Difference between revisions of "IPCC assessment of nuclear energy"
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The following excerpts concerning nuclear energy are from Chapter 7, "Energy Systems", of IPCC Working Group 3's 5th Assessment Report (AR5).
- 1 Executive Summary
- 2 7.4.3 from Resources and resource availability
- 3 7.5.4 from Mitigation technology options, practices and behavioral aspects
- 4 7.8.2 Cost assessment of mitigation measures
- 5 7.9.2 Environmental and health effects
- 6 7.9.3 Technical risks
- 7 7.9.4 Public perception
- 8 7.11.2 Energy supply in low-stabilization scenarios
- 9 7.12.2 Regulatory approaches
Multiple options exist to reduce energy supply sector GHG emissions (robust evidence, high agreement). These include energy efficiency improvements and fugitive emission reductions in fuel extraction as well as in energy conversion, transmission, and distribution systems; fossil fuel switching; and low-GHG energy supply technologies such as renewable energy (RE), nuclear power, and carbon dioxide capture and storage (CCS). [7.5, 7.8.1, 7.11]
Nuclear energy is a mature low-GHG emission source of base-load power, but its share of global electricity generation has been declining (since 1993). Nuclear energy could make an increasing contribution to low-carbon energy supply, but a variety of barriers and risks exist (robust evidence, high agreement). Its specific emissions are below 100 gCO2eq per kWh on a lifecycle basis and with more than 400 operational nuclear reactors worldwide, nuclear electricity represented 11 % of the world’s electricity generation in 2012, down from a high of 17 % in 1993. Pricing the externalities of GHG emissions (carbon pricing) could improve the competitiveness of nuclear power plants. [7.2, 7.5.4, 7.8.1, 7.12]
Barriers to and risks associated with an increasing use of nuclear energy include operational risks and the associated safety concerns, uranium mining risks, financial and regulatory risks, unresolved waste management issues, nuclear weapon proliferation concerns, and adverse public opinion (robust evidence, high agreement). New fuel cycles and reactor technologies addressing some of these issues are under development and progress has been made concerning safety and waste disposal (medium evidence, medium agreement). [7.5.4, 7.8.2, 7.9, 7.11]
7.4.3 from Resources and resource availability
The average uranium (U) concentration in the continental Earth’s crust is about 2.8 ppm, while the average concentration in ocean water is 3 to 4 ppb (Bunn et al., 2003). The theoretically available uranium in the Earth’s crust is estimated at 100 teratonnes (Tt) U, of which 25 Tt U occur within 1.6 km of the surface (Lewis, 1972). The amount of uranium dissolved in seawater is estimated at 4.5 Gt (Bunn et al., 2003). Without substantial research and development (R&D) efforts to develop vastly improved and less expensive extraction technologies, these occurrences do not represent practically extractable uranium. Current market and technology conditions limit extraction of conventional uranium resources to concentrations above 100 ppm U.
Altogether, there are 4200 EJ (or 7.1 MtU) of identified conventional uranium resources available at extraction costs of less than USD 260/kgU (current consumption amounts to about 53,760 tU per year). Additional conventional uranium resources (yet to be discovered) estimated at some 4400 EJ can be mobilized at costs larger than USD 260 / kgU (NEA and IAEA, 2012). Present uranium resources are sufficient to fuel existing demand for more than 130 years, and if all conventional uranium occurrences are considered, for more than 250 years. Reprocessing of spent fuel and recycling of uranium and plutonium in used fuel would double the reach of each category (IAEA, 2009). Fast breeder reactor technology can theoretically increase uranium utilization 50-fold or even more with corresponding reductions in high-level waste (HLW) generation and disposal requirements (IAEA, 2004). However, reprocessing of spent fuel and recycling is not economically competitive below uranium prices of USD2010 425 / kgU (Bunn et al., 2003). Thorium is a widely distributed slightly radioactive metal. Although the present knowledge of the world’s thorium resource base is poor and incomplete, it is three to four times more abundant than uranium in the Earth’s outer crust (NEA, 2006). Identified thorium resource availability is estimated at more than 2.5 Mt at production costs of less than USD2010 82/kgTh (NEA, 2008).
Further information concerning reactor technologies, costs, risks, cobenefits, deployment barriers and policy aspects can be found in Sections 7.5.4, 7.8.2, 7.9, 7.10, and 7.12, respectively.
