Environment and Health in Electricity Generation
- Electricity provision must have regard to minimising environmental and public health effects, both directly from generation and indirectly from obtaining fuels and dealing with wastes.
- With nuclear power the focus is on uranium mining and nuclear wastes.
- The health and environmental costs of nuclear power are very low relative to the main alternatives.
The need for electricity generation to be clean and safe has never been more obvious. Nor have those attributes ever been as popularly supported.
Environmental and health consequences of electricity generation are important issues, alongside the affordability of the power which is produced.
Environmental and health consequences are usually seen as external costs - those which are quantifiable but do not appear in the utility's accounts. Hence they are not passed on to the consumer, but are borne by society at large. They include particularly the effects of air pollution on human health, crop yields and buildings, as well as occupational disease and accidents. Though they are even harder to quantify and evaluate than the others, external costs include effects on ecosystems and the impact of global warming.
Production of electricity from any form of primary energy has some environmental effect, and some risk. A balanced assessment of nuclear power requires comparison of its environmental effects with those of the principal alternative, coal-fired electricity generation, as well as with other options. That comparison needs to recognise that waste and decommissioning costs are internalised in nuclear power economics much more fully than, for example, with coal-fired power generation.
Environmental effects of electricity generation
These include the effects of obtaining the fuels from mines, using the fuels, and dealing with the wastes following use of the fuel.
At a uranium mine, ordinary operating procedures normally ensure that there is no significant water or air pollution. The environmental effect of coal mining today is also small except that more extensive areas are often disturbed and may require subsequent rehabilitation, and in certain situations of geology and climate, acid mine drainage due to oxidation of sulfur can be a problem. See section below.
Burning any fossil fuel gives rise to carbon dioxide, and this is addressed in a following section.
Small amounts of radioactivity are released to the atmosphere from both coal-fired and nuclear power stations. In the case of coal combustion small quantities of uranium, radium and thorium present in the coal cause the ash to be radioactive, the level varying considerably (see NORM paper). Nuclear power stations and reprocessing plants release small quantities of radioactive gases (e.g. krypton-85 and xenon-133) and iodine-131, which may be detectable in the environment with sophisticated monitoring and analytical equipment but are never at harmful levels. Steps are being taken to reduce further emissions of both flyash from coal-fired power stations and radionuclides from nuclear power stations and other plants. At present neither constitutes a significant environmental problem.
Disposal and dispersal of wastes from power generation
The solid high-level waste from nuclear power stations is hot and very radioactive, so must be isolated from people and the environment indefinitely. It is stored for 40-50 years while the radioactivity decays to less than one percent of its original level. Then it will be finally disposed of deep underground and well away from the biosphere. In more than 50 decades of civil nuclear power experience nuclear wastes have not caused any serious health or environmental problems nor posed any real risks to people. There has been no pollution or plausible hazard from such material routinely removed from power stations and nor is any likely, either short- or very long-term. long-term.
Intermediate-level waste (radioactive but not requiring cooling) is placed in underground repositories, not necessarily deep, with little delay. Low-level waste is generally buried more conventionally. Radioactive flyash from coal-fired power stations has in the past had a much greater environmental impact largely because it was not perceived as a problem and appropriate action was measures were not taken. Today most fly ash is removed from stack gases and mixed with bottom ash before being buried where seepage and run-off can be controlled, or the ash may be used with cement in concrete.
Nuclear wastes are certainly a significant part of the nuclear power picture, and need to be managed and disposed properly. Further information about wastes from nuclear power is in the paper on Radioactive Waste Management.
Alternatives for power generation are not without challenges, and for a variety of reasons they – particularly those from coal combustion - have not always been well controlled. Flyash particularly, but also bottom ash, are often loaded with heavy metals (including uranium and thorium – see NORM paper). Flyash is mostly retained for land disposal today, and bottom ash is normally buried also, but not always securely and without effects on groundwater. Groundwater pollution with arsenic, boron, cobalt and mercury is not unusual, and the US EPA in 2011 listed 181 US coal ash ponds which posed a significant hazard, 47 of these a high hazard and threat to life. (In 2008 an earthen dam gave way and released 4.1 million cubic metres of ash slurry at TVA’s Kingston power plant, affecting a wide area and the Emory River. The ash contained mercury, selenium, arsenic and other toxic materials and took several years and some $1 billion to clean up.)
Waste heat produced due to the intrinsic inefficiency of energy conversion, and hence as a by-product of power generation, is much the same whether coal or uranium is the primary fuel. The thermal efficiency of coal-fired power stations ranges up to a possible 40 percent, with newer ones typically giving better than 35 percent. That of nuclear stations mostly ranges from 29-38 percent with the common light water reactor today giving about 34 percent.
There is no reason for preferring one fuel over the other on account of the amount of waste heat and consequent water requirements for cooling.* This is the case whether power station cooling is by water from a stream or estuary, or using atmospheric cooling towers which evaporate water. However, it is noteworthy that whereas coal-fired power plants tend to be located near a source of coal, nuclear plants can be sited according to cooling requirements, and can more readily make use of lake or sea water for direct cooling. Hence they are less likely to require expensive cooling towers or to deplete supplies of fresh water for evaporative cooling.
