Above: The radioactive capsule was located by the side of the road in the Pilbara region

A tiny radioactive capsule that was lost while in transit in Western Australia has been successfully located by the emergency services. The device involved was a 19 GBq caesium 137 source bound in a ceramic matrix and encapsulated in stainless steel. It was just 6mm by 8mm and had been lost somewhere on a 1400 km road trip between the Rio Tinto mining company’s Gudai-Darri iron ore mine north of Newman in the Pilbara area of Western Australia, and Perth.

Such sources are commonly found in the mining industry where they are used within level sensors and other similar devices. The steel prevents beta emission but allows gamma penetration which is detected to give a measure of density and/or flow rates of materials. In this instance it was being used at the Gudai-Darri mine site to measure iron ore feed in the crushing circuit of the plant.

With a half-life of just over 30 years, this type of radioactive source might be expected to have a service life of about 15 years although regulatory requirements mean it must be regularly tested. There are thousands of similar radioactive sources in use across Australia, however, this particular device was being transported to Perth for repair.

The capsule was packaged by a specialist radioactive materials handler on 10 January, transported offsite on 12 January and the casing that contained it arrived in Perth on 16 January. It was discovered that the capsule was missing over a week later, on 25 January, when the package was opened for inspection. It is believed it had fallen through a bolt hole within a secure device that had been attached to the transport truck. Once alerted, the authorities launched a massive search for the device in a ‘needle in a haystack’ mission to recover the source.

Head out on the highway

The operation, led by the State’s Department of Fire and Emergency Services, spanned hundreds of miles from the outback to metropolitan Perth.

The device was ultimately located on 1 February near Newman, some 2 metres off the northbound roadside edge of the Great Northern Highway. Its discovery brought to an end a large-scale interagency search for the missing object in just seven days.

It was discovered by a vehicle search crew from the Australian Nuclear Science and Technology Organisation (ANSTO) using specialised radiation detection equipment fitted to a vehicle. The searchers had been driving north and south along the Great Northern Highway at speeds of up to 70 kph (50 mph) deploying a modified version of ANSTO’s own custom-developed radiation detection and imaging technology CORIS360®. A wide area spectroscopic gamma-ray imaging device that detects across a broad energy range with a large 360° horizontal and 90° vertical field of view, the device overlays a radiation image onto a panoramic optical image of the scene. This makes interpretation of the data much easier, its developers say. The portable radiation detection technology was developed by Chief Technology Officer and Principal Scientist of ANSTO’s Detection and Imaging unit, Dr David Boardman, and was commercially launched in 2020.

Prior to the device deployment, ANSTO staff performed drive-by test runs of the detection equipment at Lucas Heights using an equivalent radioactive source activity, and evaluated different speeds and terrain conditions to ensure the CORIS360® could detect the missing capsule.

“For the team to find this missing source over a span of 1,400 kilometres and in the formidable conditions of the outback after only being on the ground for two days, is not only a phenomenal feat, but a testament to Australia’s highly sophisticated nuclear capabilities and our people,” said Dr Miles Apperley, ANSTO’s Group Executive for Nuclear Safety, Security, and Stewardship Group. “The sensitivity of the modified CORIS360® technology gave us the confidence it would be found,” he added.

Once it had been initially detected by staff inside the car, a handheld radiation detection device was used to find the exact location. A 20-metre exclusion zone was then established around the device where it was found and the authorities surveyed the area to discover if there had been any contamination. Having recovered the capsule undamaged it resumed its journey to Perth in a rather more securely packaged lead container.

Aftermath

Fire and Emergency Services Commissioner Darren Klemm AFSM commended the extraordinary efforts of all agencies and personnel involved in the operation, saying: “We have essentially found the needle in the haystack. When you consider the challenge of finding an object smaller than a 10-cent coin along a 1400 km stretch of Great Northern Highway, it is a tremendous result. I want to thank everyone involved in the search – we called on a large number of agencies to assist and this was a great example of working together to achieve an outstanding result.”

Rio Tinto also thanked Western Australia’s Department of Fire and Emergency Services and specialist search crews from the Australian Defence Force, the Australian Radiation Protection and Nuclear Safety Agency and the Australian Nuclear Science and Technology Organisation, as well as all other support agencies, for their role in the search and recovery efforts.

“While the recovery of the capsule is a great testament to the skill and tenacity of the search team, the fact is it should never have been lost in the first place,” said Rio Tinto Iron Ore Chief Executive Simon Trott in a statement. He added: “We are taking this incident very seriously and are undertaking a full and thorough investigation into how it happened. This sort of incident is extremely rare in our industry, which is why we need to investigate it thoroughly and learn what we can to ensure it doesn’t happen again. As part of our investigation, we will be assessing whether our processes and protocols, including the use of specialist contractors to package and transport radioactive materials, are appropriate.”

Western Australia’s Chief Health Officer and Chair of the Radiological Council, Dr Andrew Robertson, said while the chances of anyone being contaminated by the source were extremely remote, an investigation had been launched to determine how the device was lost. “I have responsibility as the chair of the Radiological Council to actually investigate and if required, prosecute offences under the act,” Robertson said in a statement, adding: “We have a number of authorised officers who are doing that. Our radiation health branch, within the Department of Health, is conducting that investigation and they will be looking at all aspects of this event.