NUCLEAR ENERGY
Although scientists have only known about radiation since the 1890s, they have developed a wide variety of uses for this natural force. Today, to benefit humankind, radiation is used in medicine, academics, and industry, as well as for generating electricity. In addition, radiation has useful applications in such areas as agriculture, archaeology (carbon dating), space exploration, law enforcement, geology (including mining), and many others. [Source: U.S. Nuclear Regulatory Commission (NRC)]
Worldwide nuclear power provides 16 percent of electricity production. About 30 countries now have nuclear power plants in operation, and about a dozen more have them under construction or on the drawing board. As of 2011 there were 211 active nuclear power plants in the world. Two thirds of them have have as many people or more living within the 30 kilometer radius as those living within a 30 kilometer radius of Fukushima nuclear power plant in Japan. There are 21 plants with at least 1 million people within a 30 kilometer radius of the plant. Six have a population that exceeds 3 million.
Nuclear Energy, Global Warming and Energy Independence
Michael A. Levi wrote in the Washington Post: “When people talk about energy independence, they’re thinking about oil, which we mostly use in vehicles and industrial production. When they talk about nuclear, though, they’re thinking about electricity. More nuclear power means less coal, less natural gas, less hydroelectric power and less wind energy. But unless we start putting nuclear power plants in our cars and semis, more nuclear won’t mean less oil. [Source: Michael A. Levi, Washington Post, March 16, 2011. Levi is , a senior fellow and director of the program on energy security and climate change at the Council on Foreign Relations, and the author of “On Nuclear Terrorism”]
“This wasn’t always the case: During the the heyday of nuclear power, the early 1970s (45 plants broke ground between 1970 and 1975), oil was a big electricity source, and boosting nuclear power was a real way to squeeze petroleum out of the economy. Alas, we’ve already replaced pretty much all the petroleum in the power sector; the opportunity to substitute oil with nuclear power is gone.
“Before the Fukushima crisis in Japan in 2011, nuclear energy was making a comeback, in part because it doesn’t produces hardly any carbon dioxide or other greenhouse gases. As demand for electricity rises and government and enterprises become more worried about the cost of oil, carbon emissions and other environmental concerns, nuclear energy is increasingly being looked upon as a means of weaning the world off fossil fuels. As of 2007, twenty-nine nuclear power plants were being built around the world and 100 more were key parts of development plans. China and India plan to build dozens of reactors. Even oil-rich countries in the Persian Gulf are planning to build some. The World Nuclear Association estimates that if all goes according to plan an additional 237 reactors will be built between 2009 and 2030.
Impact of Fukushima Disaster on Nuclear Power
The New York Times reported: “The Fukushima disaster damped the nuclear industry’s hopes for a worldwide revival of reactor building. With demand for electricity and concerns about global warming both growing, the industry had projected rapid expansion, but Japan’s nuclear crisis had already caused several countries to become skittish about nuclear power. After the crisis at Fukushima nuclear power plant there large protest against nuclear energy in places where nuclear power plants are scheduled to be built in India, Taiwan and other places. Italy proposed halting its plan to develop nuclear power. Germany, for instance, declared a temporary moratorium on building new plants. [Source: New York Times]
“Japan’s Yomiuri Shimbun reported: “In the aftermath of the disaster, the European Union decided to put all nuclear plants within its jurisdiction under review to check their earthquake resistance and other safety arrangements. In Germany, where 17 nuclear plants are in operation, seven that were built in 1980 or earlier have suspended operations for three months. German Chancellor Angela Merkel's government previously had decided to extend the lifetime of the existing nuclear reactors, in a reversal of the previous administration's policy. After Fukushima Germany reversed itself again and said it would phase all of its nuclear reactors. In a regional elections the Greens, an ecologically oriented party, made major headway against a backdrop of a surge in antinuclear public opinion. [Source: Yomiuri Shimbun, March 29, 2011]
“At the time of the 1979 Three Mile Island nuclear crisis and also after the 1986 Chernobyl disaster, misgivings about the safety of nuclear power plants became widespread in the United States and European countries, forcing them to put construction plans for new nuclear power plants on hold. From the standpoint of protecting energy security and fighting global warming, however, nuclear power plants, as long as they are managed safely, are certain to remain an important source of electric power.
“In the United States, which has more nuclear power plants than any other nation, some members of Congress have called for a freeze on the construction of new nuclear power plants. U.S. President Barack Obama, however, has remained committed to his policy of encouraging nuclear power generation, saying Washington needs to "take lessons learned from what's happening in Japan." France, which has the second largest number of nuclear power facilities, has vowed to go ahead with its construction plans for new facilities. Its sale of reactors to other countries also is continuing as scheduled. South Korea also has kept its posture of encouraging nuclear power generation unchanged.
