium, the stuff that nuclear bombs are made of, doesn't contribute much to overall radiation levels at Chernobyl, but it's nonetheless the most deadly of the inhalants. "Radioactive contamination is typically not a dose problem as long as you don't get it internally," cautions Mark Fishburn, SIP's biomedical project manager. "Inhalation, ingestion or injection—that's the way you get dosed here."
During the meltdown, the nuclear fuel in Chernobyl's core turned into slag hot enough to burn through four feet of concrete and steel. The slag flowed like lava down steam pipes into the floors below, where it solidified into glassy black blobs straight out of a science-fiction movie. Scientists categorize these blobs as "fuel-containing materials," or FCMs. About 200 tons of extremely radioactive FCMs are buried in the rubble of Unit 4, and they are the source of plutonium-laced "fuel dust."
Once a year, the Shelter's dust-suppression system, a series of nozzles visible on the Shelter's roof, douses the ruins of Unit 4 with a chemical fixative that binds up loose dust particles. Most of Unit 4 is off limits to visitors, but I was allowed to see the control room. After squeezing through a dark, narrow passage, I found myself standing in the middle of what appeared to be a set from an old episode of Star Trek. Three bulky consoles studded with black knobs stood in front of a semicircular wall of gray metal panels. All the instruments were gone except for a few analog gauges dangling from bundles of wire. Everything was encrusted in a rime of dust and dried red fixative. My Ukrainian guide warned me not to touch anything even though I was wearing an anti-contamination suit. "Plutonium," he intoned.
Scientists have explored only a third of the cave-like ruins inside the Shelter. Many basement rooms are knee-deep in water that, as it evaporates, causes FCMs to oxidize and shed tiny particles of fuel dust into the air. Scientists estimate that the Shelter contains 33 tons of the stuff, a daily hazard and a disaster in the making.
"The smallest particles don't settle with gravity," Schmieman says, "but stay suspended in the air. It's a big problem." If the Shelter collapsed, the resulting cloud of contaminated dust and debris would be disastrous. Thousands of Chernobyl workers could receive doses 25 times the annual limit. Now that SIP has stabilized the Shelter, the chances of it collapsing are slim. But dust remains a major threat. "The bogeyman in every equation," Schmieman says, "is how to keep radioactive dust from spreading."
4. "IT'S MUCH MORE COMPLICATED THAN THAT"
Ukrainian authorities once considered drilling through the side of the Shelter to access the FCMs, but engineers wisely deemed the Shelter too unstable. The only way to retrieve them without collapsing the Shelter, exposing workers to excessive radiation, or spreading contamination, would be to pull the Shelter itself apart piece by piece in a controlled environment. The arch of the New Safe Confinement will provide that environment.
The deadline for completing the arch was this April, but Novarka, the French consortium that won the contract to build it, has only recently wrapped up extensive ground preparations. The new deadline is December 2015. Laurin Dodd, SIP's managing director, considers even that date "ambitious." In computer renderings taped to his office walls, the arch looks like an oversized Quonset hut. At 280 yards wide, 160 yards long and 115 yards tall, it could swallow a college football stadium with the Statue of Liberty standing on the 50-yard line. "It's easy to think of the arch as a big barn or something, but it's much more complicated than that," Dodd says.
The Soviet engineers used standard construction cranes to build the Shelter; to demolish it, Ukrainian engineers will employ a custom-fabricated tensile-truss crane system suspended from the arch's ceiling on a web of cables. Television networks use similar technology to swoop cameras over the playing field during football games. The arch's crane system will be equipped with cameras as well, in addition to a manipulator arm, two 50-ton hoists, a drill, a jackhammer, hydraulic shears and a 10-ton vacuum cleaner. Operators will be able to peel back the Shelter's roof from the safety of a shielded control room, in effect making the arch the world's biggest glove box for handling radioactive materials.
