Waste types, classification and composition

25.1.1 Waste classification

Radioactive wastes were originally classified into high, medium and low level, but as the nuclear industry has progressed, additional categories have been introduced and some have been sub-divided (Table 25.1) . Having well-defined classifications is important, as these frequently form the basis on which national governments base their legislation relating to the disposal routes for radioactive wastes.

Several waste categories are clearly defined by their activity levels based on either the a or p/у activity. High level waste is defined by its

Table 25.1 Waste definitions

Category

Typical characteristics

Low volume very low

Contains < 4 x 105 Bqte-1 (fily)

level waste (VLLW)

High volume very low

Contains < 4 x 106 Bqte 1 (fily)

level waste (VLLW)

Low level waste (LLW)

Contains < 4 x 109 Bqte 1 (a);

Intermediate level

< 12 x 109< 12 x 109 Bqte-1 (filfi Contains > 4 x 109 Bqte-1 (a) or > 12 x 109 Bqte-1 (filf)

waste (ILW)

but for which its heat output need not be taken

High level waste

into account in the design of waste storage or disposal facilities

Radioactive waste in which the temperature may

(HLW)

rise significantly as a result of its radioactive

Transuranic waste

content, so that this factor has to be taken into account in the design of waste storage or disposal facilities

>100 nCig-1 (a) from transuranic elements with

(TRU)

half-lives >20 years.

Source: UK Committee on Radioactive Waste Management (2011).

heat-generating ability and the IAEA have recently revised their definition by removing the 2 kWm-3 threshold (IAEA, 2009).

In the UK, low volume VLLW can be disposed of safely to unspecified destinations with municipal, commercial or industrial waste, whereas high volume VLLW can only be disposed of to a specified landfill site. For wastes containing solely tritium or carbon-14, the limits are increased by an order of magnitude.

Wastes arising from nuclear weapons programmes can fall into all of the above categories, but the three of specific interest are HLW, TRU and ILW. In the early days, many of the candidates investigated for the immobiliza­tion of commercial wastes were considered, but currently ILW is generally compacted and cemented into steel drums, whilst HLW and some ILWs are vitrified in borosilicate glass; however, some of the newer wastes may require alternative immobilization techniques to be developed. Disposal routes already exist for LLW, which for the UK is in a special site at Drigg in Cumbria.

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