7.5.4 from Mitigation technology options, practices and behavioral aspects
Nuclear energy is utilized for electricity generation in 30 countries around the world (IAEA, 2013a). There are 434 operational nuclear reactors with a total installed capacity of 371 GWe as of September 2013 (IAEA, 2013a). Nuclear electricity represented 11 % of the world’s electricity generation in 2012, with a total generation of 2346 TWh (IAEA, 2013b). The 2012 share of global nuclear electricity generation is down from a high of 17 % in 1993 (IEA, 2012b; BP, 2013). The United States, France, Japan, Russia, and Korea (Rep. of) — with 99, 63, 44, 24, and 21 GWe of nuclear power, respectively — are the top five countries in installed nuclear capacity and together represent 68 % of total global nuclear capacity as of September 2013 (IAEA, 2013a). The majority of the world’s reactors are based on light-water technology of similar concept, design, and fuel cycle. Of the reactors worldwide, 354 are light-water reactors (LWR), of which 270 are pressurized water reactors (PWR) and 84 are boiling water reactors (BWR) (IAEA, 2013a). The remaining reactor types consist of 48 heavy-water reactors (PHWR), 15 gas-cooled reactors (GCR), 15 graphite-moderated reactors (RBMK/LWGR), and 2 fast breeder reactors (FBR) (IAEA, 2013a). The choice of reactor technologies has implications for safety, cost, and nuclear fuel cycle issues.
Growing demand for electricity, energy diversification, and climate change mitigation motivate the construction of new nuclear reactors.
The electricity from nuclear power does not contribute to direct GHG emissions. There are 69 reactors, representing 67 GWe of capacity, currently under construction in 14 countries (IAEA, 2013a). The bulk of the new builds are in China, Russia, India, Korea (Rep. of), and the United States — with 28, 10, 7, 5, and 3 reactors under construction, respectively (IAEA, 2013a). New reactors consist of 57 PWR, 5 PHWR, 4 BWR, 2 FBR, and one high-temperature gas-cooled reactor (HTGR) (IAEA, 2013a).
Commercial reactors currently under construction — such as the Advanced Passive-1000 (AP-1000, USA-Japan), Advanced Boiling Water Reactor (ABWR, USA-Japan), European Pressurized Reactor (EPR, France), Water-Water Energetic Reactor-1200 (VVER-1200, Russia), and Advanced Power Reactor-1400 (APR-1400, Rep. of Korea) — are Gen III and Gen III+ reactors that have evolutionary designs with improved active and passive safety features over the previous generation of reactors (Cummins et al., 2003; IAEA, 2006; Kim, 2009; Goldberg and Rosner, 2011).
Other more revolutionary small modular reactors (SMR) with additional passive safety features are under development (Rosner and Goldberg, 2011; IAEA, 2012a; Vujic et al., 2012; World Nuclear Association, 2013). The size of these reactors is typically less than 300 MWe, much smaller than the 1000 MWe or larger size of current LWRs. The idea of a smaller reactor is not new, but recent SMR designs with low power density, large heat capacity, and heat removal through natural means have the potential for enhanced safety (IAEA, 2005a, 2012a). Additional motivations for the interest in SMRs are economies of manufacturing from modular construction techniques, shorter construction periods, incremental power capacity additions, and potential for improved financing (Rosner and Goldberg, 2011; Vujic et al., 2012; World Nuclear Association, 2013). Several SMR designs are under consideration. Light-water SMRs are intended to rely on the substantial experience with current LWRs and utilize existing fuel-cycle infrastructure. Gas-cooled SMRs that operate at higher temperatures have the potential for increased electricity generation efficiencies relative to LWRs and industrial applications as a source of high-temperature process heat (EPRI, 2003; Zhang et al., 2009). A 210 MWe demonstration high-temperature pebble-bed reactor (HTR-PM) is under construction in China (Zhang et al., 2009). While several countries have interest in the development of SMRs, their widespread adoption remains uncertain.
