The World Without Us - Alan Weisman (2007)

Part III

Chapter 15. Hot Legacy

1. The Stakes


S BEFITS A chain reaction, it happened very fast. In 1938, a physicist named Enrico Fermi went from Fascist Italy to Stockholm to accept the Nobel Prize for his work with neutrons and atomic nuclei—and kept going, defecting with his Jewish wife to the United States.

That same year, word leaked that two German chemists had split uranium atoms by bombarding them with neutrons. Their work confirmed Fermi’s own experiments. He had guessed correctly that when neutrons cracked an atomic nucleus, they would set more neutrons free. Each would scatter like a subatomic shotgun pellet, and with enough uranium handy, they would find more nuclei to destroy. The process would cascade, and a lot of energy would be released. He suspected Nazi Germany would be interested in that.

On December 2, 1942, in a squash court beneath the stadium at the University of Chicago, Fermi and his new American colleagues produced a controlled nuclear chain reaction. Their primitive reactor was a beehive-shaped pile of graphite bricks laced with uranium. By inserting rods coated with cadmium, which absorbs neutrons, they could moderate the exponential shattering of uranium atoms to keep it from getting out of hand.

Less than three years later, in the New Mexico desert, they did just the opposite. The nuclear reaction this time was intended to go completely out of control. Immense energy was released, and within a month the act was repeated twice, over two Japanese cities. More than 100,000 people died instantly, and the dying continued long after the initial blast. Ever since, the human race has been simultaneously terrified and fascinated by the double deadliness of nuclear fission: fantastic destruction followed by slow torture.

If we left this world tomorrow—assuming by some means other than blowing ourselves to bits—we would leave behind about 30,000 intact nuclear warheads. The chance of any exploding with us gone is effectively zero. The fissionable material inside a basic uranium bomb is separated into chunks that, to achieve the critical mass necessary for detonation, must be slammed together with a speed and precision that don’t occur in nature. Dropping them, striking them, plunging them in water, or rolling a boulder over them would do nothing. In the tiny chance that the polished surfaces of enriched uranium in a deteriorated bomb actually met, unless forced together at gunshot speed, they would fizzle—albeit in a very messy way.

A plutonium weapon contains a single fissionable ball that must be forcibly, exactly compressed to at least twice its density to explode. Otherwise, it’s simply a poisonous lump. What will happen, however, is that bomb housings will ultimately corrode, exposing the hot innards of these devices to the elements. Since weapons-grade plutonium-239 has a half-life of 24,110 years, even if it took an ICBM cone 5,000 years to disintegrate, most of the 10 to 20 pounds of plutonium it contained would not have degraded. The plutonium would throw off alpha particles—clumps of protons and neutrons heavy enough to be blocked by fur or even thick skin, but disastrous to any creature unlucky enough to inhale them. (In humans, 1 millionth of a gram can cause lung cancer.) In 125,000 years, there would be less than a pound of it, though it would still be plenty lethal. It would take 250,000 years before the levels were lost in the Earth’s natural background radiation.

At that point, however, whatever lives on Earth would still have to contend with the still-deadly dregs of 441 nuclear plants.

2. Sunscreen

When big, unstable atoms like uranium decay naturally, or when we rip them apart, they emit charged particles and electromagnetic rays similar to the strongest X-rays. Both are potent enough to alter living cells and DNA. As these deformed cells and genes reproduce and replicate, we sometimes get another kind of chain reaction, called cancer.

Since background radiation is always present, organisms have adjusted accordingly by selecting, evolving, or sometimes just succumbing. Anytime we raise the natural background dosage, we force living tissue to respond. Two decades prior to harnessing nuclear fission, first for bombs, then for power plants, humans had already let one electromagnetic genie loose—the result of a goof we wouldn’t recognize until nearly 60 years later. In that instance, we didn’t coax radiation out but let it sneak in.

That radiation was ultraviolet, a considerably lower energy wave than the gamma rays emitted from atomic nuclei, but it was suddenly present at levels unseen since the beginning of life on Earth. Those levels are still rising, and although we have hopes to correct that over the next half century, our untimely departure could leave them in an elevated state far longer.

