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.

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.