The choice of the nuclear fuel cycle has a direct impact on uranium resource utilization, nuclear proliferation, and waste management. The use of enriched uranium fuels for LWRs in a once-through fuel cycle dominates the current nuclear energy system. In this fuel cycle, only a small portion of the uranium in the fuel is utilized for energy production, while most of the uranium remains unused. The composition of spent or used LWR fuel is approximately 94 % uranium, 1 % plutonium, and 5 % waste products (ORNL, 2012). The uranium and converted plutonium in the spent fuel can be used as new fuel through reprocessing. While the ultimate availability of natural uranium resources is uncertain (see Section 7.4.3), dependence on LWRs and the once-through fuel cycle implies greater demand for natural uranium. Transition to ore grades of lower uranium concentration for increasing uranium supply could result in higher extraction costs (Schneider and Sailor, 2008). Uranium ore costs are a small component of nuclear electricity costs, however, so higher uranium extraction cost may not have a significant impact on the competitiveness of nuclear power (IAEA, 2012b).
The necessity for uranium enrichment for LWRs and the presence of plutonium in the spent fuel are the primary proliferation concerns. There are differing national policies for the use or storage of fissile plutonium in the spent fuel, with some nations electing to recycle plutonium for use in new fuels and others electing to leave it intact within the spent fuel (IAEA, 2008a). The presence of plutonium and minor actinides in the spent fuel leads to greater waste-disposal challenges as well. Heavy isotopes such as plutonium and minor actinides have very long half-lives, as high as tens to hundreds of thousands of years (NRC, 1996), which require final waste-disposal strategies to address safety of waste disposal on such great timescales. Alternative strategies to isolate and dispose of fission products and their components apart from actinides could have significant beneficial impact on waste disposal requirements (Wigeland et al., 2006). Others have argued that separation and transmutation of actinides would have little or no practical benefit for waste disposal (NRC, 1996; Bunn et al., 2003).
Alternative nuclear fuel cycles, beyond the once-through uranium cycle, and related reactor technologies are under investigation. Partial recycling of used fuels, such as the use of mixed-oxide (MOX) fuels where U-235 in enriched uranium fuel is replaced with recycled or excess plutonium, is utilized in some nations to improve uranium resource utilization and waste-minimization efforts (OECD and NEA, 2007; World Nuclear Association, 2013). The thorium fuel cycle is an alternative to the uranium fuel cycle, and the abundance of thorium resources motivates its potential use (see Section 7.4.3). Unlike natural uranium, however, thorium does not contain any fissile isotopes. An external source of fissile material is necessary to initiate the thorium fuel cycle, and breeding of fissile U-233 from fertile Th-232 is necessary to sustain the fuel cycle (IAEA, 2005b).
Ultimately, full recycling options based on either uranium or thorium fuel cycles that are combined with advanced reactor designs — including fast and thermal neutron spectrum reactors — where only fission products are relegated as waste can significantly extend nuclear resources and reduce high-level wastes (GIF, 2002, 2009; IAEA, 2005b). Current drawbacks include higher economic costs, as well as increased complexities and the associated risks of advanced fuel cycles and reactor technologies. Potential access to fissile materials from widespread application of reprocessing technologies further raises proliferation concerns. The advantages and disadvantages of alternative reprocessing technologies are under investigation.
There is not a commonly accepted, single worldwide approach to dealing with the long-term storage and permanent disposal of high-level waste. Regional differences in the availability of uranium ore and land resources, technical infrastructure and capability, nuclear fuel cost, and societal acceptance of waste disposal have resulted in alternative approaches to waste storage and disposal. Regardless of these differences and the fuel cycle ultimately chosen, some form of long-term storage and permanent disposal, whether surface or geologic (subsurface), is required.
There is no final geologic disposal of high-level waste from commercial nuclear power plants currently in operation, but Finland and Sweden are the furthest along in the development of geologic disposal facilities for the direct disposal of spent fuel (Posiva Oy, 2011, 2012; SKB, 2011). In Finland, construction of the geologic disposal facility is in progress and final disposal of spent fuel is to begin in early 2020 (Posiva Oy, 2012). Other countries, such as France and Japan, have chosen to reprocess spent fuel to use the recovered uranium and plutonium for fresh fuel and to dispose of fission products and other actinides in a geologic repository (OECD and NEA, 2007; Butler, 2010). Yet others, such as Korea (Rep. of), are pursuing a synergistic application of light and heavy water reactors to reduce the total waste by extracting more energy from used fuels (Myung et al., 2006). In the United States, waste-disposal options are currently under review with the termination of the Yucca Mountain nuclear waste repository in Nevada (CRS, 2012). Indefinite dry cask storage of high-level waste at reactor sites and interim storage facilities are to be pursued until decisions on waste disposal are resolved.
