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Amreica’s Enery Future: Technology and Transformation 8 Nuclear Energy Utilities in the United States have recently expressed renewed interest in adding new nuclear power plants to their mix of electricity generation sources. As of July 2009, the U.S. Nuclear Regulatory Commission (USNRC) had received 17 applications for combined construction and operating licenses1 for 26 units, and it expects to receive a total of 22 applications for 33 units by the end of 2010.2 The 104 currently operating nuclear plants (largely constructed in the 1970s and 1980s) contribute substantially to the U.S. electricity supply: nuclear power provides 19 percent of U.S. electricity as a whole and about 70 percent of electricity produced without greenhouse gas emissions from operations. These plants provide electricity safely and reliably, and they have operated with capacity factors greater than 90 percent over the last few years.3 Still, hurdles remain, and no new nuclear plants have been ordered in the United States in more than 30 years. This chapter discusses the prospects for the future use of nuclear power in the United States, including an assessment of future technologies, deployment 1 Previously, the licensing process had two steps, construction and operation, each of which required a different license to be issued. The Combined Construction and Operating License is a part of the USNRC’s new “streamlined” application process. 2 The USNRC’s lists of received and expected applications are available at www.nrc.gov/reactors/new-reactors/col.html and at www.nrc.gov/reactors/new-reactors/new-licensing-files/expected-new-rx-applications.pdf, respectively; accessed July 2009. 3 The net capacity factor of a power plant is the ratio of the actual output of a power plant over a period of time and its projected output if it had operated at full nameplate capacity the entire time.
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Amreica’s Enery Future: Technology and Transformation costs, and the barriers to and impacts of increased nuclear power plant deployments by 2020, by 2035, and by 2050. Interest in new nuclear construction has also been growing around the globe, and with a new element: interest among countries that do not currently have nuclear plants. According to the International Atomic Energy Agency (IAEA), in excess of 40 new entrant countries have expressed interest, of which 20 are actively considering construction (IAEA, 2008a). In addition, the IAEA has recently estimated that 24 of the 30 countries with existing nuclear plants intend to build new reactors—a departure from policies of the past few decades in many countries (IAEA, 2008a). Following the Chernobyl accident in 1986, Italy banned construction of new nuclear reactors; the governments of Sweden and Germany pledged to phase out their own nuclear plants; resistance to new construction in the United Kingdom was strong; and Spain put in place a moratorium on new construction. These attitudes are now changing, likely as a result of subsequent uneventful nuclear operations and growing concerns about climate change and future energy needs. Thus, Italy has announced plans to build nuclear plants; Sweden, after shutting down two plants, intends to reverse the planned phase-out and construct new nuclear plants; and the Labor government in the United Kingdom has recently announced plans to replace 18 nuclear plants retiring by 2023 with new ones.4 But this new outlook is not universal. The current head of the Spanish government remains opposed to nuclear power, and the current government in Germany still intends to shut down its 17 remaining nuclear plants. Meanwhile, new construction is planned or under way in Finland, France, and Japan, countries that never wavered in their support of nuclear power. Overall, the IAEA projects that by 2030, world nuclear capacity could 4 Press articles discussing these developments in more detail include “Recalled to half-life,” The Economist, Feb. 12, 2009 (www.economist.com/world/europe/displaystory.cfm?story_id=13110000); “What Sweden’s nuclear about-face means for Berlin,” Der Spiegel, Feb. 6, 2009 (www.spiegel.de/international/world/0,1518,605957,00.html); “Italy seeks nuclear power revival with French help,” Reuters, Feb. 24, 2009 (uk.reuters.com/article/oilRpt/idUKLO72469220090224); “Spain must reconsider nuclear energy,”La Vanguardia, Feb. 25, 2009 (www.eurotopics.net/en/search/results/archiv_article/ARTICLE458-0); “Governments across Europe embrace nuclear energy,” ABC, Mar. 4, 2009 (www.abc.net.au/pm/content/2008/s2507565.htm); and “Europe looking set for a Nuclear Revival,” Your Industry News, Mar. 6, 2009 (www.yourindustrynews.com/europe+looking+set+for+a+nuclear+revival_26046.html). These articles were accessed in July 2009.