The toughest engineering challenge was designing a ventilation system for the arch that will circulate seven million cubic feet of air without lofting fuel dust. At the same time, the air must move fast enough to prevent rain clouds from forming inside the arch and causing its tubular steel skeleton to rust. Schmieman ran simulations—"millions and millions of calculations"—on software tailored for global climate research and industrial clean-room studies. He calibrated air velocities and tweaked airflow patterns until he struck a delicate balance between humidity control and the speed at which a single mote of dust settles to the ground.
The real genius of the arch isn't so much in its design, though, but in the decision to build it on less-radioactive ground 300 yards west of the site. Other companies proposed to erect a confinement structure directly over the Shelter, where dose rates are highest; more radiation translates to more workers working shorter shifts, and therefore greater costs. Once the arch is complete, it will slide to its final resting position over the Shelter on two stainless-steel rails embedded in massive concrete "ground beams." If it works, the arch will be the largest movable structure on Earth.
5. "YOU WOULD EXPOSE NUMEROUS PEOPLE"
An obligatory stop on Chernobyl bus tours is the small visitors center, which is at the edge of a parking lot a quarter-mile from the Shelter. A big glass window provides an unobstructed view of the Shelter, but otherwise there's not much to see. A dusty scale model of the Shelter sits next to a television playing a Novarka video of the New Safe Confinement project. Near the end of the nine-minute animation, the striped ventilation stack rising above the Shelter magically disappears as the arch glides into place.
SIP has scheduled the vent stack to be completely removed by 2014, but the job most likely won't go quite as smoothly as it's depicted in Novarka's video. Dodd calls it one of the "highest-risk" projects SIP has ever managed. Risky because the vent stack is enormous, reaching higher than a 40-story building and weighing more than 300 tons. Riskier still because it's been discharging radioactive aerosols for 26 years and towers over a fragile structure filled with nuclear waste. "If you were to drop that thing on the building, you would expose numerous people that are out here working to the contamination," says Marsha Brown, SIP's site-works specialist. "It could be a terrible accident."
"The smallest radioactive particles don't settle with gravity but stay suspended in the air. It's a big problem."The plan is to cut the vent stack into seven pieces and lift them off one at a time. The most important risk factor is radiation exposure to workers. The dose rate near the vent stack is "very high, about one rem per hour," Schmieman says. SIP is considering installing shielded walkways on the roof to dampen workers' exposure to gamma radiation, but the men slicing up the chimney will have to wear extra gear to protect themselves from poisonous dust and smoke.
The effects of acute radiation doses are well-documented in studies of atomic-bomb survivors. We know, for instance, that a fatal dose in 100 percent of cases is 1,000 rems. The International Atomic Energy Agency attributes 28 radiation deaths to Chernobyl, mostly firemen exposed to extreme gamma radiation in the first hours of the catastrophe. No one has received a fatal dose at Chernobyl, or any other nuclear power plant, since the disaster.
The United Nations issued a report in 2005 forecasting that an additional 4,000 people who received lower doses at Chernobyl will die from cancer. The death toll is already closer to one million, according to a compilation of Russian and Ukrainian research recently published by the New York Academy of Sciences. The huge discrepancy underscores our profound lack of knowledge about what low-dose radiation does to the human body.
No regulatory institution in the world has established a "safe" dose of radiation. Every country sets its own limits. During the Fukushima disaster, Japan more than doubled its maximum dose limit for nuclear workers, simply to keep emergency operations going. The maximum allowed in Ukraine, which has one of the strictest dose standards in the world, is two rems per year (the limit is five rems per year in the U.S.). The legal limits govern how SIP and Novarka design their work plans; without shielding in place, workers at the vent stack would reach their annual dose limit in just two hours. But only certain kinds of exposure can be predicted. Although radiation levels at the vent stack and other areas of the site are well known, the amount of contaminated dust and aerosols workers will encounter is less certain. In addition to wearing dosimeters, all workers must submit to nasal swabs, urinalysis and fecal sampling to keep tabs on their dose.