Ultraviolet rays helped to fashion life as we know it—and, oddly enough, they created the ozone layer itself, our shield against too much exposure to them. Back when the primordial goo of the planet’s surface was being pelted with unimpeded UV radiation from the sun, at some pivotal instant—perhaps sparked by a jolt of lightning—the first biological mix of molecules jelled. Those living cells mutated rapidly under the high energy of ultraviolet rays, metabolizing inorganic compounds and turning them into new organic ones. Eventually, one of these reacted to the presence of carbon dioxide and sunlight in the primitive atmosphere by giving off a new kind of exhaust: oxygen.

That gave ultraviolet rays a new target. Picking off pairs of oxygen atoms joined together—O2 molecules—they split them apart. The two singles would immediately latch onto nearby O2 molecules, forming O3: ozone. But UV easily breaks the ozone molecule’s extra atom off, reforming oxygen; just as quickly, that atom sticks to another pair, forming more ozone until it absorbs more ultraviolet and spins off again.

Gradually, beginning about 10 miles above the surface, a state of equilibrium emerged: ozone was constantly being created, pulled apart, and recombined, and thus constantly occupying UV rays so that they never reached the ground. As the layer of ozone stabilized, so did the life on Earth it was shielding. Eventually, species evolved that could never have tolerated the former levels of UV radiation bombardment. Eventually, one of them was us.

In the 1930s, however, humans started undermining the oxygen-ozone balance, which had remained relatively constant since soon after life began. That’s when we started using Freon, the trademark name for chlorofluorocarbons, the man-made chlorine compounds in refrigeration. Called CFCs for short, they seemed so safely inert that we put them into aerosol cans and asthma-medication inhalers, and blew them into polymer foams to make disposable coffee cups and running shoes.

In 1974, University of California-Irvine chemists F. Sherwood Rowland and Mario Molina began to wonder where CFCs went once those refrigerators or materials broke down, since they were so impervious to combining with anything else. Eventually, they decided that hitherto indestructible CFCs must be floating to the stratosphere, where they would finally meet their match in the form of powerful ultraviolet rays. The molecular slaughter would free pure chlorine, a voracious gobbler of loose oxygen atoms, whose presence kept those same ultraviolet rays away from Earth.

No one paid Rowland and Molina much heed until 1985, when Joe Farman, a British researcher in Antarctica, discovered that part of the sky was missing. For decades, we’d been dissolving our UV screen by soaking it with chlorine. Since then, in unprecedented cooperation, the nations of the world have tried to phase out ozone-eating chemicals. The results are encouraging, but still mixed: Ozone destruction has slowed, but a black market in CFCs thrives, and some are still legally produced for “basic domestic needs” in developing countries. Even the replacements we commonly use today, hydrochlorofluorocarbons, HCFCs, are simply milder ozone-destroyers, scheduled to be phased out themselves—though the question of with what isn’t easily answered.

Quite apart from ozone damage, both HCFCs and CFCs—and their most common chlorine-free substitute, hydrofluorocarbons, HFCs—have many times the potential of carbon dioxide to exacerbate global warming. The use of all these alphabetical concoctions will stop, of course, if human activity does, but the damage we did to the sky may last a lot longer. The best current hope is that the South Pole’s hole, and the thinning of the ozone layer everywhere else, will heal by 2060, after destructive substances are exhausted. This assumes that something safe will have replaced them, and that we’ll have found ways to get rid of existing supplies that haven’t yet drifted skyward. Destroying something designed to be indestructible, however, turns out to be expensive, requiring sophisticated, energy-intensive tools such as argon plasma arcs and rotary kilns that aren’t readily available in much of the world.

As a result, especially in developing countries, millions of tons of CFCs are still used or linger in aging equipment, or are mothballed. If we vanish, millions of CFC and HCFC automobile air conditioners, and millions more domestic and commercial refrigerators, refrigerated trucks and railroad cars, as well as home and industry air-cooling units, will all finally crack and give up the chlorofluorocarbonated ghost of a 20th-century idea that went very awry.