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Amreica’s Enery Future: Technology and Transformation increase by 27 percent under business-as–usual conditions, or in the agency’s “high case,”5 to nearly double, after accounting for retirements (IAEA, 2008b). Nonetheless, even in the high-case projections, nuclear power would rise only slightly as a percentage of total electricity generated worldwide—from 14.2 percent in 2007 to 14.4 percent in 2030—assuming business as usual for construction of fossil-fueled plants. The handful of plants that could be built in the United States before 2020, given the long time needed for licensing and construction, would need to overcome several hurdles, including high construction costs, which have been rising rapidly across the energy sector in the last few years, and public concern about the long-term issues of storage and disposal of highly radioactive waste.6 If these hurdles are overcome, if the first new plants are constructed on budget and on schedule, and if the generated electricity is competitive in the marketplace, the committee judges that it is likely that many more plants could follow these first plants. Otherwise, few new plants are likely to follow. Existing federal incentives7 for the first few nuclear plants may hasten initial construction. Even if this occurs, nuclear power’s share of U.S. electricity generation is likely to drop over the next few decades. In fact, for nuclear power to maintain its current share—19 percent of U.S. electricity—the equivalent of 21 5 The IAEA’s high estimates (IAEA, 2008b) “reflect a moderate revival of nuclear power development that could result in particular from a more comprehensive comparative assessment of the different options for electricity generation, integrating economic, social, health and environmental aspects. They are based upon a review of national nuclear power programmes, assessing their technical and economic feasibility. They assume that some policy measures would be taken to facilitate the implementation of these programmes, such as strengthening of international cooperation, enhanced technology adaptation and transfer, and establishment of innovative funding mechanisms. These estimates also take into account the global concern over climate change caused by the increasing concentration of greenhouse gases in the atmosphere, and the signing of the Kyoto Protocol.” 6 Both nuclear plants and coal plants with carbon capture and storage (CCS) present intergenerational issues: nuclear plants because of the very long-lived radioactive waste, and coal with CCS because of the need for stored CO2 to remain underground for long periods. However, the timescales differ by orders of magnitude. For radioactive waste, this timescale is on the order of a million years; for CO2 it is likely significantly less because of the availability of natural mechanisms for removing CO2 from the atmosphere (see Ha-Duong and Keith, 2003; Hepple and Benson, 2005). 7 In addition to federal incentives for construction, the first few nuclear plants benefit from incentives for operation, such as the production tax credit. This is discussed in more detail in Box 8.5 in this chapter.
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Amreica’s Enery Future: Technology and Transformation new 1.4 GW plants would need to be built by 2030 (not including new plants built to replace any that may be retired during this period), according to the reference-case projections of the U.S. Energy Information Administration (EIA, 2008).8 The amount of new U.S. nuclear generating capacity that could reasonably be added before 2020 is limited; however, if the first handful of new evolutionary plants (about 5 plants) are constructed and are successful, the potential for nuclear power after 2020 will have much increased. Thus, deployment of the first few nuclear plants would be an important first step toward ensuring a diversity of sources for future electric supply. It may prove to be important to keep the option of an expanded nuclear deployment open, particularly if carbon constraints are applied in the United States in the future. TECHNOLOGIES The existing nuclear plants in the United States were built with technology developed in the 1960s and 1970s. In the intervening decades, ways to make better use of the existing plants have been developed, as well as new technologies that are intended to improve safety and security, reduce cost, and decrease the amount of high-level nuclear waste generated, among other objectives. These technologies and their potential for deployment in the United States are explored in the following sections. Improvements to Existing Nuclear Plants Over the last few decades, there have been significant technical and operational improvements in existing nuclear power plants. These improvements have allowed nuclear power to maintain an approximately constant share of U.S. electrical capacity, even as demand has grown and no new plants have been constructed. This trend of increasing output from current plants is likely to continue over the coming decades and, before 2020, could result in additional nuclear capacity comparable to what could be produced by new plants. The potentials for improvements are focused in the following three areas: 8 According to the EIA, U.S. electricity demand could rise by as much as 29 percent between 2008 and 2030. The reader is referred to footnote 14 of Chapter 7 of this report (“Fossil-Fuel Energy”) for a discussion of uncertainty in EIA projections.
