Pathways of Radioactive Substances in the Environment

JOANNA C. RENSHAW,* STEPHANIE HANDLEY-SIDHU AND DIANA R. BROOKSHAW

ABSTRACT

The release and transport of radionuclides in the environment is a subject of great public concern. The primary sources of radionuclides in the environment are nuclear weapons testing and production, and the pro­cesses associated with the nuclear fuel cycle. Whilst nuclear weapons tests have been the main source of atmospheric contamination, resulting in global, low-level contamination, sites associated with weapon production and the nuclear fuel cycle can have localised high levels of contamination, and the spread of this contamination via aquatic pathways represents a significant environmental problem. Migration in the atmosphere will depend on the nature of the radioactive material and the prevailing meteorological conditions. Within surface water and groundwater environments, transport will be controlled by physical processes such as advection and the biogeochemical conditions in the system. In systems with significant flow, advection will be the dominant transport process, but as hydraulic conductivity decreases, chemical processes and condi­tions become increasingly important in controlling radionuclide migra­tion. Factors such as solution phase chemistry (e. g. ionic strength and ligand concentrations), Eh and the nature of mineral phases in the system have a critical effect on radionuclide speciation, controlling partitioning between solution and solid phases and hence migration. Understanding

* Corresponding author

Issues in Environmental Science and Technology, 32 Nuclear Power and the Environment Edited by R. E. Hester and R. M. Harrison © Royal Society of Chemistry 2011

Published by the Royal Society of Chemistry, www. rsc. org

the complex interplay between these parameters is essential for predicting radionuclide behaviour and migration in the environment.

1 Introduction

The primary sources of radioactive contamination are the nuclear weapons and nuclear energy programmes over the past 70 years.1,2 In addition, other sources of radionuclides in the environment include the accidental release of radioactive material used in medicine and industry; the release of naturally occurring radionuclides through other industrial processes (primarily mining and mineral processing); and, more recently, the use of depleted uranium in weapons.2 In the environment, radionuclides can be transported via the atmosphere or aquatic systems, either as surface waters or through terrestrial systems in groundwater. Figure 1 summarises the main sources of radionuclides, the environmental pathways and the key processes controlling radionuclide migration. Whilst nuclear weapons tests have been the primary source of global, low-level con­tamination via the atmosphere, the other sources of radionuclides can cause localised high levels of contamination, and the spread of this contamination via aquatic pathways, and possible uptake into the food chain, represents a real environmental risk. In this chapter, the main pathways for radionuclide migration in the environment and factors controlling migration are reviewed, focusing mainly on geochemical factors controlling transport in aquatic systems.

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Diffusion

Nuclear Weapons/Dl Munitions

Groundwater

Transport

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Figure 1 Summary of main sources of radionuclides, the environmental pathways and the key processes controlling radionuclide migration.

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