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2010/12/27-Energy Policy, Valuing the Greenhouse Gas Emissions from Nuclear Power: a Critical Survey

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ARTICLE IN PRESS Energy Policy 36 (2008) 2940- 2953 Contents lists available at ScienceDirect Energy Policy journal homepage: www.elsevier.com/locate/enpol Valuing the greenhouse gas emissions from nuclear power: A critical survey Benjamin K. Sovacool 

Energy Governance Program, Centre on Asia and Globalisation, Lee Kuan Yew School of Public Policy, National University of Singapore, 469C Bukit Timah Road, Singapore 259772, Singapore a r t i c l e in f o a b s t r a c t Article history: This article screens 103 lifecycle studies of greenhouse gas-equivalent emissions for nuclear power Received 25 February 2008 plants to identify a subset of the most current, original, and transparent studies.

Accepted 21 April 2008 It begins by brie"y detailing the separate components of the nuclear fuel cycle before explaining the Available online 2 June 2008 methodology of the survey and exploring the variance of lifecycle estimates. It calculates that while the Keywords: range of emissions for nuclear energy over the lifetime of a plant, reported from quali"ed studies Nuclear power examined, is from 1.4 g of carbon dioxide equivalent per kWh (g CO2e/kWh) to 288 g CO2e/kWh, the Lifecycle analysis mean value is 66 g CO2e/kWh. The article then explains some of the factors responsible for the disparity Greenhouse gas emissions in lifecycle estimates, in particular identifying errors in both the lowest estimates (not comprehensive) and the highest estimates (failure to consider co-products). It should be noted that nuclear power is not directly emitting greenhouse gas emissions, but rather that lifecycle emissions occur through plant construction, operation, uranium mining and milling, and plant decommissioning.

& 2008 Elsevier Ltd. All rights reserved.

1. Introduction for 19% of national electricity generation. In France, 79% of electricity comes from nuclear sources, and nuclear energy contributes to more The nuclear era began with a whimper, not a bang, on than 20% of national power production in Germany, Japan, South December 7, 1942. Amidst the polished wooden "oors of a war- Korea, Sweden, Ukraine, and the United Kingdom.

appropriated squash court at the University of Chicago, Enrico Advocates of nuclear power have recently framed it as an Fermi inserted about 50 ton of uranium oxide into 400 carefully important part of any solution aimed at "ghting climate change constructed graphite blocks. A small puff of heat exhibited the and reducing greenhouse gas emissions. The Nuclear Energy "rst self-sustaining nuclear reaction, many bottles of Chianti were Institute (2007) tells us, it is important to build emission-free consumed, and nuclear energy was born (Metzger, 1984). sources of energy like nuclear and that nuclear power is a Since then, Americans have dreamed of exotic nuclear carbon-free electricity source (1998). Patrick Moore, co-founder possibilities. Early advocates promised a future of electricity too of Greenpeace, has publicly stated that nuclear energy is the only cheap to meter, an age of peace and plenty without high prices non-greenhouse gas emitting energy source that can effectively and shortages where atomic energy provided the power needed to replace fossil fuels and satisfy global demand (Environmental desalinate water for the thirsty, irrigate deserts for the hungry, News Service, 2005). The nuclear power company Areva (2007) and fuel interstellar travel deep into outer space. Other exciting claims that one coal power station of 1 GWe emits about 6 opportunities included atomic golf balls that could always be million tons of CO2 per year while nuclear is quite CO2 free.

found and a nuclear powered airplane, which the US Federal Opponents of nuclear power have responded in kind. In their Government spent $1.5 billion researching between 1946 and calculation, ISA (2006) argues that nuclear plants are poor 1961 (Munson, 2005; Winkler, 2001; Duncan, 1978). substitutes to other less greenhouse gas intensive generators.

While nuclear technologies did not ful"ll these dreams, nuclear They estimate that wind turbines have one-third the carbon-power has still emerged to become a signi"cant source of electricity. equivalent emissions of nuclear power over their lifecycle and In 2005, 435 nuclear plants supplied 16% of the worlds power, hydroelectric one-fourth the equivalent emissions. The Oxford constituting 368 GW of installed capacity generating 2768 TWh of Research Group projects that if the percentage of world nuclear electricity (International Energy Agency, 2007). In the US alone, capacity remains what it is today, by 2050 nuclear power would which has 29.2% of the worlds reactors, nuclear facilities accounted generate as much carbon dioxide per kWh as comparable gas-

"red power stations as the grade of available uranium ore decreases (Barnaby and Kemp, 2007a, b).

 Tel.: +65 6516 7501; fax: +65 6468 4186. Which side is right? Analogous to the critical surveys of E-mail address: bsovacool@nus.edu.sg negative externalities associated with electricity production 0301-4215/$ - see front matter & 2008 Elsevier Ltd. All rights reserved.

doi:10.1016/j.enpol.2008.04.017

ARTICLE IN PRESS B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2941 conducted by Sundqvist and Soderholm (2002) and Sundqvist (2004), this article screens 103 lifecycle studies of greenhouse gas-equivalent emissions for nuclear power plants to identify a subset of the most current, original, and transparent studies. It begins by brie"y detailing the separate components of the nuclear fuel cycle before explaining the methodology of the survey and exploring the variance of lifecycle estimates. It calculates that while the range of emissions for nuclear energy over the lifetime of a plant reported from quali"ed studies examined is from 1.4 g of carbon dioxide equivalent per kWh (g CO2e/kWh) to 288 g CO2e/

kWh, the mean value is 66 g CO2e/kWh. The article then explains some of the factors responsible for the disparity in lifecycle estimates, in particular identifying errors in both the lowest estimates (not comprehensive) and the highest estimates (failure to consider co-products). It should be noted that nuclear power is not directly emitting greenhouse gas emissions, but rather that the lifecycle involves emissions occurring elsewhere and indir-ectly attributable to nuclear plant construction, operation, uranium mining and milling, and plant decommissioning.

2. The nuclear power lifecycle Engineers generally classify the nuclear fuel cycle into two types: once-through and closed. Conventional reactors oper-ate on a once-through mode that discharges spent fuel directly into disposal. Reactors with reprocessing in a closed fuel cycle separate waste products from unused "ssionable material so that it can be recycled as fuel. Reactors operating on closed cycles extend fuel supplies and have clear advantages in terms of storage of waste disposal, but have disadvantages in terms of cost, short-term reprocessing issues, proliferation risk, and fuel cycle safety (Beckjord et al., 2003).