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Amreica’s Enery Future: Technology and Transformation Existing plants can be modified to increase their power output; Existing plants’ operating lives can be extended; and Downtimes (periods when the plant is not producing power) can be further reduced. Such improvements, which are far less expensive than constructing new nuclear plants and can be implemented comparatively rapidly, are discussed below. Power Uprates A plant’s power output can be significantly increased (uprated) by replacing the fuel with higher-power-density/longer-lived fuel and by modifying major plant components. The latter includes, for example, replacing turbines and major heat exchangers with more efficient versions. Uprates are a cost-effective way to increase energy production: they typically cost hundreds of dollars per added kilowatt (kW) of capacity, compared to as much as $3000–6000 (overnight cost9) per kilowatt of electricity for new nuclear plants (see section on “Costs”). To date, 7.5 gigawatts-electric (GWe)10—amounting to about 7.5 percent of the current U.S. nuclear generating capacity—have been added through uprates.11 Many plants have already planned capacity additions. In 2008 alone, the USNRC approved 10 upgrades to existing plants, adding a total generating capacity equivalent to about half of one new nuclear plant. Eleven applications are pending, and the USNRC expects 40 more applications through 2013.12 If 9 Overnight cost is the cost of a construction project if no interest was incurred during construction, as if the project was completed “overnight.” All costs are expressed in 2007 dollars. 10 The electric power output of a nuclear power plant is often described in gigawatts-electric (or simply gigawatts [GW]). Similarly, the thermal power output of a nuclear plant is stated in gigawatts-thermal (GWt). The thermal power output is typically about three times the electric power output. This is because the thermal efficiency of nuclear plants (the efficiency of converting heat to electricity via a steam turbine generator) is typically around 33 percent. 11 The USNRC’s list of approved uprate applications is available at www.nrc.gov/reactors/operating/licensing/power-uprates/approved-applications.html; accessed July 2009. 12 In 2008, applications were approved for capacity additions of about 2178 MWt. This would result in about 720 MWe of new electric generating capacity. New plants are assumed to have a capacity of 1.35 GWe. Pending applications represented a total of 973 MWe of capacity additions as of July 2009, and applications expected at that time represented 2075 MWe of capacity additions. The USNRC’s lists of pending and expected applications are available at www.nrc.gov/reactors/operating/licensing/power-uprates/pending-applications.html (pending) and www.nrc.gov/reactors/operating/licensing/power-uprates/expected-applications.html (expected); accessed July 2009.
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Amreica’s Enery Future: Technology and Transformation approved and undertaken, these uprates would add about 3 GWe—the equivalent of about 2 new nuclear plants—in the near term. Operating License Extensions More power can be also be generated over the lifetimes of existing plants by extending their operating licenses. In the United States, the initial license term for a nuclear power plant—40 years—is subject to extensions in increments of up to 20 years.13 In the 1990s, the USNRC established a regulatory system to assess applications for such extended licenses. In the majority of cases, the owners of the currently operating U.S. plants will seek to extend plant licenses for an additional 20 years, to 60 years’ service in total. As of July 2009, 56 plants had received 20-year extensions, 16 plants were in the queue for approval, and 21 more had announced their intent to seek license extensions.14 The original 40-year limit was not technically based, but some technical challenges are involved in extending operating licenses because some structures and components may have been engineered assuming a 40-year operating life. This limitation will be avoided in new plants, which are being designed to ensure that components with expected lifetimes of less than a projected plant life of 60 years can be replaced readily. The industry has begun to assess whether it would be technically feasible and economic to extend current plant operating licenses for an additional 20-year period beyond 60 years (to 80 years). The plant modifications that might be required for another 20-year extension are potentially more difficult and expensive than those for the first 20-year extension. Degradation phenomena that affect the performance of plants operating for as long as 80 years are not well understood at a fundamental level, and further research is needed prior to decisions about further license extensions. At this point, it is not clear whether the option will be practical, although there will be strong economic incentives to pursue it. The USNRC, the U.S. Department of Energy (DOE), and industry are considering what research and development (R&D) will need to be done to prepare for the possibility of extending plant operating licenses beyond 60 years. Although participants in an USNRC/DOE workshop held in February of 2008 “did not 13 This was provided for in the Atomic Energy Act of 1954. 14 The USNRC’s list of current and expected operating life extensions is available at www.nrc.gov/reactors/operating/licensing/renewal/applications.html; accessed July 2009.
