Lesson 1: Radiation
Lesson 2: The Uses of Radiation
Lesson 3: Nuclear Reactors/Energy Generation
Lesson 4: Radioactive Waste
Lesson 1: Radiation
To stimulate students' interest in the biological effects of radiation, help students become more literate in the benefits and hazards of radiation, and inform students about the NRC's role in regulating radioactive materials. At the conclusion of this unit the student should be able to distinguish between natural and man-made radiation, detect and measure radiation using a Geiger counter, investigate the "footprints" of radiation using the Cloud Chamber, describe the principle of half-life of radioactive materials and demonstrate how half-lives can be calculated, and identify and discuss the different types of radiation.
Hypothesis made before conducting the Cloud Chamber experiment: While radiation cannot be seen, the cloud chamber allows one to see the tracks it leaves in dense gas.
1. Materials needed for the Cloud Chamber: small transparent container with transparent lid; flat black spray paint; blotter paper; pure ethyl alcohol; radioactive source; masking tape; dry ice; styrofoam square; flashlight; gloves or tongs to handle the dry ice.
2. Materials for measuring radiation with the Geiger counter; Geiger counter; radioactive sources; shielding material such as paper, aluminum foil, brick, jar of water, piece of wood, glass pane, sheet of lead.
After Cloud Chamber Experiment
Because you could not see the radiation, what kind of observation did you experience?
What is happening to the radioactive source?
What radiation "footprints" did you see? Describe them.
After the Geiger Counter Measurements
Why do we measure radiation exposure?
When you use a Geiger counter to survey a radioactive substance, why is it important to know what the background radiation level is?
Has anyone you know been helped or harmed by radiation?
Note: Give each student a 5x7 index card as he/she enters the classroom. Ask students to share their thoughts about radiation by writing on the card what they thought about. Do not put your name on the card! Initiate a discussion about radiation by reading several index cards to the class without associating any student with a particular thought. Write key words from student opinion on the board for future reference.
Radiation surrounds us, coming from the Earth and from outer space. Many forms of radiation are invisible -- we can't feel it, see it, taste it, or smell it. Yet, it can be detected and measured when present. We measure ionizing radiation in units called millirems. But what is radiation? Radioactive materials are composed of atoms that are unstable. An unstable atom gives off its excess energy until it becomes stable. The energy emitted is radiation. We can classify radiation as being either natural or man-made.
The Earth is surrounded by radiation: radon, a radioactive gas from Uranium found in soil dispersed in the air; from radioactive potassium in our food and water; from Uranium, radium, and thorium in the Earth's crust; and from cosmic rays and the sun. These types of radiation are called natural or background radiation. In the U.S. we are exposed to an average of 300 millirems of natural radiation each year (a millirem is a unit of measure for exposure to radiation). This amounts to natural radiation accounting for nearly 85 percent of our total annual exposure. The remaining 15 percent come from man-made sources. Man-made radiation sources that people can be exposed to include tobacco, television, medical x-rays, smoke detectors, lantern mantles, nuclear medicine, and building materials.
Adding it all up, the average American is exposed to a total of about 360 millirems a year from natural and man-made radiation. The sources of radiation are shown in Classroom Activity 1. Generally, when we think of exposure to radiation, we need to look at radioactive atoms produced in nuclear reactors and described as being unstable. They are unstable because they undergo a disintegrating process called decaying. During this process, unstable atoms become stable, throwing off (emitting) radiation in the form of rays and/or particles. How fast a radioactive atom decays into a stable atom depends on the atom itself. For example, the range in the rate of decay among isotopes goes from fractions of seconds to several billion years (e.g., Uranium). Let's take a look at Uranium-238 to illustrate the decay chain.