All will rise to the stratosphere, and the convalescing ozone layer will suffer a relapse. Since it won’t happen all at once, with luck the illness will be chronic, not fatal. Otherwise, the plants and animals that remain in our wake will have to select for UV tolerance, or mutate their way through a barrage of electromagnetic radiation.

3. Tactical and Practical

Uranium-235, with a half-life of 704 million years, is a relatively insignificant fraction of natural uranium ore—barely .7 percent—but we humans have concentrated (“enriched”) several thousand tons of it for use in reactors and bombs. To do that, we extract it from uranium ore, usually by chemically converting it to a gas compound, then spinning it in a centrifuge to separate the different atomic weights. This leaves behind far less potent (“depleted”) U-238, whose half-life is 4.5 billion years: in the United States alone, there’s at least a half-million tons of it.

One approach to what to do with some of it involves the fact that U-238 is an unusually dense metal. In recent decades it has proved useful, when alloyed with steel, for fashioning bullets that can pierce armor, including the walls of tanks.

With so much surplus depleted uranium lying around, this is far cheaper for U.S. and European armies than buying the non-radioactive alternative, tungsten, which is mainly found in China. Depleted uranium projectiles range from 25-millimeter bullet size to three-foot-long, 120-millimeter darts with their own internal propellants and stabilizing fins. Their use kindles outrage over human health issues, on both the firing and receiving end. Because depleted uranium ordnance bursts into flames when it strikes, it leaves a pile of ash. Depleted or not, there’s enough concentrated U-238 in the bullet points that radioactivity in this debris can exceed 1,000 times the normal background level. After we’re gone, the next archaeologists to appear may unearth arsenals of several million of these super-dense, modern versions of Clovis spear points. Not only will they look considerably more fearsome, but—possibly unbeknownst to their discoverers—they’ll emit radiation for more years than the planet likely has left.

There are far hotter things than depleted uranium that will outlast us, whether we’re gone tomorrow or 250,000 years from now. It’s a big enough problem that we contemplate hollowing out entire mountains to store them. Thus far the United States has only one such site, in salt dome formations 2,000 feet below southeastern New Mexico, similar to the chemical-storage caverns below Houston. The Waste Isolation Pilot Plant, or WIPP, operating since 1999, is the boneyard for detritus from nuclear weapons and defense research. It can handle 6.2 million cubic feet of waste, the equivalent of about 156,000 55-gallon drums. In fact, much of the plutonium-drenched scrap it receives is packaged just that way.

WIPP isn’t designed to store spent fuel from nuclear generating plants, which in the United States alone increases by 3,000 tons each year. It is a landfill only for so-called low- and midlevel waste—stuff like discarded weapons-assembly gloves, shoe coverings, and rags soaked in contaminated cleaning solvents used in fashioning nuclear bombs. It also holds the dismantled remains of machines used to build them, and even walls from rooms where that happened. All this arrives on shrink-wrapped pallets containing hot hunks of pipe, aluminum conduits, rubber, plastic, cellulose, and miles of wiring. After its first five years, WIPP was already more than 20 percent full.

Its contents come from two dozen high-security warrens across the country, such as the Hanford Nuclear Reservation in Washington, where plutonium for the Nagasaki bomb was made, and Los Alamos, New Mexico, where it was assembled. In 2000, large wildfires hit both sites. Official reports say that unburied radioactive wastes were protected—but in a world without firefighters, they won’t be. Except for WIPP, all U.S. nuclear waste-storage containment is temporary. If it remains that way, fire will eventually breach it and send clouds of radioactive ash billowing across the continent, and possibly across the oceans.

The first site to begin shipping to WIPP was Rocky Flats, a defense facility on a foothills plateau 16 miles northwest of Denver. Until 1989, the United States made plutonium detonators for atomic weapons at Rocky Flats with somewhat less than a lawful regard for safety. For years, thousands of drums of cutting oil saturated with plutonium and uranium were stacked outside on bare ground. When someone finally noticed they were leaking, asphalt was poured over the evidence. Radioactive runoff at Rocky Flats frequently reached local streams; cement was swirled into radioactive sludge in absurd attempts to try to slow seepage from cracked evaporation ponds; and radiation periodically escaped into the air. A 1989 FBI raid finally closed the place. In the new millennium, after several billion dollars’ worth of intensive cleanup and public relations, Rocky Flats was transmuted into a National Wildlife Refuge.