* For a given level of thermal efficiency and size of plant the cooling requirements for a nuclear plant are slightly greater as it does not lose heat up the stack with combustion products.
In any case the dumped heat need not always be "waste". In colder climates district heating and agricultural uses are increasingly found. In France the waste heat from a nuclear plant is used for a crocodile farm. Any such use of waste heat decreases the extent to which local fogs result from its release to the environment in winter. In dryer climates, the rejected heat can be used for desalination to provide potable water.
The main environmental matter relevant to power generation is the production of carbon dioxide (CO2) and sulfur dioxide (SO2) as a result of coal-fired electricity generation. When coal of say 2.5 percent sulfur is used to produce the electricity for one person in an industrialized country for one year, then about 9 tonnes of CO2 and 120 kg of SO2 are produced.
Sulfur dioxide emissions arise from the combustion of fossil fuels containing sulfur, as many of them do. Released in large quantities to the atmosphere it can cause (sulfuric) "acid rains" in areas downwind. In the northern hemisphere many millions of tonnes of SO2 are released annually from electricity generation, though such pollution has been dramatically reduced from earlier levels. The acid rain (rainwater having a pH of 4 and lower) in north-eastern USA and Scandinavia causes ecological changes and economic loss. In the UK and the USA electric power utilities at first sought to minimize this by increasing their use of natural gas.
It is possible to remove a lot of the SO2 from coal stack gases using flue gas desulphurization equipment, but the cost is considerable. Power utilities have spent many billions of dollars on this. On the other hand, between 1980 and 1986 SO2 emissions in France were halved simply by replacing fossil fuel power stations with nuclear ones. At the same time electricity production increased 40 percent and France became a significant exporter of electricity.
Oxides of nitrogen (NOx) from fossil fuel power stations operating at high temperatures are also an environmental problem, regardless of the fuel source. If high levels of hydrocarbons are present in the air, nitrogen oxides react with these in sunlight to form photochemical smog. Moreover, oxides of nitrogen have an adverse effect on the Earth's ozone layer, increasing the amount of ultra-violet light reaching the Earth's surface.
Health effects of power generation
Traditionally occupational health risks have been measured in terms of immediate accident, especially fatality, rates. However, today, and particularly in relation to nuclear power, there is an increased emphasis on less obvious or delayed effects of exposure to cancer-inducing substances and radiation.
Many occupational accident statistics have been generated over the last 50 years of civil nuclear power in North America and Europe. These can be compared with those from coal-fired and other electricity generation. All show that nuclear is distinctly the safer means of electric power generation in this respect. Two simple sets of figures are quoted in Tables 1 & 2. A major reason for coal showing up unfavourably is the huge amount of it which must be mined and transported to supply even a single large power station - some 20,000 times as much coal as uranium from the mine. Mining and multiple handling of so much material of any kind involves hazards, and these are reflected in the statistics.
Health risks in uranium mining are very minor today. In the 1950s exposure of some miners to radon gas led to a higher incidence of lung cancer. For over forty years, however, exposure to high levels of radon has not been a feature of uranium (or other) mines. Today, the presence of some radon around a uranium mining operation and some dust bearing radioactive decay products - as well as the hazards of inhaled coal dust in a coal mine - are well understood. In both cases, using the best current practice, the health hazards to miners are very small and certainly less than the risks of industrial accidents.
(The radiation level one metre from a drum of freshly-processed U3O8 is about half that - from cosmic rays - on a commercial jet flight.)
In other parts of the nuclear fuel cycle, radiation hazards to workers are low, and industrial accidents are few. Further comment on radiation is in the following section.
Certainly nuclear power generation is not completely free of hazards in the occupational sense, but the record shows it to be far safer than other forms of energy conversion. Table 1 covers more than 20 years.
Environmental effects of mining
The two main fuels conventionally mined for power generation are coal and uranium. Natural gas, like oil, is obtained from wells drilled into porous strata of the Earth's crust, though increasingly this uses hydraulic fracturing (fracking) of hard rock to release it.
Coal mining may be underground, with the surface effects limited to spoil heaps of rejected material, or it may be open cut, sometimes involving very extensive environmental impact.
Uranium mining may be underground, open pit, or in situ leach (ISL). The extent of any excavation is very much less than for an equivalent amount of coal, and the main environmental concern with conventional (underground or open pit) mining is the tailings resulting from removing the valuable minerals from the crushed waste rock. Tailings are fine sandy material which must be emplaced back in the mine or in engineered dams. The tailings contain most of the radioactivity from the orebody, and may also have sulphides with potential to generate acid. They comprise most of the volume of the ore that is mined. Dealing with them is straightforward and much more fully regulated than with coal ash.
With in situ leach (ISL) mining, the ore stays underground, and oxygenated groundwater is circulated to dissolve the uranium. Here the main concern is ensuring that there is no pollution of other groundwater from the operation. This is usually straightforward.
