Nuclear Power and the Environment
by John Moens
This article was originally published by the U.S. Energy Information Administration.
Nuclear power has been presented as providing net environmental benefits. Specifically, nuclear power makes no contribution to global warming through carbon dioxide emissions. Nuclear power also produces no notable sulfur oxides, nitrogen oxides, or particulates. When nuclear energy is created, nothing is burned in a conventional sense. Heat is delivered through nuclear fission, not oxidation. Nuclear power produces spent fuels of roughly the same mass and volume as the reactor’s fuel. These spent fuels are kept within the reactor’s fuel assemblies; thus, unlike fossil fuels, which emit stack gasses to the ambient environment, solid wastes at nuclear power plants are contained throughout the generation process. No particulates or ash are emitted.
Waste from a nuclear plant is primarily solid waste, spent fuel, and some process chemicals, steam, and heated cooling water. Such waste differs from a fossil fuel plant’s in that its volume and mass are small relative to the electricity produced. The plant operators and subsequent waste owners or managers, including the Department of Energy, control the waste until it is disposed of. Nuclear waste also differs from fossil fuels in that spent fuel is radioactive, while only a minute share of the waste from a fossil plant is radioactive. Solid waste from a nuclear plant or a fossil fuel plant can be toxic or damaging to the environment, often in ways unique to the particular category of plant and fuel. Waste from the nuclear power plant is managed to the point of disposal. In contrast, a substantial part of the fossil fuel waste, especially stack gases, and particulates, is unmanaged after release from the plant.
Some fossil fuel-based emissions can be limited or managed through pollution control equipment or procedures that generally increase the cost of building or managing the power plant to the plant owner or the public. Similarly, nuclear plant operators and managers must spend money to control the radioactive wastes from their plants until they are disposed of appropriately. An environmental component of any decision between building a nuclear or a fossil fuel plant is the cost of such controls and how they might change the prices of building and operating the power plant. Controversial decisions must also be made regarding what rules are appropriate.
The issue of whether nuclear plants present a net positive environmental gain compared to fossil fuels depends on the values placed on the wastes each type of plant produces. Nuclear power provides an environmental benefit by almost eliminating airborne wastes and particulates generated during power generation. Nuclear power creates a cost in the form of relatively small volumes of produced radioactive wastes that must be managed before ultimate disposal. Fossil fuels also have unwanted solid wastes though the problems associated with these wastes differ from spent nuclear fuel. Neither waste stream is desirable. On a pound-per-pound basis, the potential environmental costs of waste produced by atomic plants are usually viewed as higher than most wastes from fossil fuel plants ecological costs. The volume of trash from the nuclear plant is substantially less and better controlled. Any claim of environmental gain from atomic power compared to fossil fuels asserts that the nuclear waste stream, in the aggregate, is the lesser of two unwanted evils and that the electricity produced is worthwhile.
There are at least two alternatives for managing the waste streams from power generation. First, renewable or alternative fuels are available for power generation in addition to nuclear and fossil fuel generation. Such fuels carry their own positive and negative environmental effects. However, these power sources have not demonstrated a potential to provide electricity in volumes that can compare to nuclear and fossil fuels, though they can contribute to any environmental mitigation programs.
The second consideration is demand management. Wastes associated with power generation would decline if less power were demanded. Because there are many ways to carry out specific economic activities, the energy requirements for each alternative also vary. Less energy (or electricity) can produce desired environmental gains at lower costs. Demand management also recognizes that electricity follows daily, weekly, and seasonal cycles. Flattening such a cycle can affect fuel use and fuel choice. Demand management is separate from fuel choice, though the two processes can be complementary. This is especially relevant to nuclear power vs. fossil fuel choices when demand cycles are flattened. Nuclear power is generally considered a better fuel for base load (stable demand) conditions than for meeting cyclical peak loads. The same can, be said for coal as a better base load fuel than a peaking fuel. Leveling demand cycles might thus favor coal or nuclear power over gas or oil. Demand management might therefore be an effective tool for controlling environmental emissions. It might lead to emissions if more coal is consumed. Demand management is excluded here as a separate issue from fuel choice itself.