Despite these differences, both once-through and closed nuclear fuel cycles involve at least "ve interconnected stages that constitute a nuclear lifecycle: the frontend of the cycle where Fig. 1. The once-through nuclear fuel cycle.

uranium fuel is mined, milled, converted, enriched, and fabri-cated; the construction of the plant itself; the operation and hard ore found in granite has a lower uranium content, usually maintenance of the facility; the backend of the cycle where about 0.02% or less. Uranium mines are typically opencast pits, up spent fuel is conditioned, (re)processed, and stored; and a "nal to 250 m deep, or underground. A third extraction technique stage where plants are decommissioned and abandoned mines involves subjecting natural uranium to in situ leaching where returned to their original state. Figs. 1 and 2 provide a brief hundreds of tons of sulfuric acid, nitric acid, and ammonia are depiction of the once-through and closed nuclear fuel cycle. injected into the strata and then pumped up again after 3-25 years, yielding uranium from treated rocks.

2.1. The frontend of the nuclear lifecycle 2.1.2. Uranium milling The nuclear fuel cycle is long and complex. The primary fuel for Mined uranium must undergo a series of metallurgical nuclear power plants, uranium, is widely distributed in the earths processes to crush, screen, and wash the ore, letting the heavy crust and the ocean in minute quantities, with the exception of uranium settle as the lighter debris is funneled away. The next concentrations rich enough to constitute ore. Uranium is mined step is the mill, often situated near the mine, where acid or alkali both at the surface and underground, and after extracted it is baths leach the uranium out of the processed ore, producing a crushed, ground into a "ne slurry, and leeched in sulfuric acid. bright yellow powder, called yellowcake, that is about 75%

Uranium is then recovered from solution and concentrated into uranium oxide (whose chemical form is U3O8). In the cases where solid uranium oxide, often called yellow cake, before it is ores have a concentration of 0.1%, the milling must grind 1000 ton converted into hexa"uoride and heated. Then, hexa"uoride vapor of rock to extract 1 ton of yellowcake. Both the oxide and the is loaded into cylinders where it is cooled and condensed into a tailings (the 999 ton of remaining rock) remain radioactive, solid before undergoing enrichment through gaseous diffusion or requiring treatment. Acids must be neutralized with limestone, gas centrifuge. and made insoluble with phosphates (Fleming, 2007; Heaberlin, 2003).

2.1.1. Uranium mining Starting at the mine, rich ores embody concentrations of 2.1.3. Uranium conversion and enrichment uranium oxide as high as 10%, but 0.2% or less is usual, and most Next comes conversion and enrichment, where a series of uranium producers will consider mining ores with concentrations chemical processes are conducted to remove remaining impu-higher than 0.0004%. A majority of the usable soft ore found in rities. Natural uranium contains about 0.7% uranium-235; the rest sandstone has a concentration between 0.2% and 0.01%, and is mainly uranium-234 or uranium-238. In order to bring the

ARTICLE IN PRESS 2942 B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 Fig. 2. The closed nuclear fuel cycle.

concentration of uranium-235 up to at least 3.5% for typical The 15% that emerges as enriched uranium is converted into commercial light water reactors and about 4-5% for other modern ceramic pellets of uranium dioxide, UO2, packed in zirconium reactors, the oxide must be enriched, and the process begins by alloy tubes, and bundled together to form fuel rod assemblies for converting uranium to uranium hexa"uoride, UF6, or hex. Then, reactors.

it is enriched, and the two dominant commercial enrichment To supply enough enriched fuel for a standard 1000 MW methods are gaseous diffusion and centrifuge. reactor for 1 year, about 200 ton of natural uranium has to be Gaseous diffusion, developed during the Second World War as processed (Fleming, 2007). Moreover, uranium must be trans-part of the Manhattan Project, accounts for about 45% of world ported from the mine to processing and enrichment facilities.

enrichment capacity. The diffusion process funnels hex through a Andseta et al. (1998) found that in Canada, the uranium needed to series of porous membranes or diaphragms. The lighter uranium- create fuel rods has traveled more than 4000 km before the 235 molecules move faster than the uranium-238 molecules and process is complete. The IEA (2002) reports that in Europe most have a slightly better chance of passing through the pores in the uranium is transported 150-805 km by railway, 1250 km by boat, membrane. The process is repeated many times in a series of or 378 km by truck.

diffusion stages called a cascade, with the enriched UF6 with-drawn from one end of the cascade and the depleted UF6 removed at the other end. The gas must be processed through some 1400 2.2. Construction stages before it is properly enriched (Uranium Information Centre, 2007). The construction phase of the nuclear lifecycle involves the The gas centrifuge process, "rst demonstrated in the 1940s, fabrication, transportation, and use of materials to build gen-feeds hex into a series of vacuum tubes, and accounts for about erators, turbines, cooling towers, control rooms, and other 45% of world enrichment capacity. When the rotors are spun infrastructure. A typical nuclear plant usually contains some 50 rapidly, the heavier molecules with uranium-238 increase in miles of piping welded 25 thousand times, and 900 miles of concentration towards the outer edge of the cylinders, with a electrical cables. Thousands of electric motors, conduits, batteries, corresponding increase in uranium-235 concentration near the relays, switches, operating boards, transformers, condensers, and center. To separate the two isotopes, centrifuges rotate at very fuses are needed for the system to operate. Cooling systems high speeds, with spinning cylinders moving at roughly one necessitate valves, seals, drains, vents, gauges, "ttings, nuts, and million times the acceleration of gravity (Uranium Information bolts. Structural supports, "rewalls, radiation shields, spent fuel Centre, 2007). storage facilities, and emergency backup generators must remain In United States, the gaseous diffusion plant at Paducah, in excellent condition. Temperatures, pressures, power levels, Kentucky, primarily does enrichment while Europe and Russia radiation levels, "ow rates, cooling water chemistry, and equip-utilize mostly centrifuge methods (Fthenakis and Kim, 2007). The ment performance must all be constantly monitored. While his remaining percentage (10%) of nuclear fuel comes from the estimate is from an older 1000 MW Pressurized Water Reactor, recycling of nuclear weapons. White (1995) calculates that the typical nuclear plant needs After enrichment, about 85% of the oxide comes out as waste in 170,000 ton of concrete, 32,000 ton of steel, 1363 ton of copper, the form of depleted hex, known as enrichment tails, which and a total of 205,464 ton of other materials. Many of these are must be stored. Each year, for instance, France creates 16,000 ton carbon intense; 1 ton of aluminum has the carbon equivalent of of enrichment tails that are then exported to Russia or added to more than 10,000 ton of C02; 1 ton of lithium, 44,000 ton; one ton the existing 200,000 ton of depleted uranium within the country. of silver, 913,000 ton (White, 1995).

