ML103610409

Energy Policy, Valuing the Greenhouse Gas Emissions from Nuclear Power: a Critical Survey

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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 i n f o Article history:

Received 25 February 2008 Accepted 21 April 2008 Available online 2 June 2008 Keywords:

Nuclear power Lifecycle analysis Greenhouse gas emissions a b s t r a c t 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 lifecycle emissions occur through plant construction, operation, uranium mining and milling, and plant decommissioning.

& 2008 Elsevier Ltd. All rights reserved.

1. Introduction The nuclear era began with a whimper, not a bang, on December 7, 1942. Amidst the polished wooden "oors of a war-appropriated squash court at the University of Chicago, Enrico Fermi inserted about 50 ton of uranium oxide into 400 carefully constructed graphite blocks. A small puff of heat exhibited the "rst self-sustaining nuclear reaction, many bottles of Chianti were consumed, and nuclear energy was born (Metzger, 1984).

Since

then, Americans have dreamed of exotic nuclear possibilities. Early advocates promised a future of electricity too cheap to meter, an age of peace and plenty without high prices and shortages where atomic energy provided the power needed to desalinate water for the thirsty, irrigate deserts for the hungry, and fuel interstellar travel deep into outer space. Other exciting opportunities included atomic golf balls that could always be found and a nuclear powered airplane, which the US Federal Government spent $1.5 billion researching between 1946 and 1961 (Munson, 2005; Winkler, 2001; Duncan, 1978).

While nuclear technologies did not ful"ll these dreams, nuclear power has still emerged to become a signi"cant source of electricity.

In 2005, 435 nuclear plants supplied 16% of the worlds power, constituting 368GW of installed capacity generating 2768 TWh of electricity (International Energy Agency, 2007). In the US alone, which has 29.2% of the worlds reactors, nuclear facilities accounted for 19% of national electricity generation. In France, 79% of electricity comes from nuclear sources, and nuclear energy contributes to more than 20% of national power production in Germany, Japan, South Korea, Sweden, Ukraine, and the United Kingdom.

Advocates of nuclear power have recently framed it as an important part of any solution aimed at "ghting climate change and reducing greenhouse gas emissions. The Nuclear Energy Institute (2007) tells us, it is important to build emission-free sources of energy like nuclear and that nuclear power is a carbon-free electricity source (1998). Patrick Moore, co-founder of Greenpeace, has publicly stated that nuclear energy is the only non-greenhouse gas emitting energy source that can effectively replace fossil fuels and satisfy global demand (Environmental News Service, 2005). The nuclear power company Areva (2007) claims that one coal power station of 1 GWe emits about 6 million tons of CO2 per year while nuclear is quite CO2 free.

Opponents of nuclear power have responded in kind. In their calculation, ISA (2006) argues that nuclear plants are poor substitutes to other less greenhouse gas intensive generators.

They estimate that wind turbines have one-third the carbon-equivalent emissions of nuclear power over their lifecycle and hydroelectric one-fourth the equivalent emissions. The Oxford Research Group projects that if the percentage of world nuclear capacity remains what it is today, by 2050 nuclear power would 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).

Which side is right? Analogous to the critical surveys of negative externalities associated with electricity production ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/enpol Energy Policy 0301-4215/$ - see front matter & 2008 Elsevier Ltd. All rights reserved.

doi:10.1016/j.enpol.2008.04.017

 Tel.: +65 6516 7501; fax: +65 6468 4186.

E-mail address: bsovacool@nus.edu.sg Energy Policy 36 (2008) 2940- 2953

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 uranium fuel is mined, milled, converted, enriched, and fabri-cated; the construction of the plant itself; the operation and maintenance of the facility; the backend of the cycle where spent fuel is conditioned, (re)processed, and stored; and a "nal stage where plants are decommissioned and abandoned mines returned to their original state. Figs. 1 and 2 provide a brief depiction of the once-through and closed nuclear fuel cycle.

2.1. The frontend of the nuclear lifecycle The nuclear fuel cycle is long and complex. The primary fuel for nuclear power plants, uranium, is widely distributed in the earths crust and the ocean in minute quantities, with the exception of concentrations rich enough to constitute ore. Uranium is mined both at the surface and underground, and after extracted it is crushed, ground into a "ne slurry, and leeched in sulfuric acid.

Uranium is then recovered from solution and concentrated into solid uranium oxide, often called yellow cake, before it is converted into hexa"uoride and heated. Then, hexa"uoride vapor is loaded into cylinders where it is cooled and condensed into a solid before undergoing enrichment through gaseous diffusion or gas centrifuge.

2.1.1. Uranium mining Starting at the mine, rich ores embody concentrations of uranium oxide as high as 10%, but 0.2% or less is usual, and most uranium producers will consider mining ores with concentrations higher than 0.0004%. A majority of the usable soft ore found in sandstone has a concentration between 0.2% and 0.01%, and hard ore found in granite has a lower uranium content, usually about 0.02% or less. Uranium mines are typically opencast pits, up to 250 m deep, or underground. A third extraction technique involves subjecting natural uranium to in situ leaching where hundreds of tons of sulfuric acid, nitric acid, and ammonia are injected into the strata and then pumped up again after 3-25 years, yielding uranium from treated rocks.

2.1.2. Uranium milling Mined uranium must undergo a

series of metallurgical processes to crush, screen, and wash the ore, letting the heavy uranium settle as the lighter debris is funneled away. The next step is the mill, often situated near the mine, where acid or alkali baths leach the uranium out of the processed ore, producing a bright yellow powder, called yellowcake, that is about 75%

uranium oxide (whose chemical form is U3O8). In the cases where ores have a concentration of 0.1%, the milling must grind 1000 ton of rock to extract 1 ton of yellowcake. Both the oxide and the tailings (the 999 ton of remaining rock) remain radioactive, requiring treatment. Acids must be neutralized with limestone, and made insoluble with phosphates (Fleming, 2007; Heaberlin, 2003).

2.1.3. Uranium conversion and enrichment Next comes conversion and enrichment, where a series of chemical processes are conducted to remove remaining impu-rities. Natural uranium contains about 0.7% uranium-235; the rest is mainly uranium-234 or uranium-238. In order to bring the ARTICLE IN PRESS Fig. 1. The once-through nuclear fuel cycle.

B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2941

concentration of uranium-235 up to at least 3.5% for typical commercial light water reactors and about 4-5% for other modern reactors, the oxide must be enriched, and the process begins by converting uranium to uranium hexa"uoride, UF6, or hex. Then, it is enriched, and the two dominant commercial enrichment methods are gaseous diffusion and centrifuge.

Gaseous diffusion, developed during the Second World War as part of the Manhattan Project, accounts for about 45% of world enrichment capacity. The diffusion process funnels hex through a series of porous membranes or diaphragms. The lighter uranium-235 molecules move faster than the uranium-238 molecules and have a slightly better chance of passing through the pores in the membrane. The process is repeated many times in a series of 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 stages before it is properly enriched (Uranium Information Centre, 2007).

The gas centrifuge process, "rst demonstrated in the 1940s, feeds hex into a series of vacuum tubes, and accounts for about 45% of world enrichment capacity. When the rotors are spun rapidly, the heavier molecules with uranium-238 increase in concentration towards the outer edge of the cylinders, with a corresponding increase in uranium-235 concentration near the center. To separate the two isotopes, centrifuges rotate at very high speeds, with spinning cylinders moving at roughly one million times the acceleration of gravity (Uranium Information Centre, 2007).

In United States, the gaseous diffusion plant at Paducah, Kentucky, primarily does enrichment while Europe and Russia utilize mostly centrifuge methods (Fthenakis and Kim, 2007). The remaining percentage (10%) of nuclear fuel comes from the recycling of nuclear weapons.

After enrichment, about 85% of the oxide comes out as waste in the form of depleted hex, known as enrichment tails, which must be stored. Each year, for instance, France creates 16,000 ton of enrichment tails that are then exported to Russia or added to the existing 200,000 ton of depleted uranium within the country.

The 15% that emerges as enriched uranium is converted into ceramic pellets of uranium dioxide, UO2, packed in zirconium alloy tubes, and bundled together to form fuel rod assemblies for reactors.

