Science Fair Project Encyclopedia
Nuclear power is the energy generated from nuclear reactions or decay of an atom nucleus. It is also used to describe the use of the large scale production of electricity for commercial use or the propulsion of mainly sea vessels (mostly for military use).
All current nuclear-powered electrical power plants are based on nuclear fission. For decades there have been major research efforts dedicated to the development of nuclear fusion reactors for power generation.
Nuclear power is the subject of major controversy. On the one hand, it is lauded by some environmentalists as a plentiful source of electricity that does not contribute to the greenhouse effect. On the other hand, it is decried by other environmentalists because of the problem of nuclear waste and the severe consequences of accidents.
Nuclear power can also be generated in a radioisotope thermoelectric generator, which produces heat through subcritical (i.e. less than critical mass) radioactive decay rather than fission in a near-critical mass. These generators have been used to power space probes and some lighthouses built by the Soviet Union.
During the Second World War, the possibility of obtaining tremendous amounts of energy from nuclear reactions became clear to the world, culminating in the use of nuclear weapons to destroy the Japanese cities of Hiroshima and Nagasaki. Several nations immediately began constructing nuclear reactors for military use (in particular, for plutonium production).
On June 27, 1954, the world's first nuclear power plant that generated electricity for commercial use was officially connected to the Soviet power grid at Obninsk, USSR. The reactor was graphite moderated, water cooled and had a capacity of only 5 MW. The second reactor for commercial uses that was built was Calder Hall in Sellafield, England with a capacity of 45 MW.
Benefits and disadvantages
Proponents of nuclear power point out that the technology emits virtually no airborne pollutants, and overall far less waste material than fossil-fuel based power plants. Coal-burning plants are particularly noted for producing large amounts of radioactive ash, due to concentrating radioactive material in the coal.
However, reactors do release radioactive products—such as radioactive krypton gas (half life c. 19 days)—into the environment. The waste from highly radioactive spent fuels needs to be handled with great care and forethought due to the long half-lifes of the radioactive isotopes found in the waste. In addition, the nuclear industry produces a much greater volume of low-level radioactive waste in the form of contaminated items like clothing, hand tools, water purifier resins, and upon decomissioning the materials of which the reactor itself is built. In the United States, the NRC has repeatedly attempted to allow low-level materials to be handled as normal waste: landfilled, recycled into consumer items, etc. Much low-level waste releases very low levels of radioactivity, and is considered radioactive waste essentially because of its history. For example, according to the standards of the NRC, the radiation released by coffee is enough to treat it as low level waste.
Another concern is that civilian nuclear technology could be used to create fissile materials for use in nuclear weapons. This concern is known as nuclear proliferation, and is a major reactor design criterion. While the enriched uranium used in most nuclear reactors is not concentrated enough to build a bomb (most nuclear reactors run on 4% enriched uranium, while a bomb requires an estimated 90% enrichment), the technology used to enrich uranium could be used to make the highly enriched uranium needed to build a bomb. In addition, breeder reactor designs such as CANDU can be used to generate plutonium for bomb making materials. It is believed that the nuclear programs of India and Pakistan used CANDU-like reactors to produce the fissionables for their weapons. Nuclear material for bombs is generally made in special dedicated reactors that are quite different from commercial reactors.
Critics of nuclear power assert that any of the environmental benefits are outweighed by safety concerns and by costs related to the actual construction and operation of nuclear power plants, including spent fuel disposition and plant retirement costs. Proponents of nuclear power maintain that nuclear energy is the only power source which explicitly factors the estimated cost of waste containment and plant decommissioning into its overall cost, and that the quoted cost of fossil fuel plants is deceptively low for this reason. Nuclear power does have very useful additional advantages such as the production of radioisotopes which are used in medicine and food preservation, though the demand for these products can be satisfied by a relatively small number of plants.
The safe storage and disposal of nuclear waste is a difficult problem. Because of potential harm from radiation, spent nuclear fuel must be stored in shielded basins of water, or in dry storage vaults or containers until its radioactivity decreases naturally ("decays") to safe levels. This can take days or thousands of years, depending on the type of fuel. Most waste is currently stored in temporary storage sites, requiring constant maintenance, while suitable permanent disposal methods are discussed. See the article on the nuclear fuel cycle for more information.
