There are three practical and significantly expandable forms of electricity generation: 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 choose 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 ton 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 tones. 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 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
Coal Oil Natural Gas Nuclear
Carbon Dioxide 2249 1672 1135 0
Sulfur Dioxide 13 12 0.1 0
Nitrogen Oxides 6 4 1.7 0
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 tons/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 reactor be completed prior to the end of the present decade. Reasons given for this decline include the relatively high capital costs of building new nuclear power reactors and an array of financial risks in building new nuclear plants.
The cost of building new nuclear power plants has historically been much higher than the cost of building fossil fuel based power plants. Vendors have recently advertised construction costs for building new plants that would ultimately cost less per MWe than new coal plants, especially coal plants with full practical emission controls in place. Advertised nuclear power costs per kWh delivered would also compete with natural gas based power plants. 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 full 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 environmental gains would be an additional benefit rather than the deciding investment issue.
Conversely, if building new nuclear plants remains significantly more expensive than the cost of building fossil fuel-based power plants, environmental arguments for building nuclear power plants would carry less weight. Equivalent environmental mitigation might then be achieved at lower cost through 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 greatest interest as nuclear power become 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 evaluation of carbon emission compared to spent fuel disposal.
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