Although the sources of radiation in the various parts of the nuclear fuel cycle can be very different, the essential features of radiation protection are the same. Workers must be adequately protected from radiation in the workplace and the public and the environment must be protected from any radioactive materials that are transported or released from the nuclear facilities. All practicable measures must be taken to prevent accidents and to mitigate any consequences should an accident occur. In this section the essential features of radiation protection in uranium mining and milling facilities, at nuclear power plants in operation and during decommissioning and at radioactive waste repositories are discussed.

2.1.5 Uranium mining and milling

The hazards to workers in uranium mines are due mainly to the presence of radon gas (Rn-222) and its short lived progeny (Po-218, Pb-214, Bi-214 and Po-214). Radon gas is inert but its daughter nuclides become attached to particles in the air and can deposit in the lungs of miners. The airborne radioactivity in mine dust also contains radionuclides from the U-238 and U-235 families (U-238, U-234, Th-230, Ra-226 and Po-210) and these too present a risk when inhaled. External radiation hazards in uranium mines are due to beta and gamma radiation emitted from the ore bodies. Both of these hazards can also exist in non-uranium mines; e. g., gold mines and some coal mines where uranium is present. External radiation does not normally constitute the major hazard but can be significant where the ore grade is relatively high. In the milling process, radon and its daughters usually present only a minor inhalation hazard compared to ore and uranium dusts, although significant radon concentrations may occur in certain parts of the plant. The exposure of workers in uranium mills to external beta and gamma radiation is generally comparable to that of workers in uranium mines but it may be significantly higher in some locations. The external radiation levels vary from mill to mill depending on the grade of ore, type and grade of concentration, and type of process, but generally, external radiation hazards assume significance in the final stages of precipitation, filtration, concentrate packing and storage.

Preventing and controlling the intake by inhalation of radionuclides is a key feature of radiation protection in uranium mines. This is usually achieved by ensuring adequate ventilation and dust suppression in the workplace. For this purpose, the position of Ventilation Officer is often established in mines. Ideally he/she should work together with the Radiation Protection Officer to provide for optimized radiation protection. Appropriate personnel and workplace monitoring arrangements should be in place to enable checks to be made on the ongoing radiological situation and to ensure that local dose limits are not exceeded. A particular feature of verifying that dose limits are complied with in the case of the monitoring of radon progeny is the need to convert from the measured quantity, the potential alpha energy in the air, to committed effective dose. Detailed guidance on this and other aspects of occupational radiation protection in uranium mines is given in reference (IAEA, 2004a). Other types of hazard exist in uranium mining and milling, including those associated with the chemical toxicity of uranium and its compounds, and these must also be appropriately managed.

I n the course of the twentieth century, the methods by which uranium was obtained changed — with increasing amounts being obtained by non-underground mining methods. In situ leach (ISL) mining has been steadily increasing its share of the total. In 2009, production was as follows: conventional underground and open pit 57%, in situ leach 36%, by-product 7%. The alternative methods do not present the same occupational hazards as underground mining but can create a greater environmental impact. Although active uranium mines exist in 20 countries, about 60 % of the world’s production of uranium from mines is currently from Kazakhstan, Canada and Australia (WNA, 2011).

The radioactive waste generated in mining and milling activities differs from that generated at nuclear power plants and most other industrial operations in that it contains only low concentrations of radioactive material but is generated in much greater volumes. The management methods to be employed are therefore different and usually involve waste disposition on or near the surface, in the vicinity of the mine and/or mill sites. Furthermore, the waste contains long-lived radionuclides (i. e., radionuclides with a half-life of more than about 30 years) and this has important implications for its management because of the long time periods for which control is necessary. Radioactive waste arises from all stages of mining and milling processes and includes, in addition to mill tailings, waste rock, mineralized waste rock and process water, including leaching solutions. The hazards to humans and to the environment posed by mining and milling waste arise not only from its radioactivity but also from the presence of toxic chemicals and other materials in the waste.

A conventional mill uses uranium ore extracted by either open pit or deep mining. The ore is then crushed and sent through the mill, where extraction processes concentrate the uranium into uranium-oxygen compounds called yellowcake. The remainder of the crushed rock, in a fluid slurry, is placed in a tailings dam. Due to the long half-lives of the radioactive constituents involved, the safety of the deposit has to be guaranteed for very long periods of time. Over such long timescales, tailings piles can be subject to erosion by various processes. Rainfall, floods and animals burrowing can lead to the dispersion of material. Wind action can remove and disperse material from the surface of piles as they dry out. Seepage from tailings can transfer material into ground and surface water.

Legislation to improve the condition of tailings piles was slow to develop and in most of the affected countries it is only in the last 20 years that the situation has changed. Typical regulations define maximum contaminant concentrations for soils and admissible contaminant releases (in particular for radon). The period of time during which the measures taken must be effective is also defined (typically 200-1000 years). A further requirement is that the measures taken must assure safe disposal for the prescribed period of time without active maintenance. International guidance on the safe management of uranium mine and mill tailings can be found in reference (IAEA, 2002).

Uranium was mined and processed in many countries of the world for military purposes in the Cold War period and the residues remain — often in an untreated or partially remediated form. A number of international projects aimed at improving this situation are currently under way (NATO, 2009; IAEA, 2012b).