Energy for the World - Why Uranium?
About half a million years ago, human beings learned to make fire. By collecting and burning wood they were able to warm themselves, cook food and manufacture primitive implements. Thousands of years later the Egyptians discovered the principle of the sail. Later still came the invention of the water wheel. All these activities utilise various forms of energy - biological, chemical, solar and hydraulic.
Living standards and populations
Energy, 'the ability to do work' utilising the forces of nature or the composition of dead organic material, is essential for meeting basic human needs, extending life expectancy, and providing an acceptable living standard.
We have progressed over many thousands of years from a primitive life, which depended for energy on the food that could be gathered, to the hunters who had more food and used fire for heating and cooking, to the early farmers who used domesticated animals as a source of energy to do work.
Then we harnessed of wind and water power. Later, the industrial revolution, based on coal and providing steam power, laid the foundations for today's technological society, with significant developments such as the internal combustion engine for transport, and the large-scale generation of electricity.
Along the way, our primary energy consumption has increased more than a hundredfold. Today in the industrial countries of the world, we use between 150 and 350 gigajoules* per person each year, an increasing proportion of it in the form of electricity.
*Joule (J) - A unit of energy
Megajoule (MJ) = 106 Joules
Gigajoule (GJ) = 109 Joules.
Together with this increasing energy consumption, it has been possible for the world to sustain an ever-increasing population. Continuing rapid growth is foreseen, with the world's population rising from 6.5 billion to about 8 billion by 2025, and perhaps 10 billion later in the century. Most of the population growth will be in the developing countries, which is where more than three quarters of the world's people already live.
Such a population increase will have a dramatic impact on energy demand, at least doubling it by 2050, even if the developed countries adopt more effective energy conservation policies so that their energy consumption does not increase at all over that period.
Primary and Secondary Energy
Energy can be considered in two categories - primary and secondary.
- Primary energy is energy in the form of natural resources, such as wood, coal, oil, natural gas, natural uranium, wind, hydro power, and sunlight.
- Secondary energy is the more useable forms to which primary energy may be converted, such as electricity and petrol.
Primary energy can be renewable or non-renewable:
- Renewable energy sources include solar, wind and wave energy, biomass (wood or crops such as sugar), geothermal energy and hydro power.
- Non-renewable energy sources include the fossil fuels - coal, oil and natural gas, which together provide over 80% of our energy today, plus uranium.
The availability of energy
There is no shortage of primary energy. The sun pours an abundance on to our planet each day. We see this energy in a variety of forms, ranging from solar radiation, through wind and waves, to trees and vegetation which convert the sun's rays into plant biomass.
In addition, there is an enormous amount of energy in the materials of the Earth's crust, the fossil fuels there also storing past energy from the sun. Uranium is an energy source which has been locked into the Earth since before the solar system was formed, billions of years ago.
The challenge today is to move away from our heavy dependence on fossil fuels and utilise non-carbon energy resources more fully. Concerns about accelerating climate change are a major reason for this.
Fossil fuels have served us well. Coal was the first to be widely used industrially and to increase people's standard of living. Oil is a convenient and portable source of energy and it remains vital for much transport. Natural gas is widely used alongside coal and oil, as a very versatile fuel.
But the question of "Why Uranium?" puts the focus on energy sources which are suitable for electricity. Generating electricity already accounts for 40% of primary energy use, and at 2.7% increase per year, demand for it is growing twice as fast as for total energy worldwide.
Where should energy for electricity come from in future? To put the choices into perspective, let us look briefly at the potential and limitations of each source of electric power, beginning with 'renewables'.
Hydro-electric generating facilities have the attraction of providing electricity without polluting the atmosphere. They harness the energy of falling water, which can occur naturally, but more often has to be engineered by the construction of large dams with lakes behind them. The advantages of hrdro-electricity have long been appreciated and today it provides 16% of the world's power. In many countries most of the suitable dam sites have already been used, thus limiting further major development of this source.
Other renewable energy sources have more potential for increased use, but also have characteristics which limit their ability to play a major role in meeting electricity needs, bearing in mind that much of the demand is for continuous, reliable supply on a large scale:
Solar energy has considerable logical and popular appeal. However, for electricity generation, solar power has limited potential, as it is diffuse and intermittent. While it can be concentrated, solar input is interrupted by night and by cloud cover, which means that solar electric generation plant can typically only be used to a small proportion of its capacity. Photovoltaic conversion of the low intensity of incoming radiation directly to high-grade electricity is still relatively inefficient (less than 20%), though this has been the subject of much research over several decades and costs have come well down. World solar PV capacity at the end of 2011 was 67 GWe.
Wind, like the sun, is 'free' and is increasingly harnessed for electricity. About 238,000 megawatts capacity had been installed around the world at the end of 2011. However, it is not necessarily available when needed and some means is required to provide substitute capacity for windless periods. Nevertheless, costs have come down, and are sometimes little more than from conventional sources.
On a small scale (and at relatively high cost) it is possible to store electricity. On a large scale any solar electric or wind generation has to be worked in with other sources of electricity with full back-up. The system costs are then relatively high. The main role of solar energy in the future will be that of direct heating
Geothermal energy comes from natural heat below the Earth's surface. Where hot underground steam can be tapped and brought to the surface it may be used to generate electricity. Such geothermal sources have potential in certain parts of the world, and some 10,000 MWe of capacity is operating. There are also prospects in other areas for pumping water underground to very hot regions of the Earth's crust and using the steam thus produced for electricity generation. The rocks are hot mainly because of their high levels of radioactivity, coupled with their insulation at depth. But technical problems remain.
