1A practice is any human activity that introduces additional sources of exposure or exposure pathways or extends exposure to additional people or modifies the network of exposure pathways from existing sources, so as to increase the exposure or the likelihood of exposure of people or the number of people exposed.

2An intervention is any action intended to reduce or avert exposure or the likelihood of exposure to sources which are not part of a controlled practice or which are out of control as a consequence of an accident.

3The term ‘radionuclides of natural origin’ means radionuclides that occur naturally in significant quantities on earth. The term is usually used to refer to the primordial radionuclides potassium-40, uranium-235, uranium-238 and thorium-232 (the decay product of primordial uranium-236) and their radioactive decay products, but could also include tritium and carbon-14, low concentrations of which are generated by natural activation processes.

4The term moderate quantities means quantities that “are at most of the order of a tonne” of material [5]. Anything greater than this amount is considered bulk quantities.

5‘Exclusion’ means the deliberate exclusion of a particular category of exposure from the scope of an instrument of regulatory control on the grounds that it is not considered amenable to control through the regulatory instrument in question. Such exposure is termed excluded exposure. ‘Exemption’ means the determination by a regulatory body that a source or practice need not be subject to some or all aspects of regulatory control on the basis that the exposure (including potential exposure) due to the source or practice is too small to warrant the application of those aspects. ‘Clearance’ means the removal of radioactive materials or radioactive objects within authorized practices from any further regulatory control by the regulatory body. Removal from control in this context refers to control applied for radiation protection purposes.

6It should be noted that the relationships used in this section between exclusion and radionuclides of natural origin, and between exemption and radionuclides of artificial origin, are made for the purpose of deriving radionuclide concentration levels. For instance, exposures from some radionuclides of artificial origin, such as fallout from the testing of nuclear weapons, may be excluded by the regulatory body. Similarly, some material contaminated by radionuclides of natural origin, if used within a practice, may be a candidate for exemption or clearance, as appropriate.

7It should be noted that the justification principle applies to a practice as a whole and not separately to its component parts, such as the disposal of waste. This means that material that is contaminated as a consequence of a practice is disposed of as a matter of optimization of protection, rather than justification. One of the purposes for which the activity concentration values have been established is to permit material in bulk quantities to be ‘exempted’ or ‘cleared’ from a justified practice without further consideration.

8Trade necessarily involves the transport of material. However, requirements on activity concentrations as limits for material in transport are established in the IAEA Transport Regulations [8] and not in this Safety Guide.