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March 2001

The Laboratory in
the News

Commentary by Michael Anastasio

in the Superblock

Computer Simulation Workshop

Research with TEM

Laser Peening



Mike Anastasio

Michael Anastasio
Associate Director,
Defense and Nuclear

Safety and Security Are Enhanced by Understanding Plutonium

UNDER the Department of Energy's Stockpile Stewardship Program, Lawrence Livermore National Laboratory is working on this crucial mission: assuring the safety and reliability of the nation's nuclear weapons stockpile without underground nuclear testing. A critical task in this scientific endeavor is to determine the behavior of materials in the stockpile, in particular the behavior of plutonium.
Plutonium is a comparatively stable material in weapons; however, its properties are among the most complex of all the elements. Experiments on plutonium have revealed its unusual ground-state structure; seven distinct crystallographic phases; dimensional changes with temperature, pressure, and impurity content; pyrophoricity; a multitude of oxidation states; and a highly anomalous resistivity. These curious behaviors make plutonium the most interesting element in the periodic table.
One major accomplishment of the Stockpile Stewardship Program is a greatly improved understanding of plutonium's many unusual properties. The understanding of how plutonium ages and how that aging affects the performance of a stockpiled weapon is important. With it, we can better develop schedules for the remanufacture of plutonium parts so they are available if and when they are needed. Long lead times are required because of the limited capacity in today's DOE weapons complex for plutonium operations.
Inside Livermore's Superblock area is one of only two centers of plutonium expertise for stockpile stewardship science and technology in the U.S. The Laboratory will play an essential role over the next decade in preserving national competence in plutonium-related issues, material processing, advanced production technologies, enhanced surveillance, and material disposition. The article entitled Inside the Superblock describes the work being performed in the Superblock.

While nuclear testing was crucial for developing the stockpile, the integral nature of the test results could obscure important details. To study the subtleties of plutonium, Laboratory researchers use several scientific approaches. They are combining advances in theoretical modeling with many new nonnuclear research tools, now technically feasible and available because of investments by the Stockpile Stewardship Program. These tools include laboratory experiments to study the microstructure of plutonium, subcritical experiments at the Nevada Test Site to investigate the properties of plutonium shocked and accelerated by high explosives, and computer simulations of plutonium at the molecular and atomic scales. Through a combined theoretical, experimental, and computational approach, Laboratory scientists are solving a number of longstanding unknowns about weapon performance that arose from and remained unresolved through past nuclear testing.
Plutonium aging is examined by fabricating new plutonium metallic samples and comparing them against samples cut from weapons stockpiled over several decades. The samples are subjected to dimensional inspection, surface analysis, tensile testing, mass spectroscopic analysis, transmission electron microscopy, and other tests to establish baselines for plutonium behavior. Livermore scientists have also devised a method for accelerating the aging of plutonium to learn more about how its properties change in weapons over time.
In the Superblock, Livermore is developing modern technologies to provide preproduction fabrication support, should this need ever arise, and also to serve as backup to the Los Alamos plutonium facilities, should they face a problem in their stockpile stewardship activities. But over and above meeting all their many stockpile stewardship responsibilities, Superblock personnel observe rules and procedures that assure the safety, security, and protection of those who work there and elsewhere at the Livermore site and who live in the surrounding community.






































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UCRL-52000-01-3 | March 26, 2001