Castle Bravo, the U.S. test of the most powerful thermonuclear weapon took place on March 1, 1954. The explosion’s yield was three times greater than expected, leading to the worst radioactive contamination ever caused by the United States.
March 1, 1954, at 6:45 AM local time on Bikini Atoll, the most powerful thermonuclear bomb to date, nicknamed “Shrimp” and code-named Castle Bravo, exploded. Its yield was up to a thousand times the power of the atomic bomb dropped on Hiroshima in 1945. Although the Castle Bravo test was conducted as a secret, it quickly became an international incident that spurred calls for a ban on atmospheric testing of thermonuclear devices.
A Triple Miscalculation
In the Pacific, on that spring day in 1954, something occurred that was emblematic of humanity’s capacity for irrational action. Military physicists of the time decided to test the most powerful nuclear explosion in history. According to calculations and plans, its yield should have reached 5 megatons of TNT; however, it reached approximately three times that—15 megatons. Scientists failed to account for the fact that the newly used isotope of lithium would produce far more neutrons than anticipated.
Castle Bravo SHRIMP Device Installation
For perspective, if a bomb of the same type as Little Boy—the one dropped on Hiroshima—were detonated in the center of New York, it would result in the immediate death of 300,000 people and over half milion injuries. If it were “Shrimp,” as mentioned above, the number of immediate fatalities would rise to 4 milion with around 3,5 mil. injured.
You can simulate this yourself here: https://nuclearsecrecy.com/nukemap.
The error made by the builders of Shrimp equated to approximately 667 Hiroshima bombs. The nuclear mushroom cloud reached a height of 40 kilometers, with the base diameter extending seven kilometers. A 1.9-kilometer portion of the atoll disappeared, vaporized, and the crater reached a depth of 75 meters. The explosion also caused a temporary climate change.
Apart from the miscalculated explosion strength, a secondary factor played a role. Despite reports of weather changes that shifted the wind direction toward inhabited areas, the nuclear test was approved and the bomb was detonated. The explosion was both significantly stronger than anticipated, and the altered wind direction carried the radioactive fallout elsewhere than originally projected. The fallout and radiation impacted many of the ships involved in the test and took its toll on civilians as well.
Thousands of square miles and dozens of atolls, as well as countless fishing vessels, were contaminated. Three days after the explosion, several hundred inhabitants from the most affected islands were evacuated by the U.S. Navy.
Unfortunate Lucky Dragon
One well-documented case involves the Japanese fishing boat Daigo Fukuryu Maru (known as Lucky Dragon), which was 100 kilometers from the explosion site in an area declared “safe” by the U.S. Three hours after the blast, a fine, white, flaky dust—radioactive fallout—began to settle on its deck (its traces later reached Australia, India, Japan, even the U.S. and parts of Europe). The Japanese fishermen received high radiation doses, suffering from nausea, eye pain, burns, and other symptoms, and set sail back to Japan. Japanese media reported on the incident upon their return, and what had originally been a classified test became an international incident that spurred a significant response, especially in Japan.
However, the Japanese and U.S. governments quickly reached a political settlement, with a transfer of $15.3 million in compensation to Japan. This was of little help to one of Lucky Dragon’s fishermen, 40-year-old Aikichi Kuboyama, who died six months later from radiation exposure. The Marshall Islands still deal with the consequences of various nuclear tests to this day.
The unexpected strength of the detonation, combined with changing wind directions, caused part of the radioactive fallout to reach the inhabited atolls Rongelap and Utrik. Within 52 hours, 86 people from Rongelap and 167 from Utrik were evacuated to Kwajalein, where they received medical care. Several weeks later, many began experiencing alopecia (hair loss) and skin lesions.
Note:
Simulation from https://nuclearsecrecy.com/nukemap (the simulation does not account for actual terrain profiles or land formations).
Sources:
50 Facts About U.S. Nuclear Weapons. The Brookings Institution, August 1996. Archived 2011-07-19, retrieved 2016-05-20.
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