ARTICLE IN PRESS B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2943 2.3. Operation the total energy required for decommissioning can be as much as 50% more than the energy needed for original construction The operation phase of the lifecycle encompasses the energy (Fleming, 2007). At the uranium mine, the overburden of rock needed to manage the cooling and fuel cycles of the plant, as well covering the area must be replaced and replanted with indigenous as the energy needed for its maintenance and the fuels used for vegetation, and radioactive tailings must be treated and con-backup generators. Indirect energy use includes the provision of tained.

power during reactor outages, repairs, and shutdowns.

The heart of the operating nuclear facility is the reactor, which generates electricity through the "ssion, or splitting, of uranium 3. Review of nuclear lifecycle studies and plutonium isotopes. In a nuclear reactor, the "ssion process does not take place one atom at a time. Uranium has the rare and To assess the total carbon dioxide-equivalent emissions over productive property that when it is struck by a neutron, it splits the course of the nuclear lifecycle, this study began by reviewing into two and produces more neutrons. If one uranium-235 atom 103 studies estimating greenhouse gas emissions for nuclear collides with an atom of uranium-238, one of the other isotopes of plants. These 103 studies were narrowed according to a three-uranium, it may stay there and induce a couple of decay cycles to phase selection process.

produce plutonium-239. Plutonium-239, sharing the same prop- First, given that the availability of high-quality uranium ore erty of uranium-235, splits when struck by neutrons to act as changes with time, and that mining, milling, enrichment, additional fuel. The process can be controlled by a moderator construction, and reactor technologies change over the decades, consisting of water or graphite to speed the reaction up, and the study excluded surveys more than 10 years old (i.e., published neutron-absorbing control rods to slow it down (Fleming, 2007; before 1997). Admittedly, excluding studies more than a decade Beckjord et al., 2003). Most nuclear reactors around the world old is no guarantee that the data utilized by newer studies is in have a present lifetime of 30-40 years, but produce electricity at fact new. One analysis from Dones et al. (2004c), for instance, full power for no more than 24 years (Fleming, 2007). relied on references from the 1980s for the modeling of uranium mining; data from 1983 for modeling uranium tailing ponds; 1996 data for uranium conversion; and 2000 data for uranium 2.4. The backend of the nuclear lifecycle enrichment. Still, excluding studies more than 10 years old is an attempt to hedge against the use of outdated data, and to ensure The backend phase involves fuel processing, interim storage, that recent changes in technology and policy are included in and permanent sequestration of waste. Spent fuel must be lifecycle estimates. Table 1 lists all 40 studies excluded by their conditioned for reactors operating on a once-through fuel cycle, date.

and reprocessed for those employing a closed fuel cycle.

Second, the study excluded analyses that were not in the public Eventually, radioactive impurities such as barium and krypton, domain, cost money to access, or were not published in English.

along with transuranic elements such as americium and neptu-Table 2 details the nine studies excluded for lack of accessibility.

nium, clog the uranium fueling a nuclear reaction. After a few Third, 35 studies were excluded based on their methodology.

years, fuel elements must be removed, and fresh fuel rods These studies were most frequently discounted because they inserted. The half-life of uranium-238, one of the largest either relied on unpublished data or utilized secondary components of spent fuel, is about the same as the age of the sources. Those relying on unpublished data contained proprie-earth: 4.5 billion years.

tary information, referenced data not published along with the Spent fuel must then be stored at individual reactor sites in study, did not explain their methodology, were not transparent large pools of water for at least 10 years, after which they are about their data sources, or did not detail greenhouse gas located in large concrete casks that provide air-cooling, shielding, emission estimates for separate parts of the nuclear fuel cycle in and physical protection. While there are many different cask g CO2e/kWh. Those utilizing secondary sources merely quoted types, those in the US typically hold 20-24 Pressurized Water other previously published reports and did not provide any new Reactor fuel assemblies, sealed in a helium atmosphere inside the calculations or synthetic analysis on their own. Table 3 depicts the cask to prevent corrosion. Decay heat is transferred by helium 35 studies excluded by methodology.

from the fuel to "ns on the outside of the storage cask for cooling.

Excluding detailed studies that rely on unpublished or non-The "nal stage of the backend of the cycle involves the transparent data does run the risk of including less detailed (and sequestration of nuclear waste. Permanent geological repositories less rigorous) studies relying on published and open data. Simply must provide protection against every plausible scenario in which placing a study in the public domain does not necessarily make it radionuclides might reach the biosphere or expose humans to good. However, the author believes that this risk is more than dangerous levels of radiation. These risks include groundwater offset by the positive bene"ts of transparency and accountability.

seeping into the repository, corrosion of waste containers, Transparency enhances validity and accuracy; public knowledge is leaching of radionuclides, and migration of contaminated ground-less prone to errors, and more subject to the process of debate and water towards areas where it might be used as drinking water or dialogue that improves the quality of information. Transpar-for agriculture.

ency, says Ann Florini, an expert on governance, is the most effective error correction system humanity has yet devised 2.5. Decommissioning (Florini, 2005, p. 16). Furthermore, transparency is essential to promoting social accountability. Society simply cannot make The last stage of the nuclear lifecycle involves the decom- informed decisions about nuclear power without public discus-missioning and dismantling of the reactor, as well as reclamation sion; for these reasons, the author believes that only results in the of the uranium mine site. After a cooling off period that may last public domain should be included.

as long as 50-100 years, reactors must be dismantled and cut into The remaining 19 studies met all criteria: they were published small pieces to be packed in containers for "nal disposal. Proops et in the past 10 years, accessible to the public, transparent about al. (1996) expect nuclear plants to have an operating lifetime of 40 their methodology, and provided clear estimates of equivalent years, but expect decommissioning to be longer, taking at least 60 greenhouse gas emissions according to the separate parts of the years. While it will vary along with technique and reactor type, nuclear fuel cycle. These studies were weighed equally; that is,

ARTICLE IN PRESS 2944 B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 they were not adjusted in particular for their methodology, time equivalent emissions; decommissioning 18%; operation 17%;

of release within the past 10 years, or how rigorously they were backend 15%; and construction 12% (Fig. 4).

peer reviewed or cited in the literature. Table 4 documents the results of these 19 studies.

Statistical analysis of these 19 studies reveals a range of 4. Assessing the disparity in lifecycle estimates greenhouse gas emissions over the course of the nuclear lifecycle at the extremely low end of 1.4 g CO2e/kWh and the extremely What accounts for such a wide disparity among lifecycle high end of 288 g CO2e/kWh. Accounting for the mean values of estimates of greenhouse gas emissions associated with the emissions associated with each part of the nuclear lifecycle, the nuclear fuel cycle? Studies primarily differ in terms of their mean value reported for the average nuclear power plant is scope; assumptions regarding the quality of uranium ore; 66 g CO2e/kWh. Tables 5 and 6 and Figs. 2 and 3 provide the assumptions regarding type of mining; assumptions concerning complete breakdown of this estimate. As Fig. 3 depicts, the method of enrichment; whether they assessed emissions for a frontend component of the nuclear cycle is responsible for 38% of single reactor or for a "eet of reactors; whether they measured historical or marginal/future emissions; assumptions regarding reactor type, site selection, and operational lifetime; and type of Table 1 lifecycle analysis.

