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

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.