6. "THEY'RE GOOD AT MAKING RULES"
Last spring, Novarka transformed the weed-choked field west of the Shelter into a busy construction site. Workers scraped off the top layer of contaminated soil, brought in clean fill to reduce radiation coming from the ground, and dug two parallel trenches running from the west end of the site to the Shelter on the east end. The trenches would hold foundations for the stainless-steel rails by which the arch will be transported to the Shelter. Each trench is 500 yards long, and the distance between them (almost 300 yards) is the same width as the arch.
By summer, cement mixers and dump trucks were rumbling across the site. The air reverberated with the piercing metallic clang of hydraulic hammers pounding steel piles into the bottoms of trenches, 396 in all. Each pile is 80 feet long and three feet in diameter; together they will support the weight of the 32,000-ton arch as it's being built. Driving piles and digging trenches have progressed more slowly than expected. "Every time anybody does any excavation, they find stuff," Dodd says. "Sometimes stuff is large cranes that were buried after the accident. Sometimes it's trucks or Caterpillars. And sometimes it's fuel-containing material."
The explosions that destroyed Unit 4 scattered bits of highly radioactive nuclear fuel called "hot particles" all around the site. Dosimetrists discover them during routine scanning of excavated dirt. When that happens, all nearby activity stops until a worker scoops up the particle using a shovel with a 10-foot handle. "The dose rate drops very quickly as you move away from it," says Don Kelly, SIP's health and safety engineer. "But as you're right beside it, or carrying it around in your pocket, it's smoking."
Kelly inspects the construction site every week. He carries a camera in his jacket pocket to document any safety violations he encounters. One afternoon last September, I walked with him along the north trench into the Shelter's shadow. We paused to watch a continuous flight augur, a Caterpillar fitted with a giant corkscrew, drilling a borehole in the bottom of the trench. The process is gentler than banging steel piles into the ground, an important consideration this close to the Shelter. Seismic vibrations, which had already cracked the brick walls of a security building adjacent to the trench, might bring down the Shelter's brittle west wall.
A loader scooped watery spoil from the borehole and dropped it into a dump truck. Kelly started snapping pictures. I asked him what was wrong. "He doesn't have any signs," Kelly said, pointing to the dump truck, "or a tailgate." Chernobyl's radiation-safety office has strict rules for transporting radioactive waste. Clean trucks can haul nothing but uncontaminated fill; dirty trucks haul only radioactive soil, and they're supposed to have signs—and tailgates—to prevent cross-contamination. The unmarked, ungated dump truck drove off, slopping spoil on the ground the entire length of the trench.
Kelly sent a spoil sample from the trench to the lab for analysis. The lab report came back a few days later: the spoil wasn't contaminated enough to be classified as radioactive waste. But the rules are essential to the cleanup work and to keeping workers safe. The next time around, entire swaths of the work site might become contaminated. "They're good at making rules here, good rules, but not quite so good at following them," Mark Fishburn had told me. "People tend to get away with what they can."
7. "WE'LL DIE OF SOMETHING ELSE"
Construction workers completed ground preparations for the arch last spring. They have begun work on the two concrete ground beams that will fill the trenches, and between the beams lies a 100,000-square-yard concrete pad where the arch will be assembled. The pad is "contamination-free," Kelly says. No anti-contamination gear will be required to work there, but each worker will carry an emergency respirator in case sensors detect radioactive aerosols blowing across the site.
Out of Novarka's 650-man workforce, not one worker appears to have exceeded his dose limit. That's a remarkable achievement considering Chernobyl's poor safety record. When Dodd first visited the plant in 1994, he says, safety conditions were "horrendous" and "appalling." Most of the personnel didn't have protective equipment. Radiation-detection portals in buildings around the plant didn't work. In Pripyat, a city located near the plant that was abandoned days after the disaster, Chernobyl workers continued to swim in the community pool.