Simultaneously, similar alchemy was recasting the old Rocky Mountain Arsenal next to Denver International Airport. RMA was a chemical-weapons plant that made mustard and nerve gas, incendiary bombs, napalm—and during peacetime, insecticides; its core was once called the most contaminated square mile on Earth. After dozens of wintering bald eagles were found in its security buffer, feasting on the prodigious prairie dog population, it, too, became a National Wildlife Refuge. That required draining and sealing an Arsenal lake where ducks once died moments after landing, and where the bottoms of aluminum boats sent to fetch their carcasses rotted within a month. Although the plan is to treat and monitor toxic groundwater plumes for another century until they’re considered safely diluted, today mule deer big as elk find asylum where humans once feared to tread.

A century, however, would make little difference to uranium and plutonium residues whose half-lives start at 24,000 years and keep going. The weapons-grade plutonium from Rocky Flats was shipped to South Carolina, whose governor was enjoined from lying in front of trucks to stop it. There, at the Savannah River Site’s Defense Waste Processing Facility, where two huge buildings (“reprocessing canyons”) are so contaminated that no one knows how they might be decommissioned, high-level nuclear waste is now melted in furnaces with glass beads. When poured into stainless steel containers, it turns into solid blocks of radioactive glass.

This process, called vitrification, is also used in Europe. Glass being one of our simplest, most durable creations, these hot glass bricks may be among the longest-lasting of all human creations. However, in places like England’s Windscale plant, scene of two nuclear accidents before it was finally closed, vitrified waste is stored in air-cooled facilities. One day, should power go off permanently, a chamber full of decaying, glass-embedded radioactive material would get steadily warmer, with shattering results.

The Rocky Flats asphalt where drums of radioactive oil spilled was also scraped and shipped to South Carolina, along with three feet of soil. More than half its 800 structures were razed, including the infamous “Infinity Room,” where contamination levels rose higher than instruments could measure. Several buildings were mostly underground; after the removal of items like the glove boxes used to handle the shiny plutonium disks that triggered A-bombs, the basement floors were buried.

Atop them, a mix of native bluestem tall grass and side-oats grama grass has been planted to assure a habitat for resident elk, mink, mountain lion, and the threatened Prebel’s meadow jumping mouse, which have impressively thrived in the plant’s 6,000-acre security buffer despite the evil brewing at its center. Regardless of the grim business that went on here, these animals seem to be doing fine. However, while there are plans to monitor the human wildlife managers for radiation intake, a refuge official admits doing no genetic tests on the wildlife itself.

“We’re looking at human hazards, not damage to species. Acceptable dose levels are based on 30-year career exposures. Most animals don’t live that long.”

Maybe not. But their genes do.

Anything at Rocky Flats too hard or too hot to move was covered with concrete and 20 feet of fill, and will remain off-limits to hikers in the wildlife preserve, though how they’ll be deterred hasn’t been decided. At WIPP, where much of Rocky Flats ended up, the U.S. Department of Energy is legally required to dissuade anyone from coming too close for the next 10,000 years. After discussing the fact that human languages mutate so fast that they’re almost unrecognizable after 500 or 600 years, it was decided to post warnings in seven of them anyway, plus pictures. These will be incised on 25-foot-high, 20-ton granite monuments and repeated on nine-inch disks of fired clay and aluminum oxide, randomly buried throughout the site. More-detailed information about the hazards below will go on the walls of three identical rooms, two of them also buried. The whole thing will be surrounded by a 33-foot-tall earthen berm a half-mile square, embedded with magnets and radar reflectors to give every possible signal to the future that something lurks below.

