Categorisation of radioactive waste
Radioactive waste means radioactive material in gaseous, liquid or solid form for which no further use is foreseen [definition given by the Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management]
To assist in determining practical strategies for the safe management of radioactive waste, Member States classify waste in a number of different categories. While there is no universally agreed categorisation scheme, categories are generally based on the radioactivity content of the waste and its half-life (the time taken for the radioactivity content to decrease by half). Highly active radioactive waste generates significant levels of heat and this must to be taken into account in the management strategy.
In its publication, Classification of Radioactive Waste (2009), the IAEA describes 6 categories or classes of waste.
1. Exempt waste
2. Very short-lived waste
3. Very low level waste
4. Low level waste
5. Intermediate level waste
6. High level waste
In the European Union, at the end of 2004, there was some 647,000 m3 of radioactive waste and some 38,000 te Heavy Metal of spent fuel already in storage. Of the radioactive waste, approximately 26% was classified as very low-level waste and about 1% as highly active waste. The remainder was low and intermediate level waste.
Estimates of the additional radioactive waste and spent fuel likely to be generated by Member States between 2004 and 2020 were made in 2008. The figure for radioactive waste is 1,772,300 m3, of which approximately 25% will be very low-level waste and 0.1% will be high level waste. The figure for spent fuel is 48,000 te. Heavy Metal. These figures rely on many assumptions including the timing of decommissioning, the waste conditioning techniques to be used and the national policies regarding the management of spent fuel.
The situation varies from country to country, not only in terms of waste volume but also in the national policies and strategies for carrying out the practical management of the radioactive wastes. More up to date and detailed information for individual Member States is available from the national organisations with responsibility for radioactive waste management or from the regulatory authorities.
IAEA Scheme for Classification of Radioactive Waste
1. Exempt waste (EW) – this is waste with such a low radioactivity content, which no longer requires controlling by the regulatory authority. Once the material is cleared by the regulatory authority it is no longer considered as radioactive waste.
2. Very short-lived waste (VSLW) – this is waste that can be stored for a limited period of up to a few years to allow its radioactivity content to reduce by radioactive decay. It can subsequently be cleared from regulatory control according to arrangements approved by the regulatory authority for disposal as ordinary waste, for use or for controlled discharge. This class includes waste containing radionuclides with very short half-lives often used for research and medical purposes.
3. Very low level waste(VLLW) – this waste usually has a higher radioactivity content than EW but may, nonetheless, not need a high level of containment and isolation. It is suitable for disposal in near-surface landfill type facilities with limited regulatory control. Typical waste in this class includes soil and rubble with low levels of radioactivity which originate from sites formerly contaminated by radioactivity. It may contain small amounts of longer-lived radionuclides.
4. Low level waste (LLW) - this waste has a high radioactivity content but contains limited amounts of long-lived radionuclides. It requires robust isolation and containment for periods of up to a few hundred years and is suitable for disposal in engineered near surface facilities. It covers a very broad range of waste and 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) – this is waste that, because of its radioactivity 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 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) – this is 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.