To supply enough enriched fuel for a standard 1000 MW reactor for 1 year, about 200 ton of natural uranium has to be processed (Fleming, 2007). Moreover, uranium must be trans-ported from the mine to processing and enrichment facilities.

Andseta et al. (1998) found that in Canada, the uranium needed to create fuel rods has traveled more than 4000 km before the process is complete. The IEA (2002) reports that in Europe most uranium is transported 150-805 km by railway, 1250 km by boat, or 378 km by truck.

2.2. Construction The construction phase of the nuclear lifecycle involves the fabrication, transportation, and use of materials to build gen-erators, turbines, cooling

towers, control

rooms, and other infrastructure. A typical nuclear plant usually contains some 50 miles of piping welded 25 thousand times, and 900 miles of electrical cables. Thousands of electric motors, conduits, batteries, relays, switches, operating boards, transformers, condensers, and fuses are needed for the system to operate. Cooling systems necessitate valves, seals, drains, vents, gauges, "ttings, nuts, and bolts. Structural supports, "rewalls, radiation shields, spent fuel storage facilities, and emergency backup generators must remain in excellent condition. Temperatures, pressures, power levels, radiation levels, "ow rates, cooling water chemistry, and equip-ment performance must all be constantly monitored. While his estimate is from an older 1000 MW Pressurized Water Reactor, White (1995) calculates that the typical nuclear plant needs 170,000 ton of concrete, 32,000 ton of steel, 1363 ton of copper, and a total of 205,464 ton of other materials. Many of these are carbon intense; 1 ton of aluminum has the carbon equivalent of more than 10,000 ton of C02; 1 ton of lithium, 44,000 ton; one ton of silver, 913,000 ton (White, 1995).

ARTICLE IN PRESS Fig. 2. The closed nuclear fuel cycle.

B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2942

2.3. Operation The operation phase of the lifecycle encompasses the energy needed to manage the cooling and fuel cycles of the plant, as well as the energy needed for its maintenance and the fuels used for backup generators. Indirect energy use includes the provision of 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 and plutonium isotopes. In a nuclear reactor, the "ssion process does not take place one atom at a time. Uranium has the rare and productive property that when it is struck by a neutron, it splits into two and produces more neutrons. If one uranium-235 atom collides with an atom of uranium-238, one of the other isotopes of uranium, it may stay there and induce a couple of decay cycles to produce plutonium-239. Plutonium-239, sharing the same prop-erty of uranium-235, splits when struck by neutrons to act as additional fuel. The process can be controlled by a moderator consisting of water or graphite to speed the reaction up, and neutron-absorbing control rods to slow it down (Fleming, 2007; Beckjord et al., 2003). Most nuclear reactors around the world have a present lifetime of 30-40 years, but produce electricity at full power for no more than 24 years (Fleming, 2007).

2.4. The backend of the nuclear lifecycle The backend phase involves fuel processing, interim storage, and permanent sequestration of waste. Spent fuel must be conditioned for reactors operating on a once-through fuel cycle, and reprocessed for those employing a

closed fuel cycle.

Eventually, radioactive impurities such as barium and krypton, along with transuranic elements such as americium and neptu-nium, clog the uranium fueling a nuclear reaction. After a few years, fuel elements must be removed, and fresh fuel rods inserted.

The half-life of uranium-238, one of the largest components of spent fuel, is about the same as the age of the earth: 4.5 billion years.

Spent fuel must then be stored at individual reactor sites in large pools of water for at least 10 years, after which they are located in large concrete casks that provide air-cooling, shielding, and physical protection. While there are many different cask types, those in the US typically hold 20-24 Pressurized Water Reactor fuel assemblies, sealed in a helium atmosphere inside the cask to prevent corrosion. Decay heat is transferred by helium from the fuel to "ns on the outside of the storage cask for cooling.

The "nal stage of the backend of the cycle involves the sequestration of nuclear waste. Permanent geological repositories must provide protection against every plausible scenario in which radionuclides might reach the biosphere or expose humans to dangerous levels of radiation. These risks include groundwater seeping into the repository, corrosion of waste containers, leaching of radionuclides, and migration of contaminated ground-water towards areas where it might be used as drinking water or for agriculture.

2.5. Decommissioning The last stage of the nuclear lifecycle involves the decom-missioning and dismantling of the reactor, as well as reclamation of the uranium mine site. After a cooling off period that may last as long as 50-100 years, reactors must be dismantled and cut into small pieces to be packed in containers for "nal disposal. Proops et al. (1996) expect nuclear plants to have an operating lifetime of 40 years, but expect decommissioning to be longer, taking at least 60 years. While it will vary along with technique and reactor type, the total energy required for decommissioning can be as much as 50% more than the energy needed for original construction (Fleming, 2007). At the uranium mine, the overburden of rock covering the area must be replaced and replanted with indigenous vegetation, and radioactive tailings must be treated and con-tained.

3. Review of nuclear lifecycle studies To assess the total carbon dioxide-equivalent emissions over the course of the nuclear lifecycle, this study began by reviewing 103 studies estimating greenhouse gas emissions for nuclear plants. These 103 studies were narrowed according to a three-phase selection process.

First, given that the availability of high-quality uranium ore changes with

time, and that

mining, milling, enrichment, construction, and reactor technologies change over the decades, the study excluded surveys more than 10 years old (i.e., published before 1997). Admittedly, excluding studies more than a decade old is no guarantee that the data utilized by newer studies is in fact new. One analysis from Dones et al. (2004c), for instance, 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 enrichment. Still, excluding studies more than 10 years old is an attempt to hedge against the use of outdated data, and to ensure that recent changes in technology and policy are included in lifecycle estimates. Table 1 lists all 40 studies excluded by their date.

Second, the study excluded analyses that were not in the public domain, cost money to access, or were not published in English.

Table 2 details the nine studies excluded for lack of accessibility.

Third, 35 studies were excluded based on their methodology.

These studies were most frequently discounted because they either relied on unpublished data or utilized secondary sources. Those relying on unpublished data contained proprie-tary 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. Those utilizing secondary sources merely quoted other previously published reports and did not provide any new calculations or synthetic analysis on their own. Table 3 depicts the 35 studies excluded by methodology.

Excluding detailed studies that rely on unpublished or non-transparent data does run the risk of including less detailed (and less rigorous) studies relying on published and open data. Simply placing a study in the public domain does not necessarily make it good. However, the author believes that this risk is more than offset by the positive bene"ts of transparency and accountability.

Transparency enhances validity and accuracy; public knowledge is less prone to errors, and more subject to the process of debate and dialogue that improves the quality of information. Transpar-ency, says Ann Florini, an expert on governance, is the most effective error correction system humanity has yet devised (Florini, 2005, p. 16). Furthermore, transparency is essential to promoting social accountability. Society simply cannot make informed decisions about nuclear power without public discus-sion; for these reasons, the author believes that only results in the public domain should be included.

The remaining 19 studies met all criteria: they were published in the past 10 years, accessible to the public, transparent about their methodology, and provided clear estimates of equivalent greenhouse gas emissions according to the separate parts of the nuclear fuel cycle. These studies were weighed equally; that is, ARTICLE IN PRESS B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2943

they were not adjusted in particular for their methodology, time of release within the past 10 years, or how rigorously they were 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 greenhouse gas emissions over the course of the nuclear lifecycle at the extremely low end of 1.4 g CO2e/kWh and the extremely high end of 288 g CO2e/kWh. Accounting for the mean values of emissions associated with each part of the nuclear lifecycle, the mean value reported for the average nuclear power plant is 66 g CO2e/kWh. Tables 5 and 6 and Figs. 2 and 3 provide the complete breakdown of this estimate. As Fig. 3 depicts, the frontend component of the nuclear cycle is responsible for 38% of equivalent emissions; decommissioning 18%; operation 17%;

backend 15%; and construction 12% (Fig. 4).

4. Assessing the disparity in lifecycle estimates What accounts for such a wide disparity among lifecycle estimates of greenhouse gas emissions associated with the nuclear fuel cycle? Studies primarily differ in terms of their scope; assumptions regarding the quality of uranium ore; assumptions regarding type of mining; assumptions concerning method of enrichment; whether they assessed emissions for a 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 lifecycle analysis.

