Introduction
Radioactive wastes are spin-offs containing radionuclides from radioactive processes (Andrews 2). These substances are produced by industries, commercial nuclear power plants, and laboratories that carry out scientific and medical research. Such wastes pose a threat to human and animal life. Therefore, it is imperative to ensure that these wastes are disposed of properly. However, before deciding which method of disposal is suitable for a given radioactive waste, it is important to understand the properties of the waste.
Given the large numbers of radioactive elements and wastes, understanding the properties of each waste is not an easy task as it would mean studying hundreds of compounds. The classification of radioactive wastes was developed to enable the grouping of similar compounds in similar groups thereby providing a simplified approach to the management of wastes. This paper looks at the systems of classification of radioactive wastes in Japan and the U.S. The paper also compares these systems of classification with those set by the IAEA.
Classification of Radioactive Wastes in the U.S.
The U.S. was the first country to generate a working nuclear reactor as well as to discharge a nuclear weapon (Lowenthal 2). Consequently, guidelines that regulated the operations of nuclear substances considered nuclear plants operated by the government. Initially, the classification of radioactive wastes in the US was based on attributes such as rate of exposure, the possibilities of spreading, and the mode of production of the waste. However, the need to take precautions when disposing of wastes led to the development of a novel classification system that considered the characteristics of the disposal site (Lowenthal 1). The shift implied that the disposal of radioactive wastes was a vital procedure that could have hazardous consequences if not carried out properly.
Currently, the classification of wastes in the U.S. is based on various attributes, for example, according to statutes and regulations, worker hazards or transport, and method of disposal (Lowenthal 12). The classification of wastes according to regulations leads to the development of six groups of radioactive wastes. These groups are the high-level waste (HLW), spent nuclear fuel (SNF), transuranic waste (TRUW), uranium mining and mill tailings, low-level wastes, and naturally occurring and accelerator-produced radioactive materials (NORM/NARM) (Lowenthal 8).
High-level waste encompasses products obtained from the reprocessing of used nuclear fuel as well as irradiated reactor fuel. SNF is the fuel removed from a nuclear reactor after irradiation while TRUWs include all substances polluted by more than nine nanocuries per gram of elements whose atomic numbers exceed 92. Examples of these elements are plutonium, curium, and neptunium among others. Currently, transuranium wastes are described as substances containing transuranium radionuclides that emit alpha particles whose half-lives exceed two decades and concentrations surpass 100nCi/g. Uranium mining and milling tailings comprise wastes obtained from the removal and purification of uranium or thorium.
On the other hand, LLW includes wastes that do not fall into the above-mentioned categories. Low-level wastes fall into two broad categories depending on their mode of disposal. The first category includes wastes that can be disposed of by burying near the surface of the ground while the second category includes wastes that require deep ground disposal. The first category of LLWs is further subdivided into four subclasses namely A, B, C, and greater than class C (Lowenthal 9).
Wastes in class A are those that emit negligible quantities of radiation and heat thereby making protective gear not mandatory for workers. Class B wastes emit higher quantities of radiation than class A wastes. Therefore, workers require protective gear when handling them. Furthermore, isolation and packaging are required for these wastes. Class C wastes need five centuries to be isolated from the biosphere, and their disposal by burying requires engineered barriers in holes that are at least five meters deep.
Greater than class C LLWs wastes include trash that should be buried deep in the ground. Examples of such wastes include transuranic whose half-lives exceed five years, and their radioactivity is more than 100nCi/g. The NRC does not cover NORM/NARM wastes, which fall into two classes namely diffuse and discrete NORM/NARM. Diffuse NORM/NARM have activities less than 2nCi/g 226 Ra while discrete NORM/NARMs have activities greater than 2nCi/g 226 Ra.
Classification of Radioactive Waste in Japan
The Atomic Energy Commission developed the ‘Framework for Nuclear Energy Policy,’ which governs the use of nuclear energy and encourages studies and the development of nuclear science and engineering. This policy reiterates that a generation that enjoys the convenience of nuclear energy ought to show its appreciation by participating in efforts to dispose of radioactive wastes in a manner that safeguards the welfare of the future generation. Consequently, four tenets have been developed to govern the production and disposal of radioactive wastes to achieve safe disposal of radioactive wastes. These principles include the accountability of generators, the reduction of radioactive excess, sensible treatment and disposal, and execution founded on common understanding with people.
The accountability of generators implies that plants that spawn radioactive wastes ought to treat and dispose of their wastes carefully. Consequently, the government offers guidelines that ensure the generators of radioactive wastes are accountable for their waste. Reduction of radioactive waste means that all efforts should attempt to reduce the quantities of radioactive wastes by reusing and recycling radionuclides until the final waste contains the least possible quantity of radionuclides.
