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Concrete Bowl

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Two Mile Mesa Site; Technical Area 6
1944, Leslie Groves, J. Robert Oppenheimer, U.S. Army Corps of Engineers, and Willard C. Kruger. Los Alamos National Laboratory.
  • Concrete Bowl (Courtesy of Los Alamos National Laboratory)

Two Mile Mesa Site in Technical Area 6 includes a structure called the Concrete Bowl (TA-6-37) that used for water recovery tests. Two hundred feet in diameter, it was poured in 16 wedge-shaped sections that slope down to a raised conical platform in the center, on which was erected a 50-foot-high redwood tank holding 500 gallons of water.

One worry with the Gadget implosion device was that its explosive lenses would detonate yet fail to initiate nuclear fission, resulting in a “fizzle” that merely broadcast plutonium with the blast. In anticipation of this possibility, experiments with various containment methods were conducted at the Two Mile Mesa Site between late 1944 and spring 1945. The water recovery method relied on the 50:1 ratio of water to explosive mass to capture bomb fragments. Substituting depleted uranium for plutonium, test assemblies were detonated inside the water tank, and the water along with the uranium was then collected in the bowl.

The idea of detonating a nuclear device inside a tank of water was dropped for the more practical proposal to contain the explosion and its plutonium inside a massive steel vessel. Nicknamed Jumbo because of its gargantuan dimensions, such a vessel was shipped to Trinity Site in April 1945. Smaller prototypes called “jumbinos” had been subjected to shake tests in the Concrete Bowl after the water recovery method was abandoned. In the end, Jumbo was not needed.

The Concrete Bowl is eligible but not yet included in the Manhattan Project National Historical Park.


Los Alamos National Laboratory. The History and Legacy of the Manhattan Project at Los Alamos National Laboratory. Los Alamos, NM: Los Alamos National Laboratory, 2015.

McGehee, Ellen, Sheila McCarthy, Ken Towery, John Ronquillo, Kari Garcia, and John Isaacson. Sentinels of the Atomic Dawn: A Multiple-Property Evaluation of the Remaining Manhattan Project Properties at Los Alamos (1942–1946). Historic Building Survey Report No. 215. Los Alamos: Los Alamos National Laboratory, 2003.

National Park Service. Manhattan Project Sites. Special Resource Study/Environmental Assessment. Washington, D.C.: Department of the Interior, 2010.

Writing Credits

Christopher C. Mead
Christopher C. Mead
Regina N. Emmer

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