to Lawrence Livermore's Superblock, home to one of just two defense
plutonium research and development facilities in the U.S. Here,
behind fences, guards, and ultrathick walls, scientists are developing
ways to dispose of plutonium left over from the Cold War arms buildup.
They are researching what happens to plutonium's physical properties
over time, important knowledge in light of our aging stockpile of
nuclear weapons. Technicians are machining parts for subcritical
tests that help assure the safety and reliability of our nuclear
stockpile. To a lesser extent, scientists and technicians in the
Superblock also work with enriched uranium and tritium—a radioactive
form of hydrogen.
To say that they work carefully
is to put it mildly. They know what plutonium can do. One plutonium
isotope, plutonium-239, releases huge amounts of energy when split
(fissioned). A quick release of this energy drives a nuclear weapon.
A slow, controlled release is what powers a nuclear reactor. The
controlled release of another one of plutonium's isotopes can power
a heart pacemaker or a deep space probe.
Only small quantities of
any fissionable material can be together in one place in the Superblock
at any time. If enough material is in the right configuration to
form the critical mass needed to sustain a fission chain reaction,
a criticality incident results. Joe Sefcik, leader of Livermore's
Nuclear Materials Technology Program, which manages the Superblock,
is pleased to note, "In our years of working with plutonium and
other fissile materials, there has never been a criticality incident
in the Superblock. We currently have one of the most robust criticality
safety programs in the DOE complex."
The Department of Energy
rules and regulations that govern operation of the Superblock are
similar to those used by the Nuclear Regulatory Commission for nuclear
reactors. Activities in the Superblock also come under the scrutiny
of the Defense Nuclear Facilities Safety Board, an independent agency
chartered by Congress and appointed by the U.S. president. It is
charged with providing safety oversight of the DOE's defense nuclear
A safety analysis report
has been developed for each facility in the Superblock, and all
are updated annually. Worker safety during daily operations is key.
In addition, a multitude of systems provides protection from fire
and any other event that might threaten the public. The Superblock
is a very safe place to work.
Security at the DOE facilities
has been much in the news over the past year, and security at all
DOE sites has been tightened as a result. Getting into the Superblock
has always been a challenge, even for those who work there every
day. Entering the Radioactive Materials Area is even more complicated.
Lists of allowed personnel, metal detectors, x-ray machines, and
searches are the norm. Two fences around the Superblock with a "no
man's land" in between, elaborate electronic security, a guard tower,
and other precautions protect the Superblock from external threats.
Look behind the Fences
The Superblock houses modern
equipment for research and engineering testing of nuclear materials.
The Plutonium Facility is the largest building in the complex and
was the first to become operational, in 1961. As the place where
plutonium expertise is developed, nurtured, and applied, it is the
cornerstone of Livermore's plutonium capability. Research on highly
enriched uranium also is performed here.
Engineering tests to simulate
weapon environments are performed in the Hardened Engineering Test
Building, which is a separate facility. That building also houses
equipment for taking radiation measurements of plutonium– and uranium–containing
assemblies. Two other buildings house the Tritium Facility, which
will likely produce the tritium and deuterium targets for the National
Ignition Facility, the 192-beam laser that will be an important
experimental tool of DOE's Stockpile Stewardship Program to assure
the safety and reliability of our nuclear stockpile.
Adjacent to the Superblock
are a building for high-energy radiography of plutonium and plutonium–containing
components and another for metallurgical characterization of small
samples. Any work there, as well as the transport of parts and samples
to and from the Superblock, is done under the watchful eye of armed
security escorts and health and safety technicians.
In these facilities, the
Nuclear Materials Technology Program has the capability to handle
all phases of virtually any project related to plutonium or uranium.
A typical project often begins with analysis, design, and perhaps
some research. It proceeds through an in-depth analysis of any potential
hazards that might result from the project and the development of
appropriate measures to assure worker and public safety. Next comes
the construction of necessary equipment, performance analysis, and
demonstration