Nuclear Power Plant Wastes
There are restrictions on the disposition of such wastes. Restrictions are imposed through legislation, regulation, and the commitments of plant owners/operators. From a public perspective, such restrictions represent a collective measure of each emission type’s cost and value. The rules do not represent the values that each places on the emission. Thus opinions will vary on the adequacy of particular emission policies.
Restrictions usually vary with the type of waste. Because wastes produced from power plants change with the fuel, potential environmental controls consequently run with the kind of power plant. There are also variations in the desired level of control of some emissions from nuclear power plants. For example, coolant water discharges might affect temperature conditions in neighboring bodies of water. Such eruptions alter the ecology of these bodies of water, and it becomes a policy issue whether the change has a negative value and what that value is. The answer to such questions will determine what controls and expenses related to that coolant water disposal will be required. The levels of permitted discharge rules do vary by jurisdiction.
An operating nuclear power plant’s most significant environmental waste concern is spent fuel disposal. Because nothing is burned (oxidized) during the fission process, little fuel volume or mass is changed during nuclear power generation. The fuel exists under controlled conditions from the first insertion into the reactor until its removal from the reactor. This control continues until the “final disposition” of the spent fuel. Disagreements can exist regarding what constitutes final disposition, though with most nuclear-spent energy, that disposition is some form of burial. Burial is also the “final disposition” for most solid wastes from fossil fuel plants though restrictions on nuclear solid wastes are usually much more strict.
The nature of the nuclear fuel changes during power generation because generation produces fission and fusion products within the fuel units and materials neighboring the fuel units. Nuclear fuel becomes spent when these fission and fusion products accumulate to the extent that the nuclear fuel is no longer adequate for further power generation use. Considerable energy content of the fuel is unused in this process. Ongoing disagreement exists about whether such new content is economically usable as reprocessed power.
The spent fuel has different radiation and chemical characteristics from the initial nuclear energy. These characteristics necessitate special handling of the waste above and beyond the handling of the initial point. Such handling requires expenses that are part of the costs of nuclear power production. Potential procedures for handling spent fuel vary. Methods include recycling (reprocessing) substantial portions of the spent fuel as usable nuclear fuels and transmuting problem components of atomic power into less harmful components. In the United States, final disposition has targeted the ultimate burial of all spent fuels from nuclear power plants for policy and economic reasons. Reprocessing and transmutation remain options under periodic policy consideration though such processes also involve the maximum vault of spent fuel components. Reprocessing and transmutation would alter such burials’ timing, volume, duration, and conditions. They would also significantly increase the costs of the nuclear power plant operation. The choice is between the prices of reprocessing and transmutation compared to the higher operating costs of these processes. Additional fees are involved because reprocessing has the potential to facilitate weapons proliferation.
The U.S. Department of Energy has, by statute, ultimate responsibility for the disposal of spent nuclear fuels. The point and timing of the Department of Energy’s custody of such waste is an active subject for the court system and negotiations between power generators and the Department. A surcharge on the price of nuclear fuels funds nuclear fuel disposal costs. Presently this charge is 0.1 cents/kWh of power generated. Grants are intended to cover the costs of disposal of nuclear wastes, though they are levied on power generation and not junk. The funds accumulated for spent fuel disposal have sometimes been identified as a public subsidy to the nuclear power industry. Whether this is the case depends very much on perspective and definition. Spent fuel disposal constitutes more extensive and direct federal government involvement in waste disposal than is the case for most other forms of power generation. Views favoring government involvement include special hazards from spent fuel and national security issues arising from reprocessed spent fuels, which might be upgraded to weapons-grade conditions.