“According to the New York Times: “Experts and nuclear industry representatives said that they expected demand in two important markets — China and India — to remain strong even though those counties had said they would proceed more cautiously. Both nations have rapidly growing demand for electricity, and neither has nearly enough domestic fuel to meet its needs. A downturn in reactor construction would hurt Japanese companies that export nuclear plant designs and components, including Toshiba, which owns Westinghouse, and Hitachi, which is in a worldwide partnership with General Electric. Companies in France and South Korea also have a big stake in reactor building.
“After the Fukushima nuclear power plant U.S. President Barack Obama ordered a review of all nuclear power plants in the United States. Within two months the U.S. Nuclear regulatory Commission gave all U.S. nuclear power plant the all-clear. In Europe stress tests for all nuclear power plants were ordered. Stress tests are designed to measure how force nuclear power plants can bear during an earthquake and tsunami or other disaster. In many cases they are carried out using computer models with specs and other data from the nuclear power plants as well as on site tests of steam generators, pumps and other equipment.
Impact of Not Having Nuclear Power and the Expense of Building New Reactors
Bjorn Lomborg of Project Syndicate wrote: “While America’s commitment to nuclear power was quickly reaffirmed by President Barack Obama, some European governments took the knee-jerk decision to freeze all new nuclear-energy projects immediately, and, in the case of Germany, not to extend the life of existing reactors. For Germany, this will leave a gap that it cannot fill with alternative energy sources, leaving it little choice but to rely more heavily on coal power. [Source: Bjorn Lomborg, Project Syndicate, April 13, 2011]
“We see coal as a polluting but reasonably “safe” energy source compared to nuclear energy. Yet, in China alone, coal-mining accidents kill more than 2,000 people each year — and coal is a leading cause of smog, acid rain, global warming, and air toxicity. As a result of Germany’s decision, its annual carbon emissions are now expected to rise by as much as 10 percent — at a time when European Union emissions are rising as the continent shakes off the effects of the financial crisis. Germany doesn’t have a low-carbon alternative if it shutters its nuclear plants, and the same is true of most other countries. Alternative energy sources are too expensive and nowhere near reliable enough to replace fossil fuels.
Case for Nuclear Power After Fukushima
Mark Lynas wrote in the, Los Angeles Times; In the messy real world, countries that decide to rely less on nuclear will almost certainly dig themselves even deeper into a dependence on dirty fossil fuels, especially coal. In the short term, this is already happening. In Germany -- whose government tried to curry favor with a strongly anti-nuclear population by rashly closing seven perfectly safe nuclear plants after the Fukushima crisis began -- coal has already become the dominant factor in electricity prices once again. Regarding carbon dioxide emissions, you can do the math: Just add about 11 million tons per year for each nuclear plant replaced by a coal plant newly built or brought back onto the grid. [Source: Mark Lynas, Los Angeles Times, April 10, 2011]
“In China the numbers become even starker. Coal is cheap there (as are the thousands of human lives lost in extracting it each year), and if the hundred or so new nuclear plants previously proposed in China up to 2030 are not built, it is a fair bet that more than a billion tons can be added to annual global carbon dioxide emissions as a result.
“Japan is also heavily dependent on coal, so it is a fair bet that less nuclear power there will add substantially to the country's emissions. No wonder the Japanese are insisting on backing off from the Kyoto climate treaty. Looking at the entire global picture, I estimate that turning away from nuclear power could make the difference between whether the world warms by 2 degrees Celsius (bad but manageable) and 3 degrees Celsius (disastrous) in the next century.
“Those debating the future of nuclear power also tend to focus on out-of-date technology. No one proposes to build boiling-water reactors of 1960s-era Fukushima vintage in the 21st century. Newer designs have a much greater reliance on passive safety, as well as a host of other improvements. Fourth-generation options, such as the "integral fast reactor" reportedly being considered by Russia, could be even better. Fast-breeders like the IFR will allow us to power whole countries cleanly by burning existing stockpiles of nuclear waste, depleted uranium and military-issue plutonium. And the waste left over at the end would become safe after a mere 300 years, so no Yucca Mountains needed there. IFRs exist only on paper, however; we need to urgently research prototypes before moving on to large-scale deployment.
