A review of worldwide practices for disposal of uranium mill tailings

About the report

The world's ever increasing need for energy has led to the construction of over 400 nuclear power stations since 1950. The fuel for these plants is processed from uranium which is mined in about 18 countries. The milling of uranium ore produces a waste product, the mill tailings, which contains about 85% of the ore's original radioactivity, process reagent residues and often a wide range of heavy metals, all of which have the potential to degrade the environment. The risk to human health and the environment has only been fully appreciated in relatively recent times. Earlier disposal plans for uranium mill tailings were frequently inadequate and resulted in adverse environmental impact.

This review explains the nature of the risks to the environment and human health before describing many of the past disposal practices associated with uranium mill tailings. Current uranium mill tailings disposal practices in the major producer countries are then described, including remedial actions that have been undertaken to alleviate problems arising from earlier, inadequate and/or inappropriate disposal programs. A range of options available for tailings disposal is presented, together with a brief overview of legislation and regulations from a number of countries. Finally the report looks at how the issue might be addressed in the Alligator Rivers Region of Australia.

Summary

There are over 400 power stations in the world which rely on uranium as their fuel source. The mining and milling of the uranium fuel's raw material is a process which leaves behind substantial volumes of a radioactive waste product, the uranium mill tailings. Today there are probably more than 500 million tonnes of uranium mill tailings located in 18 countries around the world. In earlier times these process residues were often not disposed of in a thoughtful manner but abandoned at the most convenient location. Growing public awareness of the need to protect and preserve the natural environment, coupled with knowledge of the possible hazards to public health, has led to the introduction of procedures to ensure that the contamination is minimised and hazards reduced as much as possible. The prime health hazards during the operational phase and in the short term after mine close-out relate to radon emanations and the carcinogenic properties of the decay products of radon. Over the long term the concern is the release, by erosion and transport, of radionuclides and their possible subsequent ingestion by biota, including human beings. There are also health hazards related to gamma radiation, dust and possible contamination of water supplies by radionuclides and heavy metals. They are identified and discussed in this review.

Published literature relating to uranium mill tailings is limited. Examination of the available literature has shown that there are a variety of ways that this issue has been tackled in the past. Today there are three main objectives commonly considered in designing and operating containments for uranium mill tailings. Firstly, the tailings themselves must be contained in a structure that is assured of a long life, usually taken to mean at least 1000 years. Secondly, the groundwater resources of the area around the containment must be protected from contamination by the tailings or any leachates arising from the tailings; and thirdly, there must be a requirement for only minimal maintenance of the containment facility after the construction phase has been completed. In many locations the requirement is for a maintenance-free containment structure. The decision as to whether the best location for a containment is above or below grade is one which has to be site specific. There are examples of both simple and sophisticated schemes for placing tailings in old mine pits as well as some very complex above-grade structures.

The standards applied to establish the success of containment can be either very prescriptive as is the case in the United States, or site specific and risk-based which is the tendency in Australia. Some countries, eg Spain and Niger, have codes and standards which draw heavily on the experience and regulations already established in the USA and elsewhere, with a few local additions.

Within Australia there are three active uranium mines. At the Nabarlek site the tailings have been placed in the mine pit and close-out is planned for late 1995. At the Ranger uranium mine the present tailings containment is an above-grade structure built to exacting standards, as if it were a water retaining structure. The present regulations require that this structure and the enclosed tailings be returned to a mine pit at the end of operations. The mining company has indicated that they are looking into the option of rehabilitating the structure and tailings in situ, ie above-grade. The criterion for the choice of location is that the supervising authorities are satisfied that the environment will be no less well protected by this alternative scheme. The Olympic Dam mine tailings are deposited in an above ground containment which is intended to be the final repository. This containment is built as a conventional tailings dam using upstream construction methods.

This report gathers information on world-wide practice, with the objective of assessing the best solution to disposal and containment of uranium mill tailings in the Alligator Rivers Region, within the context of best practicable technology as defined and applied in the region. In particular, the criteria to be considered when assessing the in-pit disposal option are listed and discussed. No attempt is made to determine best practicable technology for the industry in general, owing to the great variety of site-specific conditions.

The conclusion is that an in-pit or below-grade disposal system may be considered as the 'prime option' in terms of long term environmental protection. This is provided that the containment site meets standards regarding groundwater contamination and geological stability.

In respect of the Alligator Rivers Region, the selection of a below-grade site and the introduction of site specific criteria rather than prescriptive standards would seem to be the most suitable option. This would enable the guidelines of the Australian Code of Practice to be met. However, the final decision will lie with the supervising authorities after the determination of what is 'best practicable technology' for these circumstances. Finally, the review lists 51 references.