Gravel Gertie
Encyclopedia
A Gravel Gertie is a type of bunker
Bunker
A military bunker is a hardened shelter, often buried partly or fully underground, designed to protect the inhabitants from falling bombs or other attacks...

 designed for the inspection, handling or dismantling of nuclear weapon
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...

s.

The Gravel Gertie was developed in 1957 by Sandia National Laboratories
Sandia National Laboratories
The Sandia National Laboratories, managed and operated by the Sandia Corporation , are two major United States Department of Energy research and development national laboratories....

 as a modification of existing igloo
Igloo
An igloo or snowhouse is a type of shelter built of snow, originally built by the Inuit....

-style conventional munitions bunkers, which are designed to contain internal explosions by venting much of the overpressure out the main door.

While this represents a good strategy for minimizing the risks posed by normal bombs, the low order detonation
Fizzle (nuclear test)
In nuclear weapons, a fizzle occurs when the testing of a nuclear bomb fails to meet its expected yield. The reason for the failure can be linked to improper bomb design, poor construction, or lack of expertise. All countries that have had a nuclear weapons testing program have experienced fizzles...

 of a nuclear warhead's high explosives would spread vaporized plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...

, tritium
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

 and uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 over the surrounding area via the air. Full nuclear detonation was highly unlikely and impossible to design against, but low-order detonations were a very real risk during assembly, disassembly and maintenance, especially of older gun-type fission weapon
Gun-type fission weapon
Gun-type fission weapons are fission-based nuclear weapons whose design assembles their fissile material into a supercritical mass by the use of the "gun" method: shooting one piece of sub-critical material into another...

s.

A Gravel Gertie has thick reinforced concrete walls but a ventilated roof covered internally by approximately 7 meters of loosely compressed porous gravel
Gravel
Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...

 suspended from steel cables above a false ceiling over the work area. In the event of an explosion, the mass of gravel is designed to compress and move upward with the initial blast, sealing the hole in the roof while allowing some of the gas pressure to escape by passing through the gravel. This "filters" the escaping gases and prevents the building from rupturing. The mass of gravel then falls down into the room when the gasses cool, trapping large amounts of radioactive particles under and within the gravel, further minimizing leakage. According to tests at Sandia, the Gravel Gertie successfully reduced the expected level of external airborne contamination by a factor of 10, which was considered satisfactory to limit exposure to the immediate area.

Gravel Gertie is named after the character of the same name from the Dick Tracy
Dick Tracy
Dick Tracy is a comic strip featuring Dick Tracy, a hard-hitting, fast-shooting and intelligent police detective. Created by Chester Gould, the strip made its debut on October 4, 1931, in the Detroit Mirror. It was distributed by the Chicago Tribune New York News Syndicate...

comics; the compressed mass of gravel forming the ceiling of the bunker reportedly reminded researchers of Gertie's grey, curly hair.

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