by Michael Anastasio
in the Superblock
Research with TEM
Defense and Nuclear
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
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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