As U-238 decays it changes into thorium-230, which changes into radium-226, which changes into radon-218, which changes into bismuth-214, and finally into lead-206 (a stable element). One peculiar thing about radioactive atoms is that no one knows exactly when the element will decay and give off radiation. There is, however, a pattern relating to how long it takes for an isotope to lose half of its radioactivity. This pattern is called half-life. If an atom, for example, has a half-life of 10 years, half of its atoms will decay in 10 years. Then in another 10 years half of that amount will decay and so on. While there are several different forms of radiation, we're concentrating on three that result from the decay of radioactive isotopes: alpha, beta, and gamma.
Beta particles are high energy electrons. Both alpha and beta particles are emitted from unstable isotopes. The alpha particle, consisting of two protons and two neutrons, is relatively large compared to beta particles. Gamma rays have no mass. Because of its size and electrical charge (+2), the alpha particle has a relatively slow speed and low penetrating distance (one to two inches in air). Alpha particles are easily stopped by a thin sheet of paper or the body's outer layer of skin. Since they do not penetrate the outer (dead) layer of skin, they present little or no hazard when they are external to the body.
However, alpha particles are considered internal hazards, because when they come into contact with live tissue they cause a large number of ionizations to occur in small areas, thus causing damage to tissues and cells. Beta radiation, while faster and lighter than alpha radiation, can travel through about 10 feet of air and penetrate very thin layers of materials such as aluminum foil. However, while clothing will stop most beta particles, they can penetrate the live layers of skin tissue. Therefore, beta radiation is considered to be both an internal and external (to skin only) hazard. Thin layers of metals and plastics can be used to shield individuals from beta radiation.
Gamma radiation, high energy light, is a little different. It is a type of electromagnetic wave, just like radio waves, light waves, and x-rays. Gamma radiation is a very strong type of electromagnetic wave, traveling at the speed of light with no mass. This is much faster than alpha and beta radiation. Because of their penetrating capability, gamma rays are considered both internal and external hazards. Thick walls of cement, lead, or steel are needed to block gamma radiation.
Ionizing radiations: alpha, beta, and gamma alter chemical structures including the delicate chemistry of the human body and other living organisms. Radiation causes the potential for malignant tumors by altering the normal body cells and normal body cell functions, resulting in uncontrolled cell growth and abnormal cell functions. The only known method of preventing the harm of ionizing radiation is to avoid exposures. Large amounts of radiation levels above the levels normally encountered can produce cancers and genetic defects in living organisms. All biological damage begins when radiation interacts with atoms forming cells, whether the source of radiation is natural or man-made, a small dose of radiation or a large dose. Radiation causes ionizations of those atoms
that will affect molecules
that may affect cells
that may affect tissues
that may affect organs
that may affect the whole
Experiment A: The Cloud Chamber While radiation cannot be seen, the cloud chamber allows you to see the tracks it leaves in a dense gas. [Complete Classroom Activity, see http://scidiv.bellevuecollege.edu/Physics/Cloudchmbr.htm]
Experiment B: Using the Geiger Counter How radioactive are different materials? [Complete Classroom Activities, see http://www.charlesedisonfund.org/Experiments/HTMLexperiments/Chapter8/8-Expt8/p1.html]
Questions with Answers from the Radiation Lesson Outline:
1. Q: Why are elements that break apart called unstable? A: They are unstable because in the process of emitting gamma rays they become stable or change into another element by emitting alpha and beta particles.
2. Q: How do things become less radioactive as time goes by? A: Unstable elements break down bit by bit emitting alpha and beta particles and gamma rays. Each unstable element also loses its radioactivity at a different rate that is defined by its half-life. Half-lives range from fractions of a second to several billion years.
3. Q: What materials are best for shielding? A: Denser materials such as lead or concrete are more effective for stopping radiation because a high density and high atomic number provides many more atoms per volume and many more electrons with which photons can interact.
Lesson 2: The Uses of Radiation
At the conclusion of this lesson students should be able to discuss the uses of radiation in science, industry, and medicine; identify different man-made radiation sources that result in exposure to members of the public and compare and contrast the benefits and risks of radiation.
