Nuclear Waste

The creation of huge quantities of long-lived radioactive waste is the most formidable problem facing the nuclear power industry today. The difficulty of waste disposal was not considered to be a big problem during the time when power plants were first introduced; it was assumed that waste could be recycled or buried. Unfortunately, finding safe ways of storing radioactive wastes so that they do not leak radiation into the environment has proved to be a much more difficult task than anticipated.

What is Radioactivity?

Radioactivity occurs when unstable nuclei of atoms decay and emit particles. These particles may have high energy and can have bad effects on living tissue. There are many types of radiation. 

How does nuclear waste get to you?

The planet's water cycle is the main way radiation gets spread about the environment. When radioactive waste mixes with water, it is ferried through this water cycle. Radionuclides in water are absorbed by surrounding vegetation and ingested by local marine and animal life. Radiation can also be in the air and can get deposited on people, plants, animals, and soil. People can inhale or ingest radionuclides in air, drinking water, or food. Depending on the half life of the radiation, it could stay in a person for much longer than a lifetime. The half life is the amount of time it takes for a radioactive material to decay to one half of its original amount. Some materials have half-lives of more than 1,000 years!
Paths of Radiation to the Body

Radioactive wastes come in many different forms including the following:

• protective clothing of people in contact with radioactive materials
• the remains of lab animals used in experiments with radionuclides
• cooling water, used fuel rods, and old tools and parts from nuclear power plants
• mill tailings from uranium-enrichment factories
• old medical radiation equipment from hospitals and clinics
• used smoke detectors which contain radioactive americium-241 sensors

Types of nuclear waste

High-level waste

Nuclear waste is divided into several categories. High-level waste consists mostly of spent nuclear reactor fuel from both commerical power plants and military facilities, as well as reprocessed materials which can emit large amounts of radiation for hundreds of thousands of years. We take an example for U.S. Commercial nuclear power plants in the U.S. produce 3,000 tons of high-level waste each year. The amount of spent fuel removed annually from the approximately 100 reactors in the U.S. would fill a football field to a depth of one foot. When spent fuel is removed from a reactor core, it still emits millions of rems of radiation.  In the absence of high-level waste repositories, nuclear power plants genearlly store their spent fuel rods in lead-lined conceete pools of water. These pools somewhat contain the spread of gamma radiation by keeping the rods relatively cool. They also help prevent fission. The average commercial power plant puts 60 used assemblies into temporary storage each year and will probably continue to do so until the year 2000, when responsibility for spent fuel will be transferred to the Department of Energy. Space is running out at many plants though. The plants have another option of storing their spent fuel at other plants still under construction. It is theoretically possible to reduce the amount of storage space that spent fuel rods require by removing them from their assemblies, bundling them tightly, and then packing them into heavily shielded dry storage, but repacking these highly radioactive rods may present too much of a challenge. For long-term storage of high-level waste, a waterproof, geologically stable repository and leak-proof waste container is required. Packaging has to be tailored to the volume of the waste, the actual radioactive isotopes of elements it contains, how radioactive it is, its isotopes' half-lives, and how much heat it still generates. One technique for packaging high-level wastes involves melting them with glass and pouring the molten material into impermeable containers. The containers could be buried in soil or in a rock pile and surrounded by fill material and a barrier wall. From the 1940s through the 1960s, barrels of radioactive waste were frequently dumped in oceans. This ended in 1970 when the EPA (Energy Protection Agency) determined that at least one-fourth of these barrels were leaking. A new, possibly safer proposal under consideration for long-term ocean storage includes offshore drilling and a procedure known as self-burial. In offshore drilling, holes would be drilled into the seabed and filled with barrels of waste. In self-burial, specially shaped barrels would be dumped and left to sink to the ocean floor. Geologic disposal is currently the most popular solution for waste disposal. During the 1980s, the U.S. government invested more than $2 billion into geologic disposal. In this form of disposal, mined tunnels with deep holes for waste canisters would be built using conventional mining techniques. Monitoring and waste retrieval would be relatively easy. In 1987, a site was chosen for the first permanent high-level commercial nuclear waste storage repository in the United States--Yucca Mountain, 100 miles northwest of Las Vegas, Nevada. Expected to cost up to $15 billion, this repository is scheduled to go into operation by the year 2010. Over the years, a number of other ideas for high-level waste disposal have been proposed and, at least temporarily, abandoned. One was disposal in space, in which sealed containers of radioactive material would be sent up into distant orbits. This would be an expensive and risky operation, as problems on the launchpad or in space could expose the earth and atmostphere to an enormous amount of radiation. Another suggestion was burying waste under the Antarctic ice sheets. However, this would risk irradiating that area and the surrounding sea. A much safer idea, which would render disposal unnecessary, is to bombard radioactive waste with subatomic particles to transform it into less harmful isotopes. Unfortunately, this attractive proposal awaits still unrealized technology.

