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Department of Nuclear Energy

Judge Nuclear on Its Merits

Dr. H-Holger Rogner, Section Head, Planning and Economic Studies; Dr. Ferenc L. Toth, senior energy economist, Planning and Economic Studies; Alan McDonald, Head of the Programme Coordination Group, Department of Nuclear Energy, IAEA

Nuclear power is a technology that is available today, has very low greenhouse gas emissions, and could be expanded substantially to reduce future greenhouse gas emissions. It is on these features - its merits with respect to climate change - that it should be judged in climate change deliberations. The current exclusion of nuclear power from the Clean Development Mechanism and Joint Implementation, indeed the exclusion of any technology with climate benefits, only limits options, flexibility and cost-effectiveness.

Very low greenhouse gas emissions

Figure 1 compares greenhouse gas (GHG) emissions from the full nuclear power life cycle - mining uranium; making fuel; building, operating and decommissioning the power plant; and dealing with the waste - tolife-cycle emissions from other power generation technologies. The panel on the left shows fossil fuel technologies like coal-fired and natural gas-fired power plants. The panel on the right shows non-fossil technologies like wind, solar and nuclear. Note that the scale for the non-fossil technologies is smaller. It only goes from zero to 180 grams of carbon dioxide equivalent per kilowatt-hour (gCO2-eq/kWh). The scale for fossil fuels in the left panel goes all the way from zero to 1800 gCO2 eq/kWh.

Figure 1 compiles the results of many studies. The bracketed numbers show how many studies were compiled for each technology. Thus there were eight studies that estimated life-cycle GHG emissions for lignite-fueled power plants, twelve studies that estimated emissions for coal-fired plants, and so on. The black dot in the middle of the coloured bar for each technology shows the mean of the emission estimates for that technology. The bar shows one standard deviation around the mean, and the black lines show the highest and lowest estimates for each technology.

Hydropower, nuclear power and wind power have the lowest life-cycle GHG emissions, more than an order of magnitude below fossil-fuel power plants and two thirds below the estimates for solar photovoltaics and biomass. For nuclear power, the mean is approximately 10 gCO2-eq/kWh, from 15 estimates ranging from 2.8 to 24 gCO2-eq/kWh. However, because of their intermittent nature, many renewables cannot provide reliable baseload electricity. Thus, while wind and solar power can complement baseload generation, they cannot fully substitute for hydro and nuclear power.

For nuclear power, most of the GHG emissions come from fuel cycle activities "upstream" of the power plant, including uranium mining, milling, enrichment and fuel fabrication. Most of the variation in nuclear power's estimates comes from different assumptions about the technologies used to enrich uranium, specifically whether gaseous diffusion or centrifuge technology is used and what electricity source is used to power the enrichment plant. Centrifuge technology needs only two per cent of the electricity needed by gaseous diffusion plants, and if the electricity for enrichment is assumed to come from coal-fired power plants, estimated GHG emissions are high; if it is assumed to come from nuclear power, hydropower and wind power, estimated emissions are low.

Figure 1. Life cycle GHG emissions for selected power generation technologies. Source: [WEISSER, D., A guide to life-cycle greenhouse gas (GHG) emissions from electric supply technologies, Energy 32 (2007) 1543-1559]. Left panel: fossil technologies. Right panel: non-fossil technologies

As centrifuge plants continue to displace retiring gaseous diffusion plants and as more of the power for enrichment plants comes from low-carbon electricity, GHG emissions from the nuclear power life cycle will tend toward the lower end of the range shown in Figure 1.

GHG emissions already avoided by nuclear power

Nuclear power has been part of the world's electricity supply for over 50 years. Today, there are 436 power reactors in operation around the world, and since the mid-1980s, nuclear power's share of global electricity production has been 14-16 per cent. Thus nuclear power has already avoided significant GHG emissions, about the same as the emissions avoided by hydropower.

The red bars in Figure 2 show the historical trend of CO2 emissions from global electricity generation. The blue, yellow and green bars are estimates of the emissions avoided by, respectively, hydropower, nuclear power and other renewables. Thus the total heights of the bars are estimates of what the emissions from global power generation would have been without these three electricity sources. In 2007, for example, global CO2 emissions from electricity generation were about 11 gigatonnes (Gt). But without renewables, hydropower and nuclear power, they would have been an estimated 16.4 Gt.

Figure. 2. Global CO2 emissions from the electricity sector and emissions avoided by three low carbon generation technologies. Source: IAEA calculations based on OECD International Energy Agency, World Energy Statistics and Balances: Energy Balances of Non-OECD Member Countries, OECD, Paris (2008)

Figure 3. Shares of non-fossil sources in the electricity sector and CO2 intensities for selected countries in 2006. Source: IAEA calculations based on OECD International Energy Agency, CO2 Emissions from Fuel Combustion, Vol. 2008 release 01

Such estimates of avoided emissions depend very much on what one assumes would have produced the replacement electricity in the absence of renewables, hydropower and nuclear power. For the estimates in Figure 2, it was assumed that the electricity generated by these three sources would have been produced by increasing the coal-, oil- and natural gas-fired generation in proportion to their respective shares in the electricity mix. This approach probably underestimates the emissions avoided by nuclear power in the 1970s and early 1980s. Many of the new nuclear plants built after the oil crises of the 1970s were intended to reduce oil and gas dependence, and coal plants would more likely have been built in their absence than a proportional mix of coal, oil and gas.

