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(Updated August 2009)
Until about 20 years ago, energy sustainability was thought of simply in terms of availability relative to the rate of use. Today, in the context of the ethical framework of sustainable development, including particularly concerns about global warming, other aspects are equally important. These include environmental effects and the question of wastes, even if they have no environmental effect. Safety is also an issue, as well as the broad and indefinite aspect of maximising the options available to future generations.
Sustainable development criteria have been pushed into the front line of energy policy. In the light of concerns about global warming due to human enhancement of the greenhouse effect, there is growing concern about how we address energy needs on a sustainable basis.
Geopolitical questions of energy security are central to the assessment of sustainability for individual countries.
A number of factors are widely agreed. The world's population will continue to grow for several decades at least. Energy demand is likely to increase even faster, and the proportion supplied by electricity will also grow faster still. However, opinions diverge as to whether the electricity demand will continue to be served predominantly by extensive grid systems, or whether there will be a strong trend to distributed generation (close to the points of use). That is an important policy question itself, but either way, it will not obviate the need for more large-scale grid-supplied power, especially in urbanised areas, over the next several decades. Much demand is for continuous, reliable supply of electricity, and this qualitative consideration will continue to dominate.
The key question is how we generate that electricity. Today, worldwide, 65% comes from fossil fuels, 15% from nuclear fission and 19% from hydro and other renewable sources. There is no prospect that we can do without any of these.
Harnessing renewable energy such as wind and solar is an appropriate first consideration in sustainable development, because apart from constructing the plant, there is no depletion of mineral resources and no direct air or water pollution. In contrast to the situation even a few decades ago, we now have the technology to access wind on a significant scale for electricity. But harnessing these 'free' sources cannot be the only option. Renewable sources other than hydro – notably wind and solar – are diffuse, intermittent, and unreliable by nature of their occurrence. These sources are intrinsically unsuited to meeting the demand for continuous, reliable supply on a large scale – which comprises most demand in developed countries.
These aspects offer a technological challenge of some magnitude, given that electricity cannot be stored on any large scale. For instance, solar-sourced electricity requires collecting energy at a peak density of about 1 kilowatt (kW) per square metre when the sun is shining to satisfy a quite different kind of electricity demand – one which mostly requires a relatively continuous supply.
Wind is the fastest-growing source of electricity in many countries, albeit from a low base, and there is a lot of scope for further expansion. While the rapid expansion of wind turbines in many countries has been welcome, capacity is seldom more than 30% utilised over the course of a week or year, a consequence of the unreliability of the source and the fact that it does not and cannot match the pattern of demand. The rapid expansion of wind farms is helped considerably by generous government-mandated grants, subsidies and other arrangements ultimately paid by consumers. But there is often a strong groundswell of opposition on aesthetic grounds from the countryside where the turbines are located.
A fuller treatment of electricity from renewable sources is in the information page on Renewable Energy and Electricity.
Apart from renewables, it is a question of what is most abundant and least polluting. Today, to a degree almost unimaginable even 25 years ago, there is known to be an abundance of many energy resources in the ground. Coal and uranium (not to mention thorium) are available and unlikely to be depleted this century.
The criteria for any acceptable energy supply will continue to be cost and safety, as well as environmental considerations. Addressing environmental effects usually has cost implications, as the current greenhouse debate makes clear. Supplying low-cost electricity with acceptable safety and low environmental impact will depend substantially on developing and deploying reasonably sophisticated technology. This includes both large-scale and small-scale nuclear energy plants, which can be harnessed directly to industrial processes such as hydrogen production or desalination, as well as their traditional role in generating electricity.
Generally 'renewable' relates to harnessing energy from natural forces which are renewed by natural processes, especially wind, waves, sun and rain, but also heat from the Earth's crust and mantle. Although it shares many attributes with technologies harnessing these natural forces – for instance radioactive decay produces much of the heat harnessed geothermally – nuclear power is usually categorised separately from ‘renewables’.