Economic subsidy issues also arise regarding whether the funds provided by nuclear power generators adequately cover the costs of the ultimate disposal of nuclear wastes. The targeted leading burial site for spent fuels, Yucca Mountain in Nevada, has not yet been opened and challenged in the courts. Ultimate disposal has thus not occurred for most spent fuels. Most spent powers are now in temporary storage at the reactors where they were produced or intermediate storage at either the reactors or alternative sites.
The Interaction of Fossil Fuel and Nuclear Power Waste Decisions
There are three practical and significantly expandable forms of electricity generation in the United States: coal, natural gas, and nuclear. Oil and oil product-based generation are less thoroughly discussed in this section because relatively high oil prices discourage use in quantity for power generation and are anticipated to continue to do so in the future. This is especially true for base load power generation, the sub-market where nuclear power has been most attractive. Alternative and renewable power sources are insufficiently expandable to compete significantly with coal, natural gas, and nuclear power.
Coal and natural gas present parallel environmental problems, though the volume and proportion of particular emissions, such as sulfur or carbon dioxide, vary. Nuclear power is sufficiently different from oil and natural gas that the tradeoffs between nuclear power and fossil fuels (oil and natural gas) vary, whether it is coal or natural gas that is replaced. In the case of coal, there is also a capacity to choose among high or low fuels in sulfur, ash, and other emission contents. Fossil fuels also permit variations in emission based on burner types, technology choices, and emission control equipment.
Sulfur dioxide emissions from coal-based power plants have been subject to “allowances” since 1995 under guidelines arranged under the Clean Air Act of 1990. An allowance permits a power plant to emit one tonne of a pollutant, such as sulfur dioxide (SO2), per year. Budgets are allocated to specific power plants that produce SO2 emissions. Thus, if a plant has 5000 allowances for the year, at the end of the year, its SO2 emissions must have must not exceed 5000 tonnes. Allowance allocation criteria have varied over time. There is a “cap and trade” arrangement for power plant emissions. Allowances are marketable (tradable) among SO2-producing firms. If one plant has less SO2 than its allowance limits, it can sell that allowance to a plant that cannot meet its limits. Overall, emission levels (the cap) are regulated by government policy. Of course, nothing is ever so simple, and other process components are not addressed here. In addition, some regional allowance systems account for emissions other than SO2.
Allowances are usually allocated based on the energy (British Thermal Unit) content of the plant’s heat input, though there are exceptions and additions to these limits. Thus, There is less reward in the form of allowances to power plants with higher thermal efficiencies. Allowances are granted primarily to power generation units that burn coal because natural gas-burning units produce little SO2. Similarly, nuclear power plants are also excluded from the allowance system. New allowances have generally not been allocated to new power plants or to upgrade existing emitting units. (This relates to the highly controversial “new source review” topic regarding coal plant modifications.) The allowance system regulates overall emissions (caps) from presently operating units. The allowance system does not directly reward firms that build non-emitting teams because these units are not usually granted allowances. However, the impact is similar, though indirect, as caps are tightened, or plants within the emitting category are permitted to expand.
Some local and regional nitrogen oxide allowances have been selectively considered for nuclear power plants during 2002 for upgrades in capacity. These allowances are minor in volume but would reward the plants for avoided emissions. Nuclear plant owners would be able to sell such allocation, improving their plants’ profitability. This would mean proportionally fewer allowances allocated to SO2 emitting plant owners or operators within the cap and trade environment, provided the total cap is not expanded.
The results of any allowance reallocations to nuclear plants would be complicated because owners of coal and nuclear plants are often the same corporations. However, the proportions of nuclear to coal plant ownership vary. Some fossil plant owners might see granting allowances to atomic plant operators as increasing their operating costs. Others might see allowances to nuclear power plants as a mechanism that would permit the prolonged and perhaps upgraded operation of their existing coal plants. The allocation system and emissions cap might be anticipated to determine individual operator attitudes.
The Environmental Protection Agency (EPA) identifies the following average emission levels in producing 1 MWh of electricity.