Whether who-or-whatever finds it someday can actually read, or heed, danger in those messages may be moot: the construction of this complex scarecrow to posterity isn’t scheduled until decades from now, after WIPP is full. Also, after just five years, plutonium-239 was already noticed leaking from WIPP’s exhaust shaft. Among the unpredictables is how all the irradiated plastic, cellulose, and radionuclides below will react as brine percolates through the salt formations, and as radioactive decay adds heat. For that reason, no radioactive liquids are allowed lest they volatilize, but many interred bottles and cans contain contaminated residues that will evaporate as temperatures rise. Head space is being left for buildup of hydrogen and methane, but whether it’s enough, and whether WIPP’s exhaust vent will function or clog, is the future’s mystery.

4. Too Cheap to Meter

At the biggest U.S. nuclear plant, the 3.8-billion-watt Palo Verde Nuclear Generating Station in the desert west of Phoenix, water heated by a controlled atomic reaction turns to steam, which spins the three largest turbines General Electric ever manufactured. Most reactors worldwide function similarly; like Enrico Fermi’s original atomic pile, all nuke plants use moveable, neutron-sopping cadmium rods to dampen or intensify the action.

In Palo Verde’s three separate reactors, these dampers are interspersed among nearly 170,000 pencil-thin, 14-foot zirconium-alloy hollow rods stuffed end to end with uranium pellets that each contain as much power as a ton of coal. The rods are bunched into hundreds of assemblies; water flowing among them keeps things cool, and, as it vaporizes, it propels the steam turbines.

Together, the nearly cubical reactor cores, which sit in 45-foot-deep pools of turquoise water, weigh more than 500 tons. Each year, about 30 tons of their fuel is exhausted. Still packed inside the zirconium rods, this nuclear waste is removed by cranes to a flat-roofed building outside the containment dome, where it is submerged in a temporary holding pond that resembles a giant swimming pool, also 45 feet deep.

Since Palo Verde opened in 1986, its used fuel has been accumulating, because there’s nowhere else to take it. In plants everywhere, spent fuel ponds have been re-racked to squeeze in thousands of more fuel assemblies. Together, the world’s 441 functioning nuclear plants annually produce almost 13,000 tons of high-level nuclear scrap. In the United States, most plants have no more pool space, so until there’s a permanent burial ground, waste-fuel rods are now mummified in “dry casks”—steel canisters clad in concrete from which the air and moisture have been sucked. At Palo Verde, where they’ve been used since 2002, these are stored vertically, and resemble giant thermos bottles.

Every country has plans to permanently entomb the stuff. Every country also has citizens terrified of events like earthquakes that could unseal buried waste, and of the chance that some truck carrying it will have a wreck or be hijacked en route to the landfill.

In the meantime, used nuclear fuel, some of it decades old, languishes in holding tanks. Oddly, it is up to a million times more radioactive than when it was fresh. While in the reactor, it began mutating into elements heavier than enriched uranium, such as isotopes of plutonium and americium. That process continues in the waste dumps, where used hot rods exchange neutrons and expel alpha and beta particles, gamma rays, and heat.

If humans suddenly departed, before long the water in the cooling ponds would boil and evaporate away—rather quickly in the Arizona desert. As the used fuel in the storage racks is exposed to air, its heat would ignite the cladding of the fuel rods, and radioactive fire would break out. At Palo Verde, like other reactors, the spent-fuels building was intended to be temporary, not a tomb, and its masonry roof is more similar to a big-box discount store’s than to the reactor’s pre-stressed containment dome. Such a roof wouldn’t last long with a radioactive fire cooking below it, and much contamination would escape. But that wouldn’t be the biggest problem.

Reloading nuclear fuel: Unit 3, Palo Verde Nuclear Generating Station.



Resembling giant enoki mushrooms, Palo Verde’s great steam columns rise a mile over the desert creosote flats, each consisting of 15,000 gallons of water evaporated per minute to cool Palo Verde’s three fission reactors. (As Palo Verde is the only U.S. plant not on a river, bay, or seacoast, the water is recycled Phoenix effluent.) With 2,000 employees to keep pumps from sticking, gaskets from leaking, and filters back-washed, the plant is a town big enough to have its own police and fire departments.