Conventional nuclear power reactors do use a mineral fuel and demonstrably deplete the available resources of that fuel. In such a reactor, the input fuel is uranium-235 (U-235), which is part of a much larger mass of uranium – mostly U-238. This U-235 is progressively 'burned' to yield heat. But about one-third of the energy yield comes from something which is not initially loaded in: plutonium-239 (Pu-239), which behaves almost identically to U-235. Some of the U-238 turns into Pu-239 through the capture of neutron particles, which are released when the U-235 is 'burned'. So the U-235 used actually renews itself to some extent by producing Pu-239 from the otherwise waste material U-238.
This process can be optimised in fast neutron reactors, which are likely to be extensively deployed in the next generation of nuclear power reactors. A fast neutron reactor can be configured to 'breed' more Pu-239 than it consumes (by way of U-235 + Pu-239), so that the system can run indefinitely. While it can produce more fuel than it uses, there does need to be a steady input of reprocessing activity to separate the fissile plutonium from the uranium and other materials discharged from the reactors. This is fairly capital-intensive but well-proven and straightforward. The used fuel from the whole process is recycled and the usable part of it increases incrementally.
As well as utilizing about 60 times the amount of energy from uranium, fast neutron reactors will unlock the potential of using even more abundant thorium as a fuel (see information page on Thorium). In addition, some 1.5 million tonnes of depleted uranium now seen by some people as little more than a waste, becomes a fuel resource. The consequence of this is that the available resource of fuel for fast neutron reactors is so plentiful that under no practical terms would the fuel source be significantly depleted.
Regardless of the various definitions of 'renewable', nuclear power therefore meets every reasonable criterion for sustainability, which is the prime concern.
There is abundant coal in many parts of the world, but with the constraints imposed by concern about global warming, it is likely that this will increasingly be seen as chemical feedstock and its large-scale use for electricity production will be scaled down. Current proposals for 'clean coal' technologies may change this outlook. The main technology involves the capture and subsequent storage of the carbon dioxide from the flue gas. Elements of the technology are proven but the challenge is to actually commercialize it and bring the cost down sufficiently to compete with nuclear power.
Natural gas is also reasonably abundant but is so valuable for direct use as heat generation, and as a chemical feedstock, that its large-scale use for power generation makes little sense and is arguably unsustainable.
Fuel for nuclear power is abundant, and uranium is even available from sea water at costs which would have little impact on electricity prices. Furthermore, if well-proven but currently uneconomic fast neutron reactor technology is used, or thorium becomes a nuclear fuel, the supply is almost limitless (see information page on Supply of Uranium).
Someday, hydrogen is expected to come into great demand as a transport fuel which does not contribute to global warming. It may be used in fuel cells to produce electricity or directly in internal combustion motors – as experimentally now.
Fuel cells are at an early stage of technological development and still require substantial, research and development input, although they are likely to be an important technology in the future.
Hydrogen may be provided by steam reforming of natural gas (in which case the emission of by-product CO2 has to be taken into account), by electrolysis of water, or (in future) by thermochemical processes (some new types of nuclear reactor such as high-temperature gas cooled reactors, operating at around 950°C have the potential for the thermochemical splitting of water to produce hydrogen).
Large-scale use of electrolysis would mean a considerable increase in electricity demand. However, this need not be continuous baseload supply, as hydrogen can be accumulated and stored, and solar or wind generation may well serve this purpose better than supplying consumer electricity demand.
However, pending the development of affordable mass-produced fuel cells, a significant increase in base-load electricity demand may result from the adoption of plug-in electric hybrid vehicles and full electric vehicles (see information page on Electricity and Cars). These are only a very short step from current availability (today's hybrid vehicles only need bigger battery capacity and the facility to use mains power for recharging).
Wastes – both those produced and those avoided – are a major concern in any consideration of sustainable development.
Burning fossil fuels produces primarily carbon dioxide as waste, which is inevitably dumped into the atmosphere. With black coal, approximately one tonne of carbon dioxide results from every thousand kilowatt hours generated. Natural gas contributes about half as much CO2 as coal from actual combustion, and also some (including methane leakage) from its extraction and distribution. Oil and gas burned in transporting fossil fuels adds to the global total. As yet, there is no satisfactory way to avoid or dispose of the greenhouse gases which result from fossil fuel combustion.
