Rob Rawson, Pat Davoren and Caroline Perkins
Department of Primary Industries and Energy
GPO Box 858, Canberra, ACT, 2601, Australia

The $A100 million rehabilitation of the former British atomic test sites at Maralinga and Emu, South Australia, is progressing with implementation of an option identified by a technical experts. The Maralinga Rehabilitation Project was agreed by the Australian and South Australian (SA) Governments, and the Maralinga Tjarutja traditional owners. The Project, which was assisted by an ex gratia payment of £20 million by the British Government, is the first clean-up of a former atomic test site, and the first to be undertaken on a commercial basis. The work program, which commenced in 1996, is proceeding on time and within budget, and is due to be completed in 2000. At Maralinga, plutonium-contaminated soil has been removed and buried in trenches at three separate sites, and the work was completed in 1997. The rehabilitated areas were monitored and cleared by the Australian Radiation Laboratory. Windrows of clean soil were distributed over most rehabilitated lots, 5 m of clean soil was placed over the trenches, and seed planted for revegetation on lots and trenches. At Taranaki, 21 plutonium-contaminated burial pits will be stabilised using in-situ vitrification (ISV), a process which melts contaminated soil by means of large electric currents applied through graphitic electrodes, producing a strong, leach resistant, glass ceramic block. Vitrification of the pits will commence in 1998. The Emu site, 190 km to the northeast of Maralinga, does not have a significant plutonium contamination hazard, and will be left without rehabilitation. Boundary markers have been placed around the Taranaki area at Maralinga, to indicate that the area is suitable for transit, but not permanent habitation, by the traditional owners, and similarly the Emu site has also be delineated by boundary markers.

Between 1953-1963, the United Kingdom conducted a program of nuclear warhead development trials at Maralinga and Emu, test sites which occupy some 3,120 km² located on the edge of the Great Victoria Desert and north of the Nullarbor Plain in South Australia (Figure 1; and 1). Seven atmospheric atomic explosions (major trials) were carried out at Maralinga (Figure 2), and two took place at Emu. Over five hundred small scale experiments or minor trials were also conducted, largely at Maralinga. The test sites were part of the traditional lands of Maralinga Tjarutja, an aboriginal community who were displaced from the area prior to the testing period. Since enactment of the Maralinga Tjarutja Land Rights Act in 1984, Maralinga Tjarutja has had freehold title to 75,000 km² of lands surrounding the former test sites.

As a result of the atmospheric tests, fission products were deposited in radioactive fallout downwind of the ground zeros, sand was fused into 'glazing' and some radioactivity was induced in the soil (2). However, the major trials sites no longer present any significant health risk. All the radioactivity released in the explosions was either widely dispersed (i.e. world-wide) at the time, or has decayed to low levels (3).

More extensive contamination was caused by the minor trials (3), safety trials which were designed to test the susceptibility of nuclear weapons to accidental detonation during transport and handling. The Vixen B Series of trials dispersed about 24 kg of plutonium, largely at the Taranaki site, with lesser amounts at the TMs, and Wewak sites. The current rehabilitation project is mainly directed at contamination from these experiments. Featherbeds, largely constructed of steel, lead and barytes bricks, were used as a base for the trials. Plutonium was deposited in surface plumes as fine dust, as small sub-millimetre particles, or as surface contamination on larger fragments of debris (4). The larger featherbed fragments were disposed of in pits in inner Taranaki.

In 1967, the British Government carried out Operation Brumby, which was intended as a "final" clean-up of the Maralinga site, before returning it to Australian Government control. The clean-up was predicated on the assumption of no significant future human habitation of the site. The project involved the burial of the most highly contaminated materials in shallow pits, with the ploughing of various areas, to depths of 15-25 cm, in order to dilute the surface activity levels by mixing with the clean lower soil. In some cases, particularly in central Taranaki, where the levels of contamination still remained unacceptably high, clean soil was imported to dilute the levels further. The clean-up failed to significantly reduce the hazard at the site, as there was no attempt to remove fragments prior to ploughing, and the monitoring devices used to measure radioactivity were not sufficiently sensitive to determine the full extent of the contamination.

