Energy: Attitudes to nuclear power are shifting in response to climate change and fears over the security of the supply of fossil fuels. The technology of nuclear power has been changing, too OVER the next few decades global electricity consumption is expected to double. At the same time, many power plants in rich countries, built back in the 1960s and 1970s, are nearing the end of their projected lifespans. Meanwhile, concern is swelling both about global warming, and about the Western world's increasing dependence on a shrinking number of hostile or unstable countries for imports of oil and gas. The solution to this conundrum, in the eyes of many governments, is nuclear power. Around the world, 31 reactors are under construction and many more are in the planning stages. Some of the most ambitious programmes are under way in developing countries. Both China and India are building several reactors and intend to increase their nuclear-generating capacity several times over in the next 15 years. Some countries, such as Turkey and Vietnam, are considering starting nuclear-power programmes, and others, including Argentina and South Africa, plan to expand their existing ones. The rich world is also re-examining the case for nuclear. America is expecting a rush of applications to build new reactors in the coming months-the first in almost 30 years. Britain's prime minister, Gordon Brown, recently affirmed his support for a new generation of nuclear power plants. Construction of a new one in Finland, western Europe's first for 15 years, began in 2005; work is just starting on another of the same design in France. Other European countries that had frozen or decided to scrap their nuclear programmes are rethinking their plans. There are good reasons for this enthusiasm. Nuclear reactors emit almost none of the greenhouse gases responsible for global warming. They are fuelled by uranium, which is relatively abundant and is available from many sources, including reassuringly stable places such as Canada and Australia. At the moment 439 nuclear reactors in 31 countries supply 15% of the world's electricity. Even without a price on carbon emissions, says Fatih Birol, the chief economist of the International Energy Agency (iea), the worldwide generating capacity of nuclear power plants will probably increase from about 370 giga-watts today to 520 gigawatts in 2030. But if there were a price on carbon dioxide, says Mr Birol, "it could grow even faster." But there are also good reasons for scepticism. Nuclear plants are expensive: each can cost several billion dollars to build. Worse, in the past, ill-conceived designs, safety scares and the regulatory delays they gave rise to made nuclear plants even more costly than their hefty price-tags suggest. Vendors of new nuclear plants, such as Areva, General Electric (ge), Hitachi and Westinghouse, argue that things are different now. The latest designs incorporate suggestions from utilities and operators with decades of experience, and should, their creators say, make new plants safer and easier to operate. They believe the simpler new reactors, with their longer lifespans and reduced maintenance costs, will also improve the economics of the industry. All nuclear reactors rely on nuclear fission, a process that was discovered in the 1930s. When certain heavy atoms are struck by a neutron, they absorb it, become unstable and split apart. This results in two lighter atoms, and two or three neutrons are ejected. The process releases large amounts of energy, much of it in the form of the kinetic energy of the fast-moving fission products. This kinetic energy is converted to heat as the fission products slow down. If the ejected neutrons go on to strike other unstable atoms nearby, those too can break apart, releasing further neutrons in a process known as a chain reaction. When enough of these neutrons produce further fissions