The implementation of climate change mitigation policies increases the competiveness of nuclear energy technologies relative to other technology options that emit GHG emissions (See 7.11, Nicholson et al., 2011). The choice of nuclear reactor technologies and fuel cycles will affect the potential risks associated with an expanded global response of nuclear energy in addressing climate change.
Nuclear power has been in use for several decades. With low levels of lifecycle GHG emissions (see Section 7.8.1), nuclear power contributes to emissions reduction today and potentially in the future. Continued use and expansion of nuclear energy worldwide as a response to climate change mitigation require greater efforts to address the safety, economics, uranium utilization, waste management, and proliferation concerns of nuclear energy use (IPCC, 2007, Chapter 4; GEA, 2012).
Research and development of the next-generation nuclear energy system, beyond the evolutionary LWRs, is being undertaken through national and international efforts (GIF, 2009). New fuel cycles and reactor technologies are under investigation in an effort to address the concerns of nuclear energy use. Further information concerning resources, costs, risks and co-benefits, deployment barriers, and policy aspects can be found in Sections 7.4.3, 7.8.2, 7.9, 7.10, and 7.12.
7.8.2 Cost assessment of mitigation measures
While nuclear power plants, which are capable of delivering baseload electrical energy with low lifecycle emissions, have low operating costs (NEA, 2011b), investments in nuclear power are characterized by very large up-front investment costs, and significant technical, market, and regulatory risks (IEA, 2011a). Potential project and financial risks are illustrated by the significant time and cost over-runs of the two novel European Pressurized Reactors (EPR) in Finland and France (Kessides, 2012). Without support from governments, investments in new nuclear power plants are currently generally not economically attractive within liberalized markets, which have access to relatively cheap coal and / or gas (IEA, 2012b). Carbon pricing could improve the competitiveness of nuclear power plants (NEA, 2011b). The post Fukushima assessment of the economics and future fate of nuclear power is mixed. According to the IEA, the economic performance and future prospects of nuclear power might be significantly affected (IEA, 2011a, 2012b). Joskow and Parsons (2012) assesses that the effect will be quite modest at the global level, albeit based on a pre-Fukushima baseline evolution, which is a moderate one itself.
7.9.2 Environmental and health effects
The handling of radioactive material23 poses a continuous challenge to the operation of the nuclear fuel chain and leads to releases of radionuclides. The most significant routine emissions of radionuclides occurs during fuel processing and mining (Simons and Bauer, 2012). The legacy of abandoned mines, sites, and waste storage causes some concerns (Marra and Palmer, 2011; Greenberg, 2013b; Schwenk-Ferrero, 2013; Skipperud et al., 2013; Tyler et al., 2013).
Epidemiological studies indicate an increase in childhood leukemia of populations living within 5 km of a nuclear power plant in a minority of sites studied (Kaatsch et al., 2008; Raaschou-Nielsen et al., 2008; Laurier et al., 2008; Heinävaara et al., 2010; Spycher et al., 2011; Koerblein and Fairlie, 2012; Sermage-Faure et al., 2012), so that the significance of a potential effect is not resolved (Fairlie and Körblein, 2010; Laurier et al., 2010).
Thermal power plants with high cooling loads and hydropower reservoirs lead to reduced surface water flows through increased evaporation (IPCC, 2008; Dai, 2011), which can adversely affect the biodiversity of rivers (Hanafiah et al., 2011) and wetlands (Amores et al., 2013; Verones et al., 2013).
7.9.3 Technical risks
SRREN indicates high fatality rates (> 20 fatalities per PWh) associated with coal, oil, and hydropower in non-OECD countries and low fatalities (< 2 fatalities per PWh) associated with renewable and nuclear power in OECD countries (Figure 9.12 in Sathaye et al., 2011). Coal and oil power in OECD countries and gas power everywhere were associated with impacts on the order of 10 fatalities per PWh.