In 1985, the Royal Commission into British nuclear tests in Australia recommended that the test sites be cleaned up to be fit for unrestricted habitation by the Aboriginal traditional owners, that all costs should be borne by the British Government, and that the Australian Government should compensate those with a traditional interest in the test site area for loss of use and enjoyment of their lands.

To address technical matters stemming from the Royal Commission, the Australian Government established the Technical Assessment Group (TAG), comprising Australian, British and US scientists. Australia and Britain made broadly similar contributions to the cost of the study program. TAG instigated a range of technical and engineering studies to quantify the health risks that the contamination posed to the indigenous population, to determine suitable clean-up criteria, and to assess the technical feasibility and cost of possible remedial options. The results and conclusions were published and summarised in a comprehensive report (3) , which was tabled in the Australian Parliament in November, 1990. The studies showed that residual plutonium contamination from the minor tests is the predominant contributor to radiation dose at Maralinga.

The TAG study considered the following rehabilitation options for contaminated areas of soil (3)

• restriction of access by exclusion and/or warning fencing
• removal and burial of contaminated soil in a specially constructed trench
• mixing soil in areas of low contamination to reduce the average concentration of activity
• processing the contaminated soil to concentrate the radioactivity into a smaller volume which would then be buried and the major portion of uncontaminated soil returned to the site
• treating burial pits to immobilise the pit contents; and
• exhuming burial pits and burying the exposed debris in either a sub-trench in the specially constructed trench referred to above, or in a specially constructed borehole.

The rehabilitation options established by TAG were based on assessment of the level at which risks for the traditional owners became unacceptable, considering social, economic, and scientific factors. Studies revealed that the semi-traditional lifestyle of the Aborigines involves the potential intake of much greater levels of dust than would be characteristic of western society. Hence the inhalation of plutonium-contaminated dust was identified as the dominant pathway for radiological exposure with the critical group being the Aboriginal children (5,6). Rehabilitation strategies were then devised to ensure that their annual dose did not exceed 5 mSv, based on 100% occupancy (3).

In selecting both the dose target and potential remedial options, it was accepted that the rehabilitation process was to be one of reducing an existing risk. The dose limit was translated by the Australian Radiation Laboratory (ARL) into acceptable residual contamination levels for various parts of the site using a quantitative risk assessment. These levels ranged from 1.8 to 4 kBq (²⁴¹Am)/m² using ²⁴¹Am (americium) as a marker for plutonium. The risk assessment used was very conservative in its assumptions. If realistic occupancy factors are used with these residual contamination levels, the received doses are likely to be much lower than the dose limit.

In 1991, in consultation with the South Australian Government and the Maralinga Tjarutja traditional aboriginal owners, the Australian Government decided from the options presented in the TAG study to pursue a remedial action broadly following TAG option 6 (c). The $A100 million rehabilitation involves a program of soil removal and burial in trenches at the Taranaki, TMs and Wewak sites, exhumation of some burial pits, and treatment of a number of highly plutonium-contaminated pits at Taranaki by in-situ vitrification (ISV).

The option permits unrestricted access to about 90% of the former restricted area, but excludes full time occupation of the remaining 120 km² area of land which was contaminated with plutonium during the Vixen B trials at Taranaki. To make the latter area suitable for permanent use, a much larger program of soil removal would have had to be undertaken, involving major environmental damage. This option was rejected by the traditional owners. The Maralinga Tjarutja claimed that the preferred rehabilitation option would not allow full access to the former test site, and, in response, the Australian Government agreed to a settlement with the traditional owners, which included a payment of $A13.5 million.

Representations by the traditional owners and by the Australian Government resulted in the British Government making an ex-gratia settlement of £20 million in 1993. This was a full and final settlement, payable annually in six instalments, which commenced in December, 1993. The British payment was equivalent to almost half the total cost of the $A100 million rehabilitation option agreed by the Australian and SA Governments, and Maralinga Tjarutja. The £20 million amount was accepted as a significant contribution to the cost of the clean-up project, and the Australian Government subsequently commenced detailed engineering and design planning for the clean-up.