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Amreica’s Enery Future: Technology and Transformation believe there is any compelling policy, regulatory, technical or industry issue precluding future extended plant operation” (USNRC/DOE, 2008), many areas were identified where R&D should begin soon. They included irradiation effects on primary structures and components (such as the reactor vessel, reactor coolant system piping, steam generators, pressurizer, and coolant pumps), aging effects on safety-related concrete structures, aging effects on safety-related cable insulation, and inspection capabilities for aging mechanisms. Much of the equipment that is of concern is embedded in the structure of the plant and would be expensive and time-consuming to replace. Thus many of the issues imposed by plant lifetime extensions and materials aging require ways of nondestructively assessing the status of operating plants. New scanning systems are being developed, but further research is needed, particularly in light of the regulatory decisions that could rely on these inspections. Decreasing Downtimes Finally, more power can be generated over the course of a year by reducing the periods when the plants are not producing electricity. Existing plants have been operated with increasing efficiency over time, and average plant capacity factors (averaged across all operating nuclear plants) have increased markedly, from 66 percent in 1990 to 91.8 percent in 2007 (NEI, 2008). Nuclear plant operators in the United States have succeeded in reducing downtimes primarily through increased on-line maintenance as well as through efforts to plan outage times so as to ensure that necessary work is done quickly and efficiently. As a result of such improvements, refueling outages—which are also used to perform necessary maintenance on the reactor—were reduced to an average of 40 days in 2007 (averaged across all currently operating U.S. plants) from 104 days in 1990. Based on the accomplishments of the best-performing plants to date, in the future these downtimes may be reducible to an average of 25–30 days while maintaining currently high levels of safety and reliability. Nuclear Reactor Technologies15 A nuclear reactor generates heat by sustaining and controlling nuclear fission, and that heat is converted to electricity. The dominant use of nuclear reactor technol- 15 For a more thorough treatment of many of the issues reviewed briefly in this section, see Annex 8.A.
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Amreica’s Enery Future: Technology and Transformation ogy is in commercial nuclear power plants, which contribute baseload16 electric power generation.17 Nuclear plants can each include one or more nuclear reactors. The waste heat18 from nuclear reactors can be utilized as well. For example, several countries, including Russia and the Ukraine, use nuclear reactors for cogeneration (or combined heat and power [CHP]). Particularly effective in cold regions, CHP uses waste heat from nuclear reactors to create steam, which is piped to heat surrounding areas. Such systems in nuclear plants have been discussed in the United States, but they are not currently deployed. In other countries (for example, Japan, India, and Pakistan), waste heat from nuclear plants is used for desalinization of seawater. The majority of reactors used for electricity generation around the world are pressurized water reactors (PWRs) and boiling-water reactors (BWRs), reactors that are collectively referred to as light-water reactors (LWRs)—that is, they are thermal reactors (see Box 8.1) that use ordinary water both as the coolant and as the neutron moderator. These are the only reactor technologies currently used in the United States for commercial power production, where 69 PWRs and 35 BWRs are currently in service. New nuclear reactor designs have been developed in the decades since these plants were deployed. In the sections that follow, the committee discusses these new designs, which are grouped into two categories: Evolutionary reactor designs, which are modifications that have evolved from LWR designs currently operating in the United States Alternative reactor designs, which range from more significant modifications of currently deployed designs to entirely different concepts 16 Baseload power is the minimum power that must be supplied by electric generation or utility companies to satisfy the expected continuous requirements of their customers. Baseload power plants generally run at steady rates, although they might cycle somewhat to meet some variation in customer demand. Typically, large-scale nuclear, coal, or hydroelectric power plants supply baseload power. 17 Nuclear reactors are also used for propulsion (particularly for naval vessels), for materials testing, and for the production of radioisotopes for medical, industrial, test, research, and teaching purposes. In the past, nuclear reactors have also been used in space missions (primarily by Russia, but also by the United States) and for nuclear weapons materials production. Nuclear reactors dedicated to the production of nuclear materials have been shut down in the United States. This report focuses on nuclear reactors used for commercial electricity generation. 18 A significant amount of the heat generated in a thermal power plant is not used to generate electricity; rather, it is vented through a cooling system to the outside environment.