4.1. Scope Some studies included just one or two parts of the nuclear fuel cycle, whereas others provided explicit details for even subcom-ponents of the fuel cycle. Vorspools et al. (2000), for example, analyzed just the emissions associated with construction and decommissioning for reactors across the world, whereas ExternE (1998) assessed the carbon equivalent for the construction of the Sizewell B nuclear reactor in the United Kingdom. Their estimates are near the low end of the spectrum, at between 3 and 11.5 g CO2e/kWh. In contrast, Storm van Leeuwen et al. (2007) looked at every single subcomponent of the fuel cycle, and produced estimates near the high end of the spectrum at 112-166 g CO2/kWh. Table 7 provides a breakdown of their estimate, which the authors emphasize is highly dependent on the quality of uranium ore being used to fuel nuclear plants. It has been included here for two reasons: to give readers a sense for how detailed lifecycle assessments can be, and because this study refers back to some of the numbers presented in this table when making comparisons below.

Storm van Leeuwen and Smiths estimate has not been universally accepted. Dones (2007) points out that while Storm van Leeuwen and Smiths analysis is transparent enough that it can be critiquedsomething positivehe believes that their estimate is too high. His own survey of lifecycle studies found a range of 2-230 g CO2e/kWh, but that the range of 2-77 g CO2e/

kWh was most common, with only 3 studies giving average estimates above 40 g CO2e/kWh. Dones also argues that Storm van Leeuwen and Smiths treatment of greenhouse gases associated with the natural gas supply chain are inconsistent, that they rely on outdated references for some of their estimates, and that some of their cost conversion estimates are too generic. Dones argues that they pay no consideration to the coproduction of minerals, a common practice where economically viable mining and milling of low-grade uranium take place with other activities, meaning ARTICLE IN PRESS Table 1 Lifecycle studies excluded by date Study Location Estimate (g CO2e/kWh)

Arron et al. (1991)

Canada Bodansky (1992)

World 5.7-17 Bowers et al. (1987)

Bude (1985)

Chapman et al. (1974)

Chapman (1975)

CRIEPI (1995)

Japan 22 DeLucchi (1993)

United States 40-69 Dones (1995)

World Dones and Frischknecht (1996)

World Dones et al. (1994)

World El-Bassioni (1980)

ERDA (1976)

United States ExternE (1995 Europe Held (1977) 20 Hohenwarter and Heindler (1988)

Germany IAEA (1996a)

World IAEA (1996b)

World IEA (1994)

World 30-60 Kivisto (1995)

Finland 17-59 Mortimer (1989)

United Kingdom Mortimer (1991a)

World 47-54 Mortimer (1991b)

World 47-54 Perry (1977)

United States Proops et al. (1996)

United Kingdom 2.83 Raeder (1977)

Rombough and Koen (1975)

Rose et al. (1983)

United States Sandgren and Sorteberg (1994)

Norway Science Concepts (1990)

United States 30 Spreng (1988)

Taylor (1996)

World 19.7 Tsoulfanidis (1980)

United States Tunbrant et al. (1996)

Sweden Uchiyama (1994)

Japan 10.5-47 Uchiyama (1996)

Yasukawa et al. (1992)

Japan Yoshioka et al. (1994)

Japan White (1995)

United States 34.1-37.7 Whittle and Cameron (1977)

United States 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 B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2944

energy expenditures allocated to uranium mining by Storm van Leeuwen and Smith may be high. As a result, Dones concludes that Storm van Leeuwen and Smith may overestimate the energy expenditures, and thus greenhouse gas emissions, associated with nuclear power.

4.2. Quality of uranium ore Studies varied in their assumptions regarding the quality of uranium ore used in the nuclear fuel cycle. Low-grade uranium ores contain less than 0.01% yellowcake, and is at least ten times less concentrated than high-grade ores, meaning it takes 10 ton of ore to produce 1 kg of yellowcake. Put another way, if uranium ore grade declines by a factor of ten, then energy inputs to mining and milling must increase by at least a factor of ten (Diesendorf and Christoff, 2006). Storm van Leeuwen et al. (2007) point out that this can greatly skew estimates, as uranium of 10% U3O8 has emissions for mining and milling at just 0.04 g CO2/kWh, whereas uranium at 0.013% grade has associated emissions more than 1500 times greater at 67 g CO2/kWh. The same trend is true for the emissions associated with uranium mine land reclamation. With uranium of 10% grade, emissions for reclamation are just 0.07 g CO2e/kWh, but at 0.013%, they are 122 g CO2/kWh.

4.3. Open-pit or underground uranium mining The type of uranium mining will also re"ect different CO2e emissions. Open-pit mining often produces more gaseous radon and methane emissions than underground mines, and Andseta et al. (1998) note that mining techniques will release varying amounts of CO2 based on the explosives and solvents they use to purify concentrate. They also point out that the carbon content associated with acid leeching used to extract uranium can vary, as well as the emissions associated with the use of lime to neutralize the resulting leached tailings. The emissions associated with uranium mining depend greatly on the local energy source for the mines. Andseta et al. (1998) note that in Canada, uranium extracted from mines closer to industrial centers relies on more ef"cient, centrally generated power. In contrast, remote mines there have relied on less ef"cient diesel generators that consumed 45,000 ton of fossil fuel per year/mine, releasing up to 138,000 ton of carbon dioxide every year (Andseta et al., 1998).

ARTICLE IN PRESS Table 3 Lifecycle studies excluded by methodologya Study Location Estimate (g CO2e/

kWh)

Reason excluded 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, United States 5-60 Relies on secondary sources 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 (2006)

World 2-20 Relies on secondary sources 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 Kingdom 3-40 Relies on unpublished data 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.

B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2945

ARTICLE IN PRESS Table 4 Overview of detailed nuclear lifecycle studiesa Study Location Assumptions Fuel cycle Individual estimate (g CO2e/kWh)

Total estimate (g CO2e/kWh)

Andseta et al.

(1998)

Canada CANDU heavy water reactor, 40-year lifecycle, high-quality natural uranium ore, enriched and charged with fossil fuel generators Frontend 0.68 15.41 Construction 2.22 Operation 11.9 Backend Decommissioning 0.61 Barnaby and Kemp (2007b)

United Kingdom 35-year lifecycle, average load factor of 85%,

uranium ore grade of 0.15%

Frontend 56 84-122 Construction 11.5 Operation Backend Decommissioning 16.5-54.5 Dones et al. (2005)

Switzerland 100-year lifecycle, Gosgen pressurized water reactor and Liebstadt boiling water reactor Frontend 3.5-10.2 5-12 Construction 1.1-1.3 Operation Backend 0.4-0.5 Decommissioning Dones et al.

(2003a, b)

Switzerland, France, and Germany 40-year lifecycle, existing boiling water reactors and pressurized water reactors using UCTE nuclear fuel chains Frontend 6-12 7.6-14.3 Construction 1.0-1.3 Operation Backend 0.6 and 1.0 Decommissioning Dones et al. (2004b)

China 20-year lifecycle, once-through nuclear cycle using centrifuge technology Frontend 7.4-77.4 9-80 Construction 1.0-1.4 Operation Backend 0.6-1.2 Decommissioning ExternE (1998)

United Kingdom Analysis of emissions for construction of Sizewell B pressurized water reactor in the United Kingdom Frontend 11.5 Construction 11.5 Operation Backend Decommissioning Fritsche and Lim (2006)b Germany Analysis of emissions for a typical 1250 MW German reactor Frontend 20 64 Construction 11 Operation Backend 33 Decommissioning Fthenakis and Kim (2007)

United States, Europe, and Japan 40-year lifecycle, 85% capacity factor, mix of diffusion and centrifuge enrichment Frontend 12-21.7 16-55 Construction 0.5-17.7 Operation 0.1-10.8 Backend 2.1-3.5 Decommissioning 1.3 Hondo (2005)