While the Earth and all things on it are constantly being bombarded by radiation from space, there are two distinct groups exposed to man-made radiation: members of the public and radiation workers. Members of the public are exposed to the most significant source of man-made radiation from medical procedures and treatments. Conversely, radiation workers are exposed according to their occupations and to the sources with which they work.
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 mankind, radiation is used in science, medicine, and industry, as well as for generating electricity. Radiation has useful applications in such areas as agriculture, medicine, space exploration, architect/engineering, industry/manufacturing, government, geology (including mining), ecology, and education. Radiation is used by doctors to diagnose illness and helps archaeologists find the age of ancient artifacts. Electricity produced by nuclear fission -- splitting the atom -- is one of its greatest uses. A reliable source of electricity is needed to give us light, help to groom and feed us, and to keep our homes and businesses running. Let me give you some specific examples of how the radiation has been used to:
1. Diagnose and treat illnesses
2. Kill bacteria and preserve food without chemicals and refrigeration
3. Process sludge for fertilizer and soil conditioner
4. Locate underground natural resources and differentiate a dry hole from a gusher
5. Make smoke detectors, nonstick cookware, and ice cream
6. Grow stronger crops
7. Power satellites and provide future electrical needs for space laboratories with people onboard
8. Design instruments, techniques, and equipment; measure air pollution
9. Validate the age of works of art and assist in determining their authenticity
Radiation in Medicine
X-rays are a type of radiation that can pass through our skin. Our bones are denser than our skin, so when x-rayed, bones and other dense materials cast shadows that can be detected on photographic film. The effect is similar to placing a pencil behind a piece of paper and holding them in front of a light. The shadow of the pencil is revealed because most light has enough energy to pass through the paper, while the denser pencil stops all the light. The difference is that we need film to see the x-rays for us. Today, doctors and dentists use x-rays to see structures inside our bodies. This allows them to spot broken bones and dental problems. X-ray machines have now been connected to computers in the development of machines called CAT scanners. These instruments provide doctors with color TV pictures that show the shape of internal organs.
Approximately 10 million nuclear medicine procedures are performed in the United States annually. Diagnostic x-rays and or radiation therapy were administered to about seven out of every 10 Americans. Medical procedures using radiation have saved thousands of lives through the detection and treatment of conditions ranging from hyperthyroidism to bone cancer. 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. Moreover, radiation is often used to treat certain types of cancer. Radioactive iodine, specifically iodine-131, is being used frequently to treat thyroid cancer, a disease which strikes about 11,000 Americans every year.
Radiation in Science
Radiation is used in science in many ways. Just as doctors can label substances inside people's bodies, scientists can label substances that pass through plants, animals, or our world. This allows us to study such things as the paths that different types of air and water pollution take through the environment. It has also helped us learn more about a wide variety of things, such as what types of soil different plants need to grow, the size of newly discovered oil fields, and the track of ocean currents. Scientists use radioactive substances to find the age of ancient objects by a process called carbon dating. For example, in the upper levels of our atmosphere, cosmic rays hit nitrogen atoms and form a naturally radioactive isotope called carbon-14. Carbon is found in all living things, and a small percentage of this carbon is carbon-14. When a plant or animal dies, it no longer takes in new carbon and the carbon-14 it contains begins the process of radioactive decay. However, new isotopes of carbon-14 continue to be formed in our atmosphere, and after a few years the percent of radioactivity in an old object is less than it is in a newer one. By measuring this difference, scientists are able to determine how old certain objects are. The measuring process is called carbon dating.
