ARPANSA - Australian Radiation Protection and Nuclear Safety Agency

The following information is an extract from a more detailed factsheet (PDF 121kb) which also contains an extensive reference list.

What caused the radioactive contamination at Maralinga?

Between 1955 and 1963, the United Kingdom conducted a program of nuclear weapons development tests at Maralinga in the remote outback of South Australia (Figure 1). This testing led to widespread dispersal of radioactive contamination to the local environment.

Seven atomic explosions took place at Maralinga in 1956 and 1957. The contamination from these “major trials” has largely decayed and no longer presents a significant health risk. Many “minor trials” were also conducted on the site. These were safety tests and other experiments designed to develop the components of a nuclear device. These tests involved the burning and explosive dispersal of plutonium, uranium, and other radionuclides. Much of the contamination from these minor trials remained on or close to the ground surface following the decommissioning of the site by the British. In many cases the radionuclides were short-lived and have long disappeared, but three sites, Taranaki, TM100/101 (TMs), and Wewak remained highly contaminated with plutonium 40 years later. This plutonium has been assessed as representing a significant health risk to potential occupants of the land.

Taranaki was the site of the last (Oct. 1957) and biggest (27 kilotons) nuclear explosion conducted at Maralinga (See factsheet for details). The device was exploded from a balloon at a height of 300 m and left the area relatively uncontaminated. The Taranaki site was subsequently used for a series of minor trials during the Vixen B series.

These Vixen B minor trials, conducted in 1960, 1961 and 1963, left Taranaki the most severely contaminated site at Maralinga. Approximately 22 kg of plutonium-239 (²³⁹Pu) and the same quantity of uranium-235 (²³⁵U) were dispersed at the site during 12 single-point safety trial.

What has been done to rehabilitate the site?

In a rehabilitation operation carried out by the UK Ministry of Defence in 1967 (Operation Brumby), an attempt was made to dilute the surface concentration of plutonium in the more highly contaminated areas, particularly in central Taranaki. This was done by turning over and mixing the surface soil. In future rehabilitation programs this area was known as the “ploughed area”.

Since the closure of the range in 1967, numerous studies have been carried out to map and characterise the contamination at Maralinga including detailed studies in 1984-85 by the Australian Radiation Laboratory (ARL, which became ARPANSA in February 1999). These studies revealed that contamination levels at the site were much greater than earlier acknowledged.

Planning of the latest clean-up began in 1993 with the establishment of the Maralinga Rehabilitation Technical Advisory Committee (MARTAC) whose purpose was to provide advice to the Department of Primary Industries and Energy (later the Department of Industry, Science and Resources, DISR), the project managers responsible for the site. MARTAC was given the responsibility for establishment of the clean-up criteria for remediation of the site. These clean-up criteria are presented and discussed in the factsheet.

The rehabilitation project consisted of defining the clean-up boundaries at the sites contaminated with plutonium, followed by bulk removal of contaminated soil from the three sites and burial within purpose-built burial trenches under at least 5 m of clean rock and soil. At Taranaki the 22 pits in which the British disposed of unknown quantities of plutonium associated with the 12 Vixen B firings also required rehabilitation. Eleven of these were treated by means of in-situ vitrification (ISV) while the remaining pits were exhumed and their contents reburied in another custom-built burial trench. Figure 2 shows the Taranaki site after removal of contaminated surface soil.

What is the risk from plutonium contamination?

Of the long-lived radionuclide contaminants at the Maralinga site, plutonium-239 presents the most significant radiological hazard. Other isotopes of plutonium contribute ~15% additional dose. The most important pathway for exposure is by inhalation. The aim of the recent rehabilitation of the Maralinga range was to reduce the risk arising from radiation exposure of individual Aborigines, living an outstation lifestyle, to a level that was acceptable to the Aboriginal community and the Australian Government.

Plutonium, being an alpha emitter, presents a health risk only if it enters the body. Of the three pathways for entry into the body (inhalation, ingestion, or through cuts and wounds), inhalation of plutonium and subsequent retention in the lungs gives rise to a risk of lung cancer. However, if the plutonium enters the body through one of the other pathways the greater risk is of bone cancer (osteosarcoma) or cancer of the liver. The degree to which each of these exposure pathways contributes to potential dose depends on the type of lifestyle practised by occupants of the land.

The plutonium at Maralinga is largely in the form of insoluble plutonium oxides. Due to this insolubility, the ingestion pathway is of much less importance to potential dose. Wound contamination is less likely to occur but does have the potential to deliver large single doses. For nomadic Aborigines such as the Maralinga Tjarutja, living an outstation lifestyle, the inhalation dose pathway is by far the most significant for both adults and children.

What is Maralinga like now?

Radiation doses for the inhalation pathway have been calculated for a range of sites and scenarios at Maralinga (See factsheet for details) following the 1994-2000 clean-up, to ensure that the whole Maralinga area has been rendered safe.

From pre-remediation dose estimates, certain areas were found to have inhalation dose rates that were too high to be acceptable under all but the most rigorously controlled circumstances. These included central areas at Taranaki, Wewak, TM100 and TM101. Now, following the rehabilitation by removal and burial at depth of contaminated surface soil, all areas at Maralinga have been shown by the dose assessments to be well within acceptable limits for all envisaged land uses.

The current restriction on permanent occupancy within a ‘restricted land-use’ (non-residential) boundary surrounding Taranaki can be seen as a purely precautionary measure as doses due to inhalation for permanent occupancy of all but a few areas (essentially within the untreated plumes) are well below the 1 mSv/y limit for members of the public. For a semi-traditional Aboriginal lifestyle, with camp sites occupying considerable area and moving regularly, it is difficult to envisage circumstances which would lead to inhalation doses, even within most of the restricted zone, above acceptable limits. The argument for maintaining restrictions on land-use at central Taranaki should perhaps be seen as restricting access to the sites of the new burial trenches (and thus discouraging intrusion).

It is now impossible for casual visitors making intermittent forays to the area, for example tourists, geological prospectors and surveyors, who do not engage in abnormal dust raising or large-scale soil-disturbance activities, to receive a committed effective dose by inhalation of anything approaching 1 mSv. The estimated doses received during ambient (calm) conditions are very low, and exposure to the substantial dust loadings observed during times of severe dust storms also results in doses which are essentially insignificant.

Further Reading

This paper presents an analysis of the historiography of the British Nuclear Tests in Australia 1952-1957. It was prepared by John Townsend, former Higher School Certificate student at Canterbury Boys’ High School, Sydney - "Historical Fallout: British Nuclear Testing in Australia and the Nature of Science" (PDF 951kb)

This document is provided for research convenience only and does not constitute endorsement by ARPANSA of its content, or an endorsement of the function, policy or status of any associated organisation, or endorsement of any product or service.

 

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