Lifecycle studies excluded by date Study Location Estimate (g CO2e/kWh) 4.1. Scope Arron et al. (1991) Canada Bodansky (1992) World 5.7-17 Some studies included just one or two parts of the nuclear fuel Bowers et al. (1987) - - cycle, whereas others provided explicit details for even subcom-Bude (1985) - - ponents of the fuel cycle. Vorspools et al. (2000), for example, Chapman et al. (1974) - - analyzed just the emissions associated with construction and Chapman (1975) - -

CRIEPI (1995) Japan 22 decommissioning for reactors across the world, whereas ExternE DeLucchi (1993) United States 40-69 (1998) assessed the carbon equivalent for the construction of the Dones (1995) World - Sizewell B nuclear reactor in the United Kingdom. Their estimates Dones and Frischknecht (1996) World - are near the low end of the spectrum, at between 3 and Dones et al. (1994) World -

11.5 g CO2e/kWh. In contrast, Storm van Leeuwen et al. (2007)

El-Bassioni (1980) - -

ERDA (1976) United States - looked at every single subcomponent of the fuel cycle, and ExternE (1995 Europe - produced estimates near the high end of the spectrum at Held (1977) - 20 112-166 g CO2/kWh. Table 7 provides a breakdown of their Hohenwarter and Heindler (1988) Germany - estimate, which the authors emphasize is highly dependent on IAEA (1996a) World -

the quality of uranium ore being used to fuel nuclear plants. It has IAEA (1996b) World -

IEA (1994) World 30-60 been included here for two reasons: to give readers a sense for Kivisto (1995) Finland 17-59 how detailed lifecycle assessments can be, and because this study Mortimer (1989) United Kingdom - refers back to some of the numbers presented in this table when Mortimer (1991a) World 47-54 making comparisons below.

Mortimer (1991b) World 47-54 Perry (1977) United States -

Storm van Leeuwen and Smiths estimate has not been Proops et al. (1996) United Kingdom 2.83 universally accepted. Dones (2007) points out that while Storm Raeder (1977) - - van Leeuwen and Smiths analysis is transparent enough that it Rombough and Koen (1975) - - can be critiquedsomething positivehe believes that their Rose et al. (1983) United States -

estimate is too high. His own survey of lifecycle studies found a Sandgren and Sorteberg (1994) Norway -

Science Concepts (1990) United States 30 range of 2-230 g CO2e/kWh, but that the range of 2-77 g CO2e/

Spreng (1988) - - kWh was most common, with only 3 studies giving average Taylor (1996) World 19.7 estimates above 40 g CO2e/kWh. Dones also argues that Storm van Tsoulfanidis (1980) United States -

Leeuwen and Smiths treatment of greenhouse gases associated Tunbrant et al. (1996) Sweden -

Uchiyama (1994) Japan 10.5-47 with the natural gas supply chain are inconsistent, that they rely Uchiyama (1996) - - on outdated references for some of their estimates, and that some Yasukawa et al. (1992) Japan - of their cost conversion estimates are too generic. Dones argues Yoshioka et al. (1994) Japan that they pay no consideration to the coproduction of minerals, a White (1995) United States 34.1-37.7 common practice where economically viable mining and milling Whittle and Cameron (1977) United States -

of low-grade uranium take place with other activities, meaning Table 2 Lifecycle studies excluded by accessibility Study Location Estimate (g CO2e/kWh) Reason excluded ANRE (1999) Japan - In Japanese Dones et al. (2003a, b) USA 5 Only available to ecoinvent subscribers Dones et al. (2004c) Switzerland 5-12 Only available to ecoinvent subscribers Dones (2003) Europe - In German Frischknecht (1995) Germany - In German Izuno et al. (2001) Japan - In Japanese Lewin (1993) Germany - In German Nuclear Energy Agency (2007) World - Only available for purchase Weis et al. (1990) Germany - In German

ARTICLE IN PRESS B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2945 Table 3 Lifecycle studies excluded by methodologya Study Location Estimate (g CO2e/ Reason excluded kWh)

Australia Coal Association (2001) Australia 30-40 Relies on unpublished data Barnaby and Kemp (2007a) OECD Countries11-130 Relies on secondary sources Commonwealth of Australia (2006) Australia, France, Germany, Japan, Sweden, Finland, 5-60 Relies on secondary sources United States Delucchi (2003) United States 26 Relies on unpublished data Denholm and Kulcinski (2004) World 10-100 Relies on secondary sources Dones et al. (2004a) World 5-80 Relies on secondary sources Echavarri (2007) World 2.6-5.5 Relies on secondary sources Fleming (2007) World 88-134 Relies on secondary sources Fritsche (1997) Germany 34 Relies on unpublished GEMIS data Fthenakis and Alsema (2006) Europe 20-40 Relies on secondary sources Gagnon et al. (2002) World 15 Relies on unpublished data Heede (2005) United States 2.5-5.7 Relies on secondary sources Koch (2000) World 2-59 Relies on unpublished data Krewitt et al. (1998) Europe 19.7 Relies on unpublished data Kulcinski (2002) World 15 Relies on secondary sources Lee et al. (2000) South Korea 2.77 Relies on unpublished data Lee et al. (2004) South Korea 0.198-2.77 Relies on unpublished data Meier (2002) United States 17 Relies on secondary sources Meier and Kulcinski (2002) United States 15 Relies on secondary sources Meier et al. (2005) United States 17 Relies on secondary sources Ontario Power Authority (2005) Canada 5-12 Relies on unpublished data Pembina Institute (2007) Canada 10-120 Relies on secondary sources Ruether et al. (2004) United States 3 Relies on secondary sources Spadaro et al. (2000) World 2.5-5.7 Relies on unpublished data Sustainable Development Commission World 2-20 Relies on secondary sources (2006)

