4.8 Radioactive minerals

Globally, uranium mining is expanding to help meet the increasing demand for supplies of raw material for use in electricity generation. Australia has the largest proportion of the world’s identified uranium resources, including the largest known single deposit, which is at Olympic Dam in South Australia. Specific radiation-related issues are associated with uranium mining and with some other mining operations that deal with naturally occurring radioactive material (NORM), such as mineral sands, phosphates, rare earths, oil and gas (see, for example, IAEA 2002, 2003abc, 2013; ARPANSA 2005, 2008). The increased exploitation of these minerals, many of which are associated with emerging technologies, has led to a greater awareness of the need to assess and monitor radiological risks in their mining and processing and in mine site remediation.

Although most current world production of uranium uses the in-situ leach method, in the medium term it is likely that most Australian production will be by underground mining. For open-pit mines and associated WRDs, environmental monitoring must cover surface water, groundwater and the air to ensure that there is no unacceptable risk to mine personnel and the general public and that the movement of radioactive contamination away from the mine is minimised. For underground mines, environmental monitoring of the groundwater in and adjacent to the mining area is obviously of extreme importance, especially to be able to ensure that the movement of radioactive contamination away from the mine is minimised. For the same reasons, environmental monitoring of TSFs in both open-pit and underground operations must cover surface water, groundwater and the air.

In-situ leaching of uranium ore bodies minimises surface disturbance and contamination. A leaching solution is injected into a confined aquifer located in a permeable uranium-bearing rock formation and pumped through the rock to dissolve uranium before the uranium-enriched solution is returned to the surface and treated to recover the uranium. There are no pits, WRDs or TSFs associated with in situ leaching. However, environmental monitoring of the groundwater in and adjacent to the mining area is extremely important, especially to be able to ensure that there are no excursions of the solution away from the mining area.

Whichever production method is used, uranium mining is similar to mining other metals. The most significant risks and issues associated with potential environmental impacts from uranium mines are rarely associated with radioactivity. All environmental protection rules and monitoring procedures required for heavy metal mines need to be applied, as well as those specifically related to the radiological aspects of the operation. The community generally maintains an extremely close watch on uranium mining operations, so monitoring programs are be expected to be nothing less than leading practice.

In these circumstances, monitoring at a uranium mine needs to pay special attention to radiochemical and radiological parameters in addition to the standard suite of physiochemical monitoring parameters that are collected for metal mines. Such radiochemical and radiological monitoring is recommended by international and Australian guidelines and codes of practice, irrespective of the fact that the most significant risks and issues associated with low-grade uranium mines in Australia are rarely associated with radiological exposure (in contrast to the situation in very high grade underground uranium mines in Canada).

Radiation protection issues are primarily related to the work health and safety of people who may be exposed to radiation in the mine and processing areas for long periods. Their exposure is monitored through radiation management plans that are required by regulatory authorities and refer to international safety standards and limits that are incorporated into Australian law. Environmental radiation monitoring is usually done at the boundaries of working areas to ensure that fugitive dust and atmospheric emissions, if present, are below the internationally agreed limits and are kept ‘as low as reasonably achievable’. The elements of such monitoring programs are listed in Appendix 2.

From an environmental monitoring perspective, some social and environmental issues specific to uranium mines need to be considered. For example, food-chain issues may be of concern if the post-mining landform or adjacent areas are used as a source of food supplies. Indigenous people, in particular, may traditionally rely on bush foods sourced from the local environment as part of their diet. In situations where mine remediation and traditional indigenous culture intersect, potential doses via the bush food ingestion pathway should be considered and assessed, taking into account the type and amount of bush foods typically consumed. Environmental monitoring to facilitate this dose assessment should include sampling and radionuclide analysis of the foods to establish transfer factors. Baseline studies are essential for understanding the naturally occurring pre-mining radiological levels, as they will be the basis for developing acceptable radiological closure criteria as specified by Australian and international guidelines.

