Nuclear Power

Nuclear power is the use of thermal energy released from radioactive decay (fission) of atomic nuclei, generally of uranium or plutonium. In a nuclear electric power plant, this heat is used to produce steam, which drives a turbine, much like any other thermal electric power plant.¹

The World Nuclear Association maintains a reactor inventory, including all reactors that are under construction, planned, or proposed.² Nuclear power is an important component of the electricity generation mix in many countries; in February 2009 there were 436 operating nuclear power plants in 131 countries,³ which accounted for about 15% of global net electricity generation.⁴ In the U.S., nuclear power accounted for about 20 percent of net electricity generation in 2007.⁵

Because the heat in a nuclear reactor is produced from radioactive decay rather than combustion, nuclear reactors generate electricity without producing greenhouse gas emissions. While uranium mining, processing, and transportation do produce emissions, there is no question that greenhouse gas emissions from nuclear power are far less than fossil-based alternatives.⁶ As such, nuclear power does present an option for large-scale greenhouse gas mitigation. However, the use of nuclear energy is controversial in many countries, and is in fact banned in New Zealand.⁷ Nuclear power presents still-unresolved issues of safety, nuclear weapons proliferation, and waste disposal, that are problematic for environmental, political, and social reasons.⁸ While there has not been a catastrophic meltdown in over 20 years, and modern reactors are built such that meltdowns should only occur about once in every 100,000 reactor years,⁹ the possibility nevertheless exists, and much of the future nuclear expansion may be in regions with less oversight than the present stock. 95% of installed nuclear capacity in 2008 was in developed countries, but developing nations account for 15% of planned future reactors, and 24% of proposed future reactors.¹⁰ Global expansion of civilian nuclear power also raises the already serious threats of nuclear proliferation and arms manufacture, and the dangers posed by the lack of methods for permanent waste disposal.

Technology basics

Nuclear power plant in Cattenom, France

Source: Author/Wikimedia Commons. Author: Stefan Kühn. Permission: Pub. under GNU Free Documentation License.

Nuclear power plants are thermal power plants, similar to coal power plants, except that the heat is derived from radioactive decay of elements such as uranium, plutonium, or thorium. The fuel is placed in a reactor and its atoms are split apart in the process of fission. The energy released from fission is used to heat water and form steam, which in turn powers turbines.

Most reactors have several main components:
• Fuel. Usually pellets of uranium oxide (UO2) arranged in tubes to form fuel rods. The rods are arranged into fuel assemblies in the reactor core.
• Moderator. This is material which slows down the neutrons released from fission so that they cause more fission. It is usually water, but may be heavy water or graphite.
• Control rods. These are made with neutron-absorbing material such as cadmium, hafnium or boron, and are inserted or withdrawn from the core to control the rate of reaction, or to halt it. (Secondary shutdown systems involve adding other neutron absorbers, usually as a fluid, to the system.)
• Coolant. A liquid or gas circulating through the core that serves to transfer heat away from the core. In light water reactors, the water moderator functions also as primary coolant. Except in BWRs, there is secondary coolant circuit where the steam is made.
• Pressure vessel or pressure tubes. Usually a robust steel vessel containing the reactor core and moderator/coolant, but it may be a series of tubes holding the fuel and conveying the coolant through the moderator.
• Steam generator. Part of the cooling system where the heat from the reactor is used to make steam for the turbine.
• Containment. The structure around the reactor core which is designed to protect it from outside intrusion and to protect those outside from the effects of radiation in case of any malfunction inside. It is typically a meter-thick concrete and steel structure."¹¹

Technology Types

There are several different types of nuclear reactors.

• Pressurized Water Reactor (PWR) - This is the most common type, with over 230 in use for power generation.¹²

• Boiling Water Reactor (BWR) - The reactor is designed to operate with 12-15% of the water in the top part of the core as steam.¹³

• Pressurized Heavy Water Reactor (PHWR or CANDU) - First devised in the 1950s in Canada, the CANDU reactor design uses natural uranium (0.7% U-235) oxide as fuel, meaning that it uses heavy water (D2O) as a moderator.¹⁴

• Advanced Gas-cooled Reactor (AGR) - Moderated by graphite and cooled by carbon dioxide, AGR reactors use uranium fuel in metal form and are designed to be refuelled without being shut off beforehand.¹⁵

• Light water graphite-moderated reactor (RBMK) - The RBMK is based from plutonium production reactors. It uses 7 meter-long vertical pressure tubes and a graphite moderator, and is cooled by water.¹⁶

• Advanced Reactors - More than a dozen advanced reactor designs are in various stages of development; some have evolved from the PWR, BWR and CANDU designs while others are based from original plans.¹⁷

Scientists are trying to perfect ways to use the element thorium to fuel reactors instead of uranium because it is three times more abundant in nature and generates 80 percent fewer plutonium-239 atoms (a key ingredient in atomic bombs).¹⁸ Thorium reactors also produce less waste, and the waste it does leave behind is harder to exploit for use in nuclear weapons.

