Radioactive waste from nuclear weapons tests could be seeping from its “concrete coffin” and leaking deadly atomic “sludge” into the Pacific Ocean.

The United Nations Secretary-General recently admitted that he was “worried” about the waste escaping from a concrete dome built to trap atomic material left over from Cold War nuclear bomb tests.

The dome is located on Runit Island in the Pacific Ocean and was created as a dumping ground for radioactive waste in the 1970s.

Speaking to students in Fiji, AFP reported that Guterres described the structure as “a kind of coffin” and said that the Pacific has been “victimized” in the past by nuclear tests carried out by the US and France in the area.

Guterres, who is touring the Pacific Islands to raise climate change awareness, observed: “The consequences of these [tests] have been quite dramatic, in relation to health, in relation to the poisoning of waters in some areas.”

“I’ve just been with the President of the Marshall Islands (Hilda Heine), who is very worried because there is a risk of leaking of radioactive materials that are contained in a kind of coffin in the area.”

Runit Island is part of the Enewetak atoll, a ring-shaped coral structure made up of lots of little islands.

A lot of people who used to live on these islands and the surrounding area had to be forcibly evacuated and resettled due to radioactive fallout.

A total of 67 American nuclear weapons tests were carried out in the region from 1946-58 including the famous 1954 “Bravo” hydrogen bomb test, the most powerful ever detonated by the US.

Bravo was 1,000 times bigger than the atomic bomb dropped on Hiroshima, estimated to have killed 90,000–146,000 people.

In an attempt to clean up the Pacific Ocean islands, radioactive soil and ash from the explosions was tipped into a crater made on Runit Island and capped with a concrete dome that is 18 inches thick.

However, it was only ever supposed to be a temporary fix so the bottom of the crater was never lined, which is causing concern that the deadly nuclear waste could now be leaking out into the sea.

Cracks have also started to form in the concrete after decades of exposure to the waste and experts think a freak weather incident could easily cause it to break apart.

Guterres has not directly said how the problem could be fixed but thinks that the Pacific’s nuclear history still needs to be addressed and compensated for.