Cover design, the selective placement of a topmost layer of material with low radioactivity levels, or both, are methods used to address food-chain and other public exposure issues during the operational and post-remediation phases, but their effectiveness requires assessment to ensure the radiation doses are within prescribed limits and as low as reasonably achievable. Post-remediation monitoring should be aimed at understanding aspects such as these and facilitating the management of risks to the general public, other land users, and flora and fauna.

Australian (ARPANSA 2014) and international (ICRP 2007) recommendations for radiological protection now specifically recognise the environmental exposure of wildlife (flora and fauna) to ionising radiation as a distinct exposure category to which assessment and protection considerations apply. Environmental exposures of wildlife should be assessed using a reference organism approach to estimate above-baseline absorbed dose rates to organisms from mine-related radionuclides in environmental media (typically soil or water) and from radionuclides accumulated in the organisms themselves. The estimated dose rates should then be compared with a protective screening level to determine the potential radiological risk to wildlife. Relevant radioecological data is necessary to assess environmental exposures, including data on the bioaccumulation of radionuclides by wildlife. A recent ARPANSA technical report (Hirth 2014) provides some general reference values on bioaccumulation factors for Australian organisms inhabiting uranium mining environments.

Current International Commission on Radiological Protection recommendations that have been adopted in Australia specify that total exposure of the general public to radiation throughout the operation of a uranium mine, as well as from a remediated uranium mine site, should be no more than 1 millisievert per year above pre-mining levels and should ideally be constrained to a lower value (‘dose constraint’) by applying the principle of optimisation of protection. To be able to demonstrate that this target has been achieved by the remediation practices that have been implemented, it is essential to conduct a robust assessment of the pre-mining radiological levels. A case study from the Wismut uranium mine remediation program in former East Germany illustrates how remediation works targeted radiation protection standards and how monitoring programs were applied to demonstrate the achievement of these goals.

Collapsed - Case study: Integrated monitoring program for a former uranium mining region in Germany

Wismut GmbH operates one of the largest environmental monitoring networks in Europe, taking roughly 30,000 samples per year and making 300,000 database entries (95% water samples). Water monitoring covers more than 1,400 investigation points for the observation of groundwater, surface water, seepage and processing water at seven former uranium mining and milling sites.

The monitoring program is the backbone for performance evaluation for multiple former uranium mine and mill sites.

Brief history

Successful prospecting for uranium immediately after World War II prompted the Soviet occupation forces to establish the Soviet company SAG Wismut in what was then the German Democratic Republic in 1947. The company, which was initially run by the Soviet military, had the sole aim of exploiting German uranium deposits for the Soviet nuclear program. In 1953, Wismut became a jointly owned Soviet–German company. By 1990, Wismut had produced 231,000 tons of uranium, making it the world’s fourth largest producer.

The environment around Wismut was adversely affected by more than 40 years of unrestrained mining and processing of uranium ores. The mining legacy included 1,400 km of underground adits and shafts, 311 million cubic metres of waste rock and 160 million cubic metres of radioactive tailings in densely populated areas.

Wismut mineWismut mine

Following German reunification in 1990, WISMUT, GmbH (limited liability company) referred to here as ‘WISMUT’ became a federal government-owned company, (www.wismut.de). Its principal business is the decommissioning, clean-up, and rehabilitation of uranium mining and processing sites, specifically:

  • mine decommissioning and flooding
  • disassembly and demolition of contaminated buildings and structures
  • remediation of mine dumps and tailings ponds (shaping and covering)
  • treatment of ascending flooding water, collected seepage and pore water.

Wismut has been mandated to ameliorate the environmental situation by eliminating or at least reducing adverse impacts to an acceptable level.

Performance evaluation

The objectives of the Wismut monitoring program are to:

  • acquire data to plan and design remedial actions
  • ensure compliance with legal and regulatory standards
  • provide feedback on rehabilitation
  • document remediation performance
  • provide evidence of the efficiency of the remedial activities.

