|Fig. 1: Above shows a low-level waste dump at Maxey Flat, Kentucky. (Source: Wikimedia) Commons)|
Generally, radioactive waste is classified based on the origin of the waste, not its physical and chemical properties. The only known way to somewhat "manage" nuclear waste is to put it in a dump (as shown in Fig. 1), keep people away, and let is burn out its radioactivity. No amount of processing can speed this up, so the waste basically has to sit around for 1000 years until it's not "hot" anymore. A universal factor across all categories of nuclear waste is the presence of at least some trace amount of long-lived nucleotides. Various categories of radioactive waste include the following:
High-Level Waste: The Department of Energy includes only reprocessing waste as high- level waste, but the Nuclear Regulatory Commission includes both spent fuel and reprocessing waste One type of high-level waste is spent fuel, which is irradiated commercial reactor fuel. Another type of high-level waste is reprocessing waste which is essentially liquid waste from solvent extraction cycles in reprocessing. This waste also includes any solids that may have resulted in the conversion of liquid waste in the reactor. 
Transuranic Waste: Transuranic waste is defined as waste that contains elements with atomic numbers greater than that of Uranium (92). Additionally, this waste is comprised of only transuranic elements that have half-lives that exceed 20 years and have concentrations that are higher than 100 nanocuries/gram. If the preceding two characteristics of transuranic waste are not met, the waste may have transuranic elements but cannot actually be classified as transuranic waste. 
Low-Level Waste: Low level waste can broken down into four distinct subcategories. These categories (described below) include Class A, Class B, Class C, and Greater than Class C, where Class A is the least hazardous waste and Greater than Class C is the most hazardous. This type of radioactive waste includes waste that is not considered as high-level, spent fuel, transuranic, or byproduct material.
Class A: Class A waste has an average concentration of 0.10 curies/cubic foot. This waste is generally the least radioactive of all the low level waste subcategories since it contains relatively short-lived radionuclides.
Class B: Class B waste has an average concentration of 2.00 curies/cubic foot. It is radioactive waste that contains a greater number of short-lived radionuclides than Class A low level waste.
Class C: Class C waste has an average concentration of 7.00 curies/cubic foot. This waste contains more short-lived radionuclides than both Class A and Class B nuclear waste and also is contaminated with some long-lived nucleotides.
Greater than Class C: Greater than Class C nuclear waste is considered to be the most radioactive out of all the subcategories of low-level nuclear waste. It has an average concentration between 300 curies/cubic foot and 2,500 curies/cubic foot. 
Nuclear waste is classified differently in different countries. In 2002, the European Commission established a more unified criteria to be used in the classification of nuclear waste. The following is what they proposed:
Transition Nuclear waste: Typically stemming from medical origins, transition nuclear waste is waste that usually fully disintegrates when it is still being temporarily stored, thus allowing it to then be considered non-radioactive waste depending on its derating values. 
Low and Intermediate Level Nuclear Waste: This is nuclear waste that has a relatively lower concentration, forcing a relatively low disposal thermal power generation. This waste is also classified into short-lived waste with a majority of radionuclides that have a half-life that is less than 30 years. Such waste can also contain trace amounts of long-lived alpha and waste radionuclides and emitters with a higher concentration than the that of short-lived waste. 
High Level Nuclear Waste: This is nuclear waste that has a relatively higher concentration of radionuclides, forcing a relatively high disposal thermal power generation. Such waste usually results from the treatment of spent fuel. 
© Léa Koob. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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 R. C. Ausness, "High-Level Radioactive Waste Management: The Nuclear Dilemma," Wes. L. Rev. 1979, 707 (1979).
 A. Andrews, "Radioactive Waste Streams: An Overview of Waste Classification for Disposal," Congressional Research Service, RL32163, December 2006.