Japan Analysis of base-case emissions for operating Japanese nuclear reactors Frontend 17 24.2 Construction 2.8 Operation 3.2 Backend 0.8 Decommissioning 0.4 IEA (2002)c Sweden and Japan 40-year lifecycle for Swedish Forsmark 3 boiling water reactor and 30 year lifecycle for Japanese boiling water reactor, advanced BWR, and fast breeder reactor Frontend 1.19-8.52 2.82-22 Construction 0.27-4.83 Operation Backend 1.19-8.52 Decommissioning 0.17 ISA (2006)d Australia Analysis of emissions for existing Australian light water reactors with uranium ore of 0.15% grade Frontend 4.5-58.5 10-130 Construction 1.1-13.5 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 heavy water reactors with uranium ore of 0.15% grade Frontend 4.5-54 10-120 Construction 1.1-12.5 Operation 2.6-31.8 Backend 1.7-20.5 Decommissioning 0.1-1.2 B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2946

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

ARTICLE IN PRESS Table 4 (continued )

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

Total estimate (g CO2e/kWh)

Rashad and Hammad (2000)

Egypt 30 year lifecycle for a pressurized water reactor operating at 75% capacity Frontend 23.5 26.4 Construction 2.0 Operation 0.4 Backend 0.5 Decommissioning Storm van Leeuwen et al. (2005)

World Analysis of emissions for existing nuclear reactors Frontend 36 84-122 Construction 12-35 Operation Backend 17 Decommissioning 23-46 Storm van Leeuwen (2006)

World Analysis of emissions for existing nuclear reactors Frontend 39 92-141 Construction 13-36 Operation Backend 17 Decommissioning 23-49 Storm van Leeuwen et al. (2007)

World Analysis of emissions for existing nuclear reactors assuming 0.06% uranium ore, 70%

centrifuge and 30% diffusion enrichment, and inclusion of interim and permanent storage and mine land reclamation Frontend 16.26-28.27 112.47-165.72 Construction 16.8-23.2 Operation 24.4 Backend 15.51-40.75 Decommissioning 39.5-49.1 Tokimatsu et al.

(2006)e Japan 60-year lifecycle, light water reactor reference case, emissions for 1960-2000 Frontend 5.9-118 10-200 Construction 1.3-26 Operation 2.0-40 Backend 0.7-14 Decommissioning 0.1-2 Vorspools et al.

(2000)

World Analysis of emissions for construction and decommissioning of existing reactors Frontend 3

Construction

2 Operation Backend Decommissioning

1 White and Kulcinski (2000)

United States 40-year lifecycle of 1000 MW pressurized water reactor operating at 75% capacity factor Frontend 9.5 15 Construction 1.9 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.

B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2947

compared to just 40 kWh per SWU for centrifuge techniques. The energy requirements for these two processes are so vastly different because gaseous diffusion is a much older technology, necessitating extensive electrical and cooling systems that are not found in centrifuge facilities.

Emissions will further vary on the local power sources at the enrichment facilities.

Dones et al.

(2004a-c) calculate 9 g CO2e/kWh for Chinese centrifuge enrichment relaying on a mix of renewable and centralized power sources, but up to 80 g CO2e/kWh if gaseous diffusion is powered completely by fossil fuels.

4.5. Individual or aggregate estimates Some studies look at just speci"c reactors, while others assess 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 emissions at 5-12 g CO2e/kWh, whereas other studies look at global reactor performance and reach estimates more than 10 times greater.

4.6. Historical or marginal/future emissions Yet another difference concerns whether researchers assessed historic, future, or prototypical emissions. Studies assessing historic emissions looked only at emissions related to real plants 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.

(2006), for instance, found historical emissions for light water reactors in Japan from 1960 to 2000 to be rather high at between 10 and 200 g CO2e/kWh. Others, such as Dones et al. (2005),

looked at future emissions for the next 100 years using more advanced pressurized water reactors and boiling water reactors.

Still other studies made different assumptions about future reactors, namely fast-breeder reactors using plutonium and thorium, and other Generation IV nuclear technology expected to be much more ef"cient if they ever reach commercial production.

4.7. Reactor type Studies varied extensively in the types of reactors they analyzed.

More than 30 commercial reactor designs exist today, and each differs in its fuel cycle, output, and cooling system. The most common are the worlds 263 pressurized water reactors, used in France, Japan, Russia and the US, which rely on enriched uranium oxide as a fuel with water as coolant. Boiling water reactors are second most common, with 92 in operation throughout the US, Japan, and Sweden, ARTICLE IN PRESS 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 12.01 300 250 200 150 100 50 0

Front End Operation Construction Backend Decommissioning Total Fig. 3. Range and mean emissions reported from quali"ed studies for the nuclear fuel cycle (g CO2e/kWh)

B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2948

which also rely on enriched uranium oxide with water as a coolant. Then come pressurized heavy water reactors, of which there are 38 in Canada, that use natural uranium oxide with heavy water as a coolant. Next comes 26 gas-cooled reactors, used predominately in the United Kingdom, which rely on natural uranium and carbon dioxide as a coolant. Russia also operates 17 light water graphite reactors that use enriched uranium oxide with water as a coolant but graphite as a moderator. A handful of experimental reactors, including fast-breeder reactors (cooled by liquid sodium) and pebble bed modular reactors (which can operate at full load while being refueled), still in the prototype stages, make up the rest of the world total (Beckjord et al. 2003).

To give an idea about how much reactor design can in"uence lifecycle emissions, Boczar et al. (1998) comment that CANDU reactors are the most neutron ef"cient commercial reactors, achieving their ef"ciency through the use of heavy water for both coolant and moderator, and reliance on low-neutron-absorbing materials in the reactor core. CANDU reactors thus have the ability to utilize low-grade nuclear fuels and refuel while still producing power, minimizing equivalent carbon dioxide emissions. This could be why Andseta et al. (1998) conclude that CANDU reactors have relatively low emissions (15 g CO2e/kWh) compared to the average emissions from quali"ed studies as described by this work (66 g CO2e/kWh). Others, such as Storm van Leeuwen et al.

(2007), contest these numbers and argue that the production of heavy water associated with CANDU reactors is very energy-intensive and can produce emissions more than a factor of one greater than the projection made by Andseta et al.

4.8. Site selection Estimates vary signi"cantly based on the speci"c reactor site analyzed.

The Sustainable Development Commission (2006) argues that location in"uences reactor performance (and con-sequential carbon-equivalent emissions). Some of the ways that location may in"uence lifetime emissions include differences in:

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

 local energy mix at that point of construction;

 travel distance for materials and fuel cycle components;

 associated carbon footprint with the transmission and dis-tribution (T&D) network needed to connect to the facility;

 cooling fuel cycle based on availability of water and local hydrology;

 environmental controls based on local permitting and siting requirements.

Each of these can substantially affect the energy intensity and ef"ciency of the nuclear fuel cycle.

Consider two extremes from Table 4. In Canada, the green-house gas-equivalent emissions associated with the CANDU lifecycle are estimated at about 15 g CO2e/kWh. CANDU reactors tend to be built with skilled labor and advanced construction ARTICLE IN PRESS Fig. 4. Mean emissions reported from quali"ed studies for the nuclear fuel cycle (g CO2e/kWh).

Table 7 Emissions for the nuclear fuel cycle from storm van Leeuwen and Smith (2007), in g CO2/kWh Nuclear process Estimate (g CO2/

kWh)

Frontend (total) 16.26-28.27 Uranium mining and milling (soft and hard ores) (uranium grade of 0.06%)

10.43 Re"ning of yellow cake and conversion to UF6 2.42-7.49 Uranium enrichment (70% UC, 30% diff) 2.83-8.03 Fuel fabrication 0.58-2.32 Construction (total) 16.8-23.2 Reactor operation and maintenance (total) 24.4 Backend (total) 15.51-40.75 Depleted uranium reconversion 2.10-6.24 Packaging depleted uranium 0.12-0.37 Packaging enrichment waste 0.16-0.46 Packaging operational waste 1.93-3.91 Packaging decommissioned waste 2.25-3.11 Sequestration of depleted uranium 0.12-0.35 Sequestration of enrichment waste 0.16-0.44 Sequestration of operational waste 1.84-3.73 Sequestration of enrichment waste 1.98-2.74 Interim storage at reactor 0.58-2.32 Spent fuel conditioning for "nal disposal 0.35-1.40 Construction, storage, and closure of permanent geologic repository 3.92-15.68 Decommissioning (total) 39.5-49.1 Decommissioning and dismantling 25.2-34.8 Land Reclamation of uranium mine (uranium grade of 0.06%)

14.3 Total 112.47-165.72 B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2949

techniques, and they utilize uranium that is produced domes-tically and relatively close to reactor sites, enriched with cleaner technologies in a regulatory environment with rigorous environ-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 reactors tend to be built using more labor-intensive construction techniques, must import uranium thousands of miles from Australia, and enrich fuel primarily with coal-"red power plants that have comparatively less stringent environmental and air-quality controls.

