Radioactive materials, definitions source material

Where two or more authorities use the same definition with only differences in format or punctuation, the definition is not duplicated it is reproduced from its source according to the following hierarchy UN, IMDG, ICAO, US, and LATA. IAEA takes precedence for all definitions related to radioactive materials. Definitions differing in wording, spelling, or pluralization, however small, are considered unique. Corrections to regulatory definitions appear within brackets [ ]. 

The basic unit of radioactivity is the curie, Ci. One curie is the amount of radioactive material that emits particles at a rate of 3.7 X 1010 disintegrations per second (dps), or 2.2 X 1012 min-1 (dpm). Amounts that large are seldom used in experimentation, so subdivisions are convenient. The milli-curie (mCi, 2.2 X 109 min-1) and microcurie (yu,Ci, 2.2 X 106 min-1) are standard units for radioactive measurements (see Table 6.2). The radioactivity unit of the meter-kilogram-seconds (MKS) system is the becquerel (Bq). A becquerel, named in honor of Antoine Becquerel, who studied uranium radiation, represents one disintegration per second. The two systems of measurement are related by the definition 1 curie = 3.70 X 1010 becquerels. Since the becquerel is such a small unit, radioactive units are sometimes reported in MBq (mega, 106) or TBq (tera, 1012). Both unit systems are in common use today, and radioisotopes received through commercial sources are labeled in curies and bequerels. 

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. 

Hazardous chemical waste is defined in RCRA regulations as a solid waste that exhibits the characteristic of ignitability, corrosivity, reactivity, or toxicity, or is a specifically listed waste. The definition of hazardous waste specifically excludes radioactive material (source, special nuclear, or byproduct material) defined in AEA. 

If the PSA is only carried out to Level 1, then the reactor core is, by definition, the focus of the analysis. If the PSA is carried out to Level 2 or Level 3, then the scope of the PSA may include contributions to risk arising from other sources of radioactive material on the site, such as used fuel and radioactive waste. These excore sources should be included whenever the intention is to address the total risk from the plant to an individual near the site. 

The frequency of each of the release categories should be calculated by summing the frequencies of each of the end points on the event trees assigned to it. When the scope of the PSA includes releases from all sources of radioactive material on the site, the releases from these ex-core sources should be taken into account at this point. This may involve the definition of additional release categories which would typically have lower off-site impact but higher frequency than those from a damaged core. 

This result points out two concerns. First, typically, only one local meteorological tower is in the site vicinity. The initial transport of radioactive material from a site after it is released to the atmosphere will be dominated by local conditions (e.g., hills, valleys, lakes, and precipitation). This single source of weather and wind information cannot give a definitive indication of winds away from the plant. Nuclear power plants are typically located in very complex areas (e.g., in river valleys or on the coast) where wind direction and flows can vary considerably within a short distance of the plant. As an example, a 180 difference in wind direction could result from sea breeze effects at a coastal site. This is the basis for taking protective actions in all directions near (within 2 or 3 miles of the plant). The events that occurred early in the TMI-2 incident, as discussed in Section 5.2.6, further illustrate the problems inherent in taking protective actions only in the downwind direction. 

The definition of solid waste in RCRA specifically excludes source, special nuclear, and byproduct materials as defined in AEA. Therefore, radioactive constituents of wastes that arise from operations of the nuclear fuel cycle are excluded from regulation as hazardous waste under RCRA. 

The statutory definitions of low-level waste apply only to radioactive waste that arises from operations of the nuclear fuel cycle i.e., to waste that contains source, special nuclear, or byproduct material as defined in AEA (see Section 4.1.2.1). This restriction, although not explicit in the definitions, is indicated by the applicability of NWPA and LLRWPAA to fuel-cycle waste only and by the reference to NRC, which can only regulate fuel-cycle waste. Thus, low-level waste does not include NARM waste. 

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). 

A striving to embody all the desired attributes of the new system, while recognizing that this may take many years and that a number of important benefits can be obtained by interim implementation of parts of the system. The most important areas in which interim implementations are likely to be beneficial include the establishment of exemption levels for radionuclides and hazardous chemicals in waste, to allow hazardous wastes to be managed as nonhazardous material or to allow mixed waste to be managed as radioactive or hazardous chemical waste only, and the elimination of source-based definitions of hazardous wastes, especially radioactive wastes. 

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