SIP paid for new safety equipment, but money couldn't buy a change in attitude, so it also installed a system to track individual radiation doses. Every worker wore a dosimeter clipped to his coveralls. If he went over his limit, he lost his job. Many workers responded by stashing their dosimeters in homemade lead boxes to keep their recorded doses below the limit. "Which is just crazy," Dodd says. "The attitude was, 'Well, we'll die of something else.' "
Two years ago, a wolf wandered near the construction site, sniffing around the doors of the facility where Novarka workers suit up before their shifts. It's not unusual to see wolves, moose or packs of wild boar crossing the empty streets in Chernobyl's exclusion zone. In fact, the resurgence of wildlife in certain areas has become something of a hazard. "Animals are vectors for contamination," Fishburn says. "If they eat material that's radioactive, they come here and they pee, and that spreads contamination."
The wolf that tried to get into the change facility bit six people, squared off with an ambulance, and killed a dog. A jittery cellphone video posted on YouTube documents part of the incident, revealing the Chernobyl workers' casual regard for danger. In the video, they open a door and whistle to the wolf. Two men manage to corner the wolf and bludgeon it with a shovel and an oxygen canister while their comrades goad them on. Miraculously, the wolf escapes, sending the men fleeing, and the video ends. Guards later tracked down the wolf and shot it.
8. "FUKUSHIMA SAY IT AGAIN"
Alexander Novikov is Chernobyl's director of safety. He's responsible for the health of everybody who works at the plant. I spoke to him one afternoon at a restaurant in Slavutych, a small city built for Chernobyl cleanup workers and former residents of Pripyat. Novikov chain-smoked strong Turkish cigarillos and spoke in halting English about the dangers that still existed inside the Shelter. "Twenty-five years after accident," he said, "I'm afraid every day, because only fool cannot be afraid."
I asked him for an example. About a year ago, Novikov said, he received a phone call in the middle of the night. The engineer on the other end of the line said that sensors had picked up traces of the radioisotope iodine-131. That meant only one thing: uncontrolled nuclear fission was occurring somewhere in the Shelter. The FCMs inside Unit 4 are fissile. If a chunk of concrete fell on one, it could alter the FCM's internal geometry, triggering a nuclear chain reaction in what's known as a "criticality event." The FCM wouldn't explode, but it would generate intense heat and radiation and could possibly melt through the concrete floor. If the FCM came into contact with water at this stage, it could cause a steam or hydrogen explosion and bring down the entire Shelter.
"Twenty-five years after accident, I'm afraid every day, because only fool cannot be afraid."Recalling the midnight phone call, Novikov put his hands around his throat and pretended to choke: "Oops!" Then he continued with his story. He instructed his engineers to check all nuclear sources at the plant and waited for results of the spectrometry analysis. "Report says iodine not Chernobyl." Novikov smiled and lit another cigarillo. "Iodine is Fukushima."
Novikov volunteered as a dosimetrist during the cleanup in 1986, leaving briefly to recuperate from radiation exposure. Chernobyl is his life. He turns philosophical, almost superstitious, when talking about it. "Chernobyl from point of view of mankind is always," he said. "A lot people think that when we build New Safe Confinement, all problems Chernobyl will be solved. I say when we build New Safe Confinement, the problem only begin."
The problem isn't dismantling the Shelter or retrieving the FCMs. These are practical matters. The real problem, Novikov said, is time. Nuclear and radiological waste cannot be "cleaned up." It cannot be eradicated. It can only be sealed in drums or concrete coffins and moved from one place to another, or buried in pits and surrounded by razor wire. In fact, no one yet has a plan for what to do with the FCMs. The arch is designed to last 100 years, and then it too will become debris for which some other engineer will have to devise a newer and safer confinement.
"Chernobyl is not problem of Ukraine. It's not problem of old Soviet Union. Fukushima say it again," Novikov said as he tapped the ash off his cigarillo and jetted a thick plume of smoke from his lips. "Chernobyl is problem of whole world."
Steve Featherstone is a writer in Syracuse, New York.