Nuclear Power Verus Alternative Energy
Mark Lynas wrote in the, Los Angeles Times, “Most environmentalists assert that a combination of renewables and efficiency can decarbonize our energy supply and save us both from global warming and the presumed dangers of nuclear power. This is technically possible but extremely unlikely in practice. [Source: Mark Lynas, Los Angeles Times, April 10, 2011]
“In terms of land use, nuclear scores very well, because the comparatively small quantities of fuel required means less land disturbed or ruined by mines, processing and related uses. According to some recent number crunching by the Breakthrough Institute, a centrist environmental think tank, phasing out Japan's current nuclear generation capacity and replacing it with wind would require a 1.3-billion-acre wind farm, covering more than half the country's total land mass. Going for solar instead would require a similar land area, and would in economic terms cost the country more than a trillion dollars.
Nuclear Materials
Nuclear materials used power nuclear power plant are plutonium, uranium-233, or uranium enriched in the isotopes uranium-233 or uranium-235. Uranium-233 and plutonium do not occur naturally but can be formed in nuclear reactors and extracted from the highly radioactive spent fuel by chemical separation. Uranium-233 can be produced in special reactors that use thorium as fuel. Only small quantities of uranium-233 have ever been made in the United States. Plutonium is produced in reactors using U-238/U-235 fuel. [Source: U.S. Nuclear Regulatory Commission (NRC)]
As the precursor to the nuclear fuel cycle, uranium recovery focuses on extracting (or mining) natural uranium ore from the Earth and concentrating (or milling) that ore. These recovery operations produce a product, called "yellowcake," which is then transported to a fuel cycle facility. There, the yellowcake is transformed into fuel for nuclear power reactors. In addition to yellowcake, uranium recovery operations generate waste products, called byproduct materials, that contain low levels of radioactivity.
Conventional milling is one of the two primary recovery methods that are currently used to extract uranium from mined ore. A conventional uranium mill is a chemical plant that extracts uranium using the following process: 1) Trucks deliver uranium ore to the mill, where it is crushed into smaller particles before being extracted (or leached). In most cases, sulfuric acid is the leaching agent, but alkaline solutions can also be used to leach the uranium from the ore. (In addition to extracting 90 to 95 percent of the uranium from the ore, the leaching agent also extracts several other "heavy metal" constituents, including molybdenum, vanadium, selenium, iron, lead, and arsenic.) 2) The mill then concentrates the extracted uranium to produce a a material, which is called "yellowcake" because of its yellowish color. 3) Finally, the yellowcake is transported to a uranium conversion facility, where it is processed through the stages of the nuclear fuel cycle to produce fuel for use in nuclear power reactors.
In situ recovery (ISR) is one of the two primary extraction methods that are currently used to obtain uranium from underground. ISR facilities recover uranium from low-grade ores where other mining and milling methods may be too expensive or environmentally disruptive. In the in situ recovery (ISR) process, injection wells (1) pump a chemical solution — typically sodium bicarbonate and oxygen — into the layer of earth containing uranium ore. The solution dissolves the uranium from the deposit in the ground, and is then pumped back to the surface through recovery wells (2) and sent to the processing plant to be converted into uranium yellowcake. Monitoring wells (3) are checked regularly to ensure that uranium and chemicals are not escaping from the drilling area.
A solution called lixiviant (typically containing water mixed with oxygen and/or hydrogen peroxide, as well as sodium carbonate or carbon dioxide) is injected through a series of wells into the ore body to dissolve the uranium. The lixiviant is then collected in a series of recovery wells, through which it is pumped to a processing plant, where the uranium is extracted from the solution through an ion-exchange process. The uranium extract is then further purified, concentrated, and dried to produce a material, which is called "yellowcake" because of its yellowish color. Finally, the yellowcake is packed in 55-gallon drums to be transported to a uranium conversion facility, where it is processed through the stages of the nuclear fuel cycle to produce fuel for use in nuclear power reactors. About 12 such ISR facilities exist in the United States.
n addition to conventional uranium milling and in situ recovery (ISR), which are currently used to extract uranium from ore, some NRC-licensed facilities used extraction methods known as heap leaching or ion-exchange. Such facilities no longer operate and are in the process of decommissioning. Nonetheless, heap leaching has also been used to extract uranium from ore at conventional mills, and ion-exchange procedures have been used to separate uranium from the liquid extract at both conventional mills and ISR facilities.