The Maralinga Rehabilitation Project was authorised by the Australian Government in mid-1995, following public hearings by a bipartisan committee of Parliament. Following a tendering process, contracts were awarded. Parliament requested an independent assessment of the ISV, and, in 1996, the use of the latter technique on pits at Taranaki was approved.

The Maralinga Rehabilitation Project commenced in 1996, and is expected to be completed in 2000. Soil removal was undertaken in 1996 and 97, and the ISV of plutonium-contaminated pits will commence in 1998. The Project is the first clean-up of a former nuclear test site, and the first to be undertaken on a commercial basis. Due to the novelty of the Project, new procedures and techniques had to be developed for the work, including health physics procedures, and soil monitoring and clearance methods.

A strong consultative network continues to be an important part of the Project, and regular meetings are held with SA Government and Maralinga Tjarutja representatives, to ensure that these key stakeholders are fully briefed on the progress of the rehabilitation. The Australian Government established the Maralinga Rehabilitation Technical Advisory Committee (MARTAC) to provide scientific and engineering oversight and advice in relation to the Project.

The Department of Primary Industries and Energy (DPIE) has responsibility for the Maralinga Rehabilitation Project; Gutteridge, Haskins and Davey (formerly, Works Australia) is project manager, Thiess Contractors are responsible for the earthworks, CH2MHill and AEA Technology are health physics providers, SHRM has responsibility for camp management, the Australian Radiation Laboratory has responsibility for radiation protection and health physics audit, and Geosafe Australia is conducting the ISV work.

After the clean-up is completed, the intention is that the site will be returned from the Commonwealth to SA, for addition to the freehold lands of the Maralinga Tjarutja, which surround the former test site.

In 1995, prior to the commencement of the remedial work, a construction camp was built at Maralinga Village. In addition, decontamination facilities, health physics laboratory, change rooms, laundry and maintenance facilities were installed at Taranaki, and were constructed at TMs and Wewak as the Project progressed.

The Australian Radiation Laboratory (ARL) defined the soil removal boundaries (7) by monitoring of the sites. Trench locations were determined after geotechnical investigations, placed close to, but outside, the soil removal boundaries.

Earthworks were undertaken by Thiess contractors at three major sites, Taranaki, TMs, and Wewak. About 2.15 km² of plutonium-contaminated soil was scraped and buried in trenches (Figure 3) - a total volume in excess of 460,00 m³. Three major trenches were constructed with capacities of 320,000 90,000, and 50,000 m³, respectively, and of dimensions, 200 x 100 x 15, 110 x 84 x 15, and 110 x 84 x 10 m, respectively.

The hazard from contaminated dust meant that modified heavy machinery had to be used for the remedial work, with operators in scrapers, graders, bulldozers, excavators, tool carriers, water carts and recovery vehicles protected within sealed and pressurised cabins. The protective system supplies absolute filtered air, and maintains a positive pressure within the cabins of 120-200 pascals. Filter paper installed in the vehicles was checked daily for radioactivity to verify seals on the vehicles.

Contaminated soil marked for removal was designated the "red area", with entry restricted to those working in the zone. The area to be rehabilitated was divided into lots, each of about 3-4 hectares. Haul roads connected lots to burial trenches. The depth of soil to be removed was decided by the Project manager, Gutteridge, Haskins and Davey Pty Ltd, in consultation with ARL, with cuts of 100 to 200 mm being made. Three scrapers removed the soil, with a bulldozer moving in behind scraper so that the latter vehicle could get full loads in one traverse. Sonic sensors allowed the scraper operator to optimise operations. To minimise the potential radiological hazard of dust generation, lots were watered before and after scraping work, in the trench, and on the haul roads. In rocky areas, vacuum cleaning by modified street sweeper was used to retrieve plutonium-contaminated dust. Additional earthmoving work involves the exhumation of pits containing radioactively-contaminated material.

The soil removal techniques generally proved to be very effective with the scrapers achieving the desired decontamination factors. Some 80% of the soil area within central Taranaki required retreatment once, and 10% twice in order to meet the required clearance limits.

