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METALS THAT FLOW LIKE FLUID
Hydrodynamic Testing
In
a nuclear weapon, metals like plutonium are squeezed so hard and heated
so much that they begin to flow and mix like fluids. Such metals
are enclosed in a heavy shell known as a tamper. So, what effects does
liquefied metal have on the tamper, particularly if the shell is old?
And what about the molten metal—what's happening within
all that bubbling turbulence?
To answer these and other questions, we conduct hydrodynamic tests—hydrotests,
for short. Hydrodynamics is a branch of science concerned with how
fluids move and how they interact with boundaries.
Bring On the Stunt Double
Conducting a hydrotest is like shooting an action sequence in a movie.
First, researchers build a full-scale nuclear weapon primary with actual
high explosives and other essential ingredients. Before the scientists
call "action," however, they replace the "actor," in this case plutonium-239,
with a stunt double.
The stunt double—a mockup—behaves a lot like
plutonium-239, having similar weight, density, and other metallurgic
properties, but cannot undergo fission. Once the mockup material is in place, scientists detonate
the surrogate primary.
Taking X-Ray Snapshots
During the detonation, researchers use super-fast, extremely intense
X-ray flashes to capture processes that occur in a
millionth of a second. These X-rays, like those used in medical CAT
scans, let researchers study the shapes, densities, and material distribution
during a weapon's
explosion.
From such studies we obtain data to help fine-tune computer models.
Such models in turn enable scientists to make better predictions regarding
weapons safety, performance, and reliability.
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METAL RESPONSES
In a hydrotest, we use high explosives as powerful electric currents to create some of the conditions inside a weapon's imploding primary. Then we take x-ray radiographs to capture the stages and show how the materials react.
We are interested in how the boundaries between fluids in a nuclear weapon interact and change.
To study them, we look at the interplay of pressure, density, and surface tension at the interface that separates two fluids.
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