Cost and finance

Nuclear power plants are extremely capital-intensive, requiring billions of dollars of up-front investment. The overnight capital cost estimates for future nuclear plant capital costs are assumed to be anywhere from $2,000/kWe¹⁹ to $4,000/kWe.²⁰ Actual project costs are even more variable, due to uncertainty about project timelines, financing options, regulatory hurdles, and the market bottlenecks in the supply chain of components. While the construction time of modern plants is typically assumed to be about four years, there are plenty of examples of plants that took a decade or more to produce any electricity.²¹

However, the high up-front costs are compensated by relatively low operating costs,²² and the fuel costs have also historically been more stable than oil or gas prices. However, the price of nuclear fuel in the U.S. nearly doubled from 2006 to 2007, and about 60% of the nuclear fuel used in power plants is imported.²³ Future fuel price volatility may become more important in the future.

The availability and cost of financing for new nuclear plants in the U.S. will depend a wide variety of factors, including: the level and certainty of federal and state government subsidies and incentives, the comparative cost and performance of renewable energy sources, the timing of capital markets’ recovery from the credit crisis, the estimated construction costs, the structure of the target electricity market (competitive market v. more traditional, regulated cost-of-service market), the assessments of a plant's lifetime capacity and performance, creditors’ and investors’ assessment of the NRC’s licensing process and staff capacity, the resolution of the long-term waste storage problem, and public opinion about nuclear power.²⁴

Advantages

Patrick Moore, famous founding member of Greenpeace, on Nuclear Power.

Credit: Strom TV

The IPCC (Intergovernmental Panel on Climate Change) identifies nuclear power as one of the five energy-related carbon mitigation strategies (along with energy efficiency, renewable energy, carbon capture and storage, and fossil fuel switching).²⁵ As such, nuclear power stands to play a large role in an emissions-constrained world.

Nuclear power plants, once constructed, have quite favorable economics. The cost of nuclear fuel is stable compared with fossil fuels, ²⁶ and estimates of global uranium resources indicate that uranium supply will be more than adequate to meet anticipated demand without prohibitive cost escalations in the next few decades.²⁷

Nuclear plants are almost always used for producing baseload electricity; the average capacity factor for U.S. nuclear plants in 2007 was 91.5%. ²⁸

Disadvantages

Nuclear power poses a number of environmental, political, and social risks, in addition to having uncertain and potentially very high economic costs.

Nuclear power plant reactor cores can melt down, in which the reactor core overheats, and carcinogenic, radioactive material escapes into the surrounding environment and community. The 1986 meltdown in Chernobyl was the last meltdown in the history of nuclear power, and the reactors currently in use are designed so that this type of meltdown will not occur.²⁹ However, in the modern era the threat of a terrorist attack on a nuclear facility does give legitimacy to the fear of future similar disasters from civilian nuclear power.

Another large-scale threat stemming from nuclear power is that reactors that produce electricity may also be used to produce nuclear weapons. A typical 1000-MW nuclear reactor is capable of making enough plutonium each year to build 40 nuclear bombs.³⁰ Widespread deployment of nuclear power, as would be required for nuclear power to become a pillar of global emissions mitigation, would therefore require a stronger international regulatory framework to track all movement of nuclear material, including fuel and waste.

Even without a catastrophic failure of a nuclear plant or the use of nuclear weapons, the operation of nuclear plants produces radioactive waste that poses health risks for hundreds of thousands of years,³¹ far longer than human civilization has existed. While a number of proposals for dealing with wastes have been proposed,³² no solution has yet been implemented at scale for secure shipping and permanent containment of waste. Even in the U.S., nuclear waste is stored in temporary storage containers, with no immediate plans for relocation to more stable, long-term sites.³³ Furthermore, this radioactive waste can be used for the production of nuclear weapons.³⁴

Cost uncertainty, and the potential for very high construction costs, constitutes a serious disadvantage for nuclear power, particularly in the U.S. While streamlined regulatory systems (e.g. in France or Japan) may alleviate this burden somewhat, there are also issues with the supply of reactor components. For instance, modern nuclear reactor containment vessels are only built by a single company, Japan Steel Works Ltd., which can produce only four per year.³⁵ While in the long term heightened demand for nuclear plants would lead to increased manufacturing capacity, in the short term an increase in demand for nuclear reactors will only serve to increase construction costs and construction times.

Applications

Nuclear power is mostly used for producing electricity, and in some countries it accounts for the majority of electricity generation. For instance, France and Lithuania generate 79% and 71% of their electricity from nuclear power, respectively.³⁶

Nuclear power has also been used as a transport fuel for sea-bound vessels; its advantage is that vessels may remain at sea for very long times without refueling, due to the low mass of the uranium fuel. About 150 ships are powered by more than 220 small nuclear reactors, and to date, more than 12,000 reactor-years of marine operation have taken place.³⁷ Most are submarines, but they range from icebreakers to aircraft carriers. The future of this application will depend on availability and costs of fossil fuels, as well as public acceptance of nuclear vessels at coastal ports. ³⁸ Nuclear energy may also some day be a fuel source for aircraft; a nuclear aircraft could likely remain aloft for weeks at a time without refueling.³⁹

Nuclear power has been proposed as a source of heat for direct industrial applications and domestic heating,⁴⁰ and also as a heat source for thermal splitting of water to produce hydrogen fuel.⁴¹ The future of nuclear energy will depend on a variety of social and political decisions, as well as the economics of the nuclear technologies of the future.