Radiation Used To Solve Crimes
After detectives search the scene of a crime for traces of paint, glass, hair, gunpowder, or blood, evidence is collected and often exposed to radiation and then analyzed to find out its exact makeup. If material is exposed to streams of neutrons, some of the neutrons can be absorbed into the nucleus of the exposed material. This makes these materials slightly radioactive and because they are unstable and decay with time, scientists are then able to read the exact chemical signatures of these substances. This laboratory process, called activation analysis, is precise enough to determine if a single hair found at a crime scene came from a certain person. Activation analysis is also used to find out the chemical makeup of materials when scientists only have small samples, as well as to prove that older works of art are not made of modern materials.
Radiation in Industry
Exposure to some types of radiation, such as x-rays, can kill germs without harming the items that are being disinfected or making them radioactive. When treated with radiation, foods take much longer to spoil, and medical equipment such as bandages, hypodermic syringes, and surgical instruments don't have to be exposed to toxic chemicals or extreme heat to be sterilized. Radiation may soon replace chlorine, a toxic and difficult-to-handle chemical, in the future to disinfect drinking water and eradicate germs in sewage.
Ultraviolet light is presently used to disinfect residential drinking water. The agricultural industry makes use of radiation to improve food production. Plant seeds, for example, have been exposed to radiation to bring about new and better types of plants. Besides making plants stronger, radiation can also be used to control insect populations, thereby decreasing the use of pesticides. Engineers use radioactive substances to measure the thickness of materials and an x-ray process called radiography to find hard to detect defects in many types of metals and machines. Radiography is also used to check such things as the flow of oil in sealed engines and the rate and way various materials wear out. The radioactive element Uranium is used as a fuel to make electricity for our cities, farms, towns, factories, etc.
In outer space, radioactive materials are also used to power space craft. Such materials have also been used to supply electricity to satellites sent on missions to the outermost regions of our solar system. Radiation has been used to help clean up toxic pollutants, such as exhaust gases from coal-fired power stations and industry. Sulfur dioxides and nitrogen oxides, for example, can be removed by electron beam radiation. Indubitably, radiation and radioactive materials have played and will continue to play a significant role in our lives. For example, polyester-cotton blend shirts are made from chemically treated fabric that has been irradiated, or treated with radiation, before being exposed to a soil-releasing agent. Radiation makes chemicals bind to fabric, keeping shirts fresh and pressed all day however, the shirt is not radioactive. Additionally, nonstick pans are treated with gamma rays, and the thickness of an eggshell is measured by a gauge containing radioactive material before packaged into an egg carton.
The turkey stored in a refrigerator and covered with irradiated polyethylene shrink wrap. Once polyethylene has been irradiated, it can be heated above its usual melting point and wrapped around the turkey to provide an airtight cover. Reflective road signs are treated with radioactive tritium and phosphorescent paint. During lunch, brother Bob has some ice cream. The amount of air whipped into that ice cream was measured by a radioisotopic gauge. After you and your family return home this evening, some of you may have soda and others may sit and relax. Nuclear science is at work here: The soda bottle was carefully filled -- a radiation detector prevented spillover. And your family is safe at home because the ionizing smoke detector, using a tiny bit of americium-241, will keep watch over you while you sleep.
Questions with Answers from the Uses of Radiation Lesson Outline:
1. Q: How can we use radioactive isotopes to detect illness? A: By replacing a few regular atoms with radioactive isotopes in substances like hormones, food, or drugs we are able to trace the path they take through our bodies. Instruments can be used to trace the isotope through the body, or parts of the body, to find problems.
2. Q: How can we use radiation to detect a weakness in the construction of buildings? A: X-rays can be used to see into many metals and machines to help find flaws that cannot be seen on the outside. This type of examination is called radiography.
3. Q: Have you ever had a bone x-rayed? Teeth x-rayed? How did this help your doctor or dentist treat you? A: The doctor or dentist is able to see exactly what the problem is and then knows how to treat it.
4. Q: Do you think the additional radiation received when people have medical x-rays, about 40 millirems per year, is worth the benefits they receive? A: Answers will vary.
