Waste classification

Radioactive wastes in the UK are categorised into low level waste (LLW), intermediate level waste (ILW) and high level waste (HLW) (Defra et al., 2007). In addition, some materials and wastes are defined as out of scope or exempt from the requirements of EPR10 (as amended) in England and Wales (Defra et al. , 2011) even though they contain some radioisotopes. Effectively, ‘out of scope’ equates to ‘not radioactive’ for the purposes of the legislation. Radioactive substances that are ‘out of scope’ are not subject to any regulatory requirement under this legislation. Other substances, which are considered to be radioactive by definition, may be exempt from the need for a permit if the level of radioactivity is below the level specified in the exemption order; however, specified conditions must be met. The levels of radioactivity that are defined as ‘out of scope’ are taken from EC guidance and are expressed as radionuclide specific activity concentrations.

For naturally occurring radioactive substances or articles used in ‘indus­trial activities’, the numerical values are based on a radiation dose of 300 pSv/year to a member of the public. For artificial radionuclides, and for naturally occurring radioactive substances or articles used for their radioac­tive, fissile or fertile properties (a ‘practice’), the values are based on a radiation dose of 10 pSv/year to a member of the public (IAEA, 1988). In effect, this recognises that naturally occurring radioactive materials (NORM) are universal and that it is not practicable to regulate such that the radiation dose criterion of 10 pSv/year to a member of the public is met (IAEA, 2004). Other media and radionuclide specific activity concentra­tions or total site activity holdings have been established for the exemption order, using the same radiological criteria.

In the case of exemption for disposal, the radiological impact assessments do not assume uncontrolled disposal of waste to the environment. The exemption levels therefore apply to specific types of substance or article (e. g., a waste sealed source), to the disposal route (e. g., to a sewer, or to a landfill), or to the management of waste (e. g., disposed of with considerable quantities of non-radioactive waste), etc. Out of scope and exempt wastes are not considered further here.

Of the radioactive wastes for which a permit is required, LLW is volu — metrically the largest component of the UK’s radioactive inventory and is classified as waste not exceeding four GBq per tonne of alpha or 12 GBq per tonne of beta/gamma activity (Defra et al., 2007). (The definition of LLW was originally set out in the Government White Paper, Command 2919 (1995) but was superseded by Defra et al., 2007.) Figure 16.3 provides

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Total volume 4.7 million m3 16.3 Relative volumes of LLW, ILW and HLW.

a breakdown of current and projected RAW arisings in the UK over the next century or so, by waste category. The UK now recognises high and low volume very low level waste (VLLW) as sub-categories of LLW (Defra et al, 2007). This offers more flexible, sustainable approaches to long-term management of wastes as alternatives to disposal to the LLW repository (LLWR) at Drigg, Cumbria.

Low volume VLLW is defined by Defra et al. (2007) as radioactive waste containing no more than 400 kBq of beta/gamma activity for each 0.1 m3 and is mostly comprised of small volumes from hospitals and universities. For carbon-14 and tritium-containing wastes, the activity limit is 4,000 kBq for each 0.1 m3 in total. High volume VLLW is defined by Defra et al. (2007) as radioactive waste with an upper limit of 4 MBq per tonne (not including tritium) that can be disposed to specified landfill sites. For tritium contain­ing wastes, the upper limit is 40 MBq per tonne.

ILW is classified on the basis of radioactivity exceeding the upper bound­aries for LLW and which does not require heating to be taken into account during storage or disposal. ILW may be sub-categorised as shorter-lived ILW or less radiotoxic ILW. These are not formally defined terms but have been used in a regulatory context to identify wastes that may be suitable for specific waste management options (e. g., Environment Agency et al., 2009; Environment Agency and Northern Ireland Environment Agency, 2009).

HLW is waste in which the temperature may rise as a result of radioactive decay and HLW may be referred to as ‘heat-generating radioactive waste’ (e. g., Defra et al;, 2008; Command 2919, 1995), although this does not dis­tinguish between types of HLW. HLW in the UK typically arises as a liquid by-product of spent fuel reprocessing. Historical stocks of liquid HLW, together with current arisings, are being conditioned through the Sellafield waste vitrification plant to form a solid material, making it passively safe and suitable for disposal. It is anticipated that by 2015, the UK’s HLW will have been converted to vitrified product and will be stored for 50 years to allow further time for radioactive decay.

The term higher activity waste (HAW) has no formal definition and should not be confused with HLW. In Scotland, HAW is used to describe wastes which would otherwise be classified as ILW but which do not gener­ate enough heat for this to need to be taken into account in the design of treatment, storage or disposal facilities (e. g., Scottish Government, 2011) but may also be taken to include LLW which, for one reason or another, is considered unsuitable for disposal as LLW (e. g., Defra and NDA, 2008). The definition of HAW in Scotland is a reflection of the fact that Scotland does not currently possess HLW. The definition of HAW in England and Wales is generally considered to encompass both ILW and HLW in addition to some LLW not suitable for disposal in the LLW repository. Other radioactive materials may be considered for disposal but are not currently classified as waste. These include spent nuclear fuel and the plutonium and uranium obtained from reprocessing spent fuel (Defra et al., 2008).

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