Tahara et al. (1997) Japan 1.8 Relies on secondary sources Tokimatsu et al. (2000) Japan 20.9 Does not separate fuel cycle estimates for "ssion reactors UKPOST (2006) United Kingdom 5 Relies on secondary sources and unpublished data Utgikar and Thiesen (2006) World 2-59 Relies on secondary sources Van De Vate (1997) World 9 Relies on unpublished FENCH data Van De Vate (2003) World 8.9 Relies on unpublished FENCH data Vattenfall (1997) Sweden 3.3 Relies on published utility data World Energy Council (2004) Australia, Germany, Sweden, Switzerland, and United 3-40 Relies on unpublished data Kingdom Weisser (2007) World 2.8-24 Relies on secondary sources World Nuclear Association (2006) Japan, Sweden, Finland 6-26 Relies on secondary sources a

The phrase relies on unpublished data means that studies contained proprietary information, referenced data not published along with the study, did not explain their methodology, were not transparent about their data sources, or did not detail greenhouse gas emission estimates for separate parts of the nuclear fuel cycle in g CO2e/

kWh. The phrase relies on secondary sources means that studies merely quoted other previously published reports and did not provide any new calculations or synthetic analysis on their own.

energy expenditures allocated to uranium mining by Storm van uranium of 10% grade, emissions for reclamation are just 0.07 g Leeuwen and Smith may be high. As a result, Dones concludes CO2e/kWh, but at 0.013%, they are 122 g CO2/kWh.

that Storm van Leeuwen and Smith may overestimate the energy expenditures, and thus greenhouse gas emissions, associated with nuclear power. 4.3. Open-pit or underground uranium mining The type of uranium mining will also re"ect different CO2e 4.2. Quality of uranium ore emissions. Open-pit mining often produces more gaseous radon and methane emissions than underground mines, and Andseta Studies varied in their assumptions regarding the quality of et al. (1998) note that mining techniques will release varying uranium ore used in the nuclear fuel cycle. Low-grade uranium amounts of CO2 based on the explosives and solvents they use to ores contain less than 0.01% yellowcake, and is at least ten times purify concentrate. They also point out that the carbon content less concentrated than high-grade ores, meaning it takes 10 ton of associated with acid leeching used to extract uranium can vary, as ore to produce 1 kg of yellowcake. Put another way, if uranium ore well as the emissions associated with the use of lime to neutralize grade declines by a factor of ten, then energy inputs to mining and the resulting leached tailings. The emissions associated with milling must increase by at least a factor of ten (Diesendorf and uranium mining depend greatly on the local energy source for the Christoff, 2006). Storm van Leeuwen et al. (2007) point out that mines. Andseta et al. (1998) note that in Canada, uranium this can greatly skew estimates, as uranium of 10% U3O8 has extracted from mines closer to industrial centers relies on more emissions for mining and milling at just 0.04 g CO2/kWh, whereas ef"cient, centrally generated power. In contrast, remote mines uranium at 0.013% grade has associated emissions more than 1500 there have relied on less ef"cient diesel generators that consumed times greater at 67 g CO2/kWh. The same trend is true for the 45,000 ton of fossil fuel per year/mine, releasing up to 138,000 ton emissions associated with uranium mine land reclamation. With of carbon dioxide every year (Andseta et al., 1998).

ARTICLE IN PRESS 2946 B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 Table 4 Overview of detailed nuclear lifecycle studiesa Study Location Assumptions Fuel cycle Individual estimate Total estimate (g CO2e/kWh) (g CO2e/kWh)

Andseta et al. Canada CANDU heavy water reactor, 40-year Frontend 0.68 15.41 (1998) lifecycle, high-quality natural uranium ore, Construction 2.22 enriched and charged with fossil fuel Operation 11.9 generators Backend -

Decommissioning 0.61 Barnaby and Kemp United 35-year lifecycle, average load factor of 85%, Frontend 56 84-122 (2007b) Kingdom uranium ore grade of 0.15% Construction 11.5 Operation -

Backend -

Decommissioning 16.5-54.5 Dones et al. (2005) Switzerland 100-year lifecycle, Gosgen pressurized water Frontend 3.5-10.2 5-12 reactor and Liebstadt boiling water reactor Construction 1.1-1.3 Operation -

Backend 0.4-0.5 Decommissioning -

Dones et al. Switzerland, 40-year lifecycle, existing boiling water Frontend 6-12 7.6-14.3 (2003a, b) France, and reactors and pressurized water reactors using Construction 1.0-1.3 Germany UCTE nuclear fuel chains Operation -

Backend 0.6 and 1.0 Decommissioning -

Dones et al. (2004b) China 20-year lifecycle, once-through nuclear cycle Frontend 7.4-77.4 9-80 using centrifuge technology Construction 1.0-1.4 Operation -

Backend 0.6-1.2 Decommissioning -

ExternE (1998) United Analysis of emissions for construction of Frontend - 11.5 Kingdom Sizewell B pressurized water reactor in the Construction 11.5 United Kingdom Operation -

Backend -

Decommissioning -

Fritsche and Lim Germany Analysis of emissions for a typical 1250 MW Frontend 20 64 (2006)b German reactor Construction 11 Operation -

Backend 33 Decommissioning -

Fthenakis and Kim United States, 40-year lifecycle, 85% capacity factor, mix of Frontend 12-21.7 16-55 (2007) Europe, and diffusion and centrifuge enrichment Construction 0.5-17.7 Japan Operation 0.1-10.8 Backend 2.1-3.5 Decommissioning 1.3 Hondo (2005) Japan Analysis of base-case emissions for operating Frontend 17 24.2 Japanese nuclear reactors Construction 2.8 Operation 3.2 Backend 0.8 Decommissioning 0.4 IEA (2002)c Sweden and 40-year lifecycle for Swedish Forsmark 3 Frontend 1.19-8.52 2.82-22 Japan boiling water reactor and 30 year lifecycle for Construction 0.27-4.83 Japanese boiling water reactor, advanced Operation -

BWR, and fast breeder reactor Backend 1.19-8.52 Decommissioning 0.17 ISA (2006)d Australia Analysis of emissions for existing Australian Frontend 4.5-58.5 10-130 light water reactors with uranium ore of Construction 1.1-13.5 0.15% grade Operation 2.6-34.5 Backend 1.7-22.2 Decommissioning 0.1-1.3 ISA (2006)d Australia Analysis of emissions for existing Australian Frontend 4.5-54 10-120 heavy water reactors with uranium ore of Construction 1.1-12.5 0.15% grade Operation 2.6-31.8 Backend 1.7-20.5 Decommissioning 0.1-1.2

ARTICLE IN PRESS B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2947 Table 4 (continued )

Study Location Assumptions Fuel cycle Individual estimate Total estimate (g CO2e/kWh) (g CO2e/kWh)

Rashad and Egypt 30 year lifecycle for a pressurized water Frontend 23.5 26.4 Hammad reactor operating at 75% capacity Construction 2.0 (2000) Operation 0.4 Backend 0.5 Decommissioning -