Nuclear wastes
Nuclear energy produces both operational and decommissioning wastes, which are contained and managed. Although experience with both storage and transport over half a century clearly shows that there is no technical problem in managing any civil nuclear wastes without environmental impact, the question has become political, focussing on final disposal. In fact, nuclear power is the only energy-producing industry which takes full responsibility for all its wastes, and costs this into the product – a key factor in sustainability.
Ethical, environmental and health issues related to nuclear wastes are topical, and their prominence has tended to obscure the fact that such wastes are a declining hazard, while other industrial wastes retain their toxicity indefinitely.
Regardless of whether particular wastes remain a problem for centuries or millennia or forever, there is a clear need to address the question of their safe disposal. If they cannot readily be destroyed or denatured, this generally means that they need to be removed and isolated from the biosphere. This may be permanent, or retrievable.
An alternative view asserts that indefinite surface storage of high-level wastes under supervision is preferable. This may be because such materials have some potential for recycling as a fuel source, or because progress towards successful geological disposal would simply encourage continued use and expansion of nuclear energy. However, there is wide consensus that dealing effectively with wastes to achieve high levels of safety and security is desirable in a 50-year perspective, ensuring that each generation deals with its own wastes.
According to the OECD's Nuclear Energy Agency: "The scientific and technical community generally feels confident that there already exist technical solutions to the spent fuel and nuclear waste conditioning and disposal question. This is a consequence of the many years of work by numerous professionals in institutions around the world... There is a wide consensus on the safety and benefits of geologic disposal."2
Ethical aspects of nuclear wastes
In a 1999 OECD article3, Claudio Pescatore outlines some ethical dimensions of this question. He starts on a very broad canvas, quoting four fundamental principles proposed by the US National Academy of Public Administration4:
These four principles resulted from a request by the US Government to elucidate principles for guiding decisions by public administrators on the basis of the international Rio and UNESCO Declarations5 which acknowledge responsibilities to future generations. The principles can be applied to the question of nuclear wastes, and in particular to their deep geological disposal, a system with inherent passive safety. Referring to relevant 1995 IAEA and NEA publicationsa, Dr Pescatore summarises the principles in this context as follows:
Dr Pescatore points out that deep geological disposal is considered as the final stage in waste management. It should ensure security and safety in a way that will not require surveillance, maintenance, or institutional control.
Some energy sources dispose of wastes to the environment or have health effects which are not costed into the product. These implicit subsidies, or external costs as they are generally called, are nevertheless real and borne by society at large. Their quantification is necessary to enable rational choices of energy sources. Nuclear energy has always provided for waste disposal and decommissioning costs in the actual cost of electricity.
The External costs of Energy (ExternE) European Research Network has compared the external costs of various means of generating electricityb. It showed that coal has the highest external costs (and about the same for all other generation costs), followed by gas, while nuclear and wind were one tenth or less of coal. The methodology included the risk of accidents and covered full fuel cycle. Hence if external costs are taken into account, nuclear energy becomes very competitive.
The safety of nuclear energy has been well demonstrated, notwithstanding the continued operation of a small number of reactors which are, by western standards, distinctly unsatisfactory. These include two old Soviet designs, one of which – before some very extensive modifications to the type – precipitated the 1986 Chernobyl disaster. Over 13,000 reactor-years of operation have shown a remarkable lack of problems in any of the reactors which are licensable in most of the world.
There is probably no other large-scale technology used worldwide with a comparable safety record. This is largely because safety was given a very high priority from the outset of the civil nuclear energy program, at least in the West. About one third of the cost of a typical reactor is due to its safety systems and structures, including containment and back-up provisions. This is a higher proportion even than in aircraft design and construction.
Any statistics comparing the safety of nuclear energy with alternative means of generating electricity show nuclear to be the safest. In fact, Chernobyl is the only blemish on a near perfect record, and is of very little relevance to the safety of most of the world's reactors.
From a national perspective, the security of future energy supplies is a major factor in assessing their sustainability. Whenever objective assessment is made of national or regional energy policies, security of supply is a priority.
France's decision in 1974 to expand dramatically its use of nuclear energy was driven primarily by considerations of energy security. However, the economic virtues have since become more prominent. The European Green Paper on the security of energy supply in 2000 put forward coal, nuclear energy and renewables as three pillars of future energy security for Europe6 and European leaders have since highlighted the importance of nuclear power for Europe's energy security and climate goals. The US and UK governments, for example, are clear that nuclear energy must play an increasing role by 2030.