Mill Tailings

Mill tailings, left over when ore is refined and processed is the largest by volume of any form of radioactive waste. Only 1% of uranium ore contains uranium--the rest is left on-site as sandlike residue. These tailings are generally left outdoors in huge piles, where they blow around, releasing radioactive materials into the surrounding air and water. By 1989, some 140 million tons of mill tailings had accumulated in the United States alone, with 10 to 15 million tons added each year. Although their radiation is generally less concentrated than other types of waste, some of the isotopes in these tailings are long-lived and can be hazardous for many thousands of years. Until their radioactive risk was known, mill tailings were sometimes used as foundation and building materials, especially in western states. When their risk was discovered, these materials in the buildings had to be monitored. These monitored sites are generally safer, although some groundwater contamination still occurs at them. It has been recommended that tailings be stored underground in clay pits, far from population centers.

Low-Level Waste

Low-level wastes are usually defined in terms of what they are not. They are not spent fuel, milling tailings, reprocessed materials, or transuranic materials. Low-level waste includes the remainder of radioactive wastes and materials generated in power plants, such as contaminated reactor water, plus those wastes created in medical laboratories, hospitals, and industry. Wastes in this category usually, although not always, release smaller amounts of radiation for a shorter amount of time. "Low level" does not mean "not dangerous," though. Although its radioactivity is usually less concentrated than that of high-level waste, low-level waste can be dangerous for up to tens of thousands of years. Most low-level wastes come from reactors. These wastes can be divided up into two categories:
• Fuel wastes are fission products that leak out of fuel rods and into cooling water.
• Nonfuel wastes result when stray neutrons bombard anything in the core other than fuel--such as the reactor vessel itself--and cause them to become radioactive.
The remainder of low-level wastes comes from industry and institutional sources, including pharmaceutical plants, universities, and medical facilities. Instead of going to low-level waste dumps, these wastes are often kept on-site for the short time it takes for them to decay to safe levels. Then they are deposited into sanitary landsfills. However, it is likely that liquid wastes are literally poured down the drain, whether or not they are still radioactive. Low-level waste landfills were first built in the 1960s. In near-surface land burial, containers of waste fill a trench and are covered and surrounded by compacted earth.  There are a number of unresolved issues regarding disposal of low-level wastes. The current institution control period (the amount of time a waste site must remain under guard after it has been filled and closed) is only 100 years. Yet the hazards presented by some low-level wastes can continue for thousands of years. What will keep future generations from uncovering and being contaminated by these substances?

So, what about the future?

Currently, better methods are being developed to decrease waste volume and make methods of separating the waste by decay rate more efficient. Development of waste storage is far from complete. There are many alternatives to consider and many techniques to develop and improve upon. There has also been much controversy about site selection and disposal methods. Although urban areas consume most of nuclear-generated electricity, radioactive wastes are dumped in rural settings, where property values decline and public health is jeopardized. Although hazards of radioactive waste are less visible than some other problems associated with nuclear energy, such as reactor accidents and nuclear weapons, they are no less dangerous, and decisions made concerning this waste will be felt far into the future.  Full article Here.  Anything to comment? Thinkquest Forum.