Storm van Leeuwen World Analysis of emissions for existing nuclear Frontend 36 84-122 et al. (2005) reactors Construction 12-35 Operation -

Backend 17 Decommissioning 23-46 Storm van Leeuwen World Analysis of emissions for existing nuclear Frontend 39 92-141 (2006) reactors Construction 13-36 Operation -

Backend 17 Decommissioning 23-49 Storm van Leeuwen World Analysis of emissions for existing nuclear Frontend 16.26-28.27 112.47-165.72 et al. (2007) reactors assuming 0.06% uranium ore, 70% Construction 16.8-23.2 centrifuge and 30% diffusion enrichment, and Operation 24.4 inclusion of interim and permanent storage Backend 15.51-40.75 and mine land reclamation Decommissioning 39.5-49.1 Tokimatsu et al. Japan 60-year lifecycle, light water reactor Frontend 5.9-118 10-200 (2006)e reference case, emissions for 1960-2000 Construction 1.3-26 Operation 2.0-40 Backend 0.7-14 Decommissioning 0.1-2 Vorspools et al. World Analysis of emissions for construction and Frontend - 3 (2000) decommissioning of existing reactors Construction 2 Operation -

Backend -

Decommissioning 1 White and Kulcinski United States 40-year lifecycle of 1000 MW pressurized Frontend 9.5 15 (2000) water reactor operating at 75% capacity Construction 1.9 factor Operation 2.2 Backend 1.4 Decommissioning 0.01 a

Frontend includes mining and milling, conversion, enrichment, fuel fabrication, and transportation. Construction includes all materials and energy inputs for building the facility. Operation includes energy needed for maintenance, cooling and fuel cycles, backup generators, and during outages and shutdowns. Backend includes fuel processing, conditioning, reprocessing, interim and permanent storage. Plant decommissioning includes deconstruction of facility and land reclamation.

b Study mentions a total of 31 g kWh for ore extraction, enrichment, and construction, and another 33 g kWh of other greenhouse gases other than carbon.

c The IEA study combined upstream and downstream emissions in their estimate. They have been divided equally over the upstream and downstream phases.

d Numbers derived from 10 to 130/120 estimate and then apportioned according to percentages given in Figs. 5.11 and 5.22.

e Numbers derived from 10 to 200 g/kWh estimate and apportioned according to percentages provided in Fig. 3(c).

Table 5 Summary statistics of quali"ed studies reporting projected greenhouse gas emissions for nuclear power plantsa (g CO2e/kWh) Frontend Construction Operation Backend Decommissioning Total Min 0.58 0.27 0.1 0.4 0.01 1.36 Max 118 35 40 40.75 54.5 288.25 Mean 25.09 8.20 11.58 9.2 12.01 66.08 N 17 19 9 15 13 a

Frontend includes mining and milling, conversion, enrichment, fuel fabrication, and transportation. Construction includes all materials and energy inputs for building the facility. Operation includes energy needed for maintenance, cooling and fuel cycles, backup generators, and during outages and shutdowns. Backend includes fuel processing, conditioning, reprocessing, interim and permanent storage. Plant decommissioning includes deconstruction of facility and land reclamation.

4.4. Gaseous diffusion or centrifuge enrichment more energy-intense, and therefore has higher associated carbon dioxide emissions. Gaseous diffusion requires 2400-2600 kWh per Another signi"cant variation concerns the type of uranium seperative work unit (a function measuring the amount of uranium enrichment. Dones et al. (2005) note that gaseous diffusion is much processed proportioned to energy expended for enrichment),

ARTICLE IN PRESS 2948 B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 Table 6 Mean statistics of quali"ed studies reporting lifecycle equivalent greenhouse gas emissions for nuclear plants Study Frontend Construction Operation Backend Decommissioning Andseta et al. (1998) 0.68 2.22 11.9 - 0.61 Barnaby and Kemp (2007b) 56 11.5 - - 35.5 Dones et al. (2005) 6.85 1.2 - 0.45 -

Dones et al. (2003a, b) 9 1.15 - 0.8 -

Dones et al. (2004b) 42.4 1.2 - 0.9 -

ExternE (1998) - 11.5 - - -

Fritsche and Lim (2006) 20 11 - 33 Fthenakis and Kim (2007) 16.85 9.1 5.41 2.8 1.3 Hondo (2005) 17 2.8 3.2 0.8 0.4 IEA (2002) 4.86 2.55 - 4.86 0.17 ISA (2006) 31.5 7.3 18.55 11.95 0.7 ISA (2006) 29.25 6.8 17.2 11.1 0.65 Rashad and Hammad (2000) 23.5 2 0.4 0.5 -

Storm van Leeuwen et al. (2005) 36 23.5 - 17 34.5 Storm van Leeuwen and Willem (2006) 39 24.5 - 17 36 Storm van Leeuwen et al. (2007) 22.27 20 24.4 28.13 44.3 Tokimatsu et al. (2006) 61.95 13.65 21 7.35 1.05 Vorspools et al. (2000) - 2 - - 1 White and Kulcinski (2000) 9.5 1.9 2.2 1.4 0.01 Mean 25.09 8.2 11.58 9.2 12.01 300 4.5. Individual or aggregate estimates Some studies look at just speci"c reactors, while others assess 250 emissions based on industry, national, and global averages. These obviously produce divergent estimates. Dones et al. (2005) look at just two actual reactors in Switzerland, the Gosgen pressurized water reactor and Liebstadt boiling water reactor and calculate 200 emissions at 5-12 g CO2e/kWh, whereas other studies look at global reactor performance and reach estimates more than 10 times greater.

150 4.6. Historical or marginal/future emissions 100 Yet another difference concerns whether researchers assessed historic, future, or prototypical emissions. Studies assessing historic emissions looked only at emissions related to real plants 50 operating in the past; studies looking at future average emissions looked at how existing plants would perform in the years to come; studies analyzing prototypical emissions looked at how advanced plants yet to be built would perform in the future. Tokimatsu et al.

0 (2006), for instance, found historical emissions for light water nd io n en ni To tE tru n pe d ng ta l reactors in Japan from 1960 to 2000 to be rather high at between ct ra ck io Fr tio Ba is 10 and 200 g CO2e/kWh. Others, such as Dones et al. (2005),

on on O s s m C ec looked at future emissions for the next 100 years using more om advanced pressurized water reactors and boiling water reactors.