Opportunity costs
Nuclear energy and renewables have one important feature in common. They give us access to virtually limitless resources of energy with negligible opportunity cost – we are not depleting resources useful for other purposes, and we are using relatively abundant rather than less abundant energy. We can envisage a time when fossil carbon-based fuels will be too valuable to burn on the present scale.
Recent analyses fail to come up with any 50-year scenario based on sustainable development principles which does not depend significantly on nuclear fission to provide large-scale, highly intensive energy, along with renewables to meet some small-scale (and especially dispersed) low-intensity needs. The alternative is either to squander fossil carbon resources or deny the aspirations of hundreds of millions of people in the next generation.
Alternative low-CO2 means of producing base-load electricity have not been credibly addressed, and wildly unrealistic projections for renewables of a few years ago have tended to become muted. Certainly all the reputable energy scenarios show the main load being carried by coal, gas, and nuclear, with the share between them depending on economic factors in the context of various levels of greenhouse gas constraints. As the notion of sustainability is increasingly supported politically, all external costs are likely to be factored in, thus affecting the economic choices among fuels for electricity generation in nuclear power's favour.
There is now sufficient solar and wind capacity operating on grid systems for their advantages and limitations to be widely evident. That will help focus public discussion on the real options for continuous, reliable (baseload) electricity generation on the large scale required. Nuclear power can – and must – contribute significantly to sustainable development.
Electricity and CarsRenewable Energy and ElectricityEnergy Subsidies and External CostsEnergy Balances and CO2 ImplicationsThoriumSupply of UraniumWaste Management in the Nuclear Fuel Cycle Appendix 5: Environmental and Ethical Aspects of Radioactive Waste Management
a. The IAEA and NEA publications referenced are discussed in Waste Management in the Nuclear Fuel Cycle Appendix 5: Environmental and Ethical Aspects of Radioactive Waste Management [Back]
b. Results and publications of the ExternE project are available on its website (www.externe.info) [Back]
1. Nuclear Energy in a Sustainable Development Perspective, OECD Nuclear Energy Agency, 2000, (ISBN: 926418278X) [Back]
2. Trends in the Nuclear Fuel Cycle: Economic, Environmental and Social Aspects, OECD Nuclear Energy Agency, 2001 (ISBN: 9789264196643) [Back]
3. Long-term management of radioactive waste – Ethics and the environment, C. Pescatore, NEA Newsletter, Spring 1999, Volume 17, No. 1, OECD Nuclear Energy Agency [Back]
4. Deciding for the Future: Balancing Risks, Costs, and Benefits Fairly Across Generations, A Report by a Panel of the National Academy of Public Administration for the U.S. Department of Energy (June 1997) [Back]
5. Rio Declaration on Environment and Development, United Nations Environment Programme (1992); Declaration on the Responsibilities of the Present Generations Towards Future Generations, United Nations Educational, Scientific and Cultural Organization (1997) [Back]
6. European Commission Green Paper – Towards a European strategy for the security of energy supply, COM/2000/0769 final (29 November 2000) [Back]
NEA Newsletter, Spring 1999, Volume 17, No. 1, OECD Nuclear Energy AgencyWorld Energy Outlook 2007 Edition (ISBN: 9789264027305) and 2006 Edition (ISBN: 9264109897), International Energy Agency. See also World Energy Outlook website (www.worldenergyoutlook.org)OECD Nuclear Energy Agency's Nuclear energy and sustainable development webpage (www.nea.fr/sd)Nuclear Energy in a Sustainable Development Perspective, OECD Nuclear Energy Agency, 2000, (ISBN: 926418278X)Trends in the Nuclear Fuel Cycle: Economic, Environmental and Social Aspects, OECD Nuclear Energy Agency, 2002 (ISBN: 9789264196643)Sustainable Development and Nuclear Power, International Atomic Energy Agency (1997)Energy for People, Energy for Peace, Results of the 18th World Energy Congress, Buenos Aires, Argentina, October 2001, World Energy Council Statement 2002