5. Q: Are there advantages to using radiation instead of pesticides to control pests, such as insects? A: Radiation can be used to control pests by sterilizing male insects that have been raised in captivity and then released into the environment. They will not be able to produce offspring. Therefore, the numbers of insects will be reduced. Another advantage is that there will be fewer chemicals added to the environment.
Lesson 3: Nuclear Reactors/Energy Generation
To ensure students understand how nuclear energy is generated, help students learn how a nuclear power plant works, and understand how the NRC regulates commercial nuclear energy.
At the conclusion of this lesson students should be able to describe the fission process, identify the various kinds of nuclear power plants, and discuss the process of energy generation with nuclear power plants.
The purpose of a nuclear power plant is to produce or release heat, boil water into steam, and generate electricity from a generator that is driven by a steam-turbine. It should be noted that while there are significant differences, there are many similarities between nuclear power plants and other electrical generating facilities. Uranium is used for fuel in nuclear power plants to make electricity.
Increasingly, our country has become a nation of electricity consumers. We depend on an abundant and affordable supply of energy to power the many machines we use in our complex society. About one-third of our energy resources are used to meet this electricity requirement.
Electricity can be produced in many ways -- most of which you already know about. Today, we're going to talk about one of those ways -- nuclear fission. In America, nuclear energy plants are the second largest source of electricity after coal -- producing approximately 21 percent of our electricity. There is something I want all of you to be aware of: The purpose of a nuclear power plant is to produce electricity. While nuclear power plants have many similarities to other types of electricity generating plants, there are some significant differences. With the exception of solar, wind, and hydroelectric plants, all others including nuclear convert water to steam that spins the propeller-like blades of a turbine that spins the shaft of a generator. Inside the generator coils of wire and magnetic fields interact to create electricity.
The energy needed to boil water into steam is produced in one of two ways: by burning coal, oil, or gas (fossil fuels) in a furnace or by splitting certain atoms of Uranium in a nuclear energy plant. Nothing is burned or exploded in a nuclear energy plant. Rather, the Uranium fuel generates heat through a process called fission. Uranium is an element that can be found in the crust of the Earth. This element, quite abundant in many areas of the world, is naturally radioactive. Certain isotopes of Uranium can be used as fuel in a nuclear power plant. The Uranium is formed into ceramic pellets about the size of the end of your finger. [Reactor Fuel Assembly] These pellets are inserted into long, vertical tubes (fuel rods) within the reactor. The reactor is the heart of the nuclear power plant. Basically, it is a machine that heats water. A reactor has four main parts: the Uranium fuel assemblies, the control rods, the coolant/moderator, and the pressure vessel. The fuel assemblies, control rods, and coolant/moderator make up what is known as the reactor core. The core is surrounded by the pressure vessel. [Franklin's Core]
We also have to understand that Uranium cannot just be thrown into a reactor the way we shovel coal into a furnace. The fuel rods, containing the Uranium, are carefully bound together into fuel assemblies, each of which contains about 240 rods. The assemblies hold the rods apart so that when they are submerged into the reactor core, water can flow between them. When the Uranium atom splits, it releases energy and two or more neutrons from its nucleus. These neutrons can then hit the nuclei of other Uranium atoms causing them to fission. The sequence of fission-triggering is called a chain reaction, releasing energy in the form of heat when the atoms split. The heat is transferred from the reactor core to the steam generator and converted to high pressure steam that turns the turbine in the electric generator.
The control rods slide up and down in between the fuel assemblies in the reactor core. They control or regulate the speed of the nuclear reaction by absorbing neutrons. Here's how it works: When the control rods absorb neutrons, fewer neutrons hit the Uranium atoms thus slowing down the chain reaction. On the other hand, when the core temperature goes down, the control rods are slowly lifted out of the core, and fewer neutrons are absorbed. Therefore, more neutrons are available to cause fission. This releases more heat energy. Just as there are different types of houses and cars, there are different types of nuclear power plants that generate electricity. The two basic types being used in the United States are the boiling water reactor (BWR) and the pressurized water reactor (PWR). These power plants are often referred to as light water reactors.
