Definitions radionuclides

Review work for future updates of our data base should focus on iron compounds and complexes. The iron system is thought to be of crucial importance for characterizing the redox behaviour of radioactive waste repositories. Preliminary applications have indicated that the lack of data for the iron system is a source of major uncertainties associated with the definition of an oxidation potential. Hence, there is little use in developing sophisticated redox models for radionuclides as long as the dominant redox processes in a repository are poorly known. 

Another important feature of the classification system for nuclear fuel-cycle wastes in the United States is the definition of low-level waste only by exclusion there is no definition of what low-level waste is, only a definition of what it is not. As a result, in contrast to the earliest descriptions of low-level waste prior to the establishment of definitions in law, this class is not restricted to waste that contains relatively low concentrations of radionuclides compared with high-level waste. Rather, low-level waste can range from virtually innocuous to highly hazardous over long time frames. 

High-level waste thus includes the concentrated wastes that arise from reprocessing of commercial or defense nuclear fuel that contain virtually all the fission products and transuranium radionuclides (except plutonium) in spent fuel. However, the definition does not mention the constituents of the waste, and it is only qualitative because concentrated is not quantified and the minimum fuel burnup that would yield high-level waste is not specified. Although the definition given above referred only to liquid (aqueous) waste, it is clear from further discussions in 10 CFR Part 50, Appendix F (AEC, 1970), that AEC intended that high-level waste also would include concentrated solid waste derived from liquid high-level waste that was suitable for permanent disposal. 

However, spent fuel is not a waste until it is so declared. As in the definitions of high-level waste discussed previously, the constituents of spent fuel and the minimum fuel bumup or concentrations of radionuclides produced by irradiation are not specified. High-level waste then is defined in two parts as ... 

The definition of high-level waste in Clause (A) of NWPA given above follows the traditional, source-based description although, for the first time, the presence of fission products is mentioned explicitly. However, the definition remains qualitative because highly radioactive material and sufficient concentrations of fission products are not quantified, nor are the minimum concentrations of alpha-emitting transuranium radionuclides. 

In 1987, NRC announced its intent to develop a quantitative and generally applicable definition of high-level waste in response to the definition in Clause (B) of NWPA (NRC, 1987). NRC indicated that the definition would specify minimum concentrations of radionuclides constituting high-level waste and would be based primarily... 

DOE also has used the traditional, source-based definition of high-level waste. In contrast to other definitions, the definition adopted in 1988 was explicit that high-level waste contains transuranium radionuclides (DOE, 1988a). Later, however, DOE essentially adopted the definition in NWPA given above (DOE, 1999a). 

This definition is based on the source of the waste, but certain incidental wastes that arise from fuel reprocessing that contain lower concentrations of fission products and alpha-emitting transuranium radionuclides than the primary reprocessing wastes have been excluded on a case-by-case basis. 

In 1982, federal agencies concurred with a recommendation to increase the lower limit on concentrations of long-lived, alpha-emitting transuranium radionuclides in transuranic waste from 0.4 to 4 kBq g 1 (Steindler, 1982). This change in the definition of transuranic waste was made in response to difficulties in routinely measuring levels of alpha activity near 0.4 kBq g 1 in bulk solid waste and analyses which indicated that risks to public health from shallow-land burial of transuranium radionuclides in concentrations up to 4 kBq g 1 should be acceptable. 

In 1985, EPA developed a regulatory definition of transuranic waste in 40 CFR Part 191 (EPA, 1985) that incorporated the increase in the lower limit on concentrations of long-lived, alpha-emitting transuranium radionuclides. This definition was retained when 40 CFR Part 191 was repromulgated in 1993 (EPA, 1993a). EPA s definition is the same as the current statutory definition described below. 

In addition to specifying the lower limit on concentrations of alpha-emitting transuranium radionuclides, this definition specifies their minimum half-life. In contrast to the earliest definition developed by AEC, this definition does not include waste that contains high concentrations of long-lived, alpha-emitting non-transuranium radionuclides (e.g., 233U). 

Although this definition specifies a lower limit on the concentration of particular radionuclides, it also depends on the qualitative, source-based definition of high-level waste and, thus, is not strictly quantitative. Alpha-emitting transuranium radionuclides with half-lives greater than 20 y are expected to be the principal constituents of most transuranic waste, but the definition does not specify any limits on the concentrations of other radionuclides that may occur in transuranic waste, including fission products, alpha-emitting nontransuranium radionuclides, and alpha-emitting transuranium radionuclides with half-lives less than 20 y. 

DOE has defined low-level waste as in Clause (A) above (DOE, 1988c 1999c). In the earlier definition (DOE, 1988c), test specimens of fissionable material irradiated for purposes of research and development could be classified as low-level waste, provided the concentration of long-lived, alpha-emitting transuranium radionuclides was... 

NRC has developed licensing criteria for near-surface disposal of waste that contains source, special nuclear, or byproduct materials in 10 CFR Part 61 (NRC, 1982a). These regulations are intended to apply primarily to disposal of commercial low-level waste. They do not include a definition of low-level waste but essentially defer to the current statutory definition in the Low-Level Radioactive Waste Policy Amendments Act of 1985. Thus, low-level waste can include wastes with high concentrations of radionuclides that are not generally acceptable for near-surface disposal in accordance with the licensing criteria in 10 CFR Part 61 (NRC, 1982a). 

The definitions of the different waste classes are not quantitative, i.e., expressed strictly in terms of limits on concentrations of radionuclides or other waste properties. 

Concepts and definitions. Two concepts are potentially useful in establishing exemption levels for radioactive waste. The first is the concept of a generally applicable negligible (de minimis) dose or risk, and the second is the concept of amounts of radionuclides that are exempt or below regulatory concern (BRC) for particular practices or sources. 

In these definitions, highly radioactive refers to high levels of decay heat and external radiation, due primarily to shorter-lived radionuclides, and requires permanent isolation refers to high concentrations of long-lived radionuclides i.e., these terms have the same interpretations as in the definitions of high-level waste in NWPA. 

Fourth, the definitions of waste classes in the United States are not related to requirements for disposal. In IAEA s waste classification system, there is some linkage between the definitions of waste classes and the types of disposal technologies that would be required, particularly for high-level waste. However, not all waste classes in IAEA s system are linked to required disposal technologies, because low-and intermediate-level waste could be acceptable for near-surface disposal or could require disposal in a geologic repository depending, for example, on the concentrations of long-lived radionuclides. 

DOE acknowledged the dual regulatory framework for mixed waste in 1987 with a notice clarifying the definition of byproduct material (DOE, 1987b). In this notice, DOE issued a final interpretive rule establishing that the exclusion of byproduct material at Section 1004(27) of RCRA applied only to the radionuclides in mixed waste and that the nonradioactive portion of the waste was subject to RCRA. In addition, in 1987, DOE recognized that RCRA LDRs (see Section 4.2.2) and other RCRA requirements applied to transuranic waste intended for disposal at the Waste Isolation Pilot Plant (see Section 4.1.2.3.2). 

---