Figure 3 shows, at the national level, the correlation between low CO2 emissions and high shares of hydropower or nuclear power. The yellow, blue and green bars and the top scale show the electricity shares of nuclear power, hydropower and renewables for each of the countries listed on the left side. The red bars and the bottom scale, which goes from right to left, show the carbon intensity of the electricity in each of the countries. The chart shows that countries with CO2 intensities that are less than 20 per cent of the world average, i.e. less than 100 gCO2/kWh, generate 80 per cent or more of their electricity from either hydropower (e.g. Norway and Brazil) or nuclear power (e.g. France) or a combination of the two (e.g. Switzerland and Sweden). At the other end of the scale, countries with high CO2 intensities of 800 gCO2/kWh or more have either no nuclear or hydropower in their electricity mix (e.g. Australia) or only limited amounts (e.g. China and India).

Large GHG avoidance potential for the future

The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) estimates the future GHG mitigation potential of various electricity options, specifically fuel switching among fossil fuels, nuclear power, hydropower, wind power, bioenergy, geothermal, solar photovoltaic, concentrating solar power, as well as coal and gas with CO2 capture and storage. The IPCC analysis starts with the reference scenario in the World Energy Outlook 2004, published by the OECD International Energy Agency. It then estimates the GHG emissions that could be avoided by 2030 by adopting various electricity generating technologies in excess of their shares in the reference scenario. The analysis assumes that each technology will be implemented as much as economically and technically possible taking into account practical constraints such as stock turnover, manufacturing capacity, human resource development and public acceptance. The estimates indicate how much more (relative to the reference scenario) of each low carbon technology could be deployed at different cost levels.

The costs are the difference between the cost of the low carbon technology and the cost of what it replaces. The estimates are shown in Figure 4 for technologies with mitigation potentials of more than 0.5 GtCO2-eq.

Figure 4. Mitigation potential in 2030 of selected electricity generation technologies in different cost ranges. Source: Based on data in Table 4.19, p. 300, of Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Metz, B., Davidson, O.R., Bosch, P.R., Dave, R., Meyer, L.A., Eds), Cambridge University Press, Cambridge (2007)

The width of each rectangle in Figure 4 is the mitigation potential of that technology for the carbon cost range shown on the vertical axis. Each rectangle's width is shown by the number directly above or below it. Thus, nuclear power (the yellow rectangles) has a mitigation potential of 0.94 GtCO2-eq at negative carbon costs plus another 0.94 GtCO2-eq for carbon costs up to $20/tCO2. (Negative cost options, in the IPCC report, are those options whose benefits such as reduced energy costs and reduced emissions of local and regional pollutants equal or exceed their costs to society, excluding the benefits of avoided climate change.) The total for nuclear power is 1.88 GtCO2-eq.

The figure indicates that nuclear power has the largest mitigation potential at the lowest average cost in the energy supply sector. Hydropower offers the second cheapest mitigation potential but its size is the lowest among the five options considered here. The mitigation potential offered by wind energy is spread across three cost ranges, yet more than one third of it can be utilized at negative cost. Bioenergy also has a significant total mitigation potential but less than half of it would be available at costs below $20/tCO2-eq by 2030.

Judge nuclear power on its merits

Nuclear power has very low greenhouse gas emissions (Figure 1), and, according to the IPCC's analysis, it has the largest mitigation potential at the lowest average cost in the energy supply sector (Figure 4). These are the merits on which nuclear power should be judged in climate change deliberations.

Yet nuclear power is currently excluded from the Clean Development Mechanism and Joint Implementation. Such exclusion cannot be based on climate concerns.

The underlying concerns about nuclear power are that it could be unsafe, uneconomic, or associated with weapons production. But we respectfully suggest that negotiations on climate change are not the appropriate forum to deal with any of these concerns. As regards safety, the Convention on Nuclear Safety provides an effective international mechanism for review. Regarding costs, it is investors who are best equipped to forecast what will be economically attractive now and in the future. And, as concerns proliferation, there is in place the now indefinitely extended Non-Proliferation Treaty, and the growing adherence to the Additional Protocol, which further strengthens the safeguards agreements under this Treaty.

The UN Commission on Sustainable Development has concluded that although countries disagree on the role of nuclear power in sustainable development, "the choice of nuclear energy rests with countries". It is not for climate change agreements to remove that choice. The best chance for sustainable development - for meeting the needs of the present without compromising the ability of future generations to meet their needs - lies in allowing those future generations to make their own decisions about energy supply options, and allowing these options to compete on a level playing field.