Research and development towards the reduction of these wastes are encouraged, for example, finding alternative uses of the radioactive wastes. Sensible disposal of radioactive waste is necessary because these wastes show variability in the extent of radioactivity and radioactive substances. Therefore, it is important to establish a system of classification that enables the treatment and disposal of a given category of wastes in a certain way. Therefore, the classification of radioactive waste is vital in ensuring that the third principle of the ‘Framework for Nuclear Energy Policy’ is fulfilled.
In Japan, radioactive wastes are placed into two key classes depending on the level of radioactivity (“Radioactive Waste Management Programmes in OECD/NEA Member Countries: Japan” 2). These two classes are high-level radioactive waste (HLW) and low-level radioactive waste (LLW). Low-level wastes are further subdivided into four subclasses based on their origin. These subclasses include waste from nuclear reactors, waste from the utilization of radioactive substances and uranium, waste from research facilities (RI/laboratory wastes), and radioactive waste that generates heat (TRU waste) (Radioactive Waste Management Project Group 48). Waste from nuclear reactors is further divided into three groups, which are relatively higher radioactive LLW, relatively lower radioactive LLW, and very low-level radioactive waste (VLLW).
High-level wastes include fluids that come from the renewal of used nuclear fuel as well as the solid wastes that arise from the transformation of the liquid wastes into the glass. These wastes have vast quantities of the outcomes of fission. All other wastes that do not fall under HLWs are classified under LLWs. Of the nuclear reactor wastes, VLLW has negligible levels of radioactivity and can be discarded near the surface of the ground without requiring to be covered up by specialized constructions.
TRU wastes, on the other hand, are generated by the recycling of used fuel and the production of oxide fuels that contain radionuclides whose atomic numbers exceed that of uranium. Other substances that make up TRU wastes include silver adsorbents with elevated concentrations of I-129, fragments with large quantities of carbon-14, and hardened wastes with large quantities of nitrates.
In addition, the National Commission Safety of Japan has set limits for the amounts of radioactive substances in wastes meant for disposal. These limits have seen the development of clearance degrees for radioactive wastes, which implies that certain substances that contain less than the specified amounts of radioactive material can be freed from radiological control.
Comparison of the Classification of Radioactive Waste in Japan and the U.S.
Japan and the U.S. have established authorities that control the handling and clearance of radioactive waste. The disposal facilities in these two countries receive radioactive waste according to the categories of the waste. However, one distinct difference in the classification schemes is that the U.S. system has more categories than the Japanese system, which has only two categories. In addition, the basis of the formation of the classes differs between the two countries. In Japan, the first two categories are based on the amount of activity present in the wastes while the subdivisions of the second category are based on the source of the wastes.
In the U.S., conversely, there is no distinct basis for the formation of the classes. Some of the classes are formed according to the source of waste while others are formed based on methods of disposal, transportation, and worker hazards. Similarly, other classes are formed based on the extent of radioactive decay while others are founded on the half-lives of the materials. Instead of laying down a common basis for the classification system, the U.S. scheme has certain classes that share one base and others that share a different basis. Therefore, there exist ‘orphan wastes,’ which are wastes that fail to fit any given category due to inadequacies in the classification system.
Lowenthal comments that some of the problematic materials in nuclear management (wPu and depleted uranium) have not been classified as wastes thereby introducing flaws in the US classification system (12). According to the U.S. Department of Energy, these substances belong to a category named ‘materials not considered as waste’ (MNCAW). In contrast, the Japanese system is well organized and does not contain classes that overlap or omit certain substances from the classification system. Therefore, each waste type can be directed to a waste management facility that is equipped to manage it safely.
Another distinct difference in the classification of wastes from these two countries is that the U.S. system does not specify lower limits for its classes hence making it impossible to exclude materials with negligible levels of activity from radioactive regulations. In contrast, the NRC in Japan has instituted BRC standards that allow some wastes to be exempted from radioactive regulatory rules.
Conventionally, waste classification systems are divided into two groups based on the approach used. The two groups are the top-down approaches and bottom-up approaches. The top-down approach categorizes wastes based on simple features and compositions of the wastes. The bottom-up approach, conversely, classifies wastes according to the features of their disposal sites. Ideally, a classification system ought to use only one of the two approaches. However, the U.S. classification system is a blend of both approaches. On the other hand, the Japanese system of classification uses the top-down approach only. Therefore, it can be concluded that the Japanese system of classification of radioactive wastes is more simplified and organized than the U.S. system of classification.
Comparison of the Classification of Radioactive Waste in Japan, USA and IAEA
The IAEA is empowered to create safety standards to safeguard the health and reduce the destruction of life and property. In addition, the body ensures that all member states meet these standards. The utilization of IAEA standards in the categorization of wastes and subsequent disposal gives a dependable, uniform way of making certain that the requirements under the agreement are fulfilled.
Designers, manufacturers and operators of radioactive substances also need to adhere to these guidelines to ensure safety in the various applications that entail radioactive materials. Most systems of waste classification associate the processes that spawn the wastes with the mode of disposal. Consequently, the sources of the wastes instead of their radiological traits determine their end (Andrews 1).