4.9. Operational lifetime How long the plants at those sites are operated and their capacity factor in"uences the estimates of their carbon dioxide-equivalent intensity. Storm van Leeuwen et al. (2007) note that a 30-year operating lifetime of a nuclear plant with a load factor of 82% tends to produce 23.2 g CO2/kWh for construction. Switch the load factor to 85% and the lifetime to 40 years, and the emissions drop about 25% to 16.8 gCO2/kWh. The same is true for decom-missioning. A plant operating for 30 years at 82% capacity factor produces 34.8 g CO2/kWh for decommissioning, but drop 28% to 25.2 g CO2/kWh if the capacity factor improves to 85% and the plant is operated for 40 years.

Most of the quali"ed studies referenced above assume lifetime nuclear capacity factors that do not seem to match actual performance. Almost all of the quali"ed studies reported capacity factors of 85-98%, where actual operating performance has been less. While the nuclear industry in the US has boasted recent capacity factors in the 90% range, average load factors over the entire life of the plants is very different: 66.3% for plants in the UK (Association of Electricity Producers, 2007) and 81% for the world average (May, 2002).

4.10. Type of lifecycle analysis The type of lifecycle analysis can also skew estimates.

Projections can be top-down, meaning they start with overall estimates of a pollutant, assign percentages to a certain activity (such as cement manufacturing or coal transportation), and derive estimates of pollution from particular plants and indus-tries. Or they can be bottom-up, meaning that they start with a particular component of the nuclear lifecycle, calculate emissions for it, and move along the cycle, aggregating them. Similarly, lifecycle studies can be process-based or rely on economic input-output analysis. Process-based studies focus on the amount of pollutant releasedin this case, carbon dioxide or its equivalentper product unit. For example, if the amount of hypothesized carbon dioxide associated with every kWh of electricity generation for a region was 10 g, and the cement needed for a nuclear reactor took 10 kWh to manufacture, a process analysis would conclude that the cement was responsible for 100 g of CO2. Input-output analysis looks at industry relations within the economy to depict how the output of one industry goes to another, where it serves as an input, and attempts to model carbon dioxide emissions as a matrix of interactions representing economic activity.

Storm van Leeuwen et al. (2007), for example, rely heavily on calculating average energy intensity for various parts of the nuclear fuel cycle and aggregate those numbers into a "nal estimate. Dones et al. (2004a-c) uses process analysis to describe the full lifecycle of speci"c industries associated with the nuclear fuel cycle, such as material and chemical manufacturing, energy conversion, electricity transmission, and waste management. The ISA (2006) uses a hybrid lifecycle assessment that combines process analysis with input and output methodologies. These different approaches produce understandably different results.

5. Conclusion The "rst conclusion is that the mean value of emissions over the course of the lifetime of a nuclear reactor (reported from quali"ed studies) is 66 g CO2e/kWh, due to reliance on existing 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 free or emissions free, even though it is much better (from purely a carbon-equivalent emissions standpoint) than coal, oil, and natural gas electricity generators, but worse than renewable and small scale distributed generators (see Table 8). For example, Gagnon et al. (2002) found that coal, oil, diesel, and natural gas generators emitted between 443 and 1050 g CO2e/kWh, far more than the 66 g CO2e/kWh attributed to the nuclear lifecycle.

However, Pehnt (2006) conducted lifecycle analyses for 15 separate distributed generation and renewable energy technolo-gies and found that all but one, solar photovoltaics (PV), emitted much less g CO2e/kWh than the mean reported for nuclear plants. In an analysis using updated data on solar PV, Fthenakis et al. (2008) found that current estimates on the greenhouse gas emissions for typical solar PV systems range from 29 to 35 g CO2e/kWh (based on insolation of 1700 kWh/m2/yr and a performance ratio of 0.8).

The second (and perhaps more obvious) conclusion is that lifecycle studies of greenhouse gas emissions associated with the nuclear fuel cycle need to become more accurate, transparent, accountable, and comprehensive. Thirty-nine percent of lifecycle studies reviewed were more than 10 years old. Nine percent, while cited in the literature, were inaccessible. Thirty-four percent did not explain their research methodology, relied completely on ARTICLE IN PRESS Table 8 Lifecycle estimates for electricity generatorsa Technology Capacity/con"guration/fuel Estimate (gCO2e/

kWh)

Wind 2.5 MW, offshore 9

Hydroelectric 3.1 MW, reservoir 10 Wind 1.5 MW, onshore 10 Biogas Anaerobic digestion 11 Hydroelectric 300 kW, run-of-river 13 Solar thermal 80 MW, parabolic trough 13 Biomass Forest wood Co-combustion with hard coal 14 Biomass Forest wood steam turbine 22 Biomass Short rotation forestry Co-combustion with hard coal 23 Biomass FOREST WOOD reciprocating engine 27 Biomass Waste wood steam turbine 31 Solar PV Polycrystalline silicone 32 Biomass Short rotation forestry steam turbine 35 Geothermal 80 MW, hot dry rock 38 Biomass Short rotation forestry reciprocating engine 41 Nuclear Various reactor types 66 Natural gas Various combined cycle turbines 443 Fuel cell Hydrogen from gas reforming 664 Diesel Various generator and turbine types 778 Heavy oil Various generator and turbine types 778 Coal Various generator types with scrubbing 960 Coal Various generator types without scrubbing 1050 a Wind, hydroelectric,

biogas, solar

thermal, biomass, and geothermal, estimates taken from Pehnt (2006). Diesel, heavy oil, coal with scrubbing, coal without scrubbing, natural gas, and fuel cell estimates taken and Gagnon et al.

(2002). Solar PV estimates taken from Fthenakis et al. (2008). Nuclear is taken from this study. Estimates have been rounded to the nearest whole number.

B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2950

secondary sources, or were not explicit about the distribution of carbon-equivalent emissions over the different stages of the nuclear fuel cycle. All in all, this meant that 81% of studies had methodological shortcomings that justi"ed excluding them from the assessment conducted here. No identi"able industry standard provides guidance for utilities and companies operating nuclear facilities concerning how to report their carbon-equivalent emissions. Regulators, utilities, and operators should consider developing formal standardization and reporting criteria for the greenhouse gas emissions associated with nuclear lifecycles similar to those that provide general guidance for environmental management and lifecycle assessment, such as ISO 14040 and 14044, but adapted exclusively to the nuclear industry.

Of the remaining 19% of studies that were relatively up to date, accessible, and methodologically explicit, they varied greatly in their comprehensiveness, some counting just construction and decommissioning as part of the fuel cycle, and others including mining, milling, enrichment, conversion, construction, operation, processing, waste storage, and decommissioning. Adding even more variation, studies differed in whether they assessed future emissions for a few individual reactors or past emissions for the global nuclear "eet; assumed existing technologies or those under development; and presumed whether the electricity needed for mining and enrichment came from fossil fuels, other nuclear plants, renewable energy technologies, or a combination thereof.

Furthermore, the speci"c reactors studied differ greatly themselves. Some utilize relatively high-quality uranium ore located close to the reactor site; others require the importation of low-quality ore from thousands of kilometers away. A nuclear plant in Canada may receive its fuel from open-pit uranium mines enriched at a gaseous diffusion facility, whereas a reactor in Egypt may receive its fuel from an underground mine enriched through centrifuge. A nuclear facility in France may operate with a load factor of 83% for 40 years on a closed fuel cycle relying on reprocessed fuel, whereas a light water reactor in the United States may operate with a load factor of 81% for 25 years on a once-through fuel cycle that generates signi"cant amounts of spent nuclear fuel.

Rather than detail the complexity and variation inherent in the greenhouse gas emissions associated with the nuclear lifecycle, most studies obscure it; especially those motivated on both sides of the nuclear debate attempting to make nuclear energy look cleaner or dirtier than it really is.