Pass out Activities 4 - Boiling Water Reactor (BWR) and 5 - Pressurized Water Reactor (PWR).
Students can label components of each type reactor during the discussion.
Boiling Water Reactor (BWR)
The boiling water reactor operates in essentially the same way as a fossil fuel generating plant. Neither of these types of power plants have a steam generator. Instead, water in the BWR boils inside the pressure vessel and the steam water mixture is produced when very pure water (reactor coolant) moves upward through the core absorbing heat. The water boils and produces steam. When the steam rises to the top of the pressure vessel, water droplets are removed, the steam is sent to the turbine generator to turn the turbine. [BWR schematic]
Pressurized Water Reactor (PWR)
The pressurized water reactor differs from the BWR in that the steam to run the turbine is produced in a steam generator. Water boils at 212/F or 100/C, expanding into steam as it boils. A pressure cooker encloses an increasing pressure inside the pot because the steam cannot escape. As the pressure increases, so does the temperature of the water in the pot. In the PWR plant, a pressurizer unit keeps the water that is flowing through the reactor vessel under very high pressure to prevent it from boiling. The hot water then flows into the steam generator where it is converted to steam. The steam passes through the turbine which produces electricity. About two-thirds of the reactor power plants in the U.S. are of the PWR type. [PWR schematic]
Questions with Answers from Nuclear Reactors/Energy Generation Lesson Outline:
1. Q: Is there a nuclear power plant near where you live? What type is it? A: Example: 40 miles south of Annapolis, MD -- Calvert Cliffs 1 & 2 (PWR).
2. Q: Why don't boiling water reactors have steam generators? A: Because the water is boiled inside the pressure vessel and the steam is used directly to turn the turbine.
3. Q: What is the purpose of a "cooling tower"? A: To remove excess heat from the reactor circulating water system.
4. Q: What percentage of our electricity in the U.S. is produced in nuclear power plants? A: Approximately 20 percent.
5. Q: Name the two types of reactor power plants in operation the U.S. What are the basic differences? A: a. Boiling Water Reactor (BWR) -- water is boiled in the pressure vessel and the steam is used directly to turn the turbine. b. Pressurized water reactor (PWR) -- water flows through a steam generator where it is heated to produce steam that then flows to the turbine to generate electricity.
Lesson 4: Radioactive Waste
To make students aware of nuclear waste shipments and the safeguards in place, and recommend that students become more familiar with the Federal agencies involved in waste transportation and pertinent public policy issues. At the conclusion of this lesson students should be able to describe the sources, handling, and disposal of radioactive wastes generated by nuclear power plants, distinguish between high- and low-level radioactive wastes, and identify the agencies having oversight responsibilities in the designation and storage of radioactive waste.
Radioactive waste is material that is radioactive, no longer needed at the plant, and can be disposed of.
Nuclear waste raises many questions that will be addressed and hopefully answered in this lesson. Quantifying garbage that people produce on a weekly, daily, or even per restaurant visit should be the basis of student reflections. Visualize how much trash results from just one visit to a fast-food restaurant -- from bags, to straws, to soft drink containers. Many other industries generate garbage from manufacturing something and the leftovers of an industrial process are called wastes and nuclear power plants produce nuclear waste. One of the main concerns about nuclear power plants is what to do with the waste. Student should assemble the nuclear waste cube to observe that in the U.S. one person's share of high-level radioactive waste from nuclear power plants for a period of 20 years could be placed inside the cube. This is the amount of waste that would be left over after all stable materials had been recycled.
The problem with nuclear power plants wastes are not the amounts, which are quite small compared to other industries, but that nuclear power plants wastes can be radioactive. Nuclear power plants are not the only producers of radioactive waste however, a large amount of radioactive waste is produced by hospitals and other industrial processes. All producers of radioactive waste must ensure that special rules and regulations are followed to transport and dispose of these materials, thereby protecting the employees, the public, and the environment. Radioactivity of the waste, half-life of the waste, and physical or chemical properties of the waste are attributes that align with acceptable methods for disposing of nuclear waste.