Heap leach/ion-exchange operations involve the following process: 1) Small pieces of uncrushed ore are placed in a "heap" on an impervious pad of plastic, clay, or asphalt, with perforated pipes under the heap. 2) An acidic solution is then sprayed over the ore to dissolve the uranium it contains. 3) The uranium-rich solution drains into the perforated pipes, where it is collected and transferred to an ion-exchange system. 4) The ion-exchange system extracts and concentrates the uranium to produce a material, which is called "yellowcake" because of its yellowish color. 5) Finally, the yellowcake is packed in 55-gallon drums to be transported to a uranium conversion facility, where it is processed through the stages of the nuclear fuel cycle to produce fuel for use in nuclear power reactors.
Uses of Nuclear Energy
Universities, colleges, high schools, and other academic and scientific institutions use nuclear materials in course work, laboratory demonstrations, experimental research, and a variety of health physics applications. For example, just as doctors can label substances inside people's bodies, scientists can label substances that pass through plants, animals, or our world. This allows researchers to study such things as the paths that different types of air and water pollution take through the environment. Similarly, radiation has helped us learn more about the types of soil that different plants need to grow, the sizes of newly discovered oil fields, and the tracks of ocean currents. In addition, researchers use low-energy radioactive sources in gas chromatography to identify the components of petroleum products, smog and cigarette smoke, and even complex proteins and enzymes used in medical research. [Source: U.S. Nuclear Regulatory Commission (NRC)]
Archaeologists also use radioactive substances to determine the ages of fossils and other objects through a process called carbon dating. For example, in the upper levels of our atmosphere, cosmic rays strike nitrogen atoms and form a naturally radioactive isotope called carbon-14. Carbon is found in all living things, and a small percentage of this is carbon-14. When a plant or animal dies, it no longer takes in new carbon and the carbon-14 that it accumulated throughout its life begins the process of radioactive decay. As a result, after a few years, an old object has a lower percent of radioactivity than a newer object. By measuring this difference, archaeologists are able to determine the object's approximate age.
Medical Uses of Nuclear Energy
Hospitals, doctors, and dentists use a variety of nuclear materials and procedures to diagnose, monitor, and treat a wide assortment of metabolic processes and medical conditions in humans. In fact, diagnostic x-rays or radiation therapy have been administered to about 7 out of every 10 Americans. As a result, medical procedures using radiation have saved thousands of lives through the detection and treatment of conditions ranging from hyperthyroidism to bone cancer. [Source: U.S. Nuclear Regulatory Commission (NRC)]
The most common of these medical procedures involve the use of x-rays — a type of radiation that can pass through our skin. When x-rayed, our bones and other structures cast shadows because they are denser than our skin, and those shadows can be detected on photographic film. The effect is similar to placing a pencil behind a piece of paper and holding the pencil and paper in front of a light. The shadow of the pencil is revealed because most light has enough energy to pass through the paper, but the denser pencil stops all the light. The difference is that x-rays are invisible, so we need photographic film to "see" them for us. This allows doctors and dentists to spot broken bones and dental problems.
X-rays and other forms of radiation also have a variety of therapeutic uses. When used in this way, they are most often intended to kill cancerous tissue, reduce the size of a tumor, or reduce pain. For example, radioactive iodine (specifically iodine-131) is frequently used to treat thyroid cancer, a disease that strikes about 11,000 Americans every year.
X-ray machines have also been connected to computers in machines called computerized axial tomography (CAT) or computed tomography (CT) scanners. These instruments provide doctors with color images that show the shapes and details of internal organs. This helps physicians locate and identify tumors, size anomalies, or other physiological or functional organ problems. In addition, hospitals and radiology centers perform approximately 10 million nuclear medicine procedures in the United States each year. In such procedures, doctors administer slightly radioactive substances to patients, which are attracted to certain internal organs such as the pancreas, kidney, thyroid, liver, or brain, to diagnose clinical conditions.
Industrial Uses of Nuclear Energy
We could talk all day about the many and varied uses of radiation in industry and not complete the list, but a few examples illustrate the point. In irradiation, for instance, foods, medical equipment, and other substances are exposed to certain types of radiation (such as x-rays) to kill germs without harming the substance that is being disinfected — and without making it radioactive. When treated in this manner, foods take much longer to spoil, and medical equipment (such as bandages, hypodermic syringes, and surgical instruments) are sterilized without being exposed to toxic chemicals or extreme heat. As a result, where we now use chlorine — a chemical that is toxic and difficult-to-handle — we may someday use radiation to disinfect our drinking water and kill the germs in our sewage. In fact, ultraviolet light (a form of radiation) is already used to disinfect drinking water in some homes. [Source: U.S. Nuclear Regulatory Commission (NRC)]
“Similarly, radiation is used to help remove toxic pollutants, such as exhaust gases from coal-fired power stations and industry. For example, electron beam radiation can remove dangerous sulphur dioxides and nitrogen oxides from our environment. Closer to home, many of the fabrics used to make our clothing have been irradiated (treated with radiation) before being exposed to a soil-releasing or wrinkle-resistant chemical. This treatment makes the chemicals bind to the fabric, to keep our clothing fresh and wrinkle-free all day, yet our clothing does not become radioactive. Similarly, nonstick cookware is treated with gamma rays to keep food from sticking to the metal surface.
