Armageddon Science (11 page)

These detection devices are accompanied by bomb-disposal equipment, including conventional tools, be they simple wire cutters or supercold liquids to disable detonators, and special apparatuses, such as foam generators producing a material specifically designed to be used to cover a nuclear device and absorb as much of the stray radiation as possible. Proactive presence, exercises, and extortion attempts aside, the only real action the NEST teams have seen is when nuclear weapons or satellites containing nuclear power sources have been involved in a crash or landed in an unexpected site.

As well as the direct activity of NEST, there is also a significant amount of passive detection in place, particular since 9/11. The Department of Homeland Security has been busy installing radiation detectors at ports, airports, and border crossings in the years following the attack on the Twin Towers. As of 2006, around one-third of all shipping containers, and well over three-quarters of the land transport that crosses the Canadian and Mexican borders, were being scanned—and these percentages continued to rise, with all cargo containers crossing the southern border passing through detectors by 2007. Several large cities also have detectors on boundaries and on airborne and van-mounted equipment. This is a threat that is being taken very seriously.

Of course, nuclear weapons aren’t the only nuclear threat to our safety. There are also nuclear power plants. Three Mile Island and Chernobyl have demonstrated that things can go wrong at a nuclear power plant. What would happen if we had a real disaster at an American power plant, comparable to or worse than Chernobyl? It’s hard to forget that nuclear reactors were first built with the sole intention of producing materials for atomic bombs.

Bearing in mind how much bigger a reactor is than a bomb, what would happen if one exploded? The possibility is frightening. Yet at the time of writing, nuclear power is being viewed more positively by governments than it has been for many years, because it is (in terms of greenhouse gas emissions) a relatively green way of generating power.

The good news is that a reactor is not going to explode like a bomb. Remember that to make a bomb, the Manhattan Project had to enrich uranium, concentrate the rare uranium 235, or to make plutonium. Reactors run on the much more common uranium 238, which isn’t capable of producing the unstable chain reaction needed for a nuclear explosion, and though plutonium can be produced as a by-product, this is removed long before there is enough to cause a threat.

That uranium 238 is not going to run away and explode, because it can’t start a chain reaction unless the neutrons emitted by it are slowed down. It needs a moderator, a material like carbon or water that will slow the neutrons enough to give them the time needed to cause fission with uranium 238. Although it is possible to have a nuclear accident, it isn’t possible for the whole thing to explode like a nuclear bomb—if the reactor started to run away, producing the kind of fast neutrons necessary for a bomb, the reaction would automatically cease.

That’s not to say that nuclear reactors can’t explode. But the explosion is a conventional one, caused by too much heat in a confined space, not a nuclear explosion. We can gauge the impact of failures of control in nuclear power stations from two well-publicized incidents: Three Mile Island and Chernobyl.

The accident at the Three Mile Island reactor, sited on an island in the Susquehanna River near Harrisburg, Pennsylvania, was by far the less significant of the two, even though its name is synonymous with dangerous nuclear accidents. The water-cooling system at the power plant failed, and there was a series of errors in the deployment of fallback systems. The containment vessel, the steel bottle that keeps all the nasty material in the reactor, was
not
breached—the reactor did not melt down—but there was some leakage of coolant that carried radioactive material, and gas was intentionally vented from the containment vessel to keep the pressure under control, again sending radioactive material out of the plant. The result was a low level of exposure that could have resulted in perhaps one death.

The Three Mile Island incident was blown up out of all proportion, so that it is still thought by many to have had a much greater impact than it actually did, for two reasons. First, the problem was picked up by those with an interest in shutting down nuclear plants, and used as a rallying cry about the deadly dangers involved. No one is saying that the accident wasn’t a bad thing. But there are many more industrial accidents each year causing greater death and destruction—it’s just that the other industries don’t have the same strength of feeling against them.