A major disadvantage of the use of nuclear reactors is the perceived threat of an accident or terrorist attack and resulting exposure to radiation. Proponents contend that the potential for a meltdown, as in Chernobyl, is very small due to the care taken in designing adequate safety systems, and that nuclear industry overall has quite a good safety record compared to other industries (Safety page). Chernobyl is thought to have been caused by a combination of a faulty reactor design, poorly trained operators, and a non-existent safety culture. Even in an accident such as Three Mile Island, the containment vessels were never breached, so that very little radiation was released into the environment. Opponents of nuclear power claim that nuclear wastes are not well protected and that they can be released in the event of terrorist attack. Proponents of nuclear power contend, however, that nuclear wastes are well protected and as proof they state that there was no accident that involved any form of nuclear waste in civilian program worldwide. In addition they point to large studies carried out by NRC and other agencies that tested robustness of both reactor and waste fuel storage and found that they should be able to sustain a terrorist attack comparable to September 11 (see Resistance to terrorist attack). Spent fuel is usually housed inside reactor containment (see [Fuel Storage).
Low-dose radiation released under normal operating conditions may also be a concern. Fission reactors produce gases such as iodine-131 or krypton-85 which have to be stored on-site for several half-lives until they have decayed to levels officially regarded as safe. But proponents point out that the radioactive contamination released from a nuclear reactor under normal circumstances is less than the exposure from the waste of a coal-fired plant. The effects of long-term exposure to very low levels of radioactivity are also a matter of current dispute.
The emissions problems of fossil fuels go beyond the area of greenhouse gases to include acid gases (sulfur dioxide and nitrogen oxides), particulates, heavy metals (notably mercury, but also including radioactive materials), and solid wastes such as ash. Some of these, including nitrogen oxides, are also greenhouse gases. Nuclear power produces spent fuels, a unique solid waste problem. In volume, spent fuels from nuclear power plants are roughly a million times smaller than fossil fuel solid wastes. However, because spent nuclear fuels are radioactive, extra care and forethought are given to faciliate their safe storage (see nuclear waste). Nuclear reactors also regularly vent radioactive gases—which have too much volume to conveniently store— after a period of radioactive decay, into the environment. In addition, the nuclear industry fuel cycle produces many tons of depleted uranium (uranium from which the easily fissile U235 element has been removed, leaving behind only U238). This material is much more concentrated than natural uranium ores, and must be disposed of. It can have commercial use in parts that have to be extra robust. They are used in aircraft production, for radiation shielding, and similar things.
As of 2003, the United States accumulated about 49,000 metric tons of spent nuclear fuel from nuclear reactors. Unlike other countries, U.S. policy forbids recycling of used fuel so it is treated as waste. After 10,000 years of radioactive decay, according to United States Environmental Protection Agency standards, the spent nuclear fuel will no longer pose a threat to public health and safety. It is unclear whether this material can be safeguarded over such a long period of time.
The dangers of nuclear power must also be weighed against the dangers of other methods of electricity generation. See environmental concerns with electricity generation for discussion of this issue. However, fear has been the single largest obstacle to the widespread use of nuclear power.
In the U.S, a single nuclear power plant is significantly more expensive to build than a single steam-based coal-fired plant. A coal plant is itself more expensive to build than a single natural gas-fired combined-cycle plant. Although the cost per megawatt for a nuclear power plant is comparable to a coal-fired plant and less than a natural gas plant, the smallest nuclear power plant that can be built is much larger than the smallest natural gas power plant, making it possible for a utility to build natural gas plants in much smaller increments.
In the U.S., licensing, inspection and certification delays add large amounts of time and cost to the construction of a nuclear plant. These delays and costs are not present when building either gas-fired or coal-fired plants. Because a power plant does not earn money during construction, longer construction times translate directly into higher interest charges on borrowed construction funds. However, the regulatory processes for siting, licensing, and constructing have since been standardized, to make construction of newer and inherently safer designs more attractive to utilities and their investors.
In the U.S., these charges require that coal and nuclear power plants must operate more cheaply than natural gas plants in order to be built. In general, coal and nuclear plants have the same operating costs (operations and maintenance plus fuel costs). However, nuclear and coal differ in the source of those costs. Nuclear has lower fuel costs but higher operating and maintenance costs than coal. In recent times in the United States these operating costs have not been low enough for nuclear to repay its high investment costs. Thus new nuclear reactors have not been built in the United States. Coal's operating cost advantages have only rarely been sufficient to encourage the construction of new coal based power generation. Around 90 to 95 percent of new power plant construction in the United States has been natural gas-fired. These numbers exclude capacity expansions at existing coal and nuclear units.