Radioactive waste includes solid, liquid, and/or gaseous materials that are neither needed nor valued at the nuclear power plant, ready for disposal:
1. Radioactive fission products inside the cladding of fuel assemblies.
2. Radioactive activation products that are collected in filters and demineralizers in the reactor cleanup systems.
3. Paper towels or rags used to wipe up radioactive water.
4. Contaminated pieces of equipment.
5. The pressure vessel, plumbing, and containment structures from a closed or decommissioned facility.
6. Radioactive waste from nuclear power plants is classified as being either low- or high-level waste.
Waste that is only slightly radioactive and gives off small amounts of radiation is called low-level waste. Low-level waste is produced in virtually every state by hospitals, universities, companies, and nuclear energy plants. This waste includes such things as filters, cleanup rags, lab supplies, and discarded protective clothing. Most radioactive waste from a nuclear power plant is low-level. The principle sources of low-level radioactive waste are the reactor coolant water and the components and equipment that come in contact with the coolant. The major constituents of low-level waste from a nuclear power plant are activation products and a very small percentage of fission products (if any leaks out of the fuel rods). It does not include used fuel from the reactor fuel assembly. Because it emits only small amounts of radiation, low-level waste is usually sealed in steel drums and buried at special sites. Today, most of the low-level waste from nuclear power plants in the U.S. is disposed of at two sites: Barnwell, South Carolina, and Hanford, Washington. Drums containing low-level waste are placed in specially designed trenches and are covered with at least six feet of soil and packed clay. To ensure that the materials remain undisturbed, the trenches are constantly monitored to detect radiation.
The radioactive particles in low-level waste emit the same types of radiation that everyone receives from nature. Most low-level waste fades away to natural levels of radioactivity in months or years. Virtually all of it diminishes to natural levels in less than 300 years. In the U.S. there is strict regulation of low-level waste. The U.S. Nuclear Regulatory Commission, for example, licenses many of the facilities that produce low-level waste, including nuclear power plants. It also regulates low-level waste disposal. The U.S. Environmental Protection Agency, on the other hand, develops general standards to protect the public from radiation. The U.S. Department of Energy coordinates national planning with the states for managing low-level waste. The U.S. Geological Survey offers technical assistance with studies of hydrology and geology of proposed sites. Legislation passed by Congress requires state governments to be responsible for disposing of the low-level waste generated in their states or for joining a regional compact. State governments are also responsible for selecting and licensing a site according to Federal standards and monitoring its operation.
Waste from power plants that is highly radioactive is called high-level waste. For example, about 99 percent of high-level waste from commercial nuclear power plants comes from used or spent nuclear fuel (Uranium pellets inside metal fuel rods) that has released much of its energy. Certain changes take place in the fuel during the fission process. Most of the fragments of fission, including the pieces left over after the atom has split, are radioactive. Over time, these trapped fission fragments reduce the efficiency of the chain reaction. About every 18 months or so, the oldest fuel assemblies, which have already released their energy, are removed and replaced with fresh fuel. Fuel that has been removed from the reactor is called spent fuel. Spent fuel is highly radioactive, and this radioactivity produces a lot of heat. Spent fuel, after being removed from the reactor, is stored at nuclear plant sites in steel-lined, concrete vaults filled with water or in dry storage casks that are air cooled. The water cools the used fuel and acts as a shield to protect workers from radiation.
