RC-5A Radiation Protection in NORM Industries
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RC-5a Radiation Protection in NORM industries J. van der Steen and A.W. van Weers NRG, Radiation & Environment, Arnhem, The Netherlands Radiation Protection in NORM industries J. van der Steen and A.W. van Weers NRG, Radiation & Environment, P.O Box 9035, 6800 ET Arnhem, The Netherlands E-mail: [email protected] 1. Introduction The International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources (the BSS) [1] specify the basic requirements for protection of health against exposure to ionising radiation. They are based on the latest recommendations of the International Commission on Radiological Protection (ICRP) [2] and regulate both 'practices'1 and 'interventions'2. Humans incur radiation doses from cosmic rays and radiation generated by x-ray machines and particle accelerators, or from exposure to radionuclides, either by external irradiation or by incorporation in the body. Some radionuclides are primordial, and they are usually referred to as 'natural'. Others have been created as a result of practices and are usually referred to as 'artificial'. The BSS apply to both natural and artificial sources of radiation. This refresher course deals only with radiation protection against natural sources of radiation. Natural radionuclides are ubiquitous in the environment. As a result of the widespread presence, a certain amount of radioactivity is always present in substances. A comprehensive review of the concentrations of naturally occurring radionuclides in soil has been published by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in its 2000 Report [3]. In most naturally occurring radioactive materials (NORM), several or all of the radioactive isotopes of the three natural decay series (235U, 238U and 232Th) and 40K are present in small concentrations in the natural matrix. In the original ores, or formations in the case of the oil and gas industry, the radionuclides within a decay series are more or less in radiological equilibrium. By industrial physical, chemical and thermal processes the natural equilibrium of the radionuclides can be disturbed resulting in either an enrichment3 or decrement of some radionuclides compared to the original matrix. Breaks in the natural equilibrium occur at the isotopes with long half-lives. In table 1 these radionuclides are given together with their half-lives. Table 1. Long-lived natural radionuclides (T½ > 1 y), with their half-life (y) 238U series 235U series 232Th series 238U 4.5 109 235U 7.0 108 232Th 1.4 1010 234U 2.4 105 131Pa 3.3 104 228Ra 5.8 230Th 8 104 227Ac 21.8 228Th 1.9 226Ra 1600 210Pb 22.3 1 A practice is defined as 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. 2 An intervention is defined as 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. 3 This is usually referred to as technologically enhanced naturally occurring radioactive materials (TENORM). 1 The presence of NORM can lead to radiation doses that are not insignificant from a radiation protection point of view. Occupational exposure from natural radiation is, in the UNSCEAR 2000 Report [3], estimated to contribute more than 80 percent of the world-wide annual collective dose from occupational exposure, uranium mining excluded. Also individual doses of workers exposed to NORM in industry can be significant. When the operator of a practice, or the regulatory authority, is not aware of the problems associated with enhanced levels of NORM in raw materials, products or residues and when no protective actions are taken, the doses to workers may even exceed the occupational dose limit. The relevant routes of exposure of workers to NORM are external radiation and internal exposure, either by inhalation of radon in workplaces or by inhalation of aerosols in dusty working conditions. Until the 1970s radon and its progeny were regarded as radiation health hazards encountered only in the mining and processing of uranium ore. This notion has changed markedly as a result of increasing efforts made in many studies to measure radon in dwellings, mines other than uranium mines, and workplaces suspected of having high atmospheric radon levels. In temperate and cold regions, energy conservation measures have been taken in buildings that have resulted in reduced ventilation rates. This increased radon concentrations, particularly in winter months. This rise in the indoor air concentration of radon was recognized as a radiation health hazard, potentially causing an increase in the incidence of lung cancer. Radon thus became a concern not only in underground mines but also in buildings in areas with elevated levels of radon in soil gas or in buildings constructed with materials containing significant levels of radium. According to the UNSCEAR 2000 Report [3], environmental radon accounts for half the human exposure to radiation from natural sources. It is not only radon that gives rise to environmental problems with natural radionuclides. Mining results in large volumes of mine tailings that may contain enhanced levels of natural radionuclides. This is not only restricted to uranium or thorium mining, but can also occur with other mines, such as copper mines, gold mines, et cetera. Leaching of the radionuclides can result in contaminated groundwater, and thereby expose members of the public. In many cases, these mines have been operating for many decades without any knowledge of the radiological aspects of the mining activity. Mine tailings even exist for centuries, from mining activities in the past, giving rise to radiological legacies that have been detected only in recent times. Other examples are coal mining, when a high concentration of 226Ra in the produced water can give rise to considerable radioactive contamination of the environment. In such cases, ponds can be heavily contaminated with radioactive deposits. Also the production of fertilizers by processing phosphate ore has resulted in large landfills with phosphogypsum, which contains elevated concentrations of 226Ra. An overview of the worldwide scale of potential environmental problems with NORM has been given in IAEA Technical Report Series No. 419 [4]. Within the European Union, Council Directive 96/29/Euratom [5] paid specific attention to natural sources of radiation. EU Member States are obliged to identify the work activities that cannot be ignored from a radiological protection point of view and declare parts of the Directive applicable in their national regulations with respect to natural sources. This has increased the awareness of the potential problems enormously, and most of the EU Member States have now implemented regulations dedicated to natural sources of radiation in their national legislation. Also the BSS [1] addresses the control of exposure to natural sources. In the last decade a number of international meetings were dedicated to the radiological consequences of NORM, leading to a world-wide cognition of the issues involved. The IAEA has provided comprehensive recommendations on occupational radiation protection in general in three Safety Guides [6-8]. Occupational and public exposure to NORM is addressed in several IAEA reports, which have been published recently or are in preparation [9-17]. Nevertheless, there still is a backlog in the knowledge of the radiation protection problems with NORM, compared to artificial radionuclides. In many countries, NORM industries traditionally have not been subject to radiological protection measures. Many data on radionuclide concentrations in raw materials, residues and waste streams, and data on exposure of workers and the public are still lacking. 2 Consequently, there is a general lack of awareness and knowledge of radiological hazards and exposure levels by legislators, regulators and operators (particularly operators of small businesses). This persists in many cases, despite the number of studies and international meetings dedicated to the radiological consequences of NORM in the last 10 to 15 years. The IAEA Technical Report 419 [4] is based mainly on a comprehensive study for Europe [18] and data from North America, but it concludes that data from less developed countries are still scarce. According to this Report, the circumstances in these countries are of particular concern, namely: - A large proportion of the world mining operations and to a lesser degree also milling operations are located in less developed countries; - Environmental and radiation protection standards may be less stringent, or their enforcement may be less strict; - Artisanal mining and milling and other artisanal industries with less stringent occupational health and safety precautions are widespread. As opposed to developed countries, such activities are still more integrated with private and family life, potentially leading to exposure of the public (e.g. residential/garden plots on or adjacent to 'industrial' sites and re-use of contaminated materials to optimise resource use); - Limited or no resources are available to deal with legacy wastes and for upgrading plants and waste management infrastructure; - Responsibilities for legacy wastes