The agricultural industry makes use of radiation to improve food production and packaging. Plant seeds, for example, have been exposed to radiation to bring about new and better types of plants. Besides making plants stronger, radiation can be used to control insect populations, thereby decreasing the use of dangerous pesticides. Radioactive material is also used in gauges that measure the thickness of eggshells to screen out thin, breakable eggs before they are packaged in egg cartons. In addition, many of our foods are packaged in polyethylene shrinkwrap that has been irradiated so that it can be heated above its usual melting point and wrapped around the foods to provide an airtight protective covering.
All around us, we see reflective signs that have been treated with radioactive tritium and phosphorescent paint. Ionizing smoke detectors, using a tiny bit of americium-241, keep watch while we sleep. Gauges containing radioisotopes measure the amount of air whipped into our ice cream, while others prevent spillover as our soda bottles are carefully filled at the factory.
Engineers also use gauges containing radioactive substances to measure the thickness of paper products, fluid levels in oil and chemical tanks, and the moisture and density of soils and material at construction sites. They also use an x-ray process, called radiography, to find otherwise imperceptible defects in metallic castings and welds. Radiography is also used to check the flow of oil in sealed engines and the rate and way that various materials wear out. Well-logging devices use a radioactive source and detection equipment to identify and record formations deep within a bore hole (or well) for oil, gas, mineral, groundwater, or geological exploration. Radioactive materials also power our dreams of outer space, as they fuel our spacecraft and supply electricity to satellites that are sent on missions to the outermost regions of our solar system.
Nuclear Power Plants
A nuclear power plant is an electrical generating facility using a nuclear reactor as its heat source to provide steam to a turbine generator. Electricity produced by nuclear fission — splitting the atom — is one of the greatest uses of radiation. In America, nuclear power plants are the second largest source of electricity (after coal-fired plants) — producing approximately 21 percent of our Nation's electricity. [Source: U.S. Nuclear Regulatory Commission (NRC)]
Most nuclear power plants have reactors that contain nuclear fuel rods that generate heat that produced steam that turn turbines to make electricity. A nuclear reactor is an enormous and extremely complex apparatus made up of 30,000 to 40,000 parts. Fuel rods which create thermal energy inside a nuclear power plant reach extremely high temperatures and contain a large quantity of radioactive material. Therefore, various safety measures are implemented at nuclear power plants to prevent such hazardous material from leaking outside.
The purpose of a nuclear power plant is to boil water to produce steam to power a generator to produce electricity. While nuclear power plants have many similarities to other types of plants that generate electricity, there are some significant differences. With the exception of solar, wind, and hydroelectric plants, power plants (including those that use nuclear fission) boil water to produce steam that spins the propeller-like blades of a turbine that turns the shaft of a generator. Inside the generator, coils of wire and magnetic fields interact to create electricity. In these plants, the energy needed to boil water into steam is produced either by burning coal, oil, or gas (fossil fuels) in a furnace, or by splitting atoms of uranium in a nuclear power plant. Nothing is burned or exploded in a nuclear power plant. Rather, the uranium fuel generates heat through a process called fission. [Source: NRC]
As of 2007 there were 442 nuclear reactor in operation in 31 countries around the world according to the Atomic Energy Agency in Vienna. The United States has the most (103, supplying 19.3 percent of the country’s electricity) followed by France (59, supplying about 78.5 percent of the country’s electricity), Japan (55, supplying 36.8 percent of the country’s electricity), Russia (31, supplying 15.8 percent of the country’s electricity), the U.K. (21, supplying 19.9 percent of the country’s electricity), and South Korea (20, supplying 44.7 percent of the country’s electricity) .
Many plants built during the wave of nuclear power plant construction in the 1970s and 80s are nearing the end of their life spans. The licenses on the some have been extended up to 60 years.
