The Environment Effects of Nuclear Power
Abstract
Nuclear power raises a number of fundamental environmental issues. Key among these is the question of how to deal with the quantities of highly radioactive waste that are produced in nuclear power plants. Underground storage for hundreds of years is considered the best option, but no secure underground repository is yet operating. Meanwhile a nuclear accident can potentially cause large-scale environmental damage and this is always a potent concern while the link between nuclear reactors and nuclear weaponry also colors the public perception of the technology. Against this, nuclear power offers a relatively carbon-free method of generating electricity.
Keywords
Energy security; nuclear waste categories; high-level nuclear waste; underground storage; waste reprocessing; nuclear accidents; global warming; power plant decommissioning; low-level radiation
The use of nuclear power raises important environmental questions and as with most environmental issues it is a matter of weighing advantages and disadvantages. The positive aspects of nuclear power include the fact that generating electricity from a nuclear station does not involve the release of any carbon dioxide into the atmosphere and so a nuclear plant can provide part of the solution to reducing global warming. Nuclear power can also provide energy security in countries that have limited natural energy resources. The negative aspects of nuclear power are all linked to the fact that nuclear generation is based on exploitation of nuclear reactions. These reactions produce a range of potentially hazardous waste products. In addition, the effects of a major accident at a nuclear power plant can be far-reaching. When there have been accidents these have had a massive effect on the popular perception of nuclear power.
Added to these considerations is another that the nuclear industry has to address, the perceived link between nuclear and nuclear weapons. While the nuclear industry would claims that the civilian use of nuclear power is a separate issue to that of atomic weapons, the situation is not that clear cut. Nuclear reactors are the source of plutonium which can be used to make a nuclear weapon. Plutonium creation depends on the reactor design and it is possible to build nuclear reactors that produce very little or no nuclear isotopes that are useful for weapons production. However the reactors that are in use today virtually all produce material that can be used for weapons. In addition, most nuclear power plants require enriched uranium and therefore rely on uranium enrichment plants. Highly enriched uranium is another material capable of being fashioned into a bomb. Both are therefore areas of international concern.
The danger is widely recognized. Part of the role of the International Atomic Energy Agency is to monitor nuclear reactors and track their inventories of nuclear material to ensure than none is being sidetracked into nuclear weapons construction. Unfortunately, this system can never be foolproof. It seems that only if all nations can be persuaded to abandon nuclear weapons can this danger be removed. Such an agreement looks highly improbable.
The effects of the detonation of a nuclear weapon are devastating, as history has clearly demonstrated. Of course a nuclear power plant is not a nuclear bomb. Unfortunately for the nuclear power industry, some of the after-effects of the detonation of a nuclear device can also be produced by a major civilian nuclear accident. The contents of a nuclear reactor core includes significant quantities of extremely radioactive nuclei. If these were released during a nuclear accident they would almost inevitably find their way into humans and animals via the atmosphere or through the food chain.
Large doses of radioactivity or exposure to large quantities of radioactive material kills relatively swiftly. Smaller quantities of radioactive material are lethal too, but over longer time scales. The most insidious effect is the genesis of a wide variety of cancers, many of which may not become apparent for 20 years or more. Other effects include genetic mutation which can lead to birth defects.
The prospect of an accident leading to a major release of radioactive nuclides has created a great deal of popular apprehension about nuclear power. The industry has gone to extreme lengths to tackle this apprehension by building ever more sophisticated safety features into their power plants. Unfortunately the accidents at Three Mile Island in the United States, Chernobyl in Ukraine, and Fukushima Daiichi in Japan suggest that it may be impossible to build a nuclear power plant that is entirely safe. For modern plants the risk of an accident may be extremely low. The difficulty is in persuading the public that any risk is acceptable when the stakes are so high.
Unfortunately the fear associated with nuclear accidents has recently been magnified by a rise in international terrorism. The threat now exists that a terrorist organization might seek to cause a nuclear power plant accident or, by exploiting contraband radioactive waste or fissile material, cause widespread nuclear contamination.
So far a peacetime nuclear incident of catastrophic proportions has been avoided, though both Chernobyl and Fukushima caused extensive disruption and in the case of the former a disputed number of deaths as a result of radioactive exposure. Smaller incidents have been more common and low-level releases of radioactive material have taken place. While these are rarely serious, they raise other issues.
One of these issues is the level of the danger from exposure to low radiation levels. The effects of low levels of radioactivity have proved difficult to quantify. Safe exposure levels are used by industry and regulators but these have been widely disputed. On one hand, some would claim that there is no safe level of exposure. On the other hand there are natural sources of radiation to which everybody on the planet is exposed, so a level of exposure that is lower than that experienced naturally might be considered insignificant. Again, it is a matter of trying to establish risk levels, and then to determine what level of risk is acceptable.
