Abstract
Sources and practices involving the exposure of people to ionising radiation are normally controlled by a system of notification and authorisation as exemplified in the Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources (BSS) (1). In general, prior to the use of radioactive materials, the operator is required to notify the Regulatory Authority of his intentions and to apply for an authorisation in the form of a registration or a license. Such authorisations may include specific provisions to ensure that doses to members of the public are kept as low as reasonably achievable and below the appropriate dose limits and constraints. However, specific sources and practices may be exempted from the system of control, if, based on an analysis of the health hazards involved, the Regulatory Authority considers the inclusion of the respective sources or practices in this system to be unnecessary. Similarly, sources, including substances, materials and objects, within notified or authorized practices may be released from further requirements of the Standards if the Regulatory Authority considers that this is warranted.
In 1988 an international (IAEA, NEA/OCDE) consensus was reached on the general principles for exemption from radiological protection measures (2). Generic exemption levels for moderate quantities of material were subsequently derived (3) and published in the BSS (1), on the basis of those principles.
In 1996 the IAEA published an interim report for comment in which unconditional clearance levels were derived for solid materials contaminated with, or containing radionuclides (4). This derivation was based on the review and analysis of several assessments that had been performed by national and international organisations and that were directed towards the low activity streams of material generally considered to be the most likely candidates for clearance from the requirements of regulatory control. As a result of the larger volumes which were necessarily considered in deriving the clearance levels, the clearance levels expressed in activity concentrations were consistently and significantly lower than the exemption levels of the BSS.
In 1998 the IAEA published TECDOC-1000 that specifically addressed clearance of materials resulting from the use of radionuclides in medicine, industry and research (5). In this document, representative clearance levels were derived for atmospheric and aquatic releases. For clearance of solid materials, it was recommended to use the exemption levels from the BSS as clearance levels in the case of moderate quantities and 10% of those values in the case of large quantities. The latter values are broadly consistent with those derived in TECDOC-855.
This paper outlines the principles for and the derivation of clearance levels at the international level. It covers the developments over the past decade. Finally it discusses briefly the reevaluation of the process of defining the scope of regulations which is now taking place as a result of the recognition that the existing system, involving several different concepts and levels, is potentially and perhaps unnecessarily confusing.