Acknowledgments Mark A. Delucchi from the University of California Davis, Paul Denholm from the National Renewable Energy Laboratory, Roberto Dones from the Swiss Laboratory for Energy Systems Analysis, V.M. Fthenakis from Brookhaven National Laboratory, Paul J. Meier from the University of Wisconsin-Madison, and Jan Willem Storm van Leeuwen provided invaluable and outstanding comments and suggestions in the revision of the manuscript. Two anonymous reviewers from Energy Policy also provided extensive and exceptional suggestions at revision. All have the deep gratitude of the author. Despite their help, of course, all errors, assumptions, and conclusions presented in the article are solely those of the author.

References Andseta, S., Thompson, M.J., Jarrell, J.P., Pendergast, D.R., 1998. CANDU reactors and greenhouse gas emissions. In: Proceedings of the 19th Annual Conference, Canadian Nuclear Society, Toronto, Ontario, Canada, October 18-21, 1998.

[ANRE] Agency for Natural Resources and Energy, 1999. Evaluation of Lifelong Measure of Utilities Nuclear Power Station and Future Concrete Measures.

Public Utilities Department, Tokyo.

Areva, 2007. Carbon disclosure project: greenhouse gas emissions. Available at

/http://www.cdproject.net/download.asp?"le=CDP4_Areva_AQ_France120.docS.

Arron, G.P., Mortimer, W.P., Ogram, G.L., Yoshiki-Gravelsins, K., 1991. Environmental evaluation of coal, oil, natural gas and uranium fuel cycles Report No. 91-225-H.

Association of Electricity Producers, 2007. Frequently asked questions about electricity Available /http://www.aepuk.com/need_info.phpS.

Australia Coal Association, 2001. Coal in a sustainable society: comparing greenhouse gas emissions from different energy sources Available at /http://

www.ciss.com.auS.

Barnaby, Frank, Kemp, James, 2007a. Too Hot to Handle? The Future of Civil Nuclear Power. Oxford Research Group, Oxford July 2007.

Barnaby, Frank, Kemp, James, 2007b. Secure Energy? Civil Nuclear Power, Security, and Global Warming. Oxford Research Group, Oxford March 2007.

Beckjord, E.S., Ansolabehere, S., Deutch, J., Driscoll, M., Gray, P.E., Holdren, J.P.,

Joscow, P.L., Lester, R.K., Moniz, E.J., Todreas, N.E., 2003. The Future of Nuclear Power: An Interdisciplinary MIT Study. MIT Press, Cambridge, MA.

Boczar, P., Dastur, A., Dormuth, K., Lee, A., Meneley, D., Pendergast, D., 1998. Global warming and sustainable energy supply with CANDU nuclear power systems.

Progress in Nuclear Energy 32 (3/4), 297-304.

Bodansky, David, 1992. Global warming and nuclear power. Nuclear Engineering and Design 136, 7-15.

Bowers, H.I., Fuller, L.C., Myers, M.L., 1987. Cost Estimating Relationships for Nuclear Power Plant Operation and Maintenance. ORNL/TM-10563. Oak Ridge National Laboratory, Oak Ridge.

Bude, R., 1985. The potential net energy gain from DT fusion power plants. Nuclear Engineering and Design/Fusion 3, 1-36.

Chapman, P.F., Leach, G., Slesser, M., 1974. The energy costs of fuels. Energy Policy 2 (September), 231-243.

Chapman, P.F., 1975. Energy analysis of nuclear power stations. Energy Policy 3, 285-298.

Commonwealth of Australia, Chapter 4: Greenhouse gas emissions and nuclear power. In: Australias Uranium: Greenhouse Friendly Fuel for an Energy Hungry World, Canberra, November 2006, pp. 141-170.

[CRIEPI]

Central Research Institute of the Electric Power Industry, 1995.

Comparison of CO2 emission factors between process analysis and I/O-analysis.

CRIEPI Working Document, Tokyo.

DeLucchi, M., 1993. Emissions of Greenhouse Gases from the Use of Transportation Fuels and Electricity, vol. 2. DE94-006166. Argonne National Laboratory, Argonne, IL.

Delucchi, M.,

2003.

Lifecycle Emissions From Transportation

Fuels, Motor Vehicles, Transportation Modes, Electricity Use, Heating and Cooking Fuels, and Materials. University of California-Davis, UCD-ITS-RR-03-17, Davis, CA December.

Denholm, Paul, Kulcinski, Gerald L., 2004. Lifecycle energy requirements and greenhouse gas emissions from large scale energy storage systems. Energy Conversion and Management 45, 2153-2172.

Diesendorf, Mark, Christoff, Peter, 2006. CO2 Emissions from the Nuclear Fuel Cycle. Energyscience.org.au, Sydney.

Dones, R., 1995. Environmental inventories for future electricity supply systems for Switzerland, results for greenhouse gases. IAEA Advisory Group Meeting on Greenhouse Gas Emission from the Full Energy Chain for Nuclear Power and Other Energy Sources, September 28, 1995, IAEA Headquarters, Vienna, Austria. International Atomic Energy Agency (IAEA), Vienna, Austria, 1995.

Dones, Roberto, 2003.

Kernenergie.

In:

Dones, R.

(Ed.),

Sachbilanzen von Energiesystemen: Grudlagen fur den Okologischen Vergleich von Energiesys-temen und den Einbezug von Energiesystemen in Kokbilanzen fur die Schweiz.

Paul Scherrer Institute, Switzerland.

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 complete nuclear energy chain. Paul Scherrer Institute Policy Report, April 10, 2007.

Dones, R., Frischknecht, R., 1996. Greenhouse gas emissions inventory for photovoltaic and wind systems in Switzerland. Assessment of greenhouse gas emissions from the full energy chain of solar and wind power and other energy sources. An international Advisory Group Meeting on Assessment of Greenhouse Gas Emission from the Full Energy Chain of Solar and Wind Power, October 21-24, 1996. IAEA Headquarters, Vienna, Austria.

Dones, R., Hirschberg, S., Knoepfel, I., 1994. Greenhouse gas emission inventory based on full chain energy analysis. Comparison of energy sources in terms of their full-energy-chain emission factors of greenhouse gases. In: Pro-ceedings of an IAEA Advisory Group Meeting/Workshop, Beijing, China, October 7, 1994. International Atomic Energy Agency (IAEA), Vienna, Austria, pp.95-114.

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

Dones, R., Heck, Thomas, Hirschberg, S., 2003b. Greenhouse Gas Emissions from Energy Systems: Comparison and Overview available at /http://gabe.web.p-si.ch/pdfs/Annex_IV_Dones_et_al_2003.pdfS.

Dones, R., Heck, Thomas, Hirshberg, S., 2004a. Greenhouse Gas Emissions from Energy Systems: Comparison and Overview. In: Cutler, Cleveland (Ed.),

Encyclopedia of Energy, vol. 3, pp. 77-95.

ARTICLE IN PRESS B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2951

Dones, R., Zhou, X., Tian, C., 2004b. Lifecycle assessment of chinese energy chains for shandong electricity scenarios. International Journal of Global Energy Issues 22 (2/3), 199-224.

Dones, Roberto, Bauer, Christian, Bolliger, Rita, Burger, Bastian, Heck, Thomas, Roder, Alexander, 2004c. Lifecycle Inventories of Energy Systems: Results for Current Systems in Switzerland and Other UCTE Countries, Data, Vol. 1. PSA, Villigen.

Dones, R., Heck, Thomas, Emmenegger, Mireille Faist, Jungbluth, Niels, 2005.

Lifecycle inventories for the nuclear and natural gas energy systems, and examples of uncertainty analysis. International Journal of Lifecycle Assessment 10 (1), 10-23.

Duncan, Otis Dudley, 1978. Sociologists should reconsider nuclear energy. Social Forces 57 (1), 1-22.

Echavarri, Luis E., 2007. Is nuclear energy at a turning point? Electricity Journal 20 (9), 89-97.

El-Bassioni, A.A., 1980. A Methodology and Preliminary Data Base for Examining the Health Risks of Electricity from Uranium and Coal Fuels. ORNL/Sub-7615/1, Oak Ridge National Laboratory, Oak Ridge, TN.