After scraping or other rehabilitation work, the health physics provider, CH2M Hill, checked the remediated area for contaminated fragments, using vehicle-based sodium-iodide detectors or hand-held monitors. If an area met the clean-up criteria, ARL provided final clearance to indicate that the site was rehabilitated to the requirements. Two sets of measurements were made (7): the first, derived from the risks associated with the inhalation pathway, measures the average level of americium, hence plutonium contamination in the surface layer of soil. The average level of contamination is determined by a gamma-ray detector, held at 4 m above ground level on a boom mounted on a light OKA truck. The second measurement technique was developed to determine the presence of particulate contamination. The vehicle -based system uses 4 thin sodium iodide crystal (Bicron Fidler) detectors, and is augmented by hand-held equipment.

After clearance, windrows of clean soil were placed on lots outside inner Taranaki, and in the latter area, clean top soil was spread as a base for the ISV work. The windrows were planted with seed for revegetation. Trenches were filled to within 3 m of the surface, and capped with 5 m of clean soil, and seeded for revegetation.

The more lightly plutonium-contaminated 120 km² area around the area of soil removal at Taranaki has been surrounded by boundary markers, signifying to the traditional owners that the land is suitable for hunting, but not for permanent habitation.

Comprehensive health physics procedures, developed by the Australian Radiation Laboratory, were put in place at Maralinga to ensure protection of workers from potential radiological hazards. For those working in areas of plutonium contamination, lung monitoring and urine monitoring occur on a monthly basis. No readings above detection limits were obtained. A recent independent report on health physics procedures on the Maralinga Rehabilitation Project, commissioned by DPIE, concluded that procedures and practices on the Project were more than adequate.

A constructive and effective partnership has been developed between the Maralinga Tjarutja and other key stakeholders in the Project. Local Aboriginals have been employed on the Project by Thiess Contractors, SHRM, and GHD. The latter company has utilised Maralinga Tjarutja workers in the installation of boundary markers, and on both seed collection and revegetation. The Maralinga Tjarutja are currently developing options for the future use of the Maralinga area, and the Maralinga Village facilities. Options include tourism, education and/or training, and scientific research.

The contents of 21 active burial pits at Taranaki will be immobilised by ISV, which involves passing an electric current through electrodes to melt and vitrify the contents of a pit. Temperatures of about 1,600 - 2,000° C are reached, and the typical process rate is 3-6 tonnes per hour, with melts up to 7 m deep and 15 m in diameter possible. When electrical power is shut off, the molten mass solidifies into a vitreous mass with excellent physical, chemical and weathering properties. The ISV technology was selected over exhumation and reburial at the Taranaki site because of advantages of improved occupational, public and environmental safety, and superior containment of radioactive materials in the glassy product.

The Taranaki pits contain plutonium and uranium as contamination on steel, lead and barytes bricks, and in sand and soil (3). The large size of the structural items buried would make excavation of the pits and removal of plutonium contamination a challenging task. In addition, the potential hazard of breathing plutonium-contaminated dust is minimised if the plutonium is effectively immobilised in a stable solid matrix.

A four phase ISV project was initiated in 1993, with the third phase of the project, which involves the design and construction of a full-scale ISV treatment plant, completed in 1997. During Phase 2, a series of onsite tests and demonstrations were conducted, including two intermediate-scale experiments involving radioactive material. The MARTAC established performance criteria for the ISV trials. Geosafe Australia Pty Ltd is conducting all phases of the ISV project.

Three trials involved the use of an intermediate-scale ISV machine to treat simulated burial pits at Taranaki and produce blocks, each weighing more than four tonnes. Items known to be present in the Taranaki pits, such as steel and barytes bricks, were added to the test pits to assess the ability of ISV to cope with a high loading of these materials. In the first two trials, the presence of plutonium oxide was simulated by the addition of known amounts of cerium oxide and uranium oxide respectively. In the final trial, plutonium was included in the melt, as would be the case of the pits at Taranaki. After cooling, the three blocks were sampled to determine the disposition of the added plutonium and surrogate materials. Samples from all three melts showed that a high degree of mixing had occurred (8). The Australian Nuclear Science and Technology Organisation (ANSTO) was engaged by DPIE to conduct an independent scientific audit of the ISV trials. ANSTO concluded that plutonium added to the test pit was dispersed throughout the vitrified block (9). The durability of the vitrified/ceramic product is sufficient to ensure that plutonium is adequately encapsulated.