Nuclear Power and Global Warming
One of the main advantages of nuclear power promoted by the nuclear industry today relates to its ability to provide low carbon electricity generation. According to the International Energy Agency (IEA), nuclear power was the largest source of low carbon electricity among the countries of the Organization for Economic Cooperation and Development (OECD) countries in 2013 with 18% of total electricity production. Across the globe as a whole its share of production was 11%, making it the second largest contributor after hydropower.1
Based on an IEA scenario for future power generation under which the rise in the global temperature is restricted to 2°C, the organization suggests that nuclear generation would need to more than double from its present level, reaching 930 GW of installed capacity by 2050, when it would provide roughly 17% of global electricity production. This would represent an ambitious program of nuclear construction. However it faces a number of hurdles.
Much of the existing nuclear capacity is in OECD countries. The members of the OECD are mostly rich, developed nations, and many of these invested in nuclear power in the early days of nuclear evolution. As a consequence, many of these countries have benefited from fleets of nuclear plants providing cheap base-load power. The cost of new nuclear power plants makes the technology inaccessible to all but the richest nations today, yet growth in generating capacity is more urgent elsewhere. Small modular nuclear power plants might make the technology more accessible but such plants are not currently available commercially.
On top of that, the recent nuclear accident in Japan has curtailed much global nuclear activity while the construction of renewable generating capacity from wind and solar power continues to grow. There is already evidence that the low cost of these technologies is beginning to undercut others, particularly nuclear power, and this trend will continue. Meanwhile the challenging financial situation across the globe in the second decade of the 21st century makes it extremely difficult to find funding for capital intensive projects like nuclear power stations.
So, while nuclear power can contribute to reducing global warming, it will not be the first choice for new generating capacity in many, if not most parts of the world. Perceptions may change and if the cost of nuclear construction can be reduced by the availability of small, standardized nuclear power units then the appetite for nuclear power may improve. The danger is that nuclear technology will be overtaken by renewable developments elsewhere and that when new nuclear technologies are available, nuclear growth will be difficult to justify economically.
Radioactive Waste
As the uranium fuel within a nuclear reactor undergoes fission, it generates a cocktail of radioactive atoms within the fuel pellets. Eventually the fissile uranium becomes of too low a concentration to sustain a nuclear reaction. At this point the fuel rod will be removed from the reactor. It must now be disposed of in a safe manner. Yet after more than 60 years of nuclear fission, no safe method of disposal is widely available.
Several options are considered viable. The best large-scale method would appear to be disposal of waste in underground bunkers built in stable rock structures. However while the principle has been agreed, finding a site where construction can take place has proved extremely difficult. Reprocessing the waste fuel to remove and reuse the uranium and plutonium fissile material it contains another option. This would reduce the volume of the residual waste, though the residue of high-level waste still requires secure disposal. Spent fuel reprocessing has been carried out in one or two countries but in most there is no agreed solution. As a result, most spent nuclear fuel has been stored in ponds at the nuclear power plants where it was produced. This is now causing its own problems as storage ponds designed to store a few years’ waste become filled, or overflowing.
Meanwhile, radioactive waste disposal has become one of the key environmental battlegrounds over which the future of nuclear power has been fought. Environmentalists argue that no system of waste disposal can be absolutely safe, either now or in the future. And since some radioactive nuclides will remain a danger for thousands of years, the future is an important consideration.
The quest to solve the problem continues. For many years underground burial has been the preferred option for the nuclear industry. This requires both a means to encapsulate the waste and a place to store the waste once encapsulated. Encapsulation techniques have already been developed. These include sealing the waste in a glass-like matrix that is then stored in heavy steel containers. The waste still generates heat, even in this form, and so must be cooled once it has been encapsulated. However the encapsulation should make it impossible for the waste to escape into the environment.
While encapsulation has been demonstrated, construction of an underground store has yet to be realized. An underground site must be in stable rock formation in a region not subject to seismic disturbance. Such locations have been identified and sites in the United States and Europe have been studied for many years but none has yet been built. The most advanced project of this type is the Onkalo repository in Finland where excavation of the underground cavern has begun but the project awaits a construction license from the government. If this is granted, the first waste fuel is expected to be stored around 2020. However this site is designed for waste from Finnish nuclear plants. Other countries still have to find their own solutions.
Fuel reprocessing may offer another, partial solution to the problem of nuclear waste. The reprocessing of spent fuel is part of the nuclear fuel cycle, enabling fissile uranium and plutonium to be recovered from the fuel waste and reused in nuclear fuel. However once reprocessing is complete there is still a significant residue that contains a variety of radioactive isotopes that are of no use in reactors. So while reprocessing reduces the volume of waste, it does not entirely solve the problem.
Other schemes have been proposed for nuclear waste disposal. It is possible to return the high-level waste containing radioactive isotopes to a reactor where they are bombarded with neutrons and where they eventually react to produce less harmful isotopes. This appears to be costly. Another involves loading the fuel into a rocket and shooting it into the sun. Yet another proposes utilizing particle accelerators to destroy the radioactive material generated during fission.