Suppose its inhabitants had to evacuate. Suppose they had enough advance warning to shut down by jamming all the moderating rods into each reactor core to stop the reaction and cease generating electricity. Once Palo Verde was unmanned, its connection to the power grid would automatically be cut. Emergency generators with a seven-day diesel supply would kick in to keep coolant water circulating, because even if fission in the core stopped, uranium would continue to decay, generating about 7 percent as much heat as an active reactor. That heat would be enough to keep pressurizing the cooling water looping through the reactor core. At times, a relief valve would open to release overheating water, then close again when the pressure dropped. But the heat and pressure would build again, and the relief valve would have to repeat its cycle.

At some point, it becomes a question of whether the water supply is depleted, a valve sticks, or the diesel pumps cut out first. In any case, cooling water will cease being replenished. Meanwhile, the uranium fuel, which takes 704 million years to lose just half its radioactivity, is still hot. It keeps boiling off the 45 feet of water in which it sits. In a few weeks at the most, the top of the reactor core will be exposed, and the meltdown will begin.

If everyone had vanished or fled with the plant still producing electricity, it would keep running until any one of thousands of parts monitored daily by maintenance personnel failed. A failure should automatically trigger a shutdown; if it didn’t, the meltdown might occur quite quickly. In 1979 something similar happened at Pennsylvania’s Three Mile Island Plant when a valve stuck open. Within two hours and 15 minutes, the top of the core was exposed and turned into lava. As it flowed to the bottom of the reactor vessel, it started burning through six inches of carbon steel.

It was a third of the way through before anyone realized. Had no one discovered the emergency, it would have dropped into the basement, and 5,000°F molten lava would have hit nearly three feet of water flooded from the stuck valve, and exploded.

Nuclear reactors have far less concentrated fissionable material than nuclear bombs, so this would have been a steam explosion, not a nuclear explosion. But reactor containment domes aren’t designed for steam explosions; as its doors and seams blow out, a rush of incoming air would immediately ignite anything handy.

If a reactor was near the end of its 18-month refueling cycle, a meltdown to lava would be more likely, because months of decay build up considerable heat. If the fuel was newer, the outcome might be less catastrophic, though ultimately just as deadly. Lower heat might cause a fire instead of a meltdown. If combustion gases shattered the fuel rods before they turned to liquid, uranium pellets would scatter, releasing their radioactivity inside the containment dome, which would fill with contaminated smoke.

Containment domes are not built with zero leakage. With power off and its cooling system gone, heat from fire and fuel decay would force radioactivity out gaps around seals and vents. As materials weathered, more cracks would form, seeping poison, until the weakened concrete gave way and radiation gushed forth.

If everyone on Earth disappeared, 441 nuclear plants, several with multiple reactors, would briefly run on autopilot until, one by one, they overheated. As refueling schedules are usually staggered so that some reactors generate while others are down, possibly half would burn, and the rest would melt. Either way, the spilling of radioactivity into the air, and into nearby bodies of water, would be formidable, and it would last, in the case of enriched uranium, into geologic time.

Those melted cores that flow to the reactor floors would not, as some believe, bore through the Earth and out the other side, emerging in China like poisonous volcanoes. As the radioactive lava melds with the surrounding steel and concrete, it would finally cool—if that’s the term for a lump of slag that would remain mortally hot thereafter.

That is unfortunate, because deep self-interment would be a blessing to whatever life remained on the surface. Instead, what briefly was an exquisitely machined technological array would have congealed into a deadly, dull metallic blob: a tombstone to the intellect that created it—and, for thousands of years thereafter, to innocent nonhuman victims that approach too closely.

5. Hot Living

They began approaching within a year. Chernobyl’s birds disappeared in the firestorm when Reactor Number Four blew that April, their nest building barely begun. Until it detonated, Chernobyl was almost halfway to becoming the biggest nuclear complex on Earth, with a dozen one-megawatt reactors. Then, one night in 1986, a collision of operator and design mistakes achieved a kind of critical mass of human error. The explosion, although not nuclear—only one building was damaged— broadcast the innards of a nuclear reactor over the landscape and into the sky, amid an immense cloud of radioactive steam from the evaporated coolant. To Russian and Ukrainian scientists that week, frantically sampling to track radioactive plumes through the soil and aquifers, the silence of a birdless world was unnerving.

