Castle Bravo

Tales from the Nuclear Age

Copyright © 2011 by Charles Glassmire


July 8, 2011

 Castle Bravo

           In the pre-dawn darkness of March 1, 1954, Operation Castle is located on the atoll of Bikini,and is quietly counting down to

The Lucky Dragon

detonate the second shot (code named Bravo Shot)  in a series of nuclear weapons detonations. Bravo is to be the second test of a new kind of weapon, known as a Hydrogen Bomb. Unknown to all, drifting quietly about 40 miles to the east of the atoll, is a Japanese fishing boat named The Lucky Dragon. Her crew is working hard and is unaware they have penetrated the waters of the declared test exclusion zone.

         Bikini Atoll, located in the South Pacific Marshall Islands chain, consists of a series of 23 islands surrounding a central deep lagoon of area about 230 square miles. By this time in 1954, the bottom of the Pacific is already a cluttered graveyard for many sunken ships from the U.S. Navy and the Japanese Navy. The ships were floated in the test areas eight years earlier in 1946 and then destroyed during a series of nuclear detonations code named Operation Crossroads. Previously the Marshall Islands were under Mandate of the Empire of Japan, but after World War II some of the islands had come under United States control as part of the Trust Territory of the Pacific Islands. Bikini became part of the Pacific Proving Grounds, and as such, became the site of more than 20 nuclear weapons tests between 1946 and 1958.

          The Ivy Mike shot, in an earlier test series of November 1952, was the nation’s first test of a thermonuclear (Hydrogen) weapon. It was measured at about 10 megatons, or about 750 times more powerful than the Hiroshima Atomic Bomb.  Mike vaporized an island and verified a bomb design known as the “Teller-Ulam”

Deuterium Tritium Fusion

design. Hydrogen weapons were long the dream of Edward Teller during development of the wartime A-Bomb at Los Alamos. Teller always referred to his concept for a hugely more powerful device as “The Super”, and he was constantly agitating Oppenheimer and the entire design team to begin developing the new concept. He said this weapon could be orders of magnitude more powerful than the Uranium-based A-Bomb.

          The Hydrogen Bomb design utilized a different technique than did the A-bomb. Instead of fissioning heavy Uranium nuclei apart into smaller fragments, the H weapon used the same mechanism as in the Sun of our Solar System. This technique fused together light nuclei of Hydrogen isotopes, thereby releasing hugh amounts of binding energy. The reaction uses two forms of Hydrogen (called Deuterium and Tritium). These Hydrogen nuclei have one and two extra neutrons respectively. When they are mixed in a very high temperature environment such as exists on our own Sun, they fuse together to make Helium, and release a neutron with large amounts of energy. An additional somewhat positive side-effect is that there are very little radioactive “fission products” generated as fallout in this type of device (except of course for particles of debris sucked into the explosion.) The Hydrogen is put into the bomb in a chemical form of Lithium Hydride.

          So, in our story, Teller finally gets his way, and Los Alamos proceeds to design and develop the new device. Teller works with

Teller/Ulam Bomb Design

another scientist named Stanislaw Ulam. One big problem arises in how to generate the extreme temperatures needed for the reaction to occur. The bomb has to burn as hot as the Sun or there will be no fusion reaction. Answer: put in an Atomic Bomb (actually two bombs) to set it off and generate enough high temperatures for fusion in the center of the massive explosion.

          The first test, Ivy Mike, is conducted on Eniwetok in 1952, and it is successful. It seems to verify the Teller/Ulam concept. Except that, as noted earlier, there was a problem. Mike needed to keep its chemicals very cold before the blast – cryogenically cold in fact. So for the test, hugh amounts of refrigeration, gas tanks, cables, pumps, plumbing, electrical generators, etc. were needed just to keep the test at liquid cryogenic temperatures during countdown. Consequently, the Mike device was hugh and very cumbersome. No way could this thing ever be used as a weapon, let alone fit into the biggest aircraft. So all the cold liquids had to be eliminated if the H-bomb was ever to be used as a practical weapon.

           Castle Bravo then, was the first test of the so-called “dry fusion” design. It used Lithium Deuteride instead of a mix of Deuterium and

The "Shrimp" H-Bomb

Tritium gas. No cryogenics; the device was still big (almost 11 tons), but perhaps small enough to fit into the biggest bombers. The assembly crew jokingly referred to the device as “the Shrimp”. (The photo has inserted the silhouette of a man for size comparison.)

          Populating areas around the Southern Pacific test waters, the crew of the Lucky Dragon was also joined by small native populations in the Marshalls. Hundreds of natives lived peacefully on the atoll of Rongelap, consisting of 61 islands surrounding a lagoon of some 1000 sq miles. Rongelap lies about 73 miles from the Castle test island. But there is no need for extra concern, since the Bravo shot is expected to be far smaller than the original Mike test of 10 megatons.

          At 06:45 on March 1, 1945 the detonation takes place.

The Castle Bravo Blast

Surprisingly, the fireball generated in less than one second measures over 4.5 miles in diameter. It vaporizes a crater of 6,500 feet across, 250 feet deep, and the mushroom cloud rapidly rises to altitude. Within 10 minutes the cloud tops 130,000 feet, with a diameter of 62 miles. At this time the radioactive cloud is expanding with a frontal velocity of 224 miles per hour.  The detonation seems to be assuming a destructive energy far greater than had been calculated by the test designers. Bravo later is measured to be more than 15 megatons, and is to become the largest thermonuclear detonation ever exploded by the United States…           

 (to be continued …)


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      Charles Glassmire Tales from the Nuclear Age

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    Castle Bravo | Tales from the Nuclear Age

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