Types and origins of RAW

Radioactive waste can arise from a number of activities and facilities. It can occur in a very broad range of physical and chemical forms, and can have a similarly wide range of associated radiological properties. These factors influence the possible mechanisms of radiation exposure to persons and other species and the potential magnitude of such exposure.

One of the major sources of RAW generation is the nuclear sector, including both the commercial nuclear power industry and the military nuclear weapons manufacturing component. Whilst having completely dif­ferent objectives, the waste types generated have many similarities, arising from uranium mining and processing, enrichment, nuclear fuel manufac­ture, reactor operation, reprocessing and decommissioning. Production and use of radioactive sources for industrial, medical and other applications is another significant source of radioactive waste generation. The sources can be reactor produced, so the waste types have some similarities to the nuclear sector, or can be accelerator produced. Radioactive sources are generally of small physical size (i. e. < centimetres) but can vary significantly in terms of radiological properties — half-life, radioactive content and radiation type emitted. Radiation sources are widely used in medicine, industry and research. A number of scientific research and development activities use or generate radioactive material and can give rise to a broad and diverse range of RAW. The other area in which RAW arises is that involving naturally occurring radionuclides, generally associated with mineral extraction and processing. Numerous ore bodies and mineral deposits contain elevated levels of naturally occurring radionuclides, often linked to the phosphate industry, coal mining and oil extraction. Water treatment for domestic use can give rise to sludges with concentrations of naturally occurring radionu­clides that warrant management as radioactive waste.

As indicated, RAW can take many different forms, a factor influencing safety and hence the way in which the waste is managed. The waste material itself can be radioactive, it can contain radioactive material or it can be contaminated on its surfaces by radioactive material. A considerable amount of waste is generated in the form of solids, varying from granular mineral forms to solid rock to civil rubble to equipment, metals, plastic and paper. Also, contaminated liquids and gases are generated whose treatment can give rise to solid waste such as ion exchange resins, cemented or bitu — menised chemical sludges and filters used to clean liquid or gas streams contaminated with particulate and volatile radioactive species.

The majority of nuclear activities commence with mining and processing uranium/thorium-bearing ores, likewise such waste can arise from other mining and mineral processing activities. The radioactive species contained in these ores originate from the primordial radionuclides with radioactive half-lives of the order of thousands of millions of years. These species, iso­topes of uranium and thorium, each head decay chains of radionuclides with radioactive half-lives varying from microseconds to thousands of years. A decay product of particular interest is radon, the radioactive noble gas whose physical characteristics influence its instant mobility and related radiological hazard potential. Like any mining and mineral processing activity, the residues are waste rock, process tailings, chemical sludges and used plant equipment and buildings. Many process fluids are used, as mines often have to be de-watered and both mines and processing buildings are normally ventilated. Thus the spectrum of physical waste types generated takes the form of solids, liquids and gases. The amounts of waste generated are large; hundreds to thousands of tonnes of rock are mined to produce a single tonne of uranium. Mine sites are also generally quite large (i. e. up to tens of square kilometres) in area and due to the bulk nature of the materials handled, stored and processed, large areas of land and buildings become radioactively contaminated during operations. On the other hand, the radio­active concentration of the materials involved is not high — on the order of becquerels per kilogramme, although various adventitious concentration mechanisms can cause these concentrations to multiply thousands of times.

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