Castle Bravo: Why the 1954 Test Was Far Bigger Than Planned

Castle Bravo, fired at Bikini Atoll on 1 March 1954, was forecast at 6 megatons and gave 15. We follow the lithium-7 in its fuel, which the designers counted as idle but which made extra tritium and neutrons. We also trace the fallout over Rongelap and Utirik and how it fed the debate that led to the 1963 test ban treaty. The short answer: the designers treated only lithium-6 as reactive, and lithium-7, 60% of the lithium, was assumed too slow to add to the yield. It was not idle. The Castle Bravo explosion became the largest nuclear detonation the United States has carried out, and the cause was the physics of the fuel, not the crew. Whether anyone could have caught the assumption before the shot is still open. The 1954 test is also where the story of the fallout begins: wind carried it east over inhabited atolls, 253 people were evacuated from Rongelap and Utirik, and the crew of a Japanese fishing boat was caught outside the zone. SOURCES Castle Bravo, Wikipedia — https://en.wikipedia.org/wiki/Castle_Bravo Castle Bravo, Atomic Heritage Foundation — https://www.atomicheritage.org/history/cas... The Bravo Accident (Conard, 1992), Marshall Islands nuclear documents archive — https://rminucleardocs.icaad.ngo/en/entity... The Limited Test Ban Treaty, 1963, US Department of State Office of the Historian — https://www.history.state.gov/milestones/1... Which question about this subject should we answer next? Tell us in the comments. #CastleBravo #CastleBravoExplosion #CastleBravo1954 Chapters: 0:00 Why was Castle Bravo so much bigger? 0:26 What was the short answer? 0:53 What was fired, and where? 1:31 What was the device burning as fuel? 2:40 Which lithium went into it? 3:40 What did the designers assume? 5:04 What does lithium-7 do to neutrons? 6:37 How far off was the forecast? 7:35 How big was the largest US test? 8:21 Where did the fallout go? 9:25 What was done once fallout landed? 10:04 Who else was caught outside? 11:03 What did this change for testing? 12:17 So was it the design or the people? Narrated by an AI voice. Pictures are AI-generated illustrations unless credited above.