The Runit Dome, also called "Cactus Dome" or locally "The Tomb", is a 115 m (377 ft) diameter, 46 cm (18 in) thick dome of concrete at sea level, encapsulating an estimated 73,000 m3 (95,000 cu yd) of radioactive debris, including some plutonium-239. The debris stems from nuclear tests conducted in the Enewetak Atoll by the United States between 1946 and 1958.
From 1977 to 1980, loose waste and top soil debris scraped off from six different islands in the Enewetak Atoll was transported here, mixed with concrete and stored in the nuclear blast crater of the "Cactus" test from May 6, 1958. Four thousand US servicemen were involved in the cleanup and it took three years to complete. The waste-filled crater was finally entombed in concrete.
In 1982, a US government task force raised concern about a probable breach if a severe typhoon were to hit the island. In 2013, a report by the US Department of Energy found that the concrete dome had weathered with minor cracking of the structure. However, the soil around the dome was found to be more contaminated than its contents, so a breach could not increase the radiation levels by any means. Because the cleaning operation in the 1970s only removed an estimated 0.8 percent of the total transuranic waste in the Enewetak atoll, the soil and the lagoon water surrounding the structure now contains a higher level of radioactivity than the debris of the dome itself, so even in the event of a total collapse, the radiation dose delivered to the local resident population or marine environment should not change significantly. Concern primarily lies in the rapid tidal response to the height of the water beneath the debris pile, with the potential for contamination of the ground-water supply with radionuclides. One particular concern is that, in order to save costs, the original plan to line the porous bottom crater with concrete was abandoned. Since the bottom of the crater consists of permeable soil, seawater is inside the dome. However as the Department of Energy report stated, the released radionuclides will be very rapidly diluted and should not cause any elevated radioactive risk for the marine environment, compared to what is already experienced. Leaking and breaching of the dome could however disperse plutonium, a radioactive element that is also a very toxic heavy metal.
In 1952, the United States dropped the nuclear bomb Ivy King 610 m (2,000 feet) north of Runit Island.
Crater created by detonation on 5 May 1958 (Operation Hardtack I, Cactus test)
- "A Visual Description of the Concrete Exterior of the Cactus Crater Containment Structure" (PDF). October 2013.
- Willacy, Mark (28 November 2017). "A poison in our island". ABC (Australia). Retrieved 28 November 2017.
- Emma Reynolds. "Deadly dome of gorgeous Pacific island leaking radioactive waste", news.com.au, 7 July 2015. Retrieved 12 May 2017.
- "Enewetak". Marshall Islands Dose Assessment & Radioecology Program. 7 April 2015. Retrieved 19 December 2017.
- Michael B. Gerrard (3 December 2014). "A Pacific Isle, Radioactive and Forgotten". The New York Times. Retrieved 4 February 2018.
- Visual Description of the Concrete Exterior of the Cactus Crater Containment Structure LLNL-TR-648143
- Jan Hendrik Hinzel, Coleen Jose and Kim Wall. "This dome in the Pacific houses tons of radioactive waste – and it's leaking", The Guardian, 3 July 2015. Retrieved 4 February 2018.
- Mark Willacy (27 November 2017). "The Dome". ABC (Australia). Retrieved 4 February 2018.
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