It had long been considered a safe way to dispose of radioactive waste. For nearly five decades, tens of thousands of tonnes of waste – sealed in watertight barrels of asphalt and cement – were dumped in international waters.
Although the practice is now banned, between 1946 and 1993, 14 European countries – including France and the UK – carried out dumping operations at more than 80 locations in the Arctic, Atlantic and Pacific.
In the northeast Atlantic, home to the most concentrated stretch of this radioactive marine waste, some 200,000 barrels lie at a depth of 4,000 metres. On June 15, a team of scientists from the CNRS (France’s National Centre for Scientific Research), Ifremer (the French national institute for ocean science and technology) and the French oceanographic fleet, will set sail from the Brittany port of Brest in a bid to locate the barrels.
The team of nuclear physicists, geologists, oceanographers, biologists and marine chemists will be joined by UlyX, a 4.5 metre autonomous underwater robot that will be their eyes and ears during the 26-day expedition.
"The robot can dive to a depth of 6,000 metres,” explained geophysicist Javier Escartin, who will co-lead the mission. “It will be able to use sonar-type systems to map large areas and detect where barrels are located. It will also be able to get close to the seabed and take photographs, enabling us to assess the barrels’ condition, establish where they are scattered, and to plan further studies at a later date."
A stable environment
The submerged barrels, which have a lifespan of between 20 and 26 years, are now long past their expiry date.
In 2000, the environmental NGO Greenpeace filmed barrels of waste at the site closest to the French coast, the Casquets trench in the English Channel, used to dump waste by Belgium and the UK. Their footage showed the rusting barrels were badly degraded and corroded.
However, the barrels dumped at sea do not contain the most hazardous waste. Most of the waste is classified as very low-, low- and medium-level radioactive waste, according to the available data.
In addition, the radioactivity emitted by radioactive waste gradually diminishes over time. The time it takes for a radioactive substance to decrease by half is called the half-life. However, this half-life period varies greatly – depending on the type of atom or radionuclide. For instance, it is approximately two years for caesium 134, approximately 13 years for plutonium 241, approximately 30 years for caesium 137 and some 4.5 billion years for uranium 238.
The radioactive waste comes in two forms: either solid or liquid. Solid waste is surrounded by a concrete or bitumen matrix before being sealed in a watertight barrel. Only the former USSR and the United States have dumped other types of waste, such as nuclear reactor tanks, some of which still contain fuel, reported the French National Agency for Nuclear Waste Management (Andra).
The total radiological activity of the submerged waste was around 85,000 terabecquerels when it was released into the ocean, Andra added.
In the postwar period, as nuclear technology spread to many sectors of activity, developed countries viewed dumping waste in deep waters as a safe option. The deep ocean is one of the most stable environments on Earth and scientists mistakenly believed it to be deserted and devoid of life.
‘A reflection of a period in history’
The history of these dumping operations remains a grey area and the practice was completely unregulated by international treaties.
It was not until 1975 that the London Convention’s moratorium came into force. And it was only in the early 1990s that the disposal of industrial and radioactive waste at sea was definitively banned.
Precise data on the dumping operations remains patchy, according to the International Atomic Energy Agency (IAEA), “due to the different ways in which records on disposal operations have been kept in different countries”.
“The information on accidents and losses at sea of radioactive material [...] is heterogeneous, the agency said in a 2015 report.
"This is a reflection of a particular period in history. At the time, we were in the midst of the rapid development of the nuclear industry and nuclear weapons. States communicated very little. Even today, we have very little information," said Patrick Chardon, a research engineer at the Clermont Auvergne Physics Laboratory (LPCA) and a specialist in the effects of radioactivity on the environment.
"There have been several campaigns to monitor the dumping zone in the northeast Atlantic, but they didn't have the tools we have now. These will enable us to pinpoint the exact location of the barrels, the discharge areas and the concentrations of radioactivity," Chardon added.
Back in 1980, the Nuclear Energy Agency (NEA) carried out a review of the “continued suitability of the dumping site for radioactive waste in the northeast Atlantic”. As the seawater samples collected showed no increase in radioactivity compared with natural levels, the NEA did not think it necessary to recover the submerged barrels or even to maintain continuous surveillance of the sites.
But this time round, scientists will be able to take much more precise measurements by sampling the water, sediment and living organisms. "Unlike previous research programmes, which were carried out somewhat in the dark, we will now have a picture of where the sampling will be most relevant based on the presence or absence of the barrels. This is a really important point when it comes to assessing the impact of waste," Escartin explained.
A possible impact on living organisms
Scientists currently have no idea how radionuclides behave in the oceans, and even less so in an environment as extreme as the deep ocean, notorious for its intense cold, darkness and phenomenal pressure.
"The mission will enable us to gain a detailed understanding of radionuclides. We will be able to observe the chemical forms in which these elements are present, and establish whether they are mobile or not, immobilised by the sediment or, on the contrary, if they can be assimilated by living organisms," explained Chardon.
"In this respect, strontium-90 is problematic because it is an analogue of calcium. In terms of biological functioning, living organisms confuse strontium with calcium. It can therefore be integrated into the food chain," Chardon continued.
On their return to dry land, the scientists will spend several months studying the samples taken near the radioactive barrels. A second mission to refine the results will then be scheduled. All the data from both missions will be made available to the public in the interests of transparency.
“This is not a mission to assess whether the releases were well or badly done,” warned Escartin. "It's an opportunity to look at what was done in the past, without passing judgment, to carry out scientific studies. Afterwards, of course, we'll have to conduct a complete inventory, because we need one."
However, during the mission, the scientists will only be able to assess the condition of a small fraction of the 200,000 barrels in the northeast Atlantic. And on each dive, the UlyX autonomous robot will only be able to focus on an area of around 20 square kilometres – a drop in the ocean given that the two research areas where the submerged barrels lie covers more than 6,000 km2.
This article has been translated from the original in French by Charlotte Wilkins.
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