A HUGE concrete “coffin” of radioactive waste is cracking OPEN sparking a probe into whether the debris could leak into the ocean.

The US Congress has ordered the Department of Energy (DOE) to investigate the Runit Dome in the Marshall Islands in the Pacific.

6 The huge concrete dome on Runit Island, containing nuclear waste, is cracking open Credit: EPA

Built in 1980, the structure covers a crater caused by a nuke bomb and contains more than three million cubic feet of nuclear waste and is now filling with sea water.

The DOE has been instructed to come up with "a detailed plan to repair the dome to ensure that it does not have any harmful effects to the local population, environment, or wildlife...", reports Military.com.

After testing atomic weaponry in the region in the 1940s and 50s, the US government created the 18-inch thick dome to seal the radioactive contents inside.

However, the 350-ft wide tomb was 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.

Around 4,000 servicemen spent three years making the dome.

NUKE COFFIN CRACKING

Of those, six died during the process and hundreds more developed radiation-related illnesses such as cancer.

In November, an investigation by the Los Angeles Times and Columbia University revealed that the concrete tomb is leaking.

A research team made five trips to the area and found that sea levels around the dome are rising every year and there is evidence of coral bleaching, fish dying and negative impacts on the health of locals.

Sea levels are reportedly rising three times faster around the Marshall Islands than the global average which experts believe has been caused by climate change.

6 The US tested 67 nuclear bombs in the region. Pictured is a second crater created by nuclear testing next the concerte lid Credit: Getty - Contributor

6 Over 100 islanders were displaced due to the tests between 1946 and 1958 Credit: Lawrence Livermore National Laboratory

Scientists say the waters around the area could be five feet higher in the coming decades, which could crack the dome open spilling the lethal waste

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, Japan, estimated to have killed up to 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.

Earlier this year, the United Nations Secretary General admitted that he was "worried" about the waste escaping from a concrete dome.

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

Guterres, who was 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."

Footage shows US cold war nuclear tests carried out in the Pacific Ocean

6 Bikini Atoll was the site of 23 nuclear bomb tests at the start of the Cold War Credit: Lawrence Livermore National Laboratory

6 Islanders began developing cancers in the 1960s following the terrifying nuke tests Credit: Getty - Contributor

6 The US government wanted to test how bombs would impact warships while dropped from the sky and detonated underwater Credit: Rex Features