[ERDA] Energy Research and Development Agency, 1976. Net Energy Analysis of Nuclear Power Production. A National Plan for Energy Research, Development, and Demonstration: Creating Energy Choices for the Future. ERDA 76/1, Washington, DC.

Environmental News Service, 2005. Greenpeace co-founded says nuclear energy is only

option, July, available at

/http://www.euronuclear.org/e-news/

e-news-9/greenpeace.htmS.

ExternE, 1995. Externalities of Energy. EUR 16520 EN, European Commission.

ExternE, 1998. Power generation and the environmenta UK perspective. ExternE-UK AEAT 3776, vol. 1, June 1998, /http://externe.jrc.es/uk.pdfS.

Fleming, David, 2007. The Lean Guide to Nuclear Energy: A Lifecycle in Trouble. The Lean Economy Connection, London.

Florini, Ann, 2005. The Coming Democracy: New Rules for Running a New World.

Brookings Institute, Washington, DC.

Frischknecht, R., 1995. Inventare fur energisysteme: beispiel regenerative En-ergiesysteme. Brennstoff/Warme/Kraft 47, 426-431.

Fritsche, Uwe R., 1997. Comparing greenhouse gas emissions and abatement costs of nuclear and alternative energy options from a lifecycle perspective. Paper presented at the CNIC Conference on Nuclear Energy and Greenhouse Gas Emissions, Tokyo, November, 1997.

Fritsche, Uwe R., Lim, Sui-San, 2006. Comparison of Greenhouse-Gas Emissions and Abatement Cost of Nuclear and Alternative Energy Options from a Life-Cycle Perspective. Oko Institute, Darmstadt, Germany (January).

Fthenakis, Vasilis, Alsema, Erik, 2006. Photovoltaics energy payback times, greenhouse gas emissions, and external costs: 2004-early 2005 status.

Progress in Photovoltaics Research and Applications 14, 275-280.

Fthenakis, Vasilis, Kim, Hyung Chul, 2007. Greenhouse-gas emissions from solar electric-and nuclear power: a life-cycle study. Energy Policy 35, 2549-2557.

Fthenakis, V.M., Kim, H.C., Alsema, M., 2008. Emissions from photovoltaic life cycles. Environmental Science and Technology 42, 2168-2174.

Gagnon, Luc, Belanger, Camille, Uchiyama, Yohji, 2002. Lifecycle assessment of electricity generation options: the status of research in year 2001. Energy Policy 30, 1267-1278.

Heaberlin, Scott W., 2003. A Case For Nuclear Generated Electricity. Batelle Press, Columbus, OH.

Heede, Richard, 2005. Aspen Emissions Inventory: Electricity Carbon Factor.

Snowmass, Colorado, December 21, 2005.

Held, C., 1977. Energy Analysis of Nuclear Power Plants and their Fuel Cycle. IAEA, Austria.

Hohenwarter, D.J., Heindler, M., 1988. Net power and energy output of the German LWR nuclear power system. Energy 13 (3), 287-300.

Hondo, Hiroki, 2005. Lifecycle GHG emission analysis of power generation systems: Japanese case. Energy 30 (2005), 2042-2056.

[IAEA] International Atomic Energy Agency, 1996a. Assessment of Greenhouse Gas Emissions from the Full Energy Chain for Hydropower, Nuclear Power, and Other Energy Sources. IAEA Advisory Group, Montreal (March).

[IAEA] International Atomic Energy Agency, 1996b. Comparison of Energy Sources in Terms of their Full Energy-Chain Emission Factors of Greenhouse Gases.

IAEA-TECDOC-892, Vienna.

[IEA] International Energy Agency, 1994. Energy and the Environment, Transport Systems Responses in the OECDGreenhouse Gas Emissions and Road Transport Technology. IEA, Paris.

[IEA] International Energy Agency, 2002. Environmental and Health Impacts of Electricity Generation: A Comparison of the Environmental Impacts of Hydropower with those of Other Generation Technologies. IEA Implementing Agreement for Hydropower Technologies and Programs, Ontario (June).

[IEA] International Energy Agency, 2007. Key World Energy Statistics. OECD, Paris, 2007.

[ISA] Integrated Sustainability Analysis, 2006. Life-Cycle Energy Balance and Greenhouse Gas Emissions of Nuclear Energy in Australia. University of Sydney, Sydney (November 3, 2006).

Izuno, N., Akutsu, N., Yamada, K., 2001. Life-cycle CO2 analysis of various power generation systems in electric power utilities. In: Proceedings of the 17th Conference on Energy, Economy, and Environment, pp. 199-202.

Kivisto, A., 1995. Energy payback period and CO2 emissions in different power generation methods in Finland. In: Proceedings of the 1995 IAEA Conference, Lappeenranta University.

Koch, Frans H., 2000. Hydropower-Internalized Costs and Externalized Bene"ts.

IEA Implementing Agreement for Hydropower Technologies and Programs, Ottawa, Canada.

Krewitt, W., Mayerhofer, P., Friedrich, R., Trukenmuller, A., Heck, T., Brebmann, A.,

1998. ExternE-Externalities of Energy. National implementation in Germany IER, Stuttgart.

Kulcinski, Gerald L., 2002. Greenhouse Gas Emissions from Nuclear and Renewable Power Plants. University of Wisconsin, College of Engineering, Madison.

Lee, E.L., Lee, K.J., Lee, Byong Whi, 2000. Environmental assessment of nuclear power generation in Korea. Progress in Nuclear Energy 37, 113-118.

Lee,, Kun-Mo, Lee, Sang-Yong, Tak,, Hur, 2004. Lifecycle inventory analysis for electricity in Korea. Energy 29 (24),87-101.

Lewin, B., 1993. CO2 emission von Kraftwerken unter Beruckichti-gung der Vor-und Nachgelagerten Enrgieketten. VDI-Berichte 1093.

May, Derek, 2002. Public or private ownership? In: World Nuclear Association Annual Symposium, 4-6 September 2002, London, available at /http://

www.world-nuclear.org/sym/2002/pdf/may.pdfS.

Meier, Paul, J., 2002. Life-Cycle Assessment of Electricity Generation Systems and Applications for Climate Change Policy Analysis.

UWFDM-1181.

Fusion Technology Institute, Madison (August).

Meier, Paul J., Kulcinski, G.L., 2002. Life-Cycle Energy Requirement and Greenhouse Gas Emissions for Building-Integrated Photovoltaics. UWFDM-1185. Fusion Technology Institute, Madison (April).

Meier, Paul J., Wilson, Paul, Kulcinski, Gerald, Denholm, Paul, 2005. US electric industry response to carbon constraint: a lifecycle assessment of supply side alternatives. Energy Policy 33, 1099-1108.

Metzger, Norman, 1984. Energy: The Continuing Crisis. Thomas Y. Crowell Company, New York.

Mortimer, Nigel, 1989. Aspects of the greenhouse effect. In: Friends of the Earth, Proof of Evidence. FOE 9, Proposed Nuclear Power Station Hinkley Point C, June 1989, pp. 8-185.

Mortimer, Nigel, 1991a. Nuclear power and carbon dioxide: the fallacy of the nuclear industrys new propaganda. The Ecologist 21 (3), 12-21.

Mortimer, Nigel, 1991b. Nuclear power and global warming. Energy Policy (January/February), 76-81.

Munson, Richard, 2005. From Edison to Enron: The Business of Power and What It Means for the Future of Electricity. Praeger, London.

Nuclear Energy Agency, 2007. Risks and Bene"ts of Nuclear Energy, available at /

http://www.oecdbookshop.org/oecd/display.asp?sf1=identi-

"ers&st1=9264035516S.

Nuclear Energy Institute, 1998. Energy Departments FY99 Budget Request Recognizes Nuclear Energys Value as Carbon-Free Electricity Source, February 2, 1998, available at /http://nei.org/newsandevents/fy99budgetrequest/S.

Nuclear Energy Institute, 2007. World Energy Outlook 2007, November 17, 2007, available at /http://neinuclearnotes.blogspot.com/2007/11/world-energy-ou-tlook-2007.htmlS.

Ontario Power Authority, 2005. Methods to Assess the Impacts of the Natural Environment of Generation Options. OPA, Richmond Hill, Ontario September.

Pehnt, Marin, 2006. Dynamic lifecycle assessment of renewable energy technol-ogies. Renewable Energy 31 (2006), 55-71.

