The Nuclear Age



NUCLEAR AGE



The Earth exploded into the nuclear age on 16 July 1945. On that day, the US tested a completely new type of weapon in the New Mexico desert. Crafted from a tennis-ball-sized plutonium sphere, the Trinity bomb produced an explosion equivalent to 20,000 tonnes of TNT.

Sixty years on, tens of thousands of tonnes of plutonium and enriched uranium have been produced. The global nuclear arsenal stands at about 27,000 bombs. Nine countries very probably possess nuclear weapons, while 40 others have access to the materials and technology to make them.

But nuclear technology has also been used for peaceful means. The first nuclear reactor to provide electricity to a national grid opened in England in 1956. Now, 442 reactors in 32 nations generate 16% of the world's electricity.

Nuclear power has been championed as a source of cheap energy. But this was undermined at the end of the 20^th century by high-profile reactor accidents, the problems of radioactive waste disposal, competition from more-efficient electricity sources and unavoidable links to nuclear weapons proliferation. Nonetheless, growing evidence for global warming had led some to argue that nuclear power is the only way to generate power without emitting greenhouse gases.

Splitting atoms

The first steps towards unleashing the power within the atomic nucleus began in 1905 when Albert Einstein established that even tiny quantities of mass are equivalent to immense amounts of energy, through his equation E=mc². In 1938, Germans Otto Hahn and Fritz Strassman split inherently unstable uranium atoms by bombarding them with neutrons. The following year, Lise Meitner and Otto Frisch elucidated this process of nuclear fission, in which atomic nuclei are split to create nuclei of lighter elements, with neutrons and energy as by-products.

In 1941 the US embarked on the top secret Manhattan Project, which developed the bombs dropped on Hiroshima and Nagasaki at the end of World War Two. These are the only times nuclear weapons have been used in combat, though about 2000 have been tested. The Manhattan project cost $2 billion dollars and involved the work of 175,000 people, eight of whom were Nobel-prize winning physicists. The list includes Robert Oppenheimer, Enrico Fermi, Richard Feynman, Niels Bohr and Leo Szilard.

Uranium is the heaviest element found in nature in more than trace amounts, and natural ores contain two isotopes: U-238 and U-235. Only U-235, which makes up just 0.7% of ores, is fissile. So the uranium must be "enriched" to remove U-238 - highly enriched weapons-grade uranium can be up to 90% U-235.

When bombarded with neutrons, U-235 atoms absorb them and become unstable. They split to form two smaller nuclei of other elements and neutrons. Some of the mass is converted to energy in the form of gamma radiation and heat. Because only one neutron is needed to trigger fission and two or three are released, a chain reaction can result. This reaction is uncontrolled in an atomic bomb but tightly controlled in a nuclear reactor.

Dropping the bomb

The Hiroshima bomb was made of enriched uranium, compressed by detonating explosives to achieve a supercritical mass. The Nagasaki bomb was made of plutonium, which is also fissile. Plutonium is produced in the spent fuel of a nuclear reactor, via the irradiation of uranium 238. It can be extracted to create weapons.

Following 1945, the US developed massively destructive hydrogen bombs. Some are equivalent to many millions of tonnes of TNT, and yield vast amounts of energy through nuclear fusion. In nuclear fusion, atomic nuclei fuse to form heavier elements. Hydrogen bombs use small fission explosions to create the huge temperatures required for heavy isotopes of hydrogen to fuse.

Nuclear weapons technology has been adapted for many military uses, such as intercontinental missiles, huge fission weapons, bunker busters, mini-nukes, gamma ray weapons, nuclear landmines and nuclear defence missiles.

By bombing Japan, the US started a worldwide arms race, and the Cold War with the Soviet Union. The Soviets developed and tested their own bomb in 1949. The United Kingdom achieved the feat in 1952, followed by France in 1960, China in 1964 and most recently India and Pakistan in 1998.

Israel is widely thought to possess nuclear weapons and North Korea declared in 2005 that it did too, though neither has conducted tests. Iraq and Libya have attempted to develop them in the past, and Iran has been accused of having a secret nuclear weapons programme.

Stemming proliferation

While up to nine nations have nuclear weapons, 187 others have pledged not to manufacture them. Twenty countries such as Switzerland, Brazil, Argentina, Canada and South Africa once had programmes; but as signatories to the 1968 Treaty on the Non-Proliferation of Nuclear Weapons (NPT), subsequently abandoned them.

The NPT aimed to limit the spread of atomic weapons and bound the five original nuclear weapons states to sharing nuclear technology and materials for peaceful means - mainly through US and Russian disarmament, the treaty has achieved the decommisioning of 38,000 warheads since 1986.