Severe nuclear accidents have occurred at Three-Mile Island in 1979, Chernobyl in 1986, and Fukushima in 2011. For Three-Mile Island, no fatalities or injuries were reported. For Chernobyl, 31 immediate fatalities occurred and 370 persons were injured (Moomaw et al., 2011a). Chernobyl resulted in high emissions of iodine-131, which has caused measureable increases of thyroid cancer in the surrounding areas (Cardis et al., 2006). The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) identified 6000 thyroid cases in individuals who were below the age of 18 at the time of the accident, 15 of which had resulted in mortalities (Balonov et al., 2011). A significant fraction of these are above the background rate. Epidemiological evidence for other cancer effects does not exist; published risk estimates often assume a linear no-threshold dose-response relationship, which is controversial (Tubiana et al., 2009). Between 14,000 and 130,000 cancer cases may potentially result (Cardis et al., 2006), and up to 9,000 potential fatalities in the Ukraine, Belarus, and Russia in the 70 years after the accident (Hirschberg et al., 1998). The potential radiation-induced increase in cancer incidence in a population of 500 million would be too low to be detected by an epidemiological study and such estimates are neither endorsed nor disputed by UNSCEAR (Balonov et al., 2011). Adverse effects on other species have been reported within the 30-km exclusion zone (Alexakhin et al., 2007; Møller et al., 2012; Geras’kin et al., 2013; Mousseau and Møller, 2013).
The Fukushima accident resulted in much lower radiation exposure. Some 30 workers received radiation exposure above 100 mSv, and population exposure has been low (Boice, 2012). Following the linear, no-threshold assumption, 130 (15–1100) cancer-related mortalities, and 180 (24–1800) cancer-related morbidities have been estimated (Ten Hoeve and Jacobson, 2012). The WHO does not estimate cancer incidence from low-dose population exposure, but identifies the highest lifetime attributable risk to be thyroid cancer in girls exposed during infancy in the Fukushima prefecture, with an increase of a maximum of 70 % above relatively low background rates. In the highest exposed locations, leukemia in boys may increase by 5 % above background, and breast cancer in girls by 4 % (WHO, 2013).
Design improvements for nuclear reactors have resulted in so-called Generation III+ designs with simplified and standardized instrumentation, strengthened containments, and ‘passive’ safety designs seeking to provide emergency cooling even when power is lost for days. Nuclear power reactor designs incorporating a ‘defence-in-depth’ approach possess multiple safety systems including both physical barriers with various layers and institutional controls, redundancy, and diversification—all targeted at minimizing the probability of accidents and avoiding major human consequences from radiation when they occur (NEA, 2008).
7.9.4 Public perception
For nuclear energy, anxieties often focus on health and safety (e. g., accidents, disposal of wastes, decommissioning) and proliferation (e. g., terrorism, civil unrest). Further, perceptions are dependent on how the debate around nuclear is framed relative to other sources of energy supply (e. g., Bickerstaff et al., 2008; Sjoberg and Drottz-Sjoberg, 2009; Corner et al., 2011; Ahearne, 2011; Visschers and Siegrist, 2012; Greenberg, 2013b; Kim et al., 2013).
7.11.2 Energy supply in low-stabilization scenarios
Bioenergy in Chapter 11; de Vries et al., 2007; Kleijn and van der Voet, 2010; Graedel, 2011). In many mitigation scenarios with low demand, nuclear energy supply is projected to increase in 2050 by about a factor of two compared to today, and even a factor of 3 or more in case of relatively high energy demand (Figure 7.11). Resource endowments will not be a major constraint for such an expansion, however, greater efforts will be necessary to improve the safety, uranium utilization, waste management, and proliferation concerns of nuclear energy use (see also Sections 7.5.4, 7.4.3, 7.8, 7.9, and 7.10).
7.12.2 Regulatory approaches
In the field of nuclear energy, a stable policy environment comprising a regulatory and institutional framework that addresses operational safety and the appropriate management of nuclear waste as well as long-term commitments to the use of nuclear energy are requested to minimize investment risks for new nuclear power plants (NEA, 2013). To regain public acceptance after the Fukushima accident, comprehensive safety reviews have been carried out in many countries. Some of them included ‘stress tests’, which investigated the capability of existing and projected reactors to cope with extreme natural and manmade events, especially those lying outside the reactor design assumptions. As a result of the accident and the subsequent investigations, a “radical revision of the worst-case assumptions for safety planning” is expected to occur (Rogner, 2013, p. 291).