Melting operations are expected to commence onsite in early 1998. Two hoods will be alternately used during the pit melting.

At the Emu test sites, 190 km north-east of Maralinga (Figure 1), the main contamination is plutonium in fused soil near the two Totem ground zeros. The minor trial sites presents no radiological hazard.

In view of the very low levels of contamination at Emu, MARTAC has recommended no major remedial works, but only the removal of the access track leading to the Totem ground zeros, and seeding to encourage regrowth. In addition, boundary markers to discourage permanent habitation have been erected 1 km from the ground zeros.

The Maralinga Rehabilitation Project, developed on the basis of rehabilitation options suggested by the TAG, and agreed to by the Australian and South Australian Governments and by the Maralinga Tjarutja, is proceeding on time and within its original budget. Completion is expected in 2000. The earthworks were completed at Maralinga at the Taranaki, TMs and Wewak sites in 1997. The ISV work on plutonium-contaminated pits at Taranaki will commence in 1998. Boundary markers indicating that lightly contaminated areas are suitable for transit by the traditional owners, but not permanent habitation, have been installed at Taranaki and at Emu.

Publication is by permission from the Department of Primary Industries and Energy. The contribution of the following to the Maralinga Rehabilitation Project are acknowledged: AEA (health physics provider), Australian Radiation Laboratory (radiation detection and health physics audit), CH2M Hill (health physics provider), Geosafe Australia Pty Ltd (in-situ vitrification), SHRM (camp management), Thiess (surface cleanup works), and Gutteridge, Haskins and Davey Pty Ltd. (WORKS Australia; project manager).

1. J.L. SYMONDS, "A history of British atomic tests in Australia," Australian Government Publishing Service (1985).

2. M.B. COOPER, I.C. DUGGLEBY, L.H. KOTLER, K.N. WISE, "Residual radioactive contamination of the Maralinga Range from nuclear weapons tests conducted in 1956 and 1957", Australian Radiation Laboratory, ARL/TR 005 (1978).

3. TECHNICAL ASSESSMENT GROUP, "Rehabilitation of former nuclear test sites in Australia," Australian Government Publishing Service (1990).

4. G.A. WILLIAMS, P.A. BURNS, and M.B. COOPER, "Plutonium contamination at Maralinga," Chemistry in Australia, 54, pp 122-125 (1987).

5. P.N. JOHNSTON, K.H. LOKAN, and G.A. WILLIAMS, "Inhalation Doses for Aboriginal People reoccupying Former Nuclear Weapons Testing Ranges in South Australia," Health Physics, 63, pp 631-640 (1992).

6. DEPARTMENT OF PRIMARY INDUSTRIES AND ENERGY AND AUSTRALIAN CONSTRUCTION SERVICES, "Statement of Evidence to be presented to the Parliamentary Standing Committee on Public Works", (1994).

7. M.B. COOPER, G.A. MARTIN, WILLIAMS, J.R. HARRIES, "Plutonium contamination at Maralinga: clean-up criteria and verification monitoring," Proceedings of Sixth International Conference on Radioactive Waste Management and Environmental Remediation (ICEM'97), Singapore, 12-16 October, 1997, p. 679-683.

8. L.E. THOMPSON and J.M. COSTELLO, "Vitrification of TRU-Contaminated Buried Waste: Results from radioactive demonstrations at Taranaki", Proceedings of Waste Management '97, Tucson, Arizona, March 2-6, 1997.

9. J.R. HARRIES, "Mixing and encapsulation of plutonium in in situ vitrification trials at Maralinga," Report to the Parliamentary Standing Committee on Public Works. ANSTO, (1996).

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