Sunday, December 27, 2009

Why nuclear energy ? / Nuclear power

2- Why nuclear energy?

World reserves of coal are, in theory, large enough to produce the electricity we shall need for more than a hundred years. However, it is likely that more and more of the coal mined in the future will be converted into the more valuable liquid fuels and so will not be available for electricity generation. There are also environmental and other problems associated with the increased mining and burning of coal .

The difference in the heat value of uranium compared with coal and other fuels is important (though both are used at about 33% thermal efficiency in the power station). A one million kilowatt (1,000 MWe) power station, operating at 80% capacity, consumes about 3.1 million tonnes of black coal each year, or about 24 tonnes of uranium (as UO2) enriched to about 4% of the useful isotope (U-235). This requires the mining of over 200 tonnes of natural uranium which may be recovered from, say, 25-100,000 tonnes of typical uranium ore.

a) Economics

The difference in fuel requirements between coal fired and nuclear power stations also affects their economics. The cost of fuel for a nuclear power station is very much less than for an equivalent coal fired power station, usually sufficient to offset the much higher capital cost of constructing a nuclear reactor. Consequently, in practical terms, electricity from nuclear reactors in many regions is competitive with electricity produced from coal, even after providing for management and disposal of radioactive wastes and the decommissioning of reactors.

As gas prices rise and coal faces the prospect of economic constraints on its emissions, nuclear energy looks increasingly attractive.

b) Electricity generation - the future fuel mix

For most countries the questions that need to be answered are: What are our likely electricity requirements? What forms of generation are available to us? Which combination will affordably provide our needs with maximum security, and the least harm to our population and environment?

In mid 2001, there were 31 countries of varying size, political persuasion and degree of industrial development, which included nuclear power in their energy mix and were operating nuclear reactors. Over 16% of the world's electricity is being produced by more than 440 reactors, with 30 more under construction. Belgium, China, France, Germany, Hungary, India, Japan, Russia, Switzerland, UK and USA are just some of the countries with major nuclear energy programs.

No country would want to be too dependent on a single energy source. For many it is therefore not a question of coal or nuclear for their main supply of electricity, but a combination of both, with as much help as possible from renewable sources, and back-up from gas.

c) Alternatives to nuclear electricity

No technology is absolutely safe or without environmental effects. We should therefore compare the production of electricity from nuclear energy with the other options available to us. Burning coal in power stations is still the major source of electricity worldwide, followed by hydro, uranium and gas.

A 1000 MWe light water reactor uses about 25 tonnes of enriched uranium a year, requiring the mining of some 50,000 tonnes of uranium ore. By comparison, a 1000 MWe coal-fired power station requires the mining, transportation, storage and burning of about 3.2 million tonnes of black coal per year. This creates around 7 million tonnes of carbon dioxide not to mention sulfur dioxide, depending on the particular coal. Solid wastes from a coal-fired power station can be substantial and cause environmental and health damage.

Many people are concerned about the possible warming of the earth through enhancement of the greenhouse effect. About half of this is due to steadily increasing carbon dioxide in the atmosphere over the past 150 years, largely from the burning of fossil fuels, particularly coal.

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