D Still other studies made different assumptions about future Fig. 3. Range and mean emissions reported from quali"ed studies for the nuclear reactors, namely fast-breeder reactors using plutonium and fuel cycle (g CO2e/kWh) thorium, and other Generation IV nuclear technology expected to be much more ef"cient if they ever reach commercial production.

compared to just 40 kWh per SWU for centrifuge techniques. The energy requirements for these two processes are so vastly different 4.7. Reactor type because gaseous diffusion is a much older technology, necessitating extensive electrical and cooling systems that are not found in Studies varied extensively in the types of reactors they centrifuge facilities. analyzed. More than 30 commercial reactor designs exist Emissions will further vary on the local power sources at today, and each differs in its fuel cycle, output, and cooling the enrichment facilities. Dones et al. (2004a-c) calculate system. The most common are the worlds 263 pressurized 9 g CO2e/kWh for Chinese centrifuge enrichment relaying on a water reactors, used in France, Japan, Russia and the US, mix of renewable and centralized power sources, but up to which rely on enriched uranium oxide as a fuel with water 80 g CO2e/kWh if gaseous diffusion is powered completely by as coolant. Boiling water reactors are second most common, fossil fuels. with 92 in operation throughout the US, Japan, and Sweden,

ARTICLE IN PRESS B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2949 Fig. 4. Mean emissions reported from quali"ed studies for the nuclear fuel cycle (g CO2e/kWh).

Table 7 To give an idea about how much reactor design can in"uence Emissions for the nuclear fuel cycle from storm van Leeuwen and Smith (2007), in lifecycle emissions, Boczar et al. (1998) comment that CANDU g CO2/kWh reactors are the most neutron ef"cient commercial reactors, Nuclear process Estimate (g CO2/ achieving their ef"ciency through the use of heavy water for both kWh) coolant and moderator, and reliance on low-neutron-absorbing materials in the reactor core. CANDU reactors thus have the ability Frontend (total) 16.26- 28.27 to utilize low-grade nuclear fuels and refuel while still producing Uranium mining and milling (soft and hard ores) (uranium 10.43 grade of 0.06%)

power, minimizing equivalent carbon dioxide emissions. This Re"ning of yellow cake and conversion to UF6 2.42-7.49 could be why Andseta et al. (1998) conclude that CANDU reactors Uranium enrichment (70% UC, 30% diff) 2.83-8.03 have relatively low emissions (15 g CO2e/kWh) compared to the Fuel fabrication 0.58-2.32 average emissions from quali"ed studies as described by this Construction (total) 16.8- 23.2 work (66 g CO2e/kWh). Others, such as Storm van Leeuwen et al.

Reactor operation and maintenance (total) 24.4 Backend (total) 15.51- 40.75 (2007), contest these numbers and argue that the production of Depleted uranium reconversion 2.10-6.24 heavy water associated with CANDU reactors is very energy-Packaging depleted uranium 0.12-0.37 intensive and can produce emissions more than a factor of one Packaging enrichment waste 0.16-0.46 greater than the projection made by Andseta et al.

Packaging operational waste 1.93-3.91 Packaging decommissioned waste 2.25-3.11 Sequestration of depleted uranium 0.12-0.35 4.8. Site selection Sequestration of enrichment waste 0.16-0.44 Sequestration of operational waste 1.84-3.73 Sequestration of enrichment waste 1.98-2.74 Estimates vary signi"cantly based on the speci"c reactor site Interim storage at reactor 0.58-2.32 analyzed. The Sustainable Development Commission (2006)

Spent fuel conditioning for "nal disposal 0.35-1.40 argues that location in"uences reactor performance (and con-Construction, storage, and closure of permanent geologic 3.92-15.68 sequential carbon-equivalent emissions). Some of the ways that repository Decommissioning (total) 39.5- 49.1 location may in"uence lifetime emissions include differences in:

Decommissioning and dismantling 25.2-34.8 Land Reclamation of uranium mine (uranium grade of 0.06%) 14.3

 construction techniques, including available materials, compo-Total 112.47-165.72 nent manufacturing, and skilled labor;

 local energy mix at that point of construction;

 travel distance for materials and fuel cycle components; which also rely on enriched uranium oxide with water as a  associated carbon footprint with the transmission and dis-coolant. Then come pressurized heavy water reactors, of which tribution (T&D) network needed to connect to the facility; there are 38 in Canada, that use natural uranium oxide with  cooling fuel cycle based on availability of water and local heavy water as a coolant. Next comes 26 gas-cooled reactors, hydrology; used predominately in the United Kingdom, which rely on  environmental controls based on local permitting and siting natural uranium and carbon dioxide as a coolant. Russia also requirements.

operates 17 light water graphite reactors that use enriched uranium oxide with water as a coolant but graphite as a Each of these can substantially affect the energy intensity and moderator. A handful of experimental reactors, including fast- ef"ciency of the nuclear fuel cycle.

breeder reactors (cooled by liquid sodium) and pebble bed Consider two extremes from Table 4. In Canada, the green-modular reactors (which can operate at full load while being house gas-equivalent emissions associated with the CANDU refueled), still in the prototype stages, make up the rest of the lifecycle are estimated at about 15 g CO2e/kWh. CANDU reactors world total (Beckjord et al. 2003). tend to be built with skilled labor and advanced construction

ARTICLE IN PRESS 2950 B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 techniques, and they utilize uranium that is produced domes- ISA (2006) uses a hybrid lifecycle assessment that combines tically and relatively close to reactor sites, enriched with cleaner process analysis with input and output methodologies. These technologies in a regulatory environment with rigorous environ- different approaches produce understandably different results.

mental controls. By contrast, the greenhouse-gas-equivalent emissions associated with the Chinese nuclear lifecycle can be as high as 80 g CO2e/kWh. This could be because Chinese 5. Conclusion reactors tend to be built using more labor-intensive construction techniques, must import uranium thousands of miles from The "rst conclusion is that the mean value of emissions over Australia, and enrich fuel primarily with coal-"red power plants the course of the lifetime of a nuclear reactor (reported from that have comparatively less stringent environmental and air- quali"ed studies) is 66 g CO2e/kWh, due to reliance on existing quality controls. fossil-fuel infrastructure for plant construction, decommissioning, and fuel processing along with the energy intensity of uranium mining and enrichment. Thus, nuclear energy is in no way carbon 4.9. Operational lifetime free or emissions free, even though it is much better (from purely a carbon-equivalent emissions standpoint) than coal, oil, How long the plants at those sites are operated and their and natural gas electricity generators, but worse than renewable capacity factor in"uences the estimates of their carbon dioxide-and small scale distributed generators (see Table 8). For example, equivalent intensity. Storm van Leeuwen et al. (2007) note that a Gagnon et al. (2002) found that coal, oil, diesel, and natural gas 30-year operating lifetime of a nuclear plant with a load factor of generators emitted between 443 and 1050 g CO2e/kWh, far more 82% tends to produce 23.2 g CO2/kWh for construction. Switch the than the 66 g CO2e/kWh attributed to the nuclear lifecycle.

