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Radioactive Waste

Radioactive waste is any waste that contains radioactive material. Radioactive (or nuclear) waste is a by-product from nuclear reactors, fuel processing plants, hospitals, various industrial applications, and research facilities. Radioactive waste is hazardous to most forms of life and the environment and is regulated by government agencies to protect human health and the environment.

For radioactive waste, this means isolating or diluting it such that the rate or concentration of any radionuclides returned to the biosphere is harmless. Time, in this case, plays a very important role since radioactivity naturally decays over time. The radioactive decay of a certain number of atoms (mass) is exponential in time. The rate of nuclear decay is also measured in terms of half-lives. The half-life is the amount of time it takes for a given isotope to lose half of its radioactivity. If a radioisotope has a half-life of 14 days, half of its atoms will have decayed within 14 days. In 14 more days, half of that remaining half will decay, and so on. Half-lives range from millionths of a second for highly radioactive fission products to billions of years for long-lived materials (such as naturally occurring uranium). Notice that short half lives go with large decay constants. Radioactive material with a short half-life is much more radioactive (at the time of production) but will lose its radioactivity rapidly. No matter how long or short the half-life is after seven half-lives have passed, there is less than 1 percent of the initial activity remaining.

Practically all radioactive waste is contained and managed, with some clearly needing deep and permanent disposal to achieve this. Current approaches to managing radioactive waste have been segregation and storage for short-lived waste, near-surface disposal for low and some intermediate level waste, and deep burial or partitioning/transmutation for high-level waste. From nuclear power generation, unlike all other forms of thermal electricity generation, all waste is regulated – none is allowed to cause pollution.

The danger of Radioactive Waste

Radioactive waste dangers are determined by many factors since it is important to note that there are many types of radiation. Dangers are usually determined by:

  • Type of Radiation. Unstable isotopes decay spontaneously through various radioactive decay pathways, most commonly alpha decay, beta decay, gamma decay, or electron capture. We must consider which type of radiation (and its energy) you are exposed to. For example, alpha radiation travels only a short distance and does not penetrate very far into a tissue, if at all. Therefore, alpha radiation is sometimes treated as non-hazardous since it cannot penetrate the surface layers of human skin. This is naturally true, but this is not valid for internal exposure to alpha radionuclides. When inhaled or ingested, alpha radiation is much more dangerous than other types of radiation. In short, the biological damage from high-LET radiation (alpha particles, protons, or neutrons) is much greater than that from low-LET radiation (gamma rays).
  • Intensity. The intensity of ionizing radiation is a key factor determining the health effects of exposure to radiation. It is similar to being exposed to heat radiation from a fire (in fact, it is also transferred by photons). If you are too close to a fire, the intensity of thermal radiation is high, and you can get burned. If you are at the right distance, you can withstand it without any problems, and it is comfortable. If you are too far from a heat source, the insufficiency of heat can also hurt you. In a certain sense, this analogy can be applied to radiation from ionizing radiation sources. We must note that radiation is all around us, and we are continually exposed to natural background radiation, which seems to be without any problem.
  • Chemical properties of the radioactive material. Chemical properties are a key factor for possible internal exposure. For example, Sr-90, Ra-226, and Pu-239 are radionuclides known as bone-seeking radionuclides. These radionuclides have long biological half-lives and are serious internal hazards. Once deposited in bone, they remain unchanged in amount during the individual’s lifetime. These radioactive chemical elements must be isolated from the environment as long as they are radioactive. On the other hand, in the case of artificial tritium ingestion or inhalation, a biological half-time of tritium is 10 days for HTO and 40 days for OBT (organically bound tritium) formed from HTO in the body of adults.

As a result, radioactive waste management assumes different approaches for different types of radioactive waste.

See also: Fear of Radiation – Is it rational?

How things become radioactive

See also: How to become radioactive

Unlike contamination, radiation cannot be spread by any medium. It travels through materials until it loses its energy. Exposure to ionizing does not necessarily mean that the object becomes radioactive (except for very rare neutron radiation). To become radioactive, you have to contain some radioactive material. In general, there are two ways how to become radioactive:

  • Exposure to neutron radiationNeutrons interact only with atomic nuclei and may be captured by the target nucleus. This reaction is known as radiative capture, making matter radioactive. The radioactive decay of these produced radionuclides is specific for each element (nuclide). Each nuclide emits the characteristic gamma rays. Significant neutron radiation is generally only found inside nuclear reactors. But it does not mean you cannot meet neutrons in everyday life. Neutrons are also produced in the upper atmosphere. Cosmic rays interact with nuclei in the atmosphere and also produce high-energy neutrons. According to UNSCEAR, the fluency of neutrons is 0.0123 cm-2s–1 at sea level for a geomagnetic latitude of 45 N. Based on this, the effective annual dose from neutrons at sea level and 50-degree latitude are estimated to be 0.08 mSv (8 mrem).
  • Intake of radioactive material. The intake of radioactive material can occur through various pathways, such as ingesting radioactive contamination in food or liquids. This is the principle behind the medical use (nuclear medicine) of many radioactive materials, as it aids in imaging, diagnosis, and other areas. Nuclear medicine uses very small amounts of radioactive materials called radiotracers, which are taken internally, for example, intravenously or orally. Between the short half-lives of the elements involved and the body’s natural means of disposing of many radioactive elements, a person’s individual radioactivity is usually short-lived.

What’s the answer? A person becomes ‘radioactive’ if dust particles containing various radioisotopes land on the person’s skin or garments. This is contamination. Once a person has been decontaminated by clothes removal and dermal scrubbing, all particulate radioactivity sources are eliminated, and the individual is no longer contaminated. But a person exposed to radiation will not become radioactive. Alpha, beta, and gamma radiations cannot activate target nuclei since they interact primarily with atomic electrons. Therefore, most types of radiation cannot activate any material. Radiation travels through materials until it loses its energy. After this, materials remain inactive. Though, as it is said, the human body is already radioactive.