Pembina Institute, 2007. Nuclear Power and Climate Change. The Pembina Institute Fact Sheet No. 1, May.

Perry, A.M., 1977. Net Energy Analysis of Five Energy Systems. ORAU/IEA(R)-77-12.

Oak Ridge Associated Universities, Oak Ridge.

Proops, J.L.R., Gay, Philip W., Speck, Stefan, Schroder, Thomas, 1996. The lifetime pollution implications of various types of electricity generation. Energy Policy 24 (3), 229-237.

Raeder, J., 1977. Energy balances of fusion power plants as the basis of systems studies. IPP4/166. Max-Planck Institute fur Plasmaphysik.

Rashad, S.M.,

Hammad, F.H.,

2000.

Nuclear power and the environment:

comparative assessment of environmental and health impacts of electricity-generating systems. Applied Energy 65, 211-229.

Rombough, C.T., Koen, B.V., 1975. Total energy investment in nuclear power plants.

Nuclear Technology 26, 5-11.

Rose, D.J., Miller, M., Agnew, C., 1983. Global energy futures and CO2-induced climate change. MITEL 83-015. MIT Energy Laboratory.

Ruether, John Al., Ramezan, Massood, Balash, Peter C., 2004. Greenhouse gas emissions from coal gasi"cation power generation systems. Journal of Infrastructure Systems 10 (3), 111-119.

Sandgren, J., Sorteberg, S., 1994. Electric power and environmental impacts. Report No. 93-3701. The Norwegian Research Council, Norway, 68pp.

Science Concepts, 1990. Reducing airborne emissions with nuclear electricity.

Study for the US Council for Energy Awareness, January 1990.

Spadaro, Joseph V., Langlois, Lucille, Hamilton, Bruce, 2000. Greenhouse gas emissions of electricity generation chains: assessing the difference. IAEA Bulletin 42 (2), 19-28.

Spreng, D.T., 1988. Electricity-producing systems. In: Net Energy Analysis and the Energy Requirements of Energy Systems. Praegar, New York, pp. 187-216.

Storm van Leeuwen, J.W., 2006. Nuclear Power and Global Warming, Brussels, October 19, 2006.

Storm van Leeuwen, J.W., Smith, P., 2005. Nuclear Power: The Energy Balance (Netherlands), available at /http://www.stormsmith.nlS.

Storm van Leeuwen, J.W., Smith, P., 2007. Nuclear Power: The Energy Balance October 2007 (Netherlands), available at /http://www.stormsmith.nlS.

Sundqvist, Thomas, 2004. What causes the disparity of electricity externality estimates? Energy Policy 32, 1753-1766.

ARTICLE IN PRESS B.K. Sovacool / Energy Policy 36 (2008) 2940-2953 2952

Sundqvist, Thomas, Soderholm, Patrik, 2002. Valuing the environmental impacts of electricity generation: a critical survey. Journal of Energy Literature 8 (2),

3-41.

Sustainable Development Commission,., 2006. The Role of Nuclear Power in a Low Carbon Economy: Reducing CO2 EmissionsNuclear and the Alternatives. SDC March 2006.

Tahara, Kojma, K.T., Inaba, A., 1997. Evaluation of CO2 payback time of power plants by LCA. Energy Conversion and Management 38, 615-620.

Taylor, Martin, 1996. Greenhouse gases and the nuclear fuel cycle? What emissions? IAEA Bulletin 39 (2), 12-19.

Tokimatsu, K., Hondo, H., Ogawa, Y., Okano, K., Yamaji, K., Katsurai, M., 2000.

Energy analysis and carbon dioxide emission of tokamak fusion power reactors. Fusion Engineering and Design 48, 483-493.

Tokimatsu, K., Kosugi, T., Asami, T., Williams, E., Kaya, Y., 2006. Evaluation of lifecycle CO2 emissions from the Japanese electric power sector in the 21st century under various nuclear scenarios. Energy Policy 34, 833-852.

Tsoulfanidis, Nicholas, 1980. Energy analysis of coal, "ssion, and fusion power plants. Nuclear Technology/Fusion 1 (April), 238-254.

Tunbrant, S., Dethlefsen, U., Bra¨nnstro¨m-Norberg, B.-M., Andersson, J.-E., Karlsson, E.-B.,

Lindholm, I., 1996.

Livscykelanalys LCAfo¨r ka¨rnkraft.

Vattenfall Energisystem AB, Stockholm, Sweden, February 15, 1996.

Uchiyama, Y., 1994. Validity of FENCH-GHG study, methodologies and databases.

Comparison of energy sources in terms of their full-energy-chain emission factors of greenhouse gases. In: Proceedings of an IAEA Advisory Group meeting/Workshop, Beijing, China, October 7, 1994. International Atomic Energy Agency (IAEA), Vienna, Austria.

Uchiyama, Y., 1996. Life-cycle analysis of electricity generation and supply systems.

In: Proceedings of a Symposium of electricity, Health, and Environment:

Comparative Assessment in Support of Decision Making, Vienna, Austria, 1996, pp. 279-291.

[UKPOST] United Kingdom Parliamentary Of"ce of Science and Technology, 2006.

Carbon footprint of electricity generation. Postnote 268 (October).

Uranium Information Centre, 2007. Uranium Enrichment. Nuclear Issues Brie"ng Paper 33 (October).

Utgikar, V., Thiesen, T., 2006. Lifecycle assessment of high temperature electrolysis for hydrogen production via nuclear energy. International Journal of Hydrogen Energy 31, 939-944.

Van De Vate, Joop F., 1997. Comparison of energy sources in terms of their full energy chain emission factors of greenhouse gases. Energy Policy 25 (1), 1-6.

Van De Vate, Joop F., 2003. Full-energy-chain greenhouse gas emissions: a comparison between nuclear power, hydropower, solar power, and wind power. International Journal of Risk Assessment and Management 3 (1), 59-74 (July).

Vattenfall, 1997. Vattenfalls Lifecycle Studies of Electricity Generation. S-16287, Stockholm, Sweden, January.

Vorspools, K.R., Brouwers, E.A., DHaeseleer, William D., 2000. Energy content and indirect greenhouse gas emissions embedded in emission-free power plants:

results for the low countries. Applied Energy 67, 307-330.

Weis, V.M., Kienle, F., Hortmann, W., 1990. Kernenergie und CO2: Energie-aufwand und CO2-Emissionen bei der Brennstoffgewinnung. Elektrizitatswirtschaft 89.

Weisser, Daniel, 2007. A guide to life-cycle greenhouse gas emissions from electric supply technologies. Energy 32, 1543-1559.

White, Scott W., 1995. Energy balance and lifetime emissions from fusion, "ssion, and coal generated electricity. M.S. Thesis, UWFDM-993, University of Wisconsin, Madison, WI.

White, Scott W., Kulcinski, Gerald L., 2000. Birth to death analysis of the energy payback ratio and CO2 gas emission rates from coal, "ssion, wind, and DT-fusion electrical power plants. Fusion Engineering and Design 48 (248), 473-481.

Whittle, C.E., Cameron, A.E., 1977. Energy Requirements for Fluidized-Bed Coal Combustion and Steam Electric Power Plants. ORAU/IEA(M)77-4. Oak Ridge Associated Universities, Oak Ridge.

Winkler, Allan M., 2001. The chimera of nuclear power. In: Shane, J. Maddock (Ed.),

Problems in American Civilization: The Nuclear Age. Houghton Mif"in Company, New York, pp. 142-144.

World Energy Council, 2004. Comparison of Energy Systems Using Lifecycle Assessment.

World Nuclear Association, 2006. Energy Analysis of Power Systems, March.

Yasukawa, S., Tadokoro, Y., Kajiyama, T., 1992. Lifecycle CO2 emissions from nuclear power reactor and fuel cycle system. In: Expert Workshop on Lifecycle Analysis of Energy Systems, Methods, and Experiences, Paris, France, pp. 151-160.

Yoshioka, K., Uchiyama, Y., Kan, M., Hondo, H., 1994. Appreciations of an input-output approach in environmental analysis: estimating CO2 emissions from thermal and nuclear power generation. Innovation and Input-Output Techniques 5 (1), 44-58.

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