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ANNUAL CHECKUPS AND PREVENTATIVE MAINTENANCE
Aging Materials–— Plutonium
At Los Alamos and Lawrence Livermore National Laboratories, scientists
are working on mitigating the effects of aging and extending the lifetimes
of the nuclear weapons in the stockpile. These weapons were originally
designed to serve 15 -20 years with routine maintenance before being
replaced.
Aging Affects Performance
To ensure the continued safety, security and reliability of the stockpile, scientists must accurately assess the lifetime
of individual components. As plutonium ages, it changes its properties
and the composition of the primary (the weapon's fission component).
Those changes could affect weapon performance, safety, and reliability.
To predict when such changes require component replacements, scientists
are accelerating the aging process of plutonium. Researchers "spike"
a plutonium alloy with 7.5 percent plutonium-238, thus initiating accelerated
aging. Spiked plutonium accumulates radiation damage 16 times faster
than unspiked plutonium alloys. As a result, in four years the spiked
material will have "aged" the equivalent of 60 years.
By understanding how plutonium components age and how such aging influences
performance of other components, scientists will be able to maintain
a nuclear weapon in peak condition throughout its lifetime.
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WHAT IS OLD?
The United States has never had a nuclear stockpile as old
as it is now, and the task of maintaining it presents great technical challenges.
The weapons contain thousands of parts, including radioactive metals, foams,
and plastics.
TESTING PARTS
Sometimes we can actually test an old part—for example, firing
a detonator to see if it still works. In other cases, we must find ways to study
material nondestructively —without destroying or altering it, such as with
resonant ultrasound spectroscopy. For some tests, we must use special techniques
to investigate sealed weapon compartments without opening them.
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