But the following spring the birds were back, and they’ve stayed. To watch barn swallows zip naked around the carcass of the hot reactor is discombobulating, especially when you are swaddled in layers of wool and hooded canvas coveralls to block alpha particles, with a surgical cap and mask to keep plutonium dust from your hair and lungs. You want them to fly away, fast and far. At the same time, it’s mesmerizing that they’re here. It seems so normal, as if apocalypse has turned out to be not so bad after all. The worst happens, and life still goes on.

Life goes on, but the baseline has changed. A number of swallows hatch with patches of albino feathers. They eat insects, fledge, and migrate normally. But the following spring, no white-flecked birds return. Were they too genetically deficient to make the winter circuit to southern Africa? Does their distinctive coloring make them unappealing to potential mates, or too noticeable to predators?

In the aftermath of Chernobyl’s explosion and fire, coal miners and subway crews tunneled underneath Number Four’s basement and poured a second concrete slab to stop the core from reaching groundwater. This probably was unnecessary, as the meltdown was over, having ended in a 200-ton puddle of frozen, murderous ooze at the bottom of the unit. During the two weeks it took to dig, workers were handed bottles of vodka, which, they were told, would inoculate them against radiation sickness. It didn’t.

At the same time, construction began on a containment housing, something that all Soviet RMBK reactors like Chernobyl lacked, because they could be refueled faster without one. By then, hundreds of tons of hot fuel had already blown onto the roofs of adjacent reactors, along with 100 to 300 times the radiation released in the 1945 bombing of Hiroshima. Within seven years, radioactivity had eaten so many holes in the hastily built, hulking, gray five-story concrete shell, already patched and caulked like the hull of a rusting scow, that birds, rodents, and insects were nesting inside it. Rain had leaked in, and no one knew what vile brews steeped in puddles of animal droppings and warm, irradiated water.

The Zone of Alienation, a 30-kilometer-radius evacuated circle around the plant, has become the world’s biggest nuclear-waste dump. The millions of tons of buried hot refuse include an entire pine forest that died within days of the blast, which couldn’t be burned because its smoke would have been lethal. The 10-kilometer radius around ground zero, the plutonium zone, is even more restricted. Any vehicles and machinery that worked there on the cleanup, such as the giant cranes towering over the sarcophagus, are too radioactive to leave.

Yet skylarks perch on their hot steel arms, singing. Just north of the ruined reactor, pines that have re-sprouted branch in elongated, irregular runs, with needles of various lengths. Still, they’re alive and green. Beyond them, by the early 1990s, forests that survived had filled with radioactive roe deer and wild boars. Then moose arrived, and lynx and wolves followed.

Dikes have slowed radioactive water, but not stopped it from reaching the nearby Pripyat River and, farther downstream, Kiev’s drinking supply. A railroad bridge leading to Pripyat, the company town where 50,000 were evacuated—some not quickly enough to keep radioactive iodine from ruining their thyroids—is still too hot to cross. Four miles south, though, you can stand above the river in one of the best birding areas today in Europe, watching marsh hawks, black terns, wagtails, golden and white-tailed eagles, and rare black storks sail past dead cooling towers.

In Pripyat, an unlovely cluster of concrete 1970s high-rises, returning poplars, purple asters, and lilacs have split the pavement and invaded buildings. Unused asphalt streets sport a coat of moss. In surrounding villages, vacant except for a few aged peasants permitted to live out their shortened days here, stucco peels from brick houses engulfed by untrimmed shrubbery. Cottages of hewn timbers have lost roof tiles to tangles of wild grapevines and even birch saplings.

Just beyond the river is Belarus; the radiation, of course, stopped for no border. During the five-day reactor fire, the Soviet Union seeded clouds headed east so that contaminated rain wouldn’t reach Moscow. Instead, it drenched the USSR’s richest breadbasket, 100 miles from Chernobyl at the intersection of Ukraine, Belarus, and western Russia’s Novozybkov region. Except for the 10-kilometer zone around the reactor, no other place received so much radiation—a fact concealed by the Soviet government lest national food panic erupt. Three years later, when researchers discovered the truth, most of Novozybkov was also evacuated, leaving fallow vast collective grain and potato fields.