Unfortunately, while there are many proposals for the disposals of radioactive waste, there are limited practical solutions available. In the meantime the volume of radioactive waste continues to increase and so does the environmental problem it represents.
Waste Categories
Spent nuclear fuel and the waste from reprocessing plants represent the most dangerous of radioactive wastes but there are other types too. These come from a variety of sources. Anything within a nuclear power plant that has even the smallest expose to any radioactive material must be considered contaminated. One of the greatest sources of such waste is the fabric of a nuclear power plant itself. This creates a large volume of waste when a nuclear power plant is decommissioned.
High-level wastes are expected to remain radioactive for thousands of years. It is these wastes which cause the greatest concern and for which some storage or disposal solution is most urgently required. But these wastes form a very small part of the nuclear waste generated by the industry. According to the World Nuclear Association the high-level waste only makes up around 3% of the total by volume. Most is low-level waste. Even so it too must be disposed of safely. In order to deal with these different wastes, regulatory authorities have developed nuclear waste categories.
In the US spend fuel and the residual waste from reprocessing plants is categorized as high-level waste2 while reminder of the waste from nuclear power plant operations is classified as low-level waste. There is also a category called transuranic waste which is waste containing traces of elements with atomic numbers greater than that of uranium (92). All elements with a higher atomic number than uranium are naturally radioactive. Low-level wastes are further subdivided into classes depending on the amount of radioactivity per unit volume they contain.
In the United Kingdom there are three categories of waste, high level, intermediate level, and low level. High level includes spent fuel and reprocessing plant waste, intermediate level is mainly the metal cases from fuel rods and low-level waste constitutes the remainder. Normally both high and intermediate level waste require some form of screening to protect workers while low-level waste can be handled without a protective radioactive screen.
Low-level waste will often disposed of by shallow burial, often after compacting, and in some cases it may be incinerated is a special waste combustion plant to reduce the volume before burial. Intermediate level waste needs has to be shielded since it contains higher levels of radioactivity. It may be sealed in concrete of bitumen before burial. However, unlike high-level waste, this type of waste does not need cooling when it is stored.
Decommissioning
A nuclear power plant will eventually reach the end of its life and when it does it must be decommissioned. At this stage the final, and perhaps largest nuclear waste problem arises. After 30 or more years3 of generating power from nuclear fission, most of the components of the plant have become contaminated and must be treated as radioactive waste. This presents a problem that is enormous in scale and costly in both manpower and financial terms.
The cleanest solution is to completely dismantle the plant and dispose of the radioactive debris safely. This is also the most expensive option. A half-way solution is to remove the most radioactive components and then seal up the plant from 20 to 50 years, allowing the low-level waste to decay, before tackling the rest. Two Magnox reactor buildings in the United Kingdom were sealed in this way in 2011 and are expected to remain in that state for 65 years. A third solution is to seal the plant up with everything inside and leave it, entombed, for hundreds of years. This has been the fate of the Chernobyl plant.
Decommissioning is a costly process. Regulations in many countries now require that a nuclear generating company put by sufficient funds to pay for decommissioning of its plants. The US Nuclear Energy Institute suggests that the cost of decommissioning a US power plant is between $450 million and $1.3 billion, based on figures from the US Nuclear Regulatory Commission from 2013. The US utility Southern California Edison has put aside $2.7 billion to decommission its San Onofre power plant, expecting this to cover around 90% of the total expenditure. Meanwhile in 2011 the UK government estimated nuclear decommissioning costs for its existing power plants to be £54 billion. When building a new nuclear plant, the cost of decommissioning must therefore be taken into account.
Normal Power Plant Environmental Effects
Aside from the nuclear aspect of a nuclear power plant there are other environmental effects which a nuclear station will share with other types of power station. There will be some environmental disruption while the plant is being constructed and significant additional vehicle movements; for a nuclear power plant this disruption will last for several years. There will be some habitat destruction, some air pollution and noise which will affect any communities or habitations in the vicinity. There will also be disruption associated with the connection of the power plant to the grid which may require a lengthy right-of-way and transmission line construction.
Once the plant starts operating there will be less vehicle movement and operation of the plant itself will be relatively quiet. However most nuclear power plants need water for cooling the steam turbine condenser and this will require the pumping of water from a local source and then returning it, but at a higher temperature. This is likely to cause changes to the aquatic or marine environment depending on whether fresh or salt water is being used for cooling.
A nuclear power plant is likely to have a long service life but when it does reach the end of its life, the process of decommissioning the plant will be long and complex and this will again involve high levels of activity and vehicle movement. Some of the activities associated with construction, operation, and decommissioning of the station will be disruptive but these are activities that would be associated with virtually any power plant construction.