US ENERGY INFORMATION ADMIN. SEPT 2010
Nuclear power has been presented as providing net environmental benefits. Specifically, nuclear power makes no contribution to global warming through the emission of carbon dioxide. Nuclear power also produces no notable sulfur oxides, nitrogen oxides, or particulates. When nuclear power is produced, nothing is burned in a conventional sense. Heat is produced through nuclear fission, not oxidation. Nuclear power does produce spent fuels of roughly the same mass and volume as the fuel that the reactor takes in. 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 a solid waste, spent fuel, and some process chemicals, steam, and heated cooling water. Such waste differs from a fossil fuel plant’s waste in that its volume and mass are small relative to the electricity produced. The waste is under the control of the plant operators and subsequent waste owners or managers, including the Department of Energy, until it is disposed. 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 from 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, while a substantial part of the fossil fuel waste, especially stack gases and particulates are unmanaged after release from the plant.
Some fossil fuel-based emission can be limited or managed through pollution control equipment or procedures that generally increase the cost of building or managing the power plant either to the plant owner or to the public. Similarly, nuclear plant operators and managers must spend money to control the radioactive wastes from their plants until the wastes are disposed in an appropriate manner. 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 costs of building and operating the power plant. Controversial decisions must also be made regarding what controls are appropriate.
The issue of whether nuclear plants actually present a net positive environmental gain compared to fossil fuels depends on the values that are placed on the wastes that each type of plant produces. Nuclear power provides an environmental benefit by almost entirely eliminating airborne wastes and particulates generated during power generation. Nuclear power creates a cost in the form of relatively small volumes of radioactive wastes that are produced that must be managed prior to ultimate disposal. Fossil fuels also produce 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 environment costs of waste produced by nuclear plant is usually viewed as higher than the environmental cost of most wastes from fossil fuels plants. The volume of waste from the nuclear plant is substantially less and better controlled. Any claim of environmental gain from nuclear power compared to fossil fuels asserts that the nuclear waste stream in 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. These power sources have not however 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. Using less energy (or electricity) can result in desired environmental gains at lower costs. Demand management also recognizes that electricity follows daily, weekly, and seasonal cycles. Flattening such cycle can affect fuel use and fuel choice. Demand management is a separate question 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 seen as a better fuel for base load (stable demand) conditions than for meeting cyclical peak loads. The same can however also be said for coal as a better base load fuel than as a peaking fuel. Levelning demand cycles might thus favor coal or nuclear power over gas or oil. Demand management might thus 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 owner/operators. From a public perspective, such restrictions represent a collective measure of the cost and value of each type of emission. The rules do not represent the values that each individual 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 vary with the fuel, potential environmental controls consequently vary with the type of power plant. There are also variations in the desired level control of some emissions from nuclear power plants. For example, coolant water discharges might affect temperature conditions in neighboring bodies of water. Such discharges 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 will be required related to that coolant water disposal. The levels of permitted discharge rules do vary by jurisdiction.
By far the greatest environmental waste concern at an operating nuclear power plant 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 “final disposition” of the spent fuel. Disagreements can exist as to what constitutes final disposition though with most nuclear spent fuel 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 also in materials neighboring the fuel units. Nuclear fuel becomes spent fuel when these fission and fusion products accumulate to an extent that the nuclear fuel is no longer adequate for additional power generation use. Considerable energy content of the fuel is unused in this process. There is ongoing disagreement whether such unused content is economically usable in the form of reprocessed fuel.
The spent fuel has different radiation and chemical characteristics from the initial nuclear fuel. These characteristics necessitate special handling of the waste above and beyond the handling of the initial fuel. Such handling requires expenses that are part of the costs of nuclear power production. Potential procedures for handling spent fuel vary. Procedures include recycling (reprocessing) substantial portions of the spent fuel as usable nuclear fuels and transmuting problem components of nuclear fuel into less harmful components. In the United States, for both policy and economic reasons, final disposition has targeted the ultimate burial of all spent fuels from nuclear power plants. Reprocessing and transmutation remain options that are under periodic policy consideration though such processes also involve the ultimate burial of spent fuel components. Reprocessing and transmutation would alter the timing, volume, duration, and conditions of such burials. They would also increase the costs of the nuclear power plant operation, probably significantly. The choice is between the costs of reprocessing and transmutation compared to the higher operating costs that these processes involve. Additional costs are involved because reprocessing has the potential of facilitating weapons proliferation.
The US Department of Energy has by statute ultimate responsibility for the disposal of spent nuclear fuels. The point and timing of Department of Energy custody of such waste is an active subject for the court system and for negotiations between power generators and the Department. Nuclear fuel disposal costs are funded by a surcharge on the cost of nuclear fuels. Presently this charge is 0.1 cents/kWh of power generated. Charges are intended to cover the costs of disposal of nuclear wastes, though they are levied on power generation and not waste. 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 the nuclear wastes. The targeted ultimate burial site for spent fuels, Yucca Mountain in Nevada, has not yet been opened and has also been challenged in the courts. Ultimate disposal has thus not occurred for most spent fuels. Most spent fuels are now in temporary storage at the reactors where they were produced or in intermediate storage either at 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 is 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 the case 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, for example sulfur dioxide or carbon dioxide, vary between them. 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 chose among fuels which are high or low 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 is a permit for a power plant to emit one tonne of a pollutant such as sulfur dioxide (SO2) per year. Allowances 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. Presently there is a “cap and trade” arrangement for power plant emissions. Allowances are marketable (tradable) among SO2 producing firms. If one plant produces 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. Nothing is ever so simple, of course, and there are further components of the process that 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. There is thus less reward in the form of allowances to power plants that have 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 for upgrades of existing emitting units. (This relates to the highly controversial topic of “new source review” regarding coal plant modifications.) The allowance system regulates overall emissions (caps) from units that presently operate. The allowance system does not directly reward firms that build non-emitting units because these units are not usually granted allowances, though the impact is similar, though indirect, as caps are tightened or as 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 allowance improving the profitability of their plants. Within the cap and trade environment this would mean proportionally less allowances being allocated to SO2 emitting plant owners or operators, provided the total cap is not expanded.
The results of any allowance re-allocations to nuclear plants would be complicated by the fact that owners of coal and nuclear plants are often the same corporations though the proportions of nuclear to coal plant ownership vary. Some fossil plant owners might see granting allowances to nuclear plant operators as increasing their own 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 actual allocation system and any emissions cap might be anticipated to determine individual operator attitudes.
|The Environmental Protection Agency (EPA) identifies the following average emission levels in the production of 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 completely burned and thus accumulate. These residues must also be disposed 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 waste, 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 greater 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 rather heavy fuel oil to liquefied petroleum gas (LPG). These products produce different sulfur dioxide and metals emissions profiles. Sulfur content of oil products also varies considerably within category group, most notably fuel oil and gasoil (diesel). Coal is even 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 fuel is replaced and which emission is of principal concern. While the gain in most airborne emissions between nuclear and coal is significant across the board, emission reductions increasingly focus on carbon emissions as one moves from solid to liquid to gaseous fuels. Within each fuel category there is also a potential to burn lower sulfur content varieties. Lower sulfur fuels thus present a partial alternative to replacement of generation capacity by nuclear power, if the aggregate (cap) emission level of sulfur is the policy goal. A more strict emission cap would be more attractive regarding nuclear power industry than a less severe cap.
The economic and environmental choice in regard to 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 nuclear power production. This view accepts the historic 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.