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  3. The Nuclear Age The Earth exploded into the nuclear age on 16 July 1945. On that day, the US tested a completely new type of

The Nuclear Age The Earth exploded into the nuclear age on 16 July 1945. On that day, the US tested a completely new type of

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问题                         The 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 (钚球), the bomb produced an explosion equivalent to 20,000 tons of TNT.
    Sixty years on, tens of thousands of tonnes of plutonium and enriched uranium (浓缩铀) have been produced. The global nuclear arsenal (兵工厂) stands at about 27,000 bombs. Nine countries very proba-bly 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 produce 16% of the world’s electricity.
    Nuclear power has been championed as a source of cheap energy. But this was weakened at the end of the 20th century by reactor accidents, the problems of radioactive waste disposal, competition from more-efficient electricity sources and unavoidable links to nuclear weapons proliferation (核武器扩散). 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.
    Dropping the bomb
    The Hiroshima (广岛) bomb was made of enriched uranium, compressed by detonating explosives to achieve a supercritical mass (超临界质量). The Nagasaki(长崎) bomb was made of plutonium.
    Following 1945, the US developed massively destructive hydrogen bombs. Some are equivalent to many millions of tons of TNT, and yield vast amounts of energy through nuclear fusion. Nuclear weapons technology has been adapted for many military uses, such as intercontinental missiles, huge fission (裂变) weapons, mini-nukes (微型核弹), gamma ray weapons, nuclear landmines (地雷), 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 (利比亚) have attempted to develop them in the past, and Iran has been accused of having a secret nuclear weapons programme.
Stopping the Spread
    While up to nine nations have nuclear weapons, 187 others have promised 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), later 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 decommissioning (退役) of 38,000 warheads (弹头) since 1986.
    However, the treaty is under strain in 2005. Nuclear-armed states stand accused of failing to reduce their arsenals (兵工厂), and of considering new weapons, like mini-nukes. Iran reached an agreement with Europe to halt uranium enrichment activities, but may renege (食言)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 approve of it in 1999.
    Controlling the remains of the Soviet Union’s vast and poorly protected nuclear arsenal is another great challenge.
    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.
    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 (五角大楼) 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 broke down 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 serious nuclear accident happened in 1986, at Chernobyl (前功联乌克兰北部城市) in Ukraine. The radiation released killed 30 people directly and spread over northern Europe.
    The accident has led to radiation induced conditions such as thyroid (甲状腺癌) cancers and leukaemia (白血病), birth defects, baby deaths and pollution of 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 Tokaimnra uranium processing plant after workers added seven times the safe quantity of uranium to a settling tank. This caused an uncontrolled chain reaction.    Many dangerous 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 coun tries; destroying 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 o{ repositories (贮藏室), 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 consider it as a good way to reduce the emissions linked to global warming. The US government has already announced plans for a number of new nuclear power stations-the first since 1979.
                                                     John    Pickerell,    8 August 2005 (Adapted)
Cleaning up decommissioned nuclear sites is ______.
选项
答案expensive and difficult
解析 见文章的倒数第二段:"Cleaning up decommissioned nuclear sites is also expensive and difficult."
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