load factor to 85% and the lifetime to 40 years, and the emissions However, Pehnt (2006) conducted lifecycle analyses for 15 drop about 25% to 16.8 gCO2/kWh. The same is true for decom-separate distributed generation and renewable energy technolo-missioning. A plant operating for 30 years at 82% capacity factor gies and found that all but one, solar photovoltaics (PV), emitted produces 34.8 g CO2/kWh for decommissioning, but drop 28% to much less g CO2e/kWh than the mean reported for nuclear 25.2 g CO2/kWh if the capacity factor improves to 85% and the plants. In an analysis using updated data on solar PV, Fthenakis plant is operated for 40 years.

et al. (2008) found that current estimates on the greenhouse Most of the quali"ed studies referenced above assume lifetime gas emissions for typical solar PV systems range from 29 to nuclear capacity factors that do not seem to match actual 35 g CO2e/kWh (based on insolation of 1700 kWh/m2/yr and a performance. Almost all of the quali"ed studies reported capacity performance ratio of 0.8).

factors of 85-98%, where actual operating performance has been The second (and perhaps more obvious) conclusion is that less. While the nuclear industry in the US has boasted recent lifecycle studies of greenhouse gas emissions associated with the capacity factors in the 90% range, average load factors over the nuclear fuel cycle need to become more accurate, transparent, entire life of the plants is very different: 66.3% for plants in the UK accountable, and comprehensive. Thirty-nine percent of lifecycle (Association of Electricity Producers, 2007) and 81% for the world studies reviewed were more than 10 years old. Nine percent, average (May, 2002).

while cited in the literature, were inaccessible. Thirty-four percent did not explain their research methodology, relied completely on 4.10. Type of lifecycle analysis Table 8 The type of lifecycle analysis can also skew estimates. Lifecycle estimates for electricity generatorsa Projections can be top-down, meaning they start with overall Technology Capacity/con"guration/fuel Estimate (gCO2e/

estimates of a pollutant, assign percentages to a certain activity kWh)

(such as cement manufacturing or coal transportation), and derive estimates of pollution from particular plants and indus- Wind 2.5 MW, offshore 9 tries. Or they can be bottom-up, meaning that they start with a Hydroelectric 3.1 MW, reservoir 10 Wind 1.5 MW, onshore 10 particular component of the nuclear lifecycle, calculate emissions Biogas Anaerobic digestion 11 for it, and move along the cycle, aggregating them. Similarly, Hydroelectric 300 kW, run-of-river 13 lifecycle studies can be process-based or rely on economic Solar thermal 80 MW, parabolic trough 13 input-output analysis. Process-based studies focus on the Biomass Forest wood Co-combustion with hard coal 14 Biomass Forest wood steam turbine 22 amount of pollutant releasedin this case, carbon dioxide or its Biomass Short rotation forestry Co-combustion with 23 equivalentper product unit. For example, if the amount of hard coal hypothesized carbon dioxide associated with every kWh of Biomass FOREST WOOD reciprocating engine 27 electricity generation for a region was 10 g, and the cement Biomass Waste wood steam turbine 31 needed for a nuclear reactor took 10 kWh to manufacture, a Solar PV Polycrystalline silicone 32 Biomass Short rotation forestry steam turbine 35 process analysis would conclude that the cement was responsible Geothermal 80 MW, hot dry rock 38 for 100 g of CO2. Input-output analysis looks at industry Biomass Short rotation forestry reciprocating engine 41 relations within the economy to depict how the output of one Nuclear Various reactor types 66 industry goes to another, where it serves as an input, and attempts Natural gas Various combined cycle turbines 443 Fuel cell Hydrogen from gas reforming 664 to model carbon dioxide emissions as a matrix of interactions Diesel Various generator and turbine types 778 representing economic activity. Heavy oil Various generator and turbine types 778 Storm van Leeuwen et al. (2007), for example, rely heavily on Coal Various generator types with scrubbing 960 calculating average energy intensity for various parts of the Coal Various generator types without scrubbing 1050 nuclear fuel cycle and aggregate those numbers into a "nal a

estimate. Dones et al. (2004a-c) uses process analysis to describe Wind, hydroelectric, biogas, solar thermal, biomass, and geothermal, estimates taken from Pehnt (2006). Diesel, heavy oil, coal with scrubbing, coal the full lifecycle of speci"c industries associated with the nuclear without scrubbing, natural gas, and fuel cell estimates taken and Gagnon et al.

fuel cycle, such as material and chemical manufacturing, energy (2002). Solar PV estimates taken from Fthenakis et al. (2008). Nuclear is taken conversion, electricity transmission, and waste management. The from this study. Estimates have been rounded to the nearest whole number.

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Acknowledgments Dones, Roberto, 2007. Critical note on the estimation by storm van Leeuwen J.W.

and Smith P. of the energy uses and corresponding CO2 emissions from the Mark A. Delucchi from the University of California Davis, Paul complete nuclear energy chain. Paul Scherrer Institute Policy Report, April 10, 2007.

Denholm from the National Renewable Energy Laboratory, Dones, R., Frischknecht, R., 1996. Greenhouse gas emissions inventory for Roberto Dones from the Swiss Laboratory for Energy Systems photovoltaic and wind systems in Switzerland. Assessment of greenhouse Analysis, V.M. Fthenakis from Brookhaven National Laboratory, gas emissions from the full energy chain of solar and wind power and other energy sources. An international Advisory Group Meeting on Assessment of Paul J. Meier from the University of Wisconsin-Madison, and Jan Greenhouse Gas Emission from the Full Energy Chain of Solar and Wind Power, Willem Storm van Leeuwen provided invaluable and outstanding October 21-24, 1996. IAEA Headquarters, Vienna, Austria.

comments and suggestions in the revision of the manuscript. Two Dones, R., Hirschberg, S., Knoepfel, I., 1994. Greenhouse gas emission inventory anonymous reviewers from Energy Policy also provided extensive based on full chain energy analysis. Comparison of energy sources in terms of their full-energy-chain emission factors of greenhouse gases. In: Pro-and exceptional suggestions at revision. All have the deep ceedings of an IAEA Advisory Group Meeting/Workshop, Beijing, China, gratitude of the author. Despite their help, of course, all errors, October 7, 1994. International Atomic Energy Agency (IAEA), Vienna, Austria, assumptions, and conclusions presented in the article are solely pp.95-114.

Dones, Roberto, Christian, Bauer, Thomas, Heck, 2003a. LCA of Current Coal, Gas, those of the author. and Nuclear Electricity Systems and Electricity Mix in the USA. Paul Scherrer Institute, Switzerland.

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