Nuclear Reactor at Nuclear Power Plants
Nuclear power plants are powered by nuclear reactors. There are two main types of nuclear reactors: 1) boiling-water reactors (BWRs); and pressurized-water reactors (PWRs). There are currently 104 licensed to operate nuclear power plants in the United States (69 PWRs and 35 BWRs), which generate about 20 percent of our nation's electrical use. [Source: U.S. Nuclear Regulatory Commission (NRC)]
Pressurized Water Reactors: In a typical commercial pressurized light-water reactor(1) the core inside the reactor vessel creates heat, (2) pressurized water in the primary coolant loop carries the heat to the steam generator, (3) inside the steam generator, heat from the steam, and (4) the steam line directs the steam to the main turbine, causing it to turn the turbine generator, which produces electricity. The unused steam is exhausted in to the condenser where it condensed into water. The resulting water is pumped out of the condenser with a series of pumps, reheated and pumped back to the steam generators. The reactor's core contains fuel assemblies that are cooled by water circulated using electrically powered pumps. These pumps and other operating systems in the plant receive their power from the electrical grid. If offsite power is lost emergency cooling water is supplied by other pumps, which can be powered by onsite diesel generators. Other safety systems, such as the containment cooling system, also need power. Pressurized-water reactors contain between 150-200 fuel assemblies. See also our animated diagram.
Boiling Water Reactors: In a typical commercial boiling-water reactor, (1) the core inside the reactor vessel creates heat, (2) a steam-water mixture is produced when very pure water (reactor coolant) moves upward through the core, absorbing heat, (3) the steam-water mixture leaves the top of the core and enters the two stages of moisture separation where water droplets are removed before the steam is allowed to enter the steam line, and (4) the steam line directs the steam to the main turbine, causing it to turn the turbine generator, which produces electricity. The unused steam is exhausted into the condenser where it is condensed into water. The resulting water is pumped out of the condenser with a series of pumps, reheated and pumped back to the reactor vessel. The reactor's core contains fuel assemblies that are cooled by water circulated using electrically powered pumps. These pumps and other operating systems in the plant receive their power from the electrical grid. If offsite power is lost emergency cooling water is supplied by other pumps, which can be powered by onsite diesel generators. Other safety systems, such as the containment cooling system, also need electric power.
One of the keys to growth in the nuclear industry is a century-old forge on the island of Hokkaido in Japan that produces 80 percent of the world’s reactors cores — highly specialized pieces of steel milled from a single 600-ton ingot. Only a few companies in the world can handle this job. Insiders in the nuclear industry told the Times of London that this is the “biggest, most overlooked bottleneck — for a nuclear revival. The owners of the forge in Hokkaido, Japan Steel Works (JSW), can only produce four of these reactor cores a year, far below what is needed to meet demand. To address problem JSW says it will invest to ramp up production to 8½ cores a year. But that still isn’t enough. Major nuclear plant producers Toshiba, Mitsubishi, Hitachi and France’s Areva have all bought stakes in JSW to secure the cores they need.
Nuclear Power Plant Safety
To prevent leakage of radiation a reactor has three layers of protection: the containment building; the containment vessel, and the metal cladding around fuel rods, which are inside the reactor. The reactor pressure vessel that covers the reactor core is designed to prevent radiation from being released should something go wrong with the nuclear fuel. Even if the reactor vessel were damaged, radiation leaks are supposed to be prevented by another container surrounding it. Around these is the reactor's outer building.
Safety measures at a nuclear power plant are based on three basic principles--stopping, cooling and confining. When pressure inside a nuclear reactor increases rapidly due to abnormal nuclear fission or for other reasons, stopping the reactor is the top priority. All control rods are inserted simultaneously to automatically stop the reactor. If that fails to bring operations to a halt, a large quantity of solution containing boric acid--which absorbs neutrons--is poured inside the reactor to stop nuclear fission.” [Source: Yomiuri Shimbun, March 17, 2011]
“Sometimes the coolant water inside a nuclear reactor is lost for some reason. To prepare for such an eventuality, reactors are equipped with an emergency core cooling system (ECCS), which pours a large quantity of water inside the reactor to cool the fuel rods. Reactors are also equipped with a device that lowers the pressure inside the reactor in order to cool extremely hot steam that has leaked into the containment vessel.”
“The last layer of defense in terms of nuclear plant safety measures is the structure in which radioactive material is encased, comprising five protective layers. Firstly, pieces of uranium fuel are fired into pellets, as with ceramics, so that radioactive material produced as a result of nuclear fission is confined in the fuel rods. Secondly, the pieces of fuel are encased in tubes made of a zirconium alloy, capable of enduring extreme heat. As long as the tubes are not damaged, the radioactive material in the fuel rods will not leak outside.”