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Amreica’s Enery Future: Technology and Transformation BOX 8.1 Fast Reactors and Thermal Reactors Nuclear reactors are often classified as “fast” or “thermal” reactors. This nomenclature refers to the energy of the neutrons that sustain the fission reaction. In fast nuclear reactors, the fission reaction is sustained by neutrons at higher energies (“fast” neutrons); in commonly deployed thermal reactors, such as light-water reactors, the fission reaction is sustained by lower-energy (“thermal” neutrons). Fast and thermal reactors are distinguished by the presence or absence of a material known as a “neutron moderator,” or simply “moderator.” This material is present in thermal reactors but not in fast reactors. Collisions with the moderator slow the neutrons emitted by fissioning nuclei to thermal energies. In the next few decades, the majority of the new nuclear plants constructed in the United States will be based on evolutionary reactor designs. In most cases, alternative reactor designs will require significant development efforts before they can be ready for deployment. Evolutionary Reactor Designs Any new nuclear plants constructed before 2020 will be evolutionary designs that are modifications (often significant) of existing U.S. reactors. These designs are intended to improve plant safety, security, reliability, efficiency, and cost-effectiveness. Some evolutionary designs include passive safety features that rely on natural forces, such as gravity and natural circulation, to provide cooling in the case of an accident. These features are intended to reduce capital cost while further enhancing safety margins. Several evolutionary reactor designs will be ready for deployment in the United States after the USNRC completes design certification.19 In some cases, this could occur as soon as 2010 or 2011. Evolutionary reactors have already been built in Japan and South Korea, and they are under construction in India, France, and Finland. U.S. utilities have expressed potential interest in building plants with the following designs in the United States: the U.S. evolutionary power reactor (USEPR), the economic simplified boiling-water reactor (ESBWR), the advanced boiling-water reactor (ABWR), the AP-1000, and the advanced pressurized water 19 Before a nuclear plant of a new design can be constructed in the United States, the design must first be certified by the USNRC.
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Amreica’s Enery Future: Technology and Transformation reactor (APWR). These designs are all modifications of current-generation LWR designs.20 Because construction of new nuclear plants is likely to require a long lead time, the first deployment of evolutionary nuclear reactors in the United States is unlikely to be until after 2015. Typical construction times for foreign plants have ranged from 4 to 7 years for plants that began construction in the last decade (IAEA, 2008c). Lead times for licensing and large component fabrication can also run to years. Current plans (as of July 2009) suggest that about 5–9 new nuclear plants could be on line in the United States by 2020, and a more substantial deployment of these plants may occur after 2020 if these first plants built in the United States meet cost, schedule, and performance targets. Moreover, actual construction will also depend on many other factors, including comparative economics and electrical demand. Further R&D over the next decade could lead to efficiency improvements both in existing reactors and in evolutionary LWRs. Some of the key areas for continuing research include the following: Improved heat transfer materials, such as high-temperature metal alloys, are being developed to improve efficiency by allowing for higher operating temperatures. Some of these materials may be available after 2025. Widespread application is likely between 2035 and 2050. Coolant additives, such as very dilute additions of nanoparticles, can improve the heat transfer capabilities of the coolant in current and evolutionary LWRs. Twenty years or more are likely needed to develop the additives and redesign current reactors for their use. Annular fuel rods could allow plants to produce significantly more power than traditional cylindrical fuel rods do. At least 10 years of work will be needed for regulatory approval and commercial-scale deployment in existing LWRs. 20 The ABWR and AP-1000 designs are currently certified by the USNRC, but applications for amendment have been received for the AP-1000 and are expected for the ABWR. The USNRC is currently reviewing design certification applications for the ESBWR, the USEPR, and the US-APWR designs. The review of the amended AP-1000 design and the ESBWR is targeted for completion in 2010, and for the USEPR and US-APWR in 2011. Available at www.nrc.gov/reactors/new-reactors/design-cert.html; accessed July 2009.