Pounds of Emissions per MWh
|Source: www.epa.gov/clean energy/impacts
For fossil fuel-burning power plants, solid waste is primarily a problem for coal-based power. Approximately 10% of the content of coal is ash. Ash often includes metal oxides and alkali. Such residues require disposal, generally burial, though some recycling is possible, in a manner that limits migration into the general environment. Volumes can be substantial. When burned in a power plant, oil also yields residues that are not entirely burned and thus accumulate. These residues must also be disposed of as solid wastes. Natural gas does not produce significant volumes of combustion-based solid wastes. Nuclear does produce spent fuels.
Nuclear power produces around 2,000 metric tonnes/per annum of spent fuel. This amounts to 0.006 lbs/MWh. If a typical nuclear power plant is 1000 MWe in capacity and operates 91% of the time, waste production would be 45,758 lbs./annum or slightly less than 23 tons. The solid waste from a nuclear power plant is thus not the volume of the trash, which is very small, but the special handling required for satisfactory disposal. A similar amount of electricity from coal would yield over 300,000 tons of ash, assuming 10% ash content in the coal. Processes (specifically scrubbing) for removing ash from coal plant emissions are generally highly successful but result in more significant volumes of limestone solid wastes (plus water) than the volume of ash removed.
The preceding discussion used averages. Different plants operate differently. This case is most stark for oil, where products used to generate electricity range from heavy fuel oil to liquefied petroleum gas (LPG). These products produce different sulfur dioxide and metal emissions profiles. The sulfur content of oil products also varies considerably within the category groups, most notably fuel oil and gasoil (diesel). Coal is more variable in energy, ash, sulfur, and metal content. Natural gas and LPG are more consistent in fuel character.
Any environmental gains from switching from fossil-based fuels to nuclear fuel thus depend on which power is replaced and which emission is of principal concern. While the increase in most airborne emissions between nuclear and coal is significant, emission reductions increasingly focus on carbon emissions as one moves from solid to liquid to gaseous fuels. Each fuel category also has the potential to burn lower sulfur content varieties. Lower sulfur fuels thus present a partial alternative to the replacement of generation capacity by nuclear power if the aggregate (cap) emission level of sulfur is the policy goal. A stricter emission cap would attract the atomic power industry more than a less severe cap.
The economic and environmental choice regarding emissions reduction thus focuses on the relative value placed on fossil fuel emission vs. spent fuel production at a nuclear power plant and on the alternative sources of emissions mitigation compared to any added cost from atomic power production. This view accepts the historical experience that nuclear power is more expensive to build than conventional fossil fuel units. The decline of new nuclear power plant construction since the 1970s and 1980s culminated in the completion of the last new nuclear power reactor in the United States in 1996 (Watts Bar 1). While as many as four construction licenses remain in effect (or are to be extended) until the early 2010s, there is little anticipation that any new nuclear plant reactor be completed before the end of the present decade. Reasons for this decline include the relatively high capital costs of building new nuclear power reactors and the financial risks of building new nuclear plants.
The cost of building new nuclear power plants has historically been much higher than building fossil fuel-based power plants. Vendors have recently advertised construction costs for building new plants that would cost less per MWe than new coal plants, especially coal plants with full practical emission controls. Advertised nuclear power costs per kWh delivered would compete with natural gas-based power plants. These cost assertions have not been tested in the U.S. power market and have received only limited international testing. Presently no orders are in place for these reactors, and the Nuclear Regulatory Commission has not yet licensed many of the newest designs. If the vendors correctly identify new nuclear power plant construction costs and if costs include complete adjustments for financial risks, then there is diminished policy importance regarding the environmental gains of replacing fossil fuels with nuclear power. The nuclear plants would be economically viable, and ecological gains would be an additional benefit rather than the deciding investment issue.