See further: Environmental Aspects of Uranium Mining paper.
Environmental (non-occupational) health effects of radiation are qualitatively similar to those occupational ones potentially affecting workers in the industry. Popular concern about ionizing radiation initially grew out of the testing of nuclear weapons, not to mention the threat of their possible use. Correspondingly, these tests provided the nuclear power industry with a strong awareness of radiation hazards. Fortunately radioactivity is readily measurable and its effects well understood compared with those of other hazards with delayed effects - including virtually all chemical cancer-inducing substances. Radiation is a weak carcinogen.
The contrast between air quality effects from coal burning for electricity and increased radiation from nuclear power is very marked: a person living next to a nuclear power plant receives less radiation from it than from a few hours flying each year. On the other hand, anyone downwind of a coal-fired power plant can expect it to have some effect on the air quality.
Typical levels and sources of radiation exposure are low, and those attributable of nuclear power are usually too low to measure. The contribution from the ground and buildings varies from place to place. Personal exposure is measured in millisieverts (mSv). In most parts of the world levels range up to 3 millisieverts per year (mSv/yr) per person for everybody.
Citizens of Cornwall, UK, receive an average of about 7mSv/yr. Hundreds of thousands of people in India, Brazil and Sudan receive up to 40 mSv/yr. Several places are known in Iran, India and Europe where natural background radiation gives an annual dose of more than 50 mSv and in Ramsar in Iran it can give up to 260 mSv . Lifetime doses from natural radiation range up to several thousand millisievert. However, there is no evidence of increased cancers or other health problems arising from these high natural levels.
Cosmic radiation dose varies with altitude and latitude. Aircrew can receive up to about 5 mSv/yr from their hours in the air, while frequent flyers can score a similar increment. In contrast, UK citizens receive about 0.0003 mSv/yr from nuclear power generation and this would be typical of countries using on nuclear power.
In the Chernobyl accident, a large number of people were subject to significantly increased radiation exposure, the actual doses being approximately known. In the Fukushima accident, few workers and very few others were subject to radiation exposure at levels of concern. Preliminary findings after 18 months by the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) show that no radiation health effects arising from the Fukushima accident had been observed among the public or the workers.
However, following the Chernobyl and Fukushima nuclear accidents, large areas were contaminated with radioactive fallout, notably caesium-137, with a 30-year half-life. The question then arises, what level of contamination will pose a health hazard to returning evacuees? This is contentious, since a purely scientific appraisal will allow most people to return home early, but political nervousness based on popular sentiment will strive for criteria based on levels far below what might be harmful.
Radiation exposure of the public from uranium mining and nuclear power is minimal, and further basic information on the subject is in the WNA info paper: Radiation and Life, or more fully, in Nuclear Radiation and Health Effects.
Greenhouse gas emissions
Greenhouse here refers to the effect of certain trace gases in the Earth's atmosphere so that long-wave radiation such as heat from the earth's surface is trapped. A build-up of greenhouse gases, notably CO2, appears to be causing a warming of the climate in many parts of the world, which will cause changes in weather patterns. Much of the greenhouse effect is due to carbon dioxide.
While our understanding of relevant processes is improving, we do not know how much carbon dioxide the environment can absorb, nor how long-term global CO2 balance is maintained. However, scientists are increasingly concerned about the steady worldwide build-up of CO2 levels in the atmosphere, and political initiatives reflect this concern. The build-up is occurring as the world's carbon-based fossil fuels from the Earth's crust are being burned and rapidly converted to atmospheric CO2 e.g. in motor vehicles, domestic and industrial furnaces, and most of all in electric power generation. Progressive clearing of the world's forests also contributes to the greenhouse effect by diminishing the removal of atmospheric CO2 by photosynthesis.
As early as 1977 a USA National Academy of Sciences report concluded that "the primary limiting factor on energy production from fossil fuels over the next few centuries may turn out to be the climatic effects of the release of carbon dioxide". Today this is conventional wisdom. The inexorable increase of CO2 levels in the atmosphere, coupled with concern about their climate effect, is now a very significant factor in the comparison of coal and nuclear power for producing electricity.
Worldwide emissions of CO2 from burning fossil fuels total about 28 billion tonnes per year. About 38% of this is from coal and about 43% from oil. Every 1000 MWe power station running on black coal produces CO2 emissions of about 7 million tonnes per year. If brown coal is used, the amount is about 9 million tonnes. Nuclear fission does not produce CO2, while emissions from other parts of the fuel cycle (e.g. uranium mining and enrichment) amount to about 2% of those from using coal, and some audited figures show considerably less than this. Every 22 tonnes of uranium (26 t U3O8) used  saves about one million tonnes of CO2 relative to coal.
There is now widespread agreement that we need resource strategies and energy policies in every country which will minimize CO2 build-up. In respect to base-load electricity generation, increased use of uranium as a fuel is the most obvious such strategy, utilizing proven technology on the scale required.