“The third is a pressure vessel made of thick steel. Even if the tubes are ruptured, the cylindrical vessel can keep radioactive material contained inside the valves. The fourth is a steel containment vessel that houses the pressure vessel, pipes, control rods, recirculation pumps and other key components. Around the containment vessel there are pools to store used fuel rods and various control devices. These are housed within the outer containment building. The building's walls comprise the fifth layer of protection. They are made of one- to two-meter-thick concrete, which prevents radioactive rays from leaking to the external environment. For extra safety, the building has no windows.”
Michael A. Levi wrote in the Washington Post: “Technology can increase safety, but there will always be risks with nuclear power. The Japanese reactors at the center of the current crisis use old technology that increased their vulnerability. Next-generation reactors will be “passively cooled,” which means that if backup power fails like it has in Japan, meltdowns will be avoided more easily. (Passive-cooling systems vary, but their common feature is a lack of dependence on external power.) Other lower-tech improvements, such as stronger containment structures, have also mitigated risk. [Source: Michael A. Levi, Washington Post, March 16, 2011]
“But what happened in Japan reminds us that unanticipated vulnerabilities are inevitable in any highly complex system. Careful engineering can minimize the chance of disasters, but it can’t eliminate them. Operators and authorities will need to make sure that they’re prepared to deal with unanticipated failures even as they work to prevent them.
“Most energy sources entail risks. In the past year, we’ve seen an oil spill in the Gulf of Mexico, fatal explosions at the Upper Big Branch coal mine in West Virginia and now the crisis in Japan. The American public will need to decide whether the risks of nuclear power — compared with those of other energy sources — are too high.
Fast- Breeder Nuclear Reactors
Japan and France are the only two countries in the world developing controversial fast-breeder nuclear technology, which produces more plutonium than it consumes. Touted as a "dream energy," the technology has problems that have not been resolved and is not expected to be widely used in reactors until 2050. Other countries consider the possibility of sodium and plutonium leaks to be to risky. Japan started research on fast breeder reactors in 1968. It is also doing research in nuclear fusion.
The basic layout of a fast breeder reactor is there is a core which contains fissionable material like Pu-239 (Plutonium) or U-235. Surrounding this core is non-fertile material, or non-fissionable material, such as U-238. Neutrons produced from the fissions in the core bombard the blanket and create new fissionable material. After reprocessing the blanket the new fissionable material can be used possibly in the core or in another core at another plant. The core is cooled using liquid sodium which can be maintained at low pressure and low temperature which adds to the safety of the reactor. The liquid metal is used as a coolant because the neutrons coming from the core do not need to be moderated, therefore water or hard water cannot be used. Moderation of neutrons would decrease the amount of breeding occurring and would inhibit the purpose of the reactor (fewer neutrons bombarding the blanket means less breeding). [Source: Devon Dodd, Student of Professional Chemistry with a focus in Nuclear Chemistry, Arkansas Tech University]
There are two basic designs for these types of reactors, although some changes are being researched for future use. The criticality or the degree of operation (0 to 100 percent) is controlled by the control rods at the top of the reactor. If the reactor needs to be shut down or the computer at the facility deems it necessary then these will be dumped into the core to absorb all neutrons being produced from fissions and this will halt the reactor (0 percent). Of course this whole unit is incased in a solid and safe building which prevents any radiation from escaping while the reactor is working and in case of an emergency.
Japan has plans to build breeder reactors and reprocessing plant that could produce fuel for thousands of nuclear weapons. Analysts aren't worried so much about Japan's nuclear capabilities as they are about such large amount of plutonium falling into the hands of terrorists or a hostile country. When North Korea was asked to close down its nuclear reprocessing plant it said, "Japan is allowed to do it why can't we." Japanese companies are involved in building a fast breeder nuclear power plant in China outside Beijing.
Small Nuclear Reactors
In February Discover magazine reported: “Small modular reactors offer a better way to harness nuclear energy to produce power, says Daniel Ingersoll, a nuclear engineer and senior program manager at Oak Ridge National Laboratory. “All the designs for small modular reactors eliminate the features in larger plants that can contribute to a potential accident,” he says. Not only are they safer, but modular reactors are (relatively) cheap. The price tag for a conventional, 1,600-megawatt nuclear power plant is about $8 billion to $10 billion, assuming anyone could get approval to build it. A 300-megawatt, $850 million modular unit is a much more plausible proposition, and it could be fabricated using domestic supply chains. “That means more high-tech jobs in the United States,” Ingersoll says. “And it gives us an opportunity to regain leadership in nuclear energy.” [Source: Discover, February 16, 2012]
“Conventional nuclear power plants circulate water through a reactor core, where it is heated and then passed via pipes to larger vessels, where it converts to steam. “What scared the bejeebies out of early designers was the prospect of a double break of the pipe that connects the two vessels,” Ingersoll says. “If that happened, you would drain the reactor of its coolant very quickly, and nasty things happen once you uncover the core.” Conventional plants have a number of systems to prevent the core from being uncovered, but modular reactors sidestep the problem entirely by housing all the system components, including the steam generators, inside a single vessel. “These designs are fundamentally different from the large plants producing electricity today,” Ingersoll says. “They are elegantly simple and eliminate accidents that could result from loss of coolant.” There are some 50 modular designs being developed globally, and while many are traditional light water reactors, which use water to cool the reactor core, others gain efficiency by using coolants such as gas, which allow reactors to reach higher temperatures.