However, the treaty is under strain in 2005. Nuclear-armed states stand accused of failing to reduce their arsenals, and of considering new weapons, like mini-nukes. Iran reached an agreement with Europe to halt uranium enrichment activities, but may renege on that deal.

The 1996 Comprehensive Nuclear Test Ban Treaty is an attempt to limit test detonations and slow nuclear armament, but the US senate refused to ratify it in 1999.

Controlling the remains of the Soviet Union's vast and poorly protected nuclear arsenal is another great challenge. The G8 have repeatedly pledged billions of dollars to help safeguard the massive stockpile.

The International Atomic Energy Agency is struggling to keep track of smuggling and the black market in nuclear materials and technology, and fears of terrorists acquiring a dirty bomb are frequently expressed. The sale of materials and information was highlighted in 2004, when a Pakistani nuclear scientist admitted to selling nuclear technology to Libya, North Korea and Pakistan.

Atoms for peace

Nuclear power generation has been linked to nuclear weapon proliferation. In fact, the first industrial-scale reactors, built in the US in 1944, were designed to produce plutonium for weapons and the energy generated was wasted. The first nuclear reactor to provide electricity to a national grid opened in Calder Hall in England in 1956. Today countries such as Japan and France use nuclear power to provide up to 75% of their energy.

Unlike in atomic weapons, nuclear reactors must tightly control the fission chain reaction. To prevent a runaway reaction, control rods are interspersed with the fuel rods of uranium or plutonium. The control rods absorb neutrons, and can be lowered into the reactor core to regulate energy output. A moderating substance, such as water or graphite, surrounds the rods, slowing neutrons emitted by the reaction, and deflecting them back to the centre.

A coolant circulates around the core, and is pumped to a heat exchanger, where water becomes steam and drives electricity-generating turbines. Advanced gas-cooled reactors, such as those used in the UK, use compressed carbon dioxide as the coolant. Light-water, heavy-water and pressurised-water reactors, use water as moderator and coolant.

These reactors are inherently inefficient, only utilising around 1% of the energy stored in the uranium fuel. To overcome this inefficiency and minimise nuclear waste, some countries re-process nuclear fuel. The Sellafield facility in the UK is the largest re-processing facility in the world, but has suffered many problems.

More advanced (but less safe) breeder reactors use liquid sodium metal as a coolant and generate plutonium fuel. Breeder reactors such Superphénix in France, Dounreay in the UK, Monju in Japan and planned reactors in India, can utilise up to 75% of the energy contained in uranium. New miniature Rapid-L reactors might one day even provide power in the basements of apartment blocks and "take-away", portable reactors are planned for the future.

Nuclear fuel has also been used to power submarines, such as Russia's doomed Kursk; spacecraft such as Cassini, Galileo and the failed Mars-96; and ice breakers, aircraft carriers and other ships. The Pentagon even briefly entertained the idea of a nuclear-powered jet.

Going critical

However, several high profile accidents damaged public confidence in nuclear power. The worst US nuclear accident was in 1979, when a cooling system malfunctioned at Three Mile Island in Pennsylvania. The reactor melted down, releasing radioactive gas into the environment. There are now concerns about safety with other ageing US reactors.

The world's most catastrophic nuclear accident happened in 1986, at Chernobyl in Ukraine. Control rods were withdrawn from the reactor in misguided safety test, causing meltdown and massive explosions. The radiation released killed 30 people directly and spread over northern Europe.

The accident has led to radiation-induced conditions such as thyroid cancers and leukaemia, birth defects, baby deaths and contamination to lakes and forests. Three other reactors at Chernobyl began working again in 1988, but the last finally closed in 2000 after Western nations eventually paid Ukraine to close it. Similar reactors in Eastern Europe may be just as dangerous.

In 1999, 70 people were exposed to radiation in Japan's Tokaimura uranium processing plant after workers added seven times the safe quantity of uranium to a settling tank. This triggered an uncontrolled chain reaction. Many other hazardous or lethal accidents have occurred in facilities such as Windscale, Sellafield, Mayak, Monju, Tsuruga and Mihama.

Radioactive nuclear waste - which remains dangerous for many thousands of years - is another serious drawback of the industry. Governments have considered disposing of it by reprocessing; burying it deep underground, such in Nevada's Yucca Mountain in the US; burning it; shipping it to other countries; zapping it with giant lasers; encasing it in glass blocks and storing it on-site at nuclear facilities.

But concerns have been raised about potential flooding of repositories, secret disposal sites and the risks of transporting waste. Cleaning up decommissioned nuclear sites is also expensive and difficult.

Yet nuclear power still has one advantage that could prompt a comeback - the lack of greenhouse gas emissions. Some now tout it as a good way to reduce the emissions linked to global warming. The US government has already announced plans for a raft of new nuclear power stations - the first since 1979.