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Amreica’s Enery Future: Technology and Transformation Higher burn-up fuel would allow a larger percentage of the fissionable content of the fuel to be used. Thus operating cycles could be prolonged, and the heat load21 and total amount of used nuclear fuel22 to be stored or disposed of could be reduced.23 This is a program of continuous improvement, but for significant breakthroughs, basic research will be required, particularly on fuel-rod swelling due to buildup of fission products and the resulting risk of cladding breach. Digital instrumentation and control (DI&C) research offers opportunities to improve control systems and to enhance control-room designs so as to facilitate appropriate operator action when needed. New LWRs will have fully integrated DI&C, and more research will be needed on the safety implications of an increased reliance on digital systems. Understanding the full implications of DI&C is likely to prove to be a long-term effort, despite the reliance on DI&C in the near term. These types of R&D could improve both current and evolutionary reactors. However, evolutionary reactor technology is technically ready for deployment, and no major additional R&D is needed for an expansion of nuclear power through 2020, and likely through 2035. Alternative Reactor Designs In addition to the evolutionary reactor designs just discussed, alternative nuclear reactor designs are being developed (and, in some countries, have been used).24 21 When nuclear fuel is removed from the reactor after use, it not only is highly radioactive, but also emits heat. This amount of heat emitted is known as the “heat load” of the fuel. 22 “Used nuclear fuel” (also referred to elsewhere as spent nuclear fuel, or SNF) refers to fuel that is removed from a nuclear reactor after use. As discussed later in this chapter, only a small fraction of the energy potentially available in the fuel is used. 23 The total amount of used fuel to be disposed of would be reduced with higher burn-ups because fewer fuel assemblies would need to be used to produce the same power output. Although high burn-up decreases the amount of nuclear fuel remaining in the fuel assemblies after use, for the first century or so, heat and radioactivity are the major challenges for used fuel disposal. This initial heat and radioactivity are dominated by fission products, isotopes produced as a result of the fission of a massive atom such as U-235. 24 For example, as mentioned previously, sodium-cooled and gas-cooled reactors have been in operation around the world for decades. These designs are significantly different from the light-water reactor (LWR) designs currently in use in the United States, and new U.S. deployments of these reactors are considered here as “alternative” designs.
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Amreica’s Enery Future: Technology and Transformation 60 years.)64 Given the current impasse on used fuel disposal, it should be anticipated that any new plant will be constructed with an eye toward the possibility that extended on-site storage of fuel may be required. This suggests that such storage could be incorporated into the design of new plants. In contrast, technologies such as advanced fuel cycles may produce waste forms that are different from those produced by current U.S. plants. For advanced fuel cycles, various waste streams emerge from the separations processes. These can include separated strontium and cesium, technetium, claddings, and hulls, along with the remaining fission products. These waste streams will require specialized waste forms. For example, in the UREX+ process, the technetium isotope that is separated from used fuel would be relatively mobile if emplaced in the Yucca Mountain geologic setting unless placed in a specially designed waste form. Separation of technetium allows it to be separately handled in a specially designed waste form. The cesium and strontium isotopes in the used fuel have comparatively short half-lives and, if separated from the high-level waste for the repository, could potentially be stored in less costly aboveground or near-surface sites. These isotopes will have essentially decayed away in a few hundred years. In general, waste form certification is at the proof-of-principle stage (DOE, 2007). 64 For new plants, operators have to sign a contract with the DOE to take title to used fuel.