Both the nuclear and coal industries must reduce new plant investment costs and construction time. The burden is clearly greater for nuclear producers than for coal producers, because investment costs are higher for nuclear plants, which have no visible advantage in operating costs over coal plants. The burden of operating costs for nuclear power plants is also greater. Operation and maintenance costs are particularly important simply because they are a large portion of nuclear operating costs.
In Japan and France, construction costs and delays are significantly less because of streamlined government licensing and certification procedures. In France, one model of reactor was type-certified, using a safety engineering process similar to the process used to certify aircraft models for safety. That is, rather than licensing individual reactors, the regulatory agency certified a particular design and its construction process to produce safe reactors. U.S. law permits type-licensing of reactors, but no type license has ever been issued by a U.S. nuclear regulatory agency.
Given the financial disadvantages of nuclear power in the U.S., it is understandable that the nuclear industry also has sought to find additional benefits to using nuclear power. Because coal-fired plants produce more airborne emissions, clearly the price differential accepted between nuclear and coal based power would be greater than the acceptable difference between nuclear power and natural gas.
Most new gas-fired plants are intended for peak supply. The larger nuclear and coal plants cannot quickly adjust their instantaneous power production, and are generally intended for baseline supply. The demand for baseline power has not increased as rapidly as the peak demand. Some new experimental reactors, notably pebble bed modular reactors, are specifically designed for peaking power.
Finally, any company seeking to construct a nuclear reactor around the world (but most acutely in the US) must deal with NIMBY issues. Given the high profile of both Three Mile Island and Chernobyl, few municipalities would welcome a new nuclear reactor within their borders, and many have issued local ordinances prohibiting the development of nuclear power.
In an attempt to encourage development of nuclear power, the US Department of Energy DOE has offered interested parties to introduce France's model for licensing and to share 50% of a construction expenses. Several applications were made but the project is still in its infancy.
Nuclear Power plants usually tend to be most competitive in areas where no other resources are readily available. For example, the province of Ontario, Canada is already using all of its best sites for hydroelectric power, and has minimal supplies of fossil fuels, so a number of nuclear plants have been built there.
- Main article: Nuclear proliferation
Critics of nuclear energy point out that nuclear technology is often dual-use, and much of the same materials and knowledge used in a civilian nuclear program can be used to develop nuclear weapons (see nuclear proliferation). To prevent this from happening, safeguards on nuclear technology were imposed through the Nuclear Non-Proliferation Treaty (NPT) and monitored by the International Atomic Energy Agency (IAEA) of 1968. Several states did not sign the treaty, however, and were able to use international nuclear technology (often procured for civilian purposes) to develop nuclear weapons (India, Pakistan, Israel, and South Africa). Of those who have signed the treaty, many states have either claimed to or be accused of attempting to use supposedly civilian nuclear power plants towards weapons ends, including Iran and North Korea. Certain types of reactors are more conducive to producing nuclear weapons materials than others, and a number of international disputes over proliferation have centered on what specific model of reactor was being contracted in a country suspected of having weapons ambitions.
International nuclear safeguards are administered by the IAEA and were formally established under the NPT which requires nations to:
- Report to the IAEA what nuclear materials they hold and their location.
- Accept visits by IAEA auditors and inspectors to verify independently their material reports and physically inspect the nuclear materials concerned to confirm physical inventories of them.
In 2000, there were 438 commercial nuclear generating units throughout the world, with a total capacity of about 351 gigawatts.
In 2004, there were 104 (69 pressurized water reactors, 35 boiling water reactors) commercial nuclear generating units licensed to operate in the United States, producing a total of 97,400 megawatts (electric), which is approximately 20 percent of the nation's total electric energy consumption. The United States is the world's largest supplier of commercial nuclear power.
The United States Navy has operates half of the nuclear reactors in the world. They have never had an incident in 60 years of near constant operation of hundreds of power plants.
In 2001, the U.S. nuclear share of electricity generation was 19%.
List of atomic energy groups
- American Nuclear Society (United States)
- Department of Energy (United States)
- Areva (France)
- EDF (France)
- MinAtom (Russia)
- EnergoAtom (Ukraine)
- Egyptian Atomic Energy Authority
- United Kingdom Atomic Energy Authority (UKAEA)
- EURATOM (Europe)
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