The primary aims of occupational and medical exposure control are to ensure that ‘this person’ (worker or patient) is adequately protected from any adverse effects of radiation exposure in ‘this place’ (i.e. a mine site, research laboratory, or radiotherapy clinic) over a defined time period (a lifetime). Public and environmental exposure control serves exactly the same end-goal, but on the grand scales of volume, time and space: it addresses the need to ensure that all people and all living organisms are protected, not just ‘here’ but everywhere, both ‘now’ and for millions of years to come.
Considering that ionizing radiation is a naturally occurring substance, and the impossibility of truly ‘controlling’ any aspect of a given environment, the challenge is huge. Thus, the focus must be on managing radiation sources so as to avoid – to the greatest extent possible – any hazard.
In fact, the far greatest contribution (85%) of radiation to the public comes from natural background radiation – and almost half of it comes from radon decay product in dwellings. This situation is the only natural exposure for which IAEA recommends Action Levels, above which householders are advised to reduce radon levels in their home. In contrast, release of radiation from human activities represents a very small fraction – less than 1% – of the global average level of exposure.
Understanding the potential sources of public and environmental radiation exposure from human activity helps to clarify the associated risks. At the highest level, sources can be divided into two categories. Radioactive effluents refer to the ‘run-off’ of ionized particles (in gas or liquid form) discharged into the atmosphere or into water. Radioactive waste represents the totality of all disused materials and equipment that contain some element of radioactive substances. In both cases, the risk factors relate directly to the substance’s characteristics: its activity concentration, its condition and its location (i.e., its proximity to population centers, drinking water and farming areas). A second consideration for safety is the cumulative effect of radiation exposure.
In the early days of nuclear science, these factors were less well understood. Between 1945 and 1980, atmospheric nuclear testing (including nuclear weapons) resulted in the largest unrestrained releases of radionuclides. It was believed that conducting these tests in remote areas was sufficient safeguard. Sixty years hence, residual levels of longer-lived radionuclides can still be found in the environment and continue to be a global source of human radiation exposure, although they contribute little to the annual exposure of the world population. In the interim, radiation science has come to recognize the vital need for a large-scale, long-term safety mentality and for source-specific safety measures.
Radioactive effluents are most commonly associated with nuclear power plants and other nuclear installations that release radioactive materials through stacks, discharging vents or drain pipes. Other sectors such as industry, agriculture and research contribute to effluents on a lesser degree. In all cases before receiving licenses for radiation-based technologies, operators must demonstrate their ability to control releases in keeping with strict international standards that are far below the level at which the most minor effects would be evident in the public or the environment. To put it succinctly, except in the case of accidents, regulations ensure that the total release of all isotopes produced by all of industry should cause only negligible levels of exposure.
All countries produce radioactive waste through civil or defense nuclear programmes or/and medicine, industry and research. These wastes must be properly managed, which implies rigorous procedures for processing, storage and final disposal to insure their isolation from the biosphere for the time needed for their radioactivity to decay to negligible levels.
Regardless of the source, effective control of public and environmental exposure harkens back to the establishment of a legislative framework and regulatory infrastructure, which clearly defines policies for clearance from regulatory control, discharge control, and waste management. The IAEA assists Member States in developing national strategies that reflect the nature and magnitude of waste in the country, as well as existing waste management options. Somewhat paradoxically, it is often the countries generating the least waste that have the weakest control, simply because they are not yet able to devote adequate resources to waste management issues.
When a site is identified that could pose a threat to the public and/or the environment, the IAEA safety standards provide guidance on how to deal with the situation. The first step involves a preliminary assessment including a basic survey, radiation monitoring and a dose assessment. This information is used to determine whether the site should be subject to regulatory control and what remedial or protective measures should be taken. Depending on the risk assessed, the appropriate response may be no action at all or measures as simple as preventing access to the site by erecting fences or posting warning signs. Higher-risk cases, which might necessitate more disruptive actions such as preventing access to agriculture or drinking water and initiating further remediation actions, warrant a more in-depth review that fully accounts for the magnitude of the risks and how local populations will be impacted by proposed actions.
Regular monitoring – both at the source of the discharge and in the receiving environment – is an essential element of public and environmental exposure control. It is generally applied to check the release of radionuclides from specific sources such as nuclear reactors, research or industrial facilities, waste storage and disposal, uranium mines and mill tailings, and land affected by radioactive residues. Monitoring provides the data needed to carry out a technical assessment and implement an appropriate response, again based on the level of potential radiation risk. If there is no known source of radiation within a given country but an identified risk from a neighboring country, then some assessment may be possible to determine if monitoring is technically justified.
The IAEA plays a key role in one final area of public exposure control. Humans acquire approximately 10% of their radiation exposure from ingesting food and water. International standards for trade and consumption in these sectors fall under the mandate of the Food and Agriculture Organization (FAO) and the World Health Organization (WHO), respectively. The IAEA acts as an advisor to both organizations and also assists its own Member States in monitoring the radiological quality of food and water resources.