The IAEA produced the Technical Report No. 476 in 2014. The mining and milling of uranium ores produce residues which must be managed safely, including wastewater, tailings and waste rock stockpiles. A number of other industries also produce residues which contain uranium or thorium series radionuclides or both. Examples include phosphogypsum from the phosphate industry and residues from mineral sands processing and from the oil, gas and coal industries. all of these residues are naturally occurring radioactive materials (NORM), for which radiological impact assessments have increasingly
been conducted in recent years.
Radionuclides of concern found in norm mainly include isotopes of U, Th, Ra, Rn, Pb and Po [1.1]. Of these, Ra is of particular importance owing to the presence of Ra isotopes in all three natural decay series, the relatively long half-lives and short lived progeny of two of the isotopes (226Ra and 228Ra), the high mobility of Ra in the environment under a number of common environmental conditions and the tendency of Ra to accumulate in bone following uptake into the body.
Radium was first identified as an important stressor for humans and the environment mobilized by uranium mining and processing industries in the early 1950s [1.2–1.8]. Significant Ra contamination has been identified in many places, arising mainly from uranium, phosphate and even gold mining and milling operations, and from coal ash. radium isotopes are also important sources of exposure in the oil, gas and coal industry. additionally, a number of
historical industrial sites have been left contaminated with residues from activities involving Ra. such sites include factories where Ra was used in luminescent paint and Th was used in Th-coated gas mantles. residual contamination is also present at many military establishments and scrapyards [1.9].
In response to the need of its member states, the IAEA has long supported efforts to develop reports on the environmental fate of Ra. In 1990, it published
the IAEA Technical reports series no. 310 (TRS 310), which compiled information for the estimation of the impact of Ra on humans and on terrestrial,
freshwater and marine environments [1.10].
TRS 310 discussed natural and technologically enhanced sources of Ra, its properties and environmental behavior as well as methods of analysis in
environmental samples, control of releases and assessment of exposure to Ra. Although the main emphasis in the report was on environmental problems caused by uranium mining and milling, it also provided a basis for environmental impact assessments for many contamination scenarios.
It is essential that the information base used for radiological assessments and subsequent remediation planning is kept up to date and this, in itself, is a strong argument for regular revisions of reference documents such as TRS 310. Since its publication, a large number of publications on Ra transfer in the environment have been produced and merit consideration. in particular, in 2004, 2009 and 2010, the IAEA issued a set of basic reports on radionuclide transfers in terrestrial, freshwater and marine environments [1.8, 1.11–1.13]. These reports provided information on key transfer processes, concepts and models that are important in radiological assessments for all radionuclides, including Ra.
Additionally, throughout most of the period from 1991 to the present (2014), the IAEA has run a series of projects aimed at improving environmental assessment and remediation. Through these projects, the environmental behavior of Ra was considered in many other IAEA reports, mainly in the context of contaminated site characterization and environmental remediation.
The topics of these reports include:
- the characterization of contaminated sites [1.14, 1.15],
- technical and non-technical factors relevant for the selection of the preferred remediation strategy and technology [1.6, 1.16],
- an overview of applicable technologies for environmental remediation [1.17],
- options for the cleanup of contaminated groundwater [1.7], and
- planning and management issues [1.18–1.21].
In addition, a number of other IAEA publications dealing with related aspects have been compiled as part of various iaea projects. These include reports on the remediation of uranium mill tailings [1.22] and dispersed contamination [1.23], the decontamination of buildings and roads, the characterization of
decommissioned sites and management of radioactive waste and radiation protection in the oil and gas industries [1.8].
Historically, interest in Ra has focused on three aspects, namely its:
(a) impact on human health through radiation exposure,
(b) application as a tracer of environmental processes and
(c) use in various industrial, medical and other applications.
This report addresses the environmental behavior of Ra and so discusses the first two of these aspects but not industrial, medical or other applications. The primary intention of the present report is to support environmental assessments and remediation in areas contaminated by Ra by presenting state of the art concepts, models and parameters rather than providing a summary of all available information on the environmental behavior of Ra.
There are four Ra isotopes naturally present in the environment: 226Ra of the uranium decay series, 228Ra and 224Ra of the thorium decay series and 223Ra of the actinium decay series. Of these, 226Ra and 228Ra have relatively long half-lives (1600 and 5.75 years, respectively), and the majority of the published literature on Ra relates to these two isotopes. however, both 223Ra and 224Ra, which have half-lives of some days, have several applications, particularly as environmental tracers. as all Ra isotopes exhibit similar behavior in the environment, the study of one isotope may provide useful information on the behavior of the other
isotopes.
Therefore, this report discusses the environmental behavior of all four naturally occurring isotopes. The radiological impact of Ra is due to exposure to the Ra isotopes themselves and also to exposure to their decay progeny. in particular, exhalation of the 226Ra decay product 222Rn and of the 224Ra decay product 220Rn from soil, building materials and NORM can result in a significant inhalation hazard. However, this report is focused exclusively on Ra, and does not discuss in detail Ra decay products (such as 222Rn and 220Rn) which may contribute to its total environmental impact. [Note: What Not ??????????]
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