Enewetak Atoll and the Runit Dome

Between 1948 and 1958, 43 devices were detonated at Enewetak, with a combined yield of about 31.8 megatons. On 31 October 1952 the Ivy Mike test, the first hydrogen bomb, at 10.4 megatons, erased an island. The Cactus test, on 5 May 1958, left on Runit Island the crater that would become the repository.

Between 1977 and 1980 about 4,000 US servicemen scraped the topsoil from six islands and brought to Runit more than 80,000 m³ of soil and debris containing plutonium-239, which was mixed with Portland cement, poured into the crater and capped with a concrete shell 46 cm thick. The plan was to line the crater's permeable floor as well, but this was dropped to save money; the operation cost 239 million dollars. In 1980 the southern and western islands were declared safe and the residents came back.

In 2013 a Department of Energy report found minor cracking in the cap and noted that the sediments around the dome are more contaminated than its contents. After a 2019 Los Angeles Times investigation into sea-level rise, Congress asked for a new assessment, delivered in June 2020. Since 2022 the servicemen who worked on the clean-up have been recognised as radiation-exposed.