Any waste that results from the use of radioactive materials for purposes that not only include electricity production by nuclear power plants, but also from various defence activities such as nuclear weapons production, from medical treatments, nuclear research, industrial processes, and mining and milling of the uranium ore.

Radioactive waste is the material that gives off radiation itself, or has become contaminated by radioactivity, and has no further use. It includes a wide variety of materials, such as: used equipment, contaminated clothing and reactor fuel components. The wastes therefore include a range of substances, from process liquids and sludges to solid objects such as contaminated overalls, maintenance equipment, and nuclear reactor components.

Radioactive wastes are classified as high level (HLW), intermediate level (ILW), low level (LLW) and very low level (VLLW) depending on their degree of radioactivity and how much heat they generate. To illustrate the contrast, the 2000 cubic metres of HLW in the UK account for 95% of the total radioactivity, and it needs to be stored in a technically complex way which disperse all the heat it generates. On the other end of the scale, some VLLW are disposed of in common landfill sites.

Radioactive substances also vary in the longevity of their radioactivity. For example, while some halve their radioactivity every few years, others remain highly radioactive for thousands of years. UK wastes have not so far been classified and organised on the basis of their longevity, so they often contain a mixture.

This range of radioactive wastes, with their different physical properties, degrees of radioactivity and longevity of radioactivity, therefore requires potentially different approaches to the containment, transport, storage and/or disposal.

The UK has produced radioactive wastes since the early 1940s. These wastes are hazardous and will continue to be hazardous for thousands of years to come. Approximately 87% of the wastes produced in the UK have come from nuclear power stations generating electricity and from the reprocessing of spent nuclear fuel. The other sources are research and development (9% of volume), the Ministry of Defence (2%) and medical and industrial uses (1%).

There are already approximately 80,000 cubic metres of solid radioactive wastes in storage awaiting a decision on how it should be managed in the long term. This figure refers to the higher level wastes. There are much larger volumes of lower level wastes.

Existing nuclear power stations will continue to produce waste until they reach the end of their working lives. At that point they are decommissioned - this means they are shut down and dismantled. As the programme of decommissioning nuclear power stations develops over the coming decades, the volumes of radioactive wastes, only from the existing power station, will increase substantially. (473,000 cubic metres by the year 2100).