The IAEA classification system for radioactive wastes consists of six categories namely exempt waste (EW), very short-lived waste (VSLW), very low-level waste (VLLW), low-level waste (LLW), Intermediate-level waste (ILW), and high-level waste (HLW) (International Atomic Energy Agency 5). Exempt wastes include all wastes with negligible quantities of radioactive substances. These wastes are excluded from rigid control for radiation safety purposes. VSLW includes wastes with relatively short half-lives, which can decay over a limited time (a few years) and are afterward released for uncontrolled discharge. More often, these wastes come from medical and research institutions, which prefer the use of radionuclides with brief half-lives.
VLLWs are not considered safe enough to be cleared but can be discharged without strict restrictions such as burying near the earth’s surface in facilities that have partial regulatory control. Examples of these wastes comprise dust and debris with small quantities of radioactivity. Compounds with prolonged half-lives are rarely found under this category. LLWs contain small quantities of radionuclides with long half-lives and are, therefore, beyond the clearance levels.
Consequently, tough separation and restraint periods (hundreds of years) are necessary for such wastes. LLWs may also contain a blend of radionuclides with short half-lives at higher concentrations and long-lived radionuclides at lower levels of activity (International Atomic Energy Agency 5). ILWs have a higher content of radionuclides with long half-lives and, therefore, require a larger extent of separation and restraint than that provided by near-surface clearance.
However, there is minimal heat dispersion during their storage and discarding. ILWs contain radionuclides that release alpha particles during decay and need to be buried ten to a hundred meters beneath the surface of the earth. HLWs include wastes with radioactivity that produces significant quantities of heat during the decay process. Additionally, these wastes contain large quantities of long-lived radionuclides. Therefore, great caution is required during the disposal of these wastes. As a rule, these wastes are usually buried in stable pits whose depth extends for several hundred meters.
A comparison of the classification system of radioactive wastes in the U.S., Japan and IAEA shows a number of similarities and differences. The U.S. and IAEA systems have six categories of radioactive wastes. Out of these, only two categories share similarities in the two systems. These two categories are low-level wastes and high-level wastes. Conversely, the Japanese system of classification has only two categories of wastes. However, the subclasses of the second category in the Japanese system contain four subclasses that share a number of characteristics with the main groups of the IAEA system.
The classification systems in Japan and the IAEA include categories of wastes that are exempted from regulations that govern radioactive materials. However, the U.S. system does not specify such classes. Lowenthal (11) asserts that most classes of wastes in the U.S. do not possess lower limits implying that even the natural radioactivity is not let off the laws of radioactive wastes. Therefore, there is no established yardstick for BRC (below regulatory concern) quantities of radioactive materials. In contrast, the NRC in Japan has established BRC paradigms that exempt some wastes from radioactive regulations.
It is worth noting that the system in Japan shares many similarities with the IAEA classification compared to the U.S. system. It is easier to match the IAEA classes with the main classes and subclasses of the Japanese system than the classes in the U.S. system.
There are two similarities among the three systems of waste classification. The category of wastes that contains the highest concentrations of radioactive substances is designated high-level waste (HLW) in all three systems. It is also evident that these wastes come from nuclear energy. Another similarity is the presence of a low-level waste category in the three systems. However, the description of this category varies among the systems. For example, in Japan, the LLW class comprises a major category in the classification system, whereas in the U.S., LLWs are wastes that fail to fit in the source-defined categories and TRU wastes. In the IAEA system, LLWs comprise wastes that contain small quantities of radionuclides with long half-lives.
Conclusion
A number of systems have been devised to categorize radioactive wastes based on their natural, chemical, or radiological traits, which are suitable for clearance in specific facilities and situations. These systems have led to the development of varying terminologies that differ from one country to another as well as in different facilities within the same country. Consequently, these differences make it impossible to establish uniform radioactive waste managing strategies, which can affect the levels of safety. These differences also make communications on waste management practices difficult especially in the international arena.
In addition, it becomes difficult to make direct comparisons of information in available scientific literature as well as to comprehend waste management practices within and between states. However, a common trait of all the systems of waste classification is that they aim to ease waste management and ensure there is safety when handling radioactive materials. Therefore, it can only be hoped that the various systems of classification serve the interests of the countries that formulate them.
Works Cited
Andrews, Anthony 2006, Radioactive Waste Streams: Waste Classification for Disposal. Web.
International Atomic Energy Agency 2009, Classification of Radioactive Waste General Safety Guide. Web.
Lowenthal, Micah D 1997, Radioactive-Waste Classification in the United States: History and Current Predicaments. Web.
Radioactive Waste Management Programmes in OECD/NEA Member Countries: Japan 2011. Web.
Radioactive Waste Management Project Group 2007, Updated Consolidated Report on Radioactive Waste Management in FNCA Countries. Web.