RAW classifications

Radioactive waste can be classified according to different schemes for dif­ferent purposes such as operational segregation and treatment, e. g. com­pressible waste and combustible waste. At an international level, an agreed system of classification has been developed based on long-term safety con­siderations [3]. The scheme is used at a national policy and strategy level for exchange of information and for the purposes of international safety standards and international safety conventions. The scheme is based on linking waste types to corresponding disposal options. The waste classes defined are summarised in Box 3.1.

The classification scheme is illustrated graphically in Fig. 3.1. The ordi­nate is the radioactivity content of the waste and the abscissa the half-life. The diagram illustrates the need for greater levels of containment and isola­tion for higher activity and longer lived radioactive waste.

Box 3.1 IAEA classification of radioactive waste

(1) Exempt waste (EW): Waste that meets the criteria for clearance, exemption or exclusion from regulatory control for radiation protection purposes.

(2) Very short lived waste (VSLW): Waste that can be stored for decay over a limited period of up to a few years and subsequently cleared from regulatory control according to arrangements approved by the regulatory body, for uncontrolled disposal, use or discharge. This class includes waste containing primarily radionuclides with very short half-lives often used for research and medical purposes.

(3) Very low level waste (VLLW): Waste that does not necessarily meet the criteria of EW, but that does not need a high level of containment and isola­tion and, therefore, is suitable for disposal in near-surface landfill-type facili­ties with limited regulatory control. Such landfill-type facilities may also contain other hazardous waste. Typical waste in this class includes soil and rubble with low levels of activity concentration. Concentrations of longer lived radionuclides in VLLW are generally very limited.

(4) Low level waste (LLW): Waste that is above clearance levels, but with limited amounts of long-lived radionuclides. Such waste requires robust isolation and containment for periods of up to a few hundred years and is suitable for disposal in engineered near-surface facilities. This class covers a very broad range of waste. LLW may include short-lived radionuclides at higher levels of activity concentration, and also long-lived radionuclides, but only at rela­tively low levels of activity concentration.

(5) Intermediate level waste (ILW): Waste that, because of its content, particu­larly of long-lived radionuclides, requires a greater degree of containment and isolation than that provided by near-surface disposal. However, ILW needs no provision, or only limited provision, for heat dissipation during its storage and disposal. ILW may contain long-lived radionuclides, in particular, alpha-emitting radionuclides that will not decay to a level of activity concen­tration acceptable for near-surface disposal during the time for which insti­tutional controls can be relied upon. Therefore, waste in this class requires disposal at greater depths, of the order of tens of metres to a few hundred metres.

(6) High level waste (HLW): Waste with levels of activity concentration high enough to generate significant quantities of heat by the radioactive decay process or waste with large amounts of long-lived radionuclides that need to be considered in the design of a disposal facility for such waste. Disposal in deep, stable geological formations usually several hundred metres or more below the surface is the generally recognised option for disposal of HLW.

 

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