Castle Bravo Facts for Kids

Quick facts for kids Castle Bravo
Film of the Bravo detonation and subsequent mushroom cloud
Information
Country	United States
Test series	Operation Castle
Test site	Bikini Atoll
Date	1 March 1954; 70 years ago (1954-03-01)
Test type	Atmospheric
Yield	15 megatons of TNT (63 PJ)
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Castle Bravo was the first in a series of high-yield thermonuclear weapon design tests conducted by the United States at Bikini Atoll, Marshall Islands, as part of Operation Castle. Detonated on 1 March 1954, the device remains the most powerful nuclear device ever detonated by the United States and the first lithium deuteride-fueled thermonuclear weapon tested using the Teller-Ulam design. Castle Bravo's yield was 15 megatons of TNT [Mt] (63 PJ), 2.5 times the predicted 6 Mt (25 PJ), due to unforeseen additional reactions involving lithium-7, which led to radioactive contamination in the surrounding area.

Fallout, the heaviest of which was in the form of pulverized surface coral from the detonation, fell on residents of Rongelap and Utirik atolls, while the more particulate and gaseous fallout spread around the world. The inhabitants of the islands were evacuated only three days later and suffered radiation sickness. Twenty-three crew members of the Japanese fishing vessel Daigo Fukuryū Maru ("Lucky Dragon No. 5") were also contaminated by the heavy fallout, experiencing acute radiation syndrome, including the death six months later of Kuboyama Aikichi, the boat's chief radioman. The blast incited a strong international reaction over atmospheric thermonuclear testing.

The Bravo Crater is located at 11°41′50″N 165°16′19″E / 11.69722°N 165.27194°E / 11.69722; 165.27194. The remains of the Castle Bravo causeway are at 11°42′6″N 165°17′7″E / 11.70167°N 165.28528°E / 11.70167; 165.28528.

Detonation
International incident
Health impacts
Gallery
See also

Detonation

Bravo detonation and fireball.

The device was mounted in a "shot cab" on an artificial island built on a reef off Namu Island, in Bikini Atoll. A sizable array of diagnostic instruments were trained on it, including high-speed cameras trained through an arc of mirror towers around the shot cab.

The detonation took place at 06:45 on 1 March 1954, local time (18:45 on 28 February GMT).

When Bravo was detonated, within one second it formed a fireball almost 4.5 miles (7.2 km) across. This fireball was visible on Kwajalein Atoll over 250 miles (400 km) away. The explosion left a crater 6,500 feet (2,000 m) in diameter and 250 feet (76 m) in depth. The mushroom cloud reached a height of 47,000 feet (14,000 m) and a diameter of 7 miles (11 km) in about a minute, a height of 130,000 feet (40 km) and 62 mi (100 km) in diameter in less than 10 minutes and was expanding at more than 160 meters per second (580 km/h; 360 mph). As a result of the blast, the cloud contaminated more than 7,000 square miles (18,000 km²) of the surrounding Pacific Ocean, including some of the surrounding small islands like Rongerik, Rongelap, and Utirik.

Castle Bravo mushroom cloud a few seconds after detonation

In terms of energy released (usually measured in TNT equivalence), Castle Bravo was about 1,000 times more powerful than the atomic bomb that was dropped on Hiroshima during World War II. Castle Bravo is the sixth largest nuclear explosion in history, exceeded by the Soviet tests of Tsar Bomba at approximately 50 Mt, Test 219 at 24.2 Mt, and three other (Test 147, Test 173 and Test 174) ≈20 Mt Soviet tests in 1962 at Novaya Zemlya.

International incident

The fallout spread traces of radioactive material as far as Australia, India and Japan, and even the United States and parts of Europe. Though organized as a secret test, Castle Bravo quickly became an international incident, prompting calls for a ban on the atmospheric testing of thermonuclear devices.

Health impacts

Following the test, the United States Department of Energy estimated that 253 inhabitants of the Marshall Islands were impacted by the radioactive fallout. This single test exposed the surrounding populations to varying levels of radiation. The fallout levels attributed to the Castle Bravo test are the highest in history. Populations neighboring the test site were exposed to high levels of radiation resulting in mild radiation sickness of many (nausea, vomiting, diarrhea). The unexpected strength of the detonation, combined with shifting wind patterns, sent some of the radioactive fallout over the inhabited atolls of Rongelap and Utrik. Within 52 hours, the 86 people on Rongelap and 167 on Utrik were evacuated to Kwajalein for medical care. Several weeks later, many people began suffering from alopecia (hair loss) and skin lesions.

The exposure to fallout has been linked to increase the likelihood of several types of cancer such as leukemia and thyroid cancer. The relationship between iodine-131 levels and thyroid cancer is still being researched. There are also correlations between fallout exposure levels and diseases such as thyroid disease like hypothyroidism. Populations of the Marshall Islands that received significant exposure to radionuclides have a much greater risk of developing cancer.

There is a presumed association between radiation levels and functioning of the female reproductive system.