The Wismut monitoring program includes both environmental and operational monitoring. Parameters monitored include concentrations of radionuclides (such as U-238, Ra-226, Rn-222) as well as of non-radiological parameters (salinity, trace elements and so on). The program also gathers data on hydrological and meteorological parameters.

Wismut makes a distinction between background monitoring and rehabilitation monitoring (see Figure 2). Background monitoring involves long-term atmospheric and water pathways monitoring using a network of fixed monitoring locations and measurements that occur independently of remedial actions. Rehabilitation monitoring assesses the performance of the rehabilitation project. After the end of physical rehabilitation, a long-term monitoring program provides evidence on the performance of the remediation process. Final land uses include sheep grazing, greening, solar parks and golf courses. The monitoring conducted depends on the land use and the particular site (such as covered stockpiles and tailings and open pits). Parameters measured include plant growth and cover, soil characteristics and hydrological properties.

Figure 2: Structure of the Wismut monitoring program

Structure of the Wismut monitoring program

Note: Includes requirements of the German Government to control, summarise and report all natural radioactivity outflow and effects on the environment. The term ‘immission’ refers to the receiving point where emissions are monitored.

Integration of monitoring and spatial data

The huge amount of data collected requires efficient data management and stringent quality assurance. Quality-assured data is stored in a central environmental database. The environmental database is linked to a geographical information system (GIS) that allows the interpretation, presentation and goal-oriented analysis of environmental data.

How monitoring data is used to evaluate the success of rehabilitation: an example

  • Many waste rock dumps cause elevated concentrations of radon in the air near residential areas around the Schlema-Alberoda site. Figure 3 shows dump #366 after intensive reshaping and the construction of a 1-metre thick radon barrier over the reshaped landform. Figure 4 shows how remediation has resulted in significantly diminished radon concentrations in ambient air. Taking a background level for radon (Rn) of 20 Bq/m³ into account, the measured concentrations of 70 Bq/m³ (that is, 50 Bq/m³ from the dump) correspond to an effective dose of 1 mSv/a for local people. This dose value serves as a criterion for the remediation success.

Figure 3: Dump #366 at Schlema site after remediation with measuring

Dump #366 at Schlema site after remediation with measuringDump #366 at Schlema site after remediation with measuring

Figure 4: Time series of radon concentration measured (at the red star) and the limit of additional dose

Time series of radon concentration measured and the limit of additional dose

Conclusion

Managing such a vast regional mine closure monitoring program requires clear monitoring program objectives for both background and rehabilitation monitoring measuring a range of parameters from remote data sources. Such a program would not be possible without the leadership and continuity provided by a well-qualified and experienced monitoring team ensuring quality assurance of all elements; data gathering, storage, interpretation and reporting of data over very long time frames. This project provides leading practice principles which can be applied to complex monitoring programs.

Legacy mine programs may require the development of site-specific limits to be derived as part of the remediation activity, in accordance with accepted international leading practice for what is described as an ‘existing exposure situation’, as opposed to a planned exposure situation (IAEA 2011). An existing exposure situation is one that already exists when a decision on the need for control needs to be taken. Such situations include exposure to natural background radiation that is amenable to control, exposure due to residual radioactive material that arose from past practices that were never subject to regulatory control, and exposure due to residual radioactive material arising from a nuclear or radiation emergency after the emergency has ended.

Similar concerns to those expressed about uranium mining are often expressed about other operations dealing with NORM, such as mineral sands or phosphate processing facilities. Again, the main concerns for public and biota protection usually relate to chemistry rather than radioactivity. Where applicable, workers in NORM-producing industries are monitored by a radiation management plan operated in accordance with regulatory requirements.

Comprehensive discussion of the above issues is in reference documents produced by the IAEA and the ARPANSA (see the ‘Further reading’ section of this handbook). A best practice guide for in-situ leach mining of uranium in Australia has been produced by Geoscience Australia (2010).

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