Footnotes

¹U.S. Nuclear Regulatory Commission (2008). NRC: Students' Corner.

²World Nuclear Association (2008). World Nuclear Power Reactors 2007-09 and Uranium Requirements.

³World Nuclear Association (2008). World Nuclear Power Reactors 2007-09 and Uranium Requirements.

⁴International Energy Agency (2007). Energy Balances of OECD Countries 1960-2005 and Energy Balances of non-OECD Countries 1971-2005.

⁵U.S. Energy Information Administration (2008). Annual Energy Review 2007, Table 8.2a: Electricity Net Generation: Total (All Sectors), Selected Years 1949-2007.
⁶Kleiner, K. (2008). Nuclear Energy: Assessing the Emissions. Nature Reports Climate Change, Nature Publishing Group, September 24, 2008.

⁷New Zealand Nuclear Free Zone, Disarmament, and Arms Control Act of 1987 no. 86 (as of September 3, 2007).

⁸Massachusetts Institute of Technology (2003). The Future of Nuclear Power, Chapter 1.

⁹Massachusetts Institute of Technology (2003). The Future of Nuclear Power, p.48.

¹⁰World Nuclear Association (2008). World Nuclear Power Reactors 2007-09 and Uranium Requirements.

¹¹World Nuclear Association Electricity Generation - Nuclear Power Reactors. Retrieved on: 21 February 2009.

¹²Global Greenhouse Warming, Nuclear Pressurized Water Reactors. Retrieved on: 21 February 2009.
¹³Global Greenhouse Warming, Nuclear Boiling Water Reactors. Retrieved on: 21 February 2009.
¹⁴Global Greenhouse Warming, Nuclear Pressurized Heavy Water Reactor. Retrieved on: 21 February 2009.
¹⁵Nation Master Encyclopedia - Advanced Gas Cooled Reactor. Retrieved on: 21 February 2009.
¹⁶World Nuclear Institution, Nuclear Power Reactors. Retrieved on: 21 February 2009.
¹⁷World Nuclear Institution, Nuclear Power Reactors. Retrieved on: 21 February 2009.

¹⁸Amit Asaravala, Wired (5 July, 2005) "How Nuclear Power Works," p. 1, 2.

¹⁹Massachusetts Institute of Technology (2003). The Future of Nuclear Power, Table A-5.A.2.

²⁰Severance, C. (2009). Business Risks and Costs of New Nuclear Power.

²¹World Nuclear Association (2009). The Economics of Nuclear Power.
²²World Nuclear Association. The Economics of Nuclear Power, U.S. Electricity Production Costs.

²³U.S. Energy Information Administration (2008). Annual Energy Review 2007, Table 9.3: Uranium Overview, Selected Years, 1949-2007.
²⁴World Nuclear Association. The Economics of Nuclear Power. Retrieved on: 21 February 2009.

²⁵Intergovernmental Panel on Climate Change (2007). Climate Change 2007: Synthesis Report, IPCC Fourth Assessment Report, Figure 5.2.
²⁶Nuclear Energy Institute. Emissions Avoided by the U.S. Nuclear Industry (1995-2007). Retrieved on: 21 February 2009.

²⁷OECD Nuclear Energy Agency and the International Atomic Energy Agency (2008). Uranium 2007: Resources, Production, and Demand.
²⁸U.S. Energy Information Administration (2008). Annual Energy Review 2007, Table 9.2: Nuclear Power Plant Operations, 1957-2007.
²⁹World Nuclear Association (2007). Chernobyl Accident.

³⁰Nuclear Information and Resource Service (1996). Nuclear Power Plant Fuel: a Source of Plutonium for Weapons?

³¹U.S. Nuclear Regulatory Commission (2007). High-Level Waste.

³²Office of Civilian Radioactive Waste Management (2003). Managing Nuclear Waste: Options Considered. U.S. Department of Energy.

³³Office of Civilian Radioactive Waste Management (2009). OCRWM: Virtual Media Guide. U.S. Department of Energy.

³⁴Nuclear Regulatory Commission (2007). NRC: Fact Sheet on Dirty Bombs.

³⁵Bloomberg (2008). Samurai Sword-Maker's Reactor Monopoly May Cool Nuclear Revival. March13, 2008.

³⁶International Energy Agency (2007). Energy Balances of OECD Countries 1960-2005 and Energy Balances of non-OECD Countries 1971-2005.

³⁷World Nuclear Association (2008). Nuclear-Powered Ships.

³⁸World Nuclear Association(2008). Nuclear-Powered Ships. Retrieved on: 21 February 2009.

³⁹Times Online (2008), Nuclear-powered passenger aircraft "to transport millions," says expert. October 27, 2008.

⁴⁰International Atomic Energy Agency (1997). Nuclear Power Applications: Supplying Heat for Homes and Industries.

⁴¹Idaho National Laboratory (2009). Nuclear Science and Technology.