The other problem arose from the indiscriminate use of Geiger counters. Worried about the radioactive leaks from the plant, amateurs measured radiation levels around the area and were horrified to discover that the readings were as much as 30 percent above the national average. This sounded scary. This level was high enough to cause up to sixty times as many deaths as the official impact of the leak. Clearly, it was thought, there was a cover-up. Only there wasn’t. This was just the natural level of radioactivity in the area, caused by the radioactive radon gas that is naturally produced from such neighborhoods built on rocks like granite.

It puts the impact of the Three Mile Island accident into perspective that the natural radiation danger from just living in that area, a danger that was present before the power station was built and would continue even if it were totally removed, was sixty times higher than the risk from the accident itself—and some areas have even higher natural background radiation levels.

Three Mile Island, then, was not as bad as it is often portrayed. But no one can suggest that Chernobyl was a minor incident. The worst nuclear power station accident the world has seen, Chernobyl in Ukraine really did suffer an explosion leading to a breach of the containment vessel, the nightmare scenario for anyone dealing with nuclear safety.

On the night of April 25, 1986, engineers at the Chernobyl nuclear plant carried out a planned test of the emergency core cooling system, the central system that ensures that the operational part of the nuclear reactor does not overheat to such an extent that it disrupts the massive vessel that contains it.

As the test commenced, an operator made an error, bringing the reactor to a nearly shut-down condition. To have enough power to continue the test, engineers had to manually override the safety system to be able to withdraw the control rods that moderate the nuclear reaction. As the engineers repeatedly canceled safety warnings, temperature soared, a massive buildup of steam blasted the top off the reactor, and the Chernobyl disaster began to unfold. (Note once again, this was not a nuclear explosion like that from a nuclear bomb, it was steam pressure that blew the containment vessel open.)

That this could happen is partly attributable to the bad design of that plant. Most nuclear reactors are designed to be self-regulating systems. As they heat up, neutron activity increases, and the result is loss of the chain reaction, because the neutrons are whizzing around too fast to cause a chain reaction in uranium 238. But the Chernobyl design
increased
the reaction rate as temperature increased, providing a positive feedback loop that, with control systems inactive, meant it was impossible to overcome the problem. Worse still, the reactor vessel was not inside the type of concrete containment building used in U.S. designs. It blew open its metal container to send radioactive materials spewing into the atmosphere. The smoke billowing from the ensuing fire contained massive amounts of radioactive particles.

The result was a spate of deaths, over the few days following the explosion, among those exposed to deadly amounts of radiation as they tried to control the fire, followed by a long-term death toll that could have reached as much as four thousand (this number has subsequently been queried) as cancer rates in nearby areas shot up, particularly in neighboring Belarus in the direction the wind was blowing.

The commercial impact of the accident was huge too. Hundreds of miles away in the United Kingdom, sheep flocks had to be destroyed because the radioactive levels in the grass they were eating had temporarily increased (though no one in the United Kingdom is thought to have suffered enough of an increased exposure from the Chernobyl fallout to be at risk). Areas of the countryside around Chernobyl were evacuated and are still considered unsafe.

What should be repeated, though, because there is often still misunderstanding about out-of-control reactors, is that there was no runaway chain reaction causing a nuclear explosion. The chairman of the Senate Intelligence Committee made a public statement that the Soviets were lying about what was happening at Chernobyl because they said that the loss of coolant meant the chain reaction had stopped. They weren’t—it had. The coolant has a secondary effect of slowing down the neutrons emitted, and without slow neutrons there is no chain reaction. It stops dead. There is still plenty of radioactivity—and much too much heat—but no potential for a runaway chain reaction leading to nuclear explosion.

This was, by any means of measurement, a terrible accident. Yet there have been even worse industrial accidents, killing more people, causing more devastation. And the impact of Chernobyl on the environment around it has proved less dramatic than was first thought. There is still contamination, but studies of the flora and fauna around Chernobyl show that they are surprisingly normal. Those used to postapocalyptic landscapes from fiction may also be surprised that giant rats and cockroaches haven’t taken over. In fact, rodents have a bigger tendency to die off than the larger animals, and cockroaches apparently don’t deserve their reputation for being good at resisting radiation either.