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Amreica’s Enery Future: Technology and Transformation ANNEX 8.E: SAFETY AND SECURITY IMPACTS OF NUCLEAR TECHNOLOGIES The primary impact of concern in the event of an accident or an intentional attack on a nuclear power plant is the same: major off-site releases of radioactive material. This section examines potential safety65 and security66 impacts arising from the operation of nuclear power plants in the United States. The following discussion is drawn from a recent National Research Council report on the safety and security of commercial spent nuclear fuel storage (NRC, 2006). There are two potential sources for off-site radioactive releases: the nuclear fuel in the reactor core and in used fuel storage. An accident or terrorist attack that disrupts cooling of the fuel could damage the fuel and release radioactive material to the environment. The fuel in the reactor core of a nuclear plant generates substantial quantities of heat and radioactivity. The plant’s cooling system is designed to remove this heat from the core so it can be used for electricity generation. A loss of coolant would cause temperatures in the core to increase, even after the reactor is shut down.67 At about 1000°C, the fuel cladding68 would begin to oxidize rapidly in the presence of air or steam (if the core did not remain covered with water). This exothermic reaction releases large quantities of heat that would further raise temperatures. At about 1800°C, the cladding and fuel would begin to melt, releasing radioactive gases and aerosols into the core. These radioactive materials could be released to the surrounding environment if the reactor pressure vessel69 and the containment70 were to fail. Such releases could endanger local populations and contaminate the environment. An accident or terrorist attack on a used-fuel pool could have similar con- 65 “Safety” is defined here as measures that would protect nuclear facilities against failure, damage, human error, or other accidents that would disperse radioactivity into the environment. 66 “Security” is defined here as measures to protect nuclear facilities against sabotage, attacks, or theft. 67 This “heat” is the product of radioactive decay in the fuel. 68 “Fuel cladding” is a thin-walled metal tube that forms the outer jacket of a nuclear fuel rod. It prevents corrosion of the nuclear fuel and the release of fission products into the coolant. 69 The “reactor pressure vessel” is a thick-walled cylindrical steel vessel enclosing the reactor core in a nuclear power plant. 70 A “containment building” is a steel or reinforced concrete structure enclosing a nuclear reactor. The containment building is typically an airtight steel structure enclosing the reactor, sealed off from the outside atmosphere and attached to a concrete shield. In the United States, the design and thickness of the containment and the shield are governed by federal regulations (10 CFR 50.55a).
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Amreica’s Enery Future: Technology and Transformation sequences. After its removal from the reactor, used fuel continues to generate heat and must be actively cooled. Fuel is stored in water-filled pools that have active cooling systems to remove this heat and water filtering systems to remove radioactive contamination. An accident or terrorist attack that results in the loss of coolant from the pool could raise fuel temperatures, possibly resulting in cladding oxidation and fuel melting with a consequent release of radioactive gases and aerosols. These processes would likely unfold more slowly than would the events following a disruption of core coolant, because the used fuel stored in pools generally has lower rates of heat generation. Consequently, plant operators would have more time to implement backup cooling measures. The pools themselves are constructed with thick reinforced concrete walls and stainless steel liners. A 2006 National Research Council report concluded that successful terrorist attacks on used-fuel pools would be difficult, and “an attack that damages a power plant or its spent fuel storage facilities would not necessarily result in the release of any radioactivity to the environment” (NRC, 2006, p. 6). The report also noted that used fuel in dry cask storage poses considerably less risk. Nuclear plants have backup systems and procedures designed to prevent or mitigate the consequences from the accidental disruption of coolant flow to the reactor core or used-fuel pool. For example, the reactor containment is designed to limit the release of any radioactive material from the reactor core in the event of an accident. Plants have multiple backup supplies of cooling water as well as emergency cooling systems that can flood or spray the fuel in the core with water. They also have backup sources of water for the used-fuel pools, and water sprays could be deployed to cool the fuel even if the pool could not be refilled (NRC, 2006). In addition to these backup systems, plant operators are required to perform probabilistic analyses to understand and mitigate the consequences of accidental disruptions of core cooling, as well as to develop and implement plans to notify authorities and residents living near their plants in the event of emergencies. Safety Efforts to improve safety in U.S. plants have focused in part on reducing the probability of the most likely sequences of events or failures that could result in a radioactive release. Most early nuclear plants were designed to conform to particular design rules, such as an insistence that the design incorporate multiple barriers and provide the means to prevent an event from resulting in a radioactive release to the public, as well as conservative engineering assumptions as to the