Conversely, if building new nuclear plants remains significantly more expensive than building fossil fuel-based power plants, environmental arguments for building nuclear power plants would carry less weight. Equivalent environmental mitigation might be achieved at a lower cost by refitting fossil fuel plants with emission controls, burning lower sulfur fuels, or replacing coal-fired plants with natural gas-fired plants.
Any environmental gains in switching power generation from fossil to nuclear fuels would thus be of most interest as atomic power becomes economically competitive regarding operating and construction costs. The extent of such gains would vary with which fossil fuel is under consideration and how one evaluates the emissions avoided and gained. Coal has many unwanted emissions. Replacing natural gas with nuclear power would depend more on the relative carbon emission evaluation than spent fuel disposal.
Summary: The Environmental Position of Nuclear Power
Views on the suitability of nuclear power for reducing emissions of greenhouse gases, acid gases, particulates, and metals are highly charged. No question that producing an increased share of electric power using nuclear fuels instead of fossil fuels will reduce greenhouse gas emissions. Substantial replacement of fossil fuels will result in significant declines in acid gas emissions and particulate and solid waste production if coal is replaced. Such changes would increase the volume of nuclear-spent fuel that must be disposed of.
Many of the identical reductions in emissions might also be obtained by switching electricity production from coal to natural gas or lower sulfur coal. Emission control technologies are also an alternative. Because crude gas-based power production produces many of the same emissions as coal-based power production, a greater volume of replaced generation capacity would be required to replace coal-based power using natural gas than would be necessary using nuclear power. Because raw gas-based ability involves different proportions of particular emissions than coal-based power, reductions in sulfur dioxide, nitrogen oxides, and particulate production would be more substantial than reductions in carbon emissions, though carbon emissions would also decline. Sulfur dioxide emissions across the board could be reduced substantially by choosing lower sulfur versions of a specific fuel. Emissions control devices and improved operating procedures can reduce the output and disposal of particular emissions from power. These conclusions regarding fossil fuels and emissions abstract from the very substantial issue of the availability of specific fossil fuels and the impact of increased consumption on their prices.
The suitability of nuclear power as an alternative method of reducing power emissions thus turns on three issues:
- What level of emissions reduction is desired
- What are the costs of obtaining emissions reductions by using nuclear power when compared to other methods
- Do any costs of switching to nuclear power (such as spent fuel disposal) offset any environmental gains from the displaced emissions?
Within this context, if nuclear power is substantially more expensive than alternative fossil fuel-based power, then the alternative methods of emissions reductions will be more attractive than nuclear power. If nuclear power proved less costly to build and operate than fossil fuel-based power, any environmental arguments for nuclear power would not be a diminished factor in economic decisions. Emissions reduction arguments in favor of nuclear power carry their most significant weight when nuclear power approaches the cost of alternative fossil fuels and when atomic force presents the least cost alternative for obtaining the emissions control gains.
Emissions from fossil fuels vary by fuel. Environmental reasons for replacing coal-fired power with nuclear power can cover the entire stack gas, particulate, and solid waste spectrum. Replacing natural gas-fired power generation with nuclear for environmental reasons depends more substantially on greenhouse gas emissions targets. These evaluations would be made within the context of non-economic values placed on nuclear power and its “emissions.”
Emission to the ambient environment is, of course, the point of disposal. There is always the question of the retirement of decommissioned nuclear power plants. This issues paper focuses on operating plants. This does not mean that the disposal of decommissioned plants is a minor concern. A slight reduction in mass does occur. Another limiting note must be added. The actual removal of nuclear wastes might be included in a future issues paper. This paper addresses the issue that costs are incurred in disposing of spent fuel and not the details of the final disposal method nor their exact worth. It is, however, not the exclusive case. The government is actively involved in water discharge practices from hydroelectric plants, for example. The concept of “safety” risks or perceptions of safety risks is included as a financial risk. The management of safety risks is the responsibility of the Nuclear Regulatory Commission, which has licensed several reactor designs to be safe and is licensing additional procedures.