Scientists warn of deteriorating Runit Dome in the Marshall Islands as risks grow

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Fears huge nuclear dump buried under concrete dome could be unleashed into the sea | News World

The Runit Dome was built to contain radioactive waste from nuclear experiments in the middle of the 20th century (Picture: US Defense Special Weapons Agency/Cover Media)

A Pacific Island is sitting atop a nuclear time bomb that could pollute the oceans for centuries.

Scientists have discovered that a concrete structure built to contain radioactive waste from Cold War-era testing is showing signs of deterioration.

The site, known as Runit Dome, sits on Runit Island in the Enewetak atoll in the Marshall Islands.

Although Runit itself is uninhabitable, the atoll is home to around 300.

The dome sits close to the ocean’s edge and rising sea levels and shifting groundwater bring seawater into close contact.

It dates back to a period of intensive nuclear testing. Between 1946 and 1958, the United States conducted 67 nuclear tests across Enewetak Atoll and Bikini Atoll, displacing more than 300 Marshallese people.

One test in particular, an 18-kiloton explosion known as “Cactus”, destroyed part of Runit Island and sent a mushroom cloud approximately six kilometres into the sky.

The Crater created by the Cactus explosion on May 5, 1958. It was later used as a burial pit to inter 84, 000 cubic meters of radioactive soil (Picture: US Defense Special Weapons Agency/Cover Media)

In the late 1970s, the 10 metre deep crater left by the blast was used to store more than 120,000 tonnes of radioactive soil and debris collected from across the atoll.

The site was then sealed with an 18-inch (46cm) concrete cap, forming what is now known as the Runit Dome.

More than five decades later, the structure is showing visible signs of ageing. Cracks have appeared across its surface, and groundwater is able to flow beneath it.

Researchers say this water moves in and out with the tides, potentially carrying radioactive material into the surrounding lagoon. Studies have also indicated that the dome is not watertight.

Ivana Nikolic-Hughes, of Columbia University and president of the Nuclear Age Peace Foundation, observed cracks during a visit in 2018 while measuring radiation levels.

‘These results provide further demonstration of the continuing impact of radioactive fallout on the Marshall Islands and will inform future work to understand how the presence of this isotope might affect current inhabitants and potential resettlement,’ she writes.

The Enewetak atoll from above. Runit is in the lower right of the picture. (Picture: NASA Earth Observatory/Cover Media)

American officials have said the structure is not at immediate risk of collapse.

But experts have warned that some of the radioactive elements involved pose extremely long-term risks. Plutonium-239, used in nuclear weapons, remains hazardous for more than 24,000 years.

Arjun Makhijani, president of the Institute for Energy and Environmental Research, said no concrete structure could be expected to last even a fraction of that time.

He noted that cracks have already appeared within decades, highlighting the challenge of containing radioactive material over such long timescales.

‘There are already cracks in it in less than 50 years,’ he told Australian broadcaster ABC.

Scientists say the dome illustrates a broader problem. Certain places we regard as being safe spaces to dump toxic waste, may become less so due to climate change. If sea levels rise and rain increases, water and food supplies change.

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