Australian scientists pave the way to the first International standards needed to safeguard against contamination from nuclear testing.

More than 100kg of highly toxic uranium (U) and plutonium (Pu) was dispersed in the form of tiny ‘hot’ radioactive particles after the British detonated nine atomic bombs in remote areas of South Australia, including Maralinga. Scientists have new evidence to show these radioactive particles persist in soils to this day, more than 60 years after the detonations. Previously, we had a limited understanding of how Pu was released from these “hot” particles into the environment for uptake by wildlife around Maralinga.

But a new study published today in Nature’s Scientific Reports, and led by Monash University researchers, warns that the hot particles are much more complex and varied than previously thought. Currently, there are no international best practice standards for the environmental impact or risk assessment of Pu–U rich hot particles released during nuclear testing.

This study provides the first mechanism for future modelling to predict the environmental life cycle of Pu from hot particles, including how they are slowly broken down in the environment over a long period, and potentially exposed to animals and humans through inhalation, soil or groundwater. The British detonated nine nuclear bombs and conducted hundreds of nuclear tests in outback South Australia between 1953 and 1963. “The resulting radioactive contamination and cover-up continue to haunt us,” said lead study author Dr Megan Cook, from the Monash University School of Earth, Atmosphere and Environment.

“The results of our study profoundly change our understanding of the nature of hot particles at Maralinga – despite the fact that those were some of the best-studied particles anywhere in the world.” The research team used synchrotron radiation at the Diamond Light Source near Oxford, UK to decipher the physical and chemical make-up of the particles. At Monash University, they dissected some of the hot particles using a nano-sized ion beam, and further characterised the complex make-up of these particles down to the nano-size in exquisite details. “It’s a major breakthrough,” said study co-author Associate Professor Vanessa Wong.

“Our observations of the hot particles from the Maralinga provide a clear explanation for the complex and variable behaviour of different hot particles with respect to the chemical and physical weathering that has hindered predictive modelling to this day.” “This study provides a mechanistic foundation for predicting the future evolution of hot particles from high-temperature nuclear events and the likely exposure pathways.” The researchers demonstrated that the complexity of the hot particles arose from the cooling of polymetallic melts from thousands of degrees Celsius in the explosion cloud during their formation. “We found that the particles contained low-valence plutonium-uranium-carbon compounds that are typically highly reactive – which is unexpected for particles that survived for over 30 years in the environment,” said corresponding author Dr Barbara Etschmann.

Between 1950 and 1988 alone, there were more than 230 recorded nuclear weapon accidents, including at least 10 with the documented release of radioactive particles into the environment. The risks of such incidents are only increasing as international treaties such as the Intermediate-Range Nuclear Forces Treaty were cancelled. “Our study invites a revisit of the implications of earlier results for the fate of Pu at Maralinga,” said study co-author Professor Joël Brugger. “Understanding the fate of hot particles in the arid environment setting of the Australian outback is critical for securing Australia in case of nuclear incidents in the region, and returning all the native land affected by the British tests to the traditional Anangu owners of the Maralinga Tjarutja lands.”

Australian singer-songwriter Paul Kelly highlighted the plight of the South Australian outback where the nuclear tests took place with his evocative song Maralinga.