Rather than being a blasted wasteland, much of the abandoned territory around Chernobyl teems with wildlife—even bear, beaver, lynx, and bison which rarely survive in Europe. Apart from some distortion in trees, particularly pine, whose sticky coatings tended to hang on to radioactive dust, there is little obvious mutation. There are no monster creatures, or fish with three eyes as those familiar with the nuclear plant in
The Simpsons
might expect. In fact, mutation among surviving animals seems rare—apparently the most common effect of exposure to nuclear radiation is for animals to die, and those that do survive in a damaged form are less attractive for breeding, so mutants have not transformed the biological landscape.

We mustn’t underplay the significance of Chernobyl. Due to a combination of poor design, bad systems and maintenance, and incompetence on the part of the operators, the accident caused terrible damage and many avoidable deaths. Yet in apocalyptic terms, this was no Armageddon. The impact was smaller than an industrial accident like Bhopal, and vastly smaller than the destruction caused by many of the wars that have taken place over the last hundred years.

There remains the concept of the China Syndrome. With reactors unable to provide a true nuclear explosion, this is usually put forward as the ultimate disaster scenario for a nuclear power plant, as portrayed in the movie of the same name. It’s a truly frightening idea. The dramatic name implies a runaway meltdown that doesn’t just make the reactor building collapse. Instead, the overheating reactor eats through the land beneath it and goes on to melt its way through the Earth’s core, all the way though the planet until it pops out in China.

If anything even vaguely like this were to happen it would be truly catastrophic. You don’t even have to get all the way through. Unlike Jules Verne’s friendly picture of a network of caverns under the ground in
Journey to the Center of the Earth,
there is intensely hot liquid rock down there, plus natural nuclear reactions that maintain the heat, and immensely high pressure. If a sustained meltdown plunged deep enough into the Earth it could cause the supervolcano to end all supervolcanoes.

Thankfully, though, dramatic though the image is, it just couldn’t ever happen. Leaving aside the lack of nuclear reactors on the side of the planet opposite China (despite popular public opinion, China is not on the opposite side of the globe from the United States; it’s opposite parts of South America and a lot of ocean), a nuclear reactor could not melt far into the Earth’s crust. It wouldn’t stay a concentrated, superhot blob, but would spread out and cool on contact with the surrounding ground, its temperature rapidly dropping back to normal levels.

As we’ve seen, the poor design of Chernobyl’s reactor was part of the reason for its failure. All Western nuclear power stations were already safer before the accident—and the safety of the USSR’s stations was enhanced after the disaster. There is, however, a way to make generating nuclear power far safer still. There is a totally different design of reactor called a pebble-bed reactor, where the uranium sits in a bed of pebbles made of a special type of graphite (carbon).

The key safety element of the pebble-bed reactor is that it is inherently not susceptible to the usual cause of reactor failure. As we’ve already seen, if a reactor loses cooling its chain reaction stops, and the danger comes instead from the way the intense heat produced can set the graphite control rods alight and the resultant fire can melt through the containment vessel. In a pebble-bed reactor, the pebbles are made of pyrolytic graphite, which is so resistant to heat that the temperatures reached would not cause them any damage. There would be no meltdown, no fire to damage the containment vessel. If the reactor ran out of control it would simply heat up, peak, and cool down without ever threatening its environment. What’s more, such reactors are also more efficient than the traditional design because they run at a higher temperature.

It is bizarre that as the nuclear states build more nuclear power plants to manage their electricity needs with less global warming, few seem to be seriously considering pebble-bed reactors. It would be a major step away from possible future nuclear disasters.

The other alternative to make nuclear power safer is nuclear fusion. Here the power of the Sun is brought to Earth. Given that fusion is the process that makes the difference between a thermonuclear bomb and a conventional fission bomb, it might seem that fusion power stations would be taking nuclear madness to a new level, but in fact fusion power is both vastly safer and cleaner in terms of nuclear waste than is fission.