The fallout, mainly cesium-137 and strontium-90, by-products of uranium fission with 30-year half-lives, will significantly irradiate Novozybkov’s soils and food chain until at least AD 2135. Until then, nothing here is safe to eat, for either humans or animals. What “safe” means is wildly debated. Estimates of the number of people who will die from cancer or blood and respiratory diseases due to Chernobyl range from 4,000 to 100,000. The lower figure comes from the International Atomic Energy Agency, whose credibility is tinged by its dual role as both the world’s atomic watchdog agency and the nuclear power industry’s trade association. The higher numbers are invoked by public health and cancer researchers and by environmental groups like Greenpeace International, all insisting that it’s too early to know, because radiation’s effects accumulate over time.

Whatever the correct measure of human mortality may be, it applies to other life-forms as well, and in a world without humans the plants and animals we leave behind will have to deal with many more Chernobyls. Little is still known about the extent of genetic harm this disaster unleashed: genetically damaged mutants usually fall to predators before scientists can count them. However, studies suggest that the survival rate of Chernobyl swallows is significantly lower than that of returning migrants of the same species elsewhere in Europe.

“The worst-case scenario,” remarks University of South Carolina biologist Tim Mousseau, who visits here often, “is that we might see extinction of a species: a mutational meltdown.”

“Typical human activity is more devastating to biodiversity and abundance of local flora and fauna than the worst nuclear power plant disaster,” dourly observe radioecologists Robert Baker, of Texas Tech University, and Ronald Chesser, of the University of Georgia’s Savannah River Ecology Laboratory, in another study. Baker and Chesser have documented mutations in the cells of voles in Chernobyl’s hot zone. Other research on Chernobyl’s voles reveals that, like its swallows, the life-spans of these rodents are also shorter than those of the same species elsewhere. However, they seem to compensate by sexually maturing and bearing offspring earlier, so their population hasn’t declined.

If so, nature may be speeding up selection, upping the chances that somewhere in the new generation of young voles will be individuals with increased tolerance to radiation. In other words, mutations—but stronger ones, evolved to a stressed, changing environment.

Disarmed by the unexpected beauty of Chernobyl’s irradiated lands, humans have even tried to encourage nature’s hopeful bravado by reintroducing a legendary beast not seen in these parts for centuries: bison, brought from Belarus’s Belovezhskaya Pushcha, the relic European forest it shares with Poland’s Białowiea Puszcza. So far, they’re grazing peacefully, even nibbling the bitter namesake wormwood—chornobylin Ukrainian.

Whether their genes will survive the radioactive challenge will only be known after many generations. There may be more challenges: A new sarcophagus to enclose the old, useless one, isn’t guaranteed to last, either. Eventually, when its roof blows away, radioactive rainwater inside and in adjacent cooling ponds could evaporate, leaving a new lode of radioactive dust for the burgeoning Chernobyl menagerie to inhale.

After the explosion, the radionuclide count was high enough in Scandinavia that reindeer were sacrificed rather than eaten. Tea plantations in Turkey were so uniformly dosed that Turkish tea bags were used in Ukraine to calibrate dosimeters. If, in our wake, we leave the cooling ponds of 441 nuclear plants around the world to dry and their reactor cores to melt and burn, the clouds enshrouding the planet will be far more insidious.

Meanwhile, we are still here. Not just animals but people too have crept back into Chernobyl’s and Novozybkov’s contaminated zones. Technically, they’re illegal squatters, but authorities don’t try very hard to dissuade the desperate or needy from gravitating to empty places that smell so fresh and look so clean, as long as no one checks those dosimeters. Most of them aren’t simply seeking free real estate. Like the swallows who returned, they come because they were here before. Tainted or not, it’s something precious and irreplaceable, even worth the risk of a shorter life.

It’s their home.