Most forests and agricultural crops are technically capable of being used as some kind of fuel, even if the primary purpose of the crop is to provide food. There are also some 'energy farms', where crops are produced solely for energy production. Such farms however compete with other crops for water, fertiliser and land use, thus requiring some choice between fuel and food.
Biomass does provide a useful and growing source of energy, especially for rural communities in third world countries, and organic waste and water plants can be used to produce methane or 'biogas'. Nevertheless, it is only likely to play a small role overall.
The only energy resources available for economic large-scale electricity generation are likely to be gas, coal and uranium. All the above renewable sources together only provide about 3% of world electricity.
Oil has generally become too expensive to use for electricity and it has the great advantage of being a portable fuel suitable for transport. Wherever possible it is conserved for special uses, such as transport and in the petrochemical industry.
Gas can be seen in the same way as oil, as being too valuable to squander for uses such as large-scale electricity generation. But after the oil price shocks of the 1970s, increased exploration efforts revealed huge deposits of natural gas in many parts of the world and today these are extensively used for power stations, providing 21% of world electricity. The main virtue of gas however is that it can be reticulated safely and cheaply to domestic and industrial users and burned there to provide heat very efficiently. It is also a valuable chemical feedstock.
Coal is abundant and world production is about 6 billion tonnes per year, most of this being used for electricity. It dominates the scene, and produces 40% of all electricity worldwide, while uranium produces 13.5%. In OECD countries the figures are closer together: 37% and 23% respectively.
Uranium is also abundant, and technologies exist which can extend its use 60-fold if demand requires it. World mine production is about 60,000 tonnes per year, but a lot of the market is being supplied from secondary sources such as stockpiles, including material from dismantled nuclear weapons. Practically all of it is used for electricity.
Energy Conversion: Typical Heat Values of Various Fuels
|Brown coal (lignite)
|Black coal (low quality)
|Black coal (hard)
|Uranium - in typical reactor
||500,000 MJ/kg (of natural U)
MJ = Megajoules
Which should be used?
World resources 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 rather than being available for electricity generation. There are also environmental and other problems associated with the increased mining and burning of coal (see Uranium, Electricity and Climate Change in this series).
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) coal-fired power station consumes about 3.2 million tonnes of black coal each year, and its nuclear counterpart consumes about 24 tonnes of uranium (as 27 t 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, over 20,000 tonnes of typical uranium ore.
The enormous difference in the quantities of fuel used also directly affects the quantities of waste that remain after the electricity has been generated.
The 27 tonnes or so of used fuel taken each year from a 1000 MWe nuclear power station is highly radioactive and gives off a lot of heat. Some is reprocessed so that 97% of the 27 tonnes is recycled. The remaining 3%, about 700 kg, is high-level radioactive waste which is potentially hazardous and needs to be isolated from the environment for a very long time (though it does become much less hazardous even in a few decades). However, the small quantity makes it readily manageable. Even where the used fuel is not reprocessed, the yearly amount of 27 tonnes is modest compared with the quantities of waste from a similar sized coal-fired power station. Its safe isolation in both storage and transport is easily achieved.
See also The Nuclear Fuel Cycle
The 1,000 MWe coal-fired power station produces about 7 million tonnes of carbon dioxide each year, plus perhaps 200,000 tonnes of sulfur dioxide which in many cases remains a major source of atmospheric pollution. Other waste products from the burning of coal include large quantities of fly ash (typically 200,000 tonnes per year), containing toxic metals and other unpleasant materials, as well as naturally-occurring radioactive substances.
If not fully contained, these routine wastes can cause environmental and health damage even at great distances from the site of the power station. For example, acid rain caused by the release of sulfur dioxide has crossed national boundaries and caused severe damage to lakes, rivers and forests in Canada, Scandinavia and elsewhere.
Any means of producing electricity involves some wastes and environmental hazard. The nuclear industry is unique in that it is the only energy-producing industry that takes full responsibility for the management and disposal of all its wastes and meets the full cost of doing so. Nuclear energy today saves the emission of about 2.6 billion tonnes of carbon dioxide each year (compared with about 10 billion tonnes per year actually emitted from fossil fuel electricity generation).
Economics and energy security
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 plant. 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.
Allied to this is the question of energy security. Many countries import most of their energy, so there is a great advantage if a couple of years' supply of fuel for electricity can be stored easily and economically.
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 technical and political reliability, and the least harm to our population and environment?
In mid 2011, there are 30 countries of varying size, political persuasion and degree of industrial development, which include nuclear power in their energy mix and are operating nuclear reactors. About 13.5% of the world's electricity is being produced by more than 440 reactors, with 60 more under construction. Belgium, Canada, China, France, Germany, Hungary, India, Japan, Russia, South Korea, Sweden, Switzerland, Ukraine, 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. With global climate change as a high-profile concern, nuclear power is increasingly seen as an indispensable part of the mix.
To quote an Indian physicist, the late Dr Homi Bhabha: "No energy is more expensive than no energy".