Originally posted by glyn
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There are many materials in a nuclear weapon, including metals, high explosives, polymers, and ceramics. The aging of any one of these materials could affect weapon performance, which is why scientists with a wide range
of materials expertise are working to understand aging processes. The challenges these scientists face are illustrated by the aging issues for uranium.
Uranium is the main heavy metal used in a weapon's "rad case" to redirect the x-ray radiation produced by the weapon's fission primary. It is also sometimes used in other weapon parts.Uranium and its alloys age in several ways.
Like steel, pure uranium "rusts" when exposed to the oxygen in air. It is also corroded by hydrogen. Although nuclear warheads are sealed in airtight metal containers to reduce oxidation and corrosion, the high explosives, plastics,
and other organic materials also in the container emit tiny amounts of oxygen, hydrogen, and water vapor that, over time, can cause problems.
Uranium alloys also change their crystal structures, or phases, over time, which also presents aging problems. Materials scientists manufacture a part to have a specific phase in order to optimize its strength, density, or
corrosion resistance. However, the strain a part accumulates during fabrication and the temperature variations a weapon experiences in the field can, over time, change the phase, thereby degrading a part's properties.
Subjected to the considerable heat given off by a weapon's radioactive plutonium, for example, a uranium part—and all other weapon parts—can reach temperatures as high as 40°C (about 100°F). A weapon can also experience temperature extremes in its storage environment, such as a desert. Temperature-induced phase changes that degrade uranium's mechanical properties are a major concern.
The information above is from the Los Alamos National Labratory website.
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