In 1980, the United States military completed the construction of a concrete dome 115 meters in diameter on a small piece of land in the Pacific, to contain more than 85,000 cubic meters of radioactive waste from its nuclear tests. The structure, nicknamed "The Tomb," was initially presented as a temporary solution to a dark chapter of the Cold War. Today, scientists and residents of the Marshall Islands are concerned about a fundamental flaw in the structure that has existed since its construction. The Runit dome, built between 1977 and 1980 on a nuclear test crater, never had a watertight base, allowing the porous coral soil beneath the radioactive waste to remain as it was. Progressive cracks appear in the concrete slab, which the United Nations described as not watertight, while the U.S. Department of Energy downplays their impact. The plutonium-239 enclosed under the dome remains dangerous for more than 24,000 years, while the concrete already shows signs of aging in less than fifty years, a discrepancy aggravated by rising sea levels. Runit Island is located at the northeastern end of the Enewetak atoll in the Marshall Islands. Between 1948 and 1958, the United States conducted 43 nuclear tests there, including a 18-kiloton bomb named Cactus. Its explosion literally vaporized part of the island and propelled an atomic mushroom cloud six kilometers into the air, leaving behind an open crater ten meters deep. Twenty years later, between 1977 and 1980, this same crater was chosen as a burial site for debris and contaminated soil recovered from the entire atoll, approximately 111,000 cubic meters of radioactive materials, including lethal quantities of plutonium. Once the cleanup was complete, the military poured a 18-inch thick concrete slab to seal it all, giving birth to the famous Runit dome. The structure was never given a watertight base, allowing seawater and groundwater to freely circulate beneath it according to the tides. This is not a manufacturing defect or an accidental flaw in the concrete, but an engineering decision made from the start, at a time when the project was conceived as a temporary solution rather than a permanent containment. The problem is that this "provisional" solution has become definitive due to a lack of alternatives. In recent years, several observations have documented the appearance of cracks that progressively spread through the concrete slab. A United Nations report has pointed out that the structure is not watertight. The organization's secretary-general, Antonio Guterres, described the dome as "a kind of coffin." The U.S. Department of Energy sought to downplay the issue, explaining that these cracks remain consistent with the natural aging of the concrete, and that the surrounding lagoon already contains significant amounts of radioactive material inherited from past tests. According to this interpretation, an additional leak from the dome would remain minimal in comparison. However, this argument does not reassure many people on site, especially when one knows that the plutonium-239 present under the dome remains dangerous for more than 24,000 years, while cracks are already visible in the concrete in less than fifty years of existence. For the residents of the Marshall Islands, Runit is not only a geological curiosity or a relic of the Cold War: it is the symbol of a commitment that never materialized. The dome was presented as a lasting response to contamination, a way to finally close a painful chapter. But with the rise in ocean levels linked to climate change, erosion is accelerating, further weakening a structure already aging and never designed to withstand such a time horizon. This discrepancy between the lifespan of the concrete, just a few decades, and that of the plutonium enclosed beneath it, several tens of thousands of years, summarizes the absurdity of the initial gamble. One has sealed a problem without ever really solving it, betting on the fact that no one would have to worry about it for a very, very long time. Today, as the waters continue to circulate under the dome at the pace of the tides, exactly as they have since the first day, Runit reminds us of an uncomfortable truth: some solutions presented as radical are sometimes only hastily applied bandages on wounds far too deep. The question remains of how long this bandage will last, and especially, what will be decided to do with it before it finally gives way.