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Amreica’s Enery Future: Technology and Transformation capabilities of materials and equipment. Over time, an analysis technique termed probabilistic risk assessment (PRA) was developed that allows the systematic evaluation of the various sequences of events or failures that could result in a release and the determination of the probability that any given sequence might arise. PRAs suggest that the likelihood of an accidental release in the United States from the currently operating reactors is small. According to the Reactor Safety Study undertaken by the U.S. Atomic Energy Commission in 1975, the probability of such an occurrence was estimated at one in 17,000 per reactor per year (USNRC, 1975). However, more recent studies have concluded that the core damage frequency is between 10−5 and 10−6 events per reactor per year for current plants (Sheron, 2008).71 Extensive efforts have been undertaken by the USNRC and the licensees to consider the accident sequences presenting the greatest risk and to implement measures to thwart them. Some critics contend that safety problems continue to arise associated with nuclear reactors in the United States due to inadequate enforcement of standards by the USNRC (UCS, 2008), pointing to 36 instances that have occurred since 1979 where individual reactors have been shut down for more than a year to restore safety standards (Lochbaum, 2006). However, it should be noted that these shutdowns to restore standards were initiated by the USNRC. Security In addition to reactor accidents, after the attacks of September 11, 2001, terrorist threats to nuclear power plants have become a concern. As noted above, the primary concern is that a terrorist attack on a nuclear reactor might result in a radioactive release to the surrounding area. Every U.S. nuclear plant has a security plan that must be approved by the USNRC to respond to an attack at the level of the Design Basis Threat (DBT)72 or below. The details of the DBT are not available to the public, but it is described as an attack carried out by a well-armed land force aided by a knowledgeable insider. The plants defend against this threat primarily through the use of a 71 These results are attributed to the USNRC State of the Art Reactor Consequence Analysis assessment. Final results from this study are planned for release in 2009 (Sheron, 2008). 72 The DBT is a profile of the type, composition, and capabilities of an adversary. The USNRC and its licensees use the DBT as a basis for designing safeguards systems to protect against acts of radiological sabotage and to prevent the theft of special nuclear material. The DBT is described in Title 10, Section 73, of the Code of Federal Regulations [10 CFR 73].
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Amreica’s Enery Future: Technology and Transformation layered security system involving access controls and requirements, physical barriers (including standoff protection for bombs), armed guards, and armored firing positions. Attacks that are beyond the DBT are also a concern, including, in particular, air attacks. The industry and its regulator (the USNRC) have stated that defending against these types of attacks is the federal government’s responsibility,73 not that of the plant operator. Since the September 11, 2001, attacks, the USNRC and the nuclear industry have undertaken analyses of existing plants to determine their vulnerability to aircraft attacks and have made modifications to the designs and operations to mitigate the consequences of such attacks. In addition, the DBT has been increasd in severity, with the result that the capacity to withstand terrorist attacks of all types has been enhanced. U.S. plant operators report that they have spent in excess of a billion dollars on physical upgrades and security since September 11, 2001 (www.nei.org/keyissues/safetyandsecurity/factsheets/powerplantsecurity; accessed July 2009). These include changes to plant access controls, operating procedures, and other security measures. The details of these analyses and modifications have not been released to the public (due to security concerns), and the committee has not reviewed this information. Impacts from Expanded or New Deployments New evolutionary nuclear plant designs are intended to improve both safety and security over currently operating plant designs. Some modern designs for reactors of the types that are proposed for near-term construction in the United States (discussed in Annex 8.A) promise to reduce core damage frequency by a factor of 10 to 100 from the probability of such an event in an existing plant. In addition, these designs include enhanced physical protection of the core and used-fuel pools intended to reduce their vulnerabilities to beyond-DBT attacks such as air attacks; designs of core cooling systems that rely on passive systems (using gravity and natural circulation) to maintain cooling in the case of an accident or terrorist attack; and the design and placement of multiple independent safety systems to provide spatial redundancy intended to improve survivability in accidents or attacks (and also to allow some maintenance on these systems to occur while the 73 Measures have been taken to defend against these kinds of attacks, including increased security at airports, locks on cockpit doors, and armed air marshals and pilots.
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Amreica’s Enery Future: Technology and Transformation plant is operating). In addition, the USNRC recently promulgated a rule requiring applicants for new nuclear reactors to identify features and functional capabilities of their designs that would provide additional inherent protection from or mitigate the effects of aircraft attacks. Plants are either acceptable as designed or will be upgraded.
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