2.3.1 The IAEA classification

The IAEA identifies six types of waste, focusing on solid waste. There have been limited disputes over the management strategies for the first four categories of waste described below (up to and including low-level waste). While some countries have in place long-term management strategies for waste that falls into these categories (for example, the UK and France), others pursue at best interim storage strategies (such as Germany and Japan).

The main issues where political controversies arise, and where there are not yet any agreed and operational long-term management facilities anywhere in the world, concern the categories of intermediate-level and, especially, high-level waste. In relating waste categories to management options, the IAEA assumes that these options will always take the form of various kinds of land-based disposal. This includes surface disposal and a variety of sub-surface options, in the latter case including ‘disposal’ in deep geological repositories.

The IAEA system takes varying account of all three characteristics outlined above and defines the six following categories:

EXEMPT

This category involves very low concentrations of radionuclides so that there is no need, in the view of the IAEA, for any specific radiation protection measures. The IAEA safety guide suggests that this is waste suitable for exemption (from regulatory control)10, exclusion, or clearance. In principle, such material can thus be transferred from one country to another without any form of regulatory oversight.

VERY SHORT-LIVED WASTE (VSLW)

This category contains radionuclides with a very short half-life, which are often stored until their activity levels allow them to be re-categorized as exempt. Some gaseous and liquid waste is categorized as VSLW. In general terms, the recommended management strategy is storage for decay and is supposed to be applied for radionuclides with half-lives of the order of 100 days or less.

VERY LOW-LEVEL WASTE (VLLW)

Within this category, substantial amounts of waste stem from the operation and decommissioning of nuclear facilities, as well as waste arising from the mining and processing of uranium ores. Managing this waste, unlike those in the two categories above, requires full account of radiation protection and safety. Characteristic activity levels of radionuclides that fall within this category are between ten and a hundred times those of levels for exempt waste. The IAEA suggests that safe management for this waste will involve engineered surface landfill facilities, requiring both active and passive institutional controls over a significant but unspecified period.

The classification systems for many countries do not recognize the categories Exempt and VSLW, and some like the US reject the idea that any radioactive material should fall outside continuing regulatory oversight.

LOW-LEVEL WASTE (LLW)

Low-level waste (LLW) is defined as waste with levels of radioactivity low enough for near-surface or sub-surface disposal, if the disposal sites offer robust containment and isolation for what the IAEA describes as “limited periods of time”. However, these limited periods of time turn out to be up to a few

hundred years. In a number of countries, the essentially arbitrary assumption is made that institutional controls can be relied on for periods up to 300 years. However, for waste from mining and processing of uranium, activity levels fall slowly, so control needs to be postulated for longer periods than 300 years (and disposal in near-surface facilities is rare in developing countries).

This category covers a very wide range of waste and may contain low levels of long-lived radionuclides. Typical materials that fall into the LLW category include clothing, packaging material, soil, and significant products of reactor decommissioning, such as steel and piping. Depending on the exact composition of the wastes, the IAEA recommends disposal practices ranging from surface storage to burial at depths of up to 30 meters. Precise boundaries between LLW and the next category (intermediate-level waste or ILW) are not provided generically, as much depends on the characteristics of different kinds of disposal facility designs. Some countries have combined disposal of LLW and short-lived ILW with planned separate disposal of long-lived ILW. For the waste categories above, there are, for most countries, operational facilities to manage this waste.

INTERMEDIATE-LEVEL WASTE (ILW)

This is waste of higher activity levels than LLW, containing relatively large quantities of long-lived radionuclides. There is hence a need to engineer facilities that do not depend on institutional controls in the long-term. However, ILW does not produce heat from radioactive decay and thus does not need to take heat into account in its management. Characteristic sources of ILW are nuclear fuel cladding, some reactor components during decommissioning, and various types of sludge from treating radioactive liquid effluents. In addition, where spent fuel is reprocessed, large volumes of ILW are also created.

Today, in most cases, this waste is packaged in cement-based materials and enclosed within large drums or containers, often of steel. In France, tens of thousands of bituminized waste packages stem from the early commercial reprocessing activities that are not suitable for final disposal and thus need complex, expensive reconditioning. The IAEA recommends disposal at depths of between a few tens and a few hundreds of meters below ground in sites where natural geological barriers and engineered barriers have the potential to achieve long periods of isolation from the surface environment.

HIGH-LEVEL WASTE (HLW)

High-level waste (HLW) is the category comprising the most radioactive wastes. It contains large concentrations of both short-lived and long-lived radionuclides. It is also defined as waste that generates significant quantities of heat from radioactive decay, and will continue to do so for long periods into the future. Heat dissipation thus has to be taken into account in designing management routes. Many official and independent experts consider that deep geological disposal is necessary, in stable geological formations, and with the additional use of multiple engineered barriers to try to ensure that the chances of radioactivity returning to the biosphere are extremely low.

Essentially, HLW arises from nuclear fission (the irradiation of nuclear fuel), and is managed either as spent fuel, where this is treated directly as waste, or as the streams of actinide and fission products separated in reprocessing.