“Small reactors can't address all the problems standing in the way of more nuclear investment, but they can address the biggest barriers — the economic ones," Richard Lester, head of nuclear science and engineering at MIT, told National Geographic . Building giant reactors, he points out, isn't the only way to achieve economies of scale; another way is to mass produce inexpensive mini-nukes. If they're designed as modules, a single unit might power a remote town or mine, while a dozen used in tandem could match the output of a traditional nuclear plant. In the developing world, small reactors would place less strain on fragile electrical grids. And the ability to start small and gradually add power modules could appeal to cash-strapped utilities everywhere. [Source: National Geographic, Chris Carroll ]
Efforts to Build Small Nuclear Reactors
Chris Carroll wrote in National Geographic: “None of the new small reactors have been deployed yet. Some, like the one designed by NuScale Power, are light-water reactors that resemble ones long used on warships. Others are more novel. Toshiba and the Japanese Central Research Institute of Electric Power Industry are working on a liquid-sodium-cooled "nuclear battery." Delivered partially assembled and installed underground, the reactor would generate ten megawatts for 30 years until it needed refueling. The isolated Alaska village of Galena is in discussions with Toshiba to become its first customer. [Source: National Geographic, Chris Carroll ]
“Besides costing less to build, some small reactors could be inherently safer, says Vladimir Kuznetsov of the International Atomic Energy Agency. NuScale's design requires no reactor cooling pumps, while Toshiba's pumps are electromagnetic, without moving parts; either approach diminishes the possibility of a disastrous failure. Chinese researchers, meanwhile, are developing a small reactor in which the nuclear reaction itself is self-limiting. In a dramatic 2004 demonstration, they turned off the cooling system; the reaction just burned itself out. With any of the new reactors, of course, there will still be radioactive waste to contend with.”
Discover reported: “The Nuclear Regulatory Commission is working with the Nuclear Energy Institute, an industry group, to revamp the licensing procedure for nuclear power plants to include new rules tailored to small modular reactors. “The existing regulatory paradigm must change,” says Paul Genoa, director of policy development at the Nuclear Energy Institute. “There shouldn’t be any reduction in the safety of the operation of these plants. But we need to change the regulatory structure to allow for more flexibility in introducing multiple designs.” advertisement | article continues below [Source: Discover, February 16, 2012]
“The Tennessee Valley Authority recently announced plans to build the nation’s first small modular reactor in eastern Tennessee. If it receives funding and passes regulatory hurdles, the reactor could be operational by 2020 and power up to 70,000 homes. The Department of Energy is developing a prototype modular reactor at its Savannah River site in Georgia, and Argonne National Laboratory in Illinois and Sandia National Laboratories in New Mexico are also considering modular plants.
Meanwhile, other countries like Russia and China are fast-tracking similar projects. “We’re in a race,” Genoa says. “When we deploy these new small reactors, will we build them at home or buy them from China?” There are 56 reactors under construction in the world today, 19 in China alone. But with energy demand soaring — and the threat of climate change looming — even that much construction will not greatly increase nuclear's share of the global electricity supply. Small reactors could help, Lester says. "The point is to scale up low-carbon energy sources rapidly. Nuclear has great potential to do this." If regulators go along, that is. In the U.S., officials say some designs may win certification within five years. More innovative ones may take longer.
Image Sources: U.S. Department of Energy; Wikimedia Commons
Text Sources: New York Times, Washington Post, Los Angeles Times, Times of London, The Guardian, National Geographic, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Wall Street Journal, The Atlantic Monthly, The Economist, Global Viewpoint (Christian Science Monitor), Foreign Policy, U.S. Department of Energy, Wikipedia, BBC, CNN, NBC News, Fox News and various books and other publications.
Last updated August 2012