French expedition hunts for Cold War nuclear barrels on Atlantic seabed

A French research vessel will leave Brest on 15 June for a 26-day expedition to locate and examine some of the 200,000 barrels of radioactive waste dumped in the northeast Atlantic between 1946 and 1993. The mission, led by the CNRS, Ifremer and the French oceanographic fleet, will deploy UlyX, a 4.5-metre autonomous underwater robot capable of diving to 6,000 metres, to map the seabed and photograph the corroded containers lying at 4,000 metres depth.

Fourteen European nations, including France and the UK, used more than 80 sites across the Arctic, Atlantic and Pacific for nuclear disposal during the early decades of the atomic age. The practice was halted by a 1975 London Convention moratorium and banned outright in the early 1990s, but the barrels, designed to last 20 to 26 years, have long exceeded their engineered lifespan.

What the waste contains

According to Andra, France's national radioactive waste agency, the submerged inventory holds roughly 85,000 terabecquerels of activity, mostly very low-, low- and intermediate-level waste solidified in concrete or bitumen matrices. The most hazardous high-level waste and spent fuel were not dumped here, though the USSR and United States disposed of reactor components elsewhere. Radioactivity decays at different rates: caesium-137 has a half-life of about 30 years, while uranium-238 persists for 4.5 billion years.

Gaps in the historical record

Precise locations and inventories remain patchy. The International Atomic Energy Agency noted in a 2015 report that national records were kept inconsistently, and Cold War secrecy meant states communicated little about accidents or losses at sea. A 1980 review by the Nuclear Energy Agency found no elevated radioactivity in seawater samples and concluded recovery was unnecessary, but that assessment predated today's analytical capabilities.

"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,"

Said geophysicist Javier Escartin, who co-leads the mission. The team, nuclear physicists, geologists, oceanographers, biologists and marine chemists, will collect water, sediment and biological samples around any barrels UlyX locates.

Why the deep sea matters

Scientists still know little about how radionuclides behave under the extreme pressure, cold and darkness of the abyssal plain. Of particular concern is strontium-90, a calcium analogue that organisms can incorporate into bones and shells, potentially entering the food chain. The robot can only survey about 20 square kilometres per dive across a 6,000 km² study area, so the expedition will characterise a fraction of the total inventory.

All data will be published openly. A second cruise is planned to refine the findings. Escartin stressed the mission is not an audit of past decisions but a scientific baseline: "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."