During storage, the spent fuel cools down and also begins to lose most of its radioactivity through radioactive decay, which we've already discussed. In three months, for example, the spent fuel will have lost 50 percent of its radiation; in one year it will have lost about 80 percent; and in 10 years it will have lost 90 percent. Nevertheless, because some radioactivity remains hazardous for thousands of years, the waste must be carefully and permanently isolated from the environment. While storage on site has been environmentally safe, what is needed today is a permanent disposal site, or repository, for existing and future high-level waste. To date, scientists around the world agree that deep underground disposal is the way to solve the high-level waste storage problem. In fact, deep underground geologic repositories have been endorsed by independent scientific organizations such as the National Academy of Sciences. In 1982, the U.S. Congress passed the Nuclear Waste Policy Act. This law set up a schedule for selecting a site, constructing, and operating America's first high-level nuclear waste storage facility. In 1987, Congress directed DOE to explore Yucca Mountain for a repository.
In February 2002, DOE recommended that Yucca Mountain be developed as America's first high-level nuclear waste storage facility however, before the site can be approved, or a repository built and operated, there must be scientific proof that public health and safety will be protected for thousands of years. The facility must meet strict safety requirements of the U.S. Nuclear Regulatory Commission. Additional oversight would be provided by the U.S. Environmental Protection Agency, the State of Nevada, and a Technical Review Board appointed by the President of the United States. This high-level waste will most likely be converted into a ceramic material that will not rust, melt, or dissolve, even over very long periods. This ceramic waste will then be sealed in heavy metal canisters which will be buried deep underground in solid rock formations. Repositories may be located in stable, dry types of rock formations because it is absolutely necessary that radioactive substances do not leak into underground water. Nuclear energy, a powerful force that should never be treated lightly, requires a high degree of professional and technical care. But neither should its risks be exaggerated. The technology exists to isolate high-level waste safely and responsibly, without harm to humans or the environment. Creating a permanent repository will help ensure that. And, with the help of nuclear energy, America will have clean, abundant electricity in the years ahead.
Classroom Activity 6: Nuclear Waste Cube
Experiment: Student assembly of the nuclear waste cube. In the U.S. one person's share of high-level radioactive waste from nuclear power plants for a 20-year period could be placed inside the cube. This is the amount of waste that would be left over after all stable materials had been recycled.
Questions with Answers from Radioactive Waste Lesson Outline:
1. Q: Would a small leak of radioactive waste from a nuclear repository be detected? Why or why not? A: Yes, radiation can be detected with devices similar to and including Geiger counters.
2. Q: How would immediate detection of even a very small leak of radioactive waste differ from leak detection of other types of industrial toxic wastes? A: Because radioactivity can be easily detected with Geiger counters, it would be easier to detect than most other hazardous or toxic wastes. Leaks of hazardous or toxic wastes other than radioactive wastes are often detected by smell, color, or sensitive chemical analytical methods which take time to perform.
3. Q: Why are there special sites for disposal of low-level waste? A: Because it must be isolated from the environment.
4. Q: Why have some states formed compacts to support a single nuclear waste disposal site that would serve several states? A: The Low-Level Radioactive Waste Policy Act passed by the U.S. Congress in 1980 requires each State to provide for disposal of the low-level waste produced within its borders.
5. Q: Why is there a controversy over the selection of a high-level nuclear waste disposal site? A: Because the waste that will be stored in these sites is highly radioactive and will remain so for thousands of years, many people don't want it located near them. They are worried that some of the radioactive material may somehow get (leak) into the environment.
6. Q: How would it affect health care in your State (e.g., Maryland) if there were no low-level waste disposal sites available? A: If no low-level waste site is available, radioactive materials may not be used in the state.
7. Q: Are special packaging containers built to protect the contents or keep the contents from getting in contact with the environment? How are containers or a burial site designed to prevent the contents from entering the environment? A: They are designed to keep the contents from getting in contact with the environment.
8. Q: How are liquids processed to remove radioactive impurities? A: a. filtering; b. routing through demineralizers; c. boiling off the water and leaving the solid impurities to be processed as solid waste; d. storing the liquid to allow the radioactive material to decay.