Sources of Radioactive Waste

Radioactive waste comes from many sources. Radioactive (or nuclear) waste is a by-product of nuclear reactors, fuel processing plants, hospitals, various industrial applications, and research facilities. Radioactive waste is also naturally occurring radioactive materials (NORM) that can be concentrated due to the processing or consumption of coal, oil, gas, and some minerals.

  • Nuclear Fuel Cycle. The nuclear fuel cycle is a process chain consisting of various stages. The nuclear fuel cycle starts with the mining of uranium and ends with the disposal of nuclear waste. Radioactive waste from the front end of the nuclear fuel cycle is usually alpha-emitting waste from the extraction of uranium, and it often contains radium and its decay products. The back end of the nuclear fuel cycle involves managing the spent fuel after irradiation. Spent nuclear fuel is due to the presence of a high amount of radioactive fission fragments and transuranic elements that are very hot and very radioactive.
  • Medical Waste. Radiation is used in a variety of medical examinations and treatments. Doses from medical radiation sources are determined by whether a person underwent a treatment or not. In general, radiation exposures from medical diagnostic examinations are low (especially in diagnostic uses). Doses may also be high (only for therapeutic uses). Still, in each case, they must always be justified by the benefits of accurate diagnosis of possible disease conditions or by benefits of accurate treatment. These doses include contributions from medical and dental diagnostic radiology (diagnostic X-rays), clinical nuclear medicine, and radiation therapy. Radioactive medical waste tends to contain beta particles and gamma rays emitters. It can be divided into two main classes. In diagnostic nuclear medicine, many short-lived gamma emitters such as technetium-99m are used. Many of these can be disposed of by leaving them to decay for a short time before disposal as normal waste.
  • Industrial Waste. Industrial waste can contain alpha, beta, neutron, or gamma emitters. Gamma emitters are used in many industrial uses, such as radiography, a non-destructive testing method where many types of manufactured components can be examined to verify the internal structure and integrity of the specimen. Neutron emitting sources are used in various applications, such as oil well logging.
  • NORM. Naturally occurring radioactive materials (NORM) and Technologically Enhanced Naturally Occurring Radioactive Materials (TENORM) consist of materials, usually industrial wastes or by-products, enriched with radioactive elements found in the environment, such as uranium, thorium, and potassium and any of their decay products, such as radium and radon. For example, coal, a combustible black or brownish-black sedimentary rock, contains a substantial amount of the radioactive elements uranium and thorium. According to the UNSCEAR, the average specific activity of both uranium-238 and thorium-232 in coal is generally around 20 Bq/kg (range 5-300 Bq/kg). Coal mines in Freital, Germany, which have uranium concentrations of 15000 Bq/kg, are an exception. Burning coal gasifies its organic materials, concentrating its inorganic components into the remaining waste, called fly ash. Around 10% of coal is fly ash, and fly ash is hazardous and toxic to human beings and other living things. Fly ash also contains the radioactive elements uranium and thorium, concentrated by a factor of 10.

Types of Radioactive Waste

As was written, radioactive waste is any waste that contains radioactive material. This material is either intrinsically radioactive or contaminated by radioactive material, which is deemed to have no further use. The basic classification is based on a material’s intensity (specific activity). Therefore, there are three broad categories of radioactive waste.:

  • Low-level Waste. Low-level waste, LLW, comes from reactor operations and medical, academic, industrial, and other commercial uses of radioactive materials. Low-level wastes include paper, rags, tools, clothing, filters, and other materials which contain small amounts of mostly short-lived radioactivity. Low-level waste (LLW) has a radioactive content not exceeding 4 giga-becquerels per tonne (GBq/t) of the alpha activity or 12 GBq/t beta-gamma activity. LLW usually does not require shielding during handling and transport, and most LLW is suitable for shallow land burial. It is often compacted or incinerated before disposal to reduce its volume.
  • Intermediate-level Waste. Intermediate-level waste (ILW) contains higher amounts of radioactivity and generally requires shielding. Still, the heat it generates (<2 kW/m3) is insufficient to be considered in the design or selection of storage and disposal facilities. Intermediate-level wastes include ion-exchange resins, chemical sludge, contaminated materials from reactor decommissioning, and radioactive sources used in radiation therapy. Intermediate-level radioactive waste that requires long-term management. The owners and the producers of intermediate-level radioactive waste are responsible for managing the waste they produce. It may be solidified in concrete or bitumen for disposal. Generally, short-lived waste (mainly non-fuel materials from reactors) is buried in shallow repositories. In contrast, long-lived waste (from fuel and fuel reprocessing) is deposited in a geological repository.
  • High-level Waste. High-level waste, HLW,  is primarily spent fuel removed from reactors after producing electricity. HLW is also a type of nuclear waste created by reprocessing spent nuclear fuel (e.g., waste formed by vitrification of high-level liquid waste). High-level waste is sufficiently radioactive for its decay heat (>2kW/m3) to increase its temperature and the temperature of its surroundings significantly. As a result, high-level waste requires cooling and sufficient shielding. HLW accounts for over 95 percent of the total radioactivity produced in the process of nuclear electricity generation. HLW contains both long-lived and short-lived components, depending on the length of time it will take for the radioactivity of particular radionuclides to decrease to levels considered non-hazardous for people and the surrounding environment. If short-lived fission products are generally separated from long-lived actinides, this distinction becomes important in the management and disposal of HLW.
Nuclear and Reactor Physics:
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Advanced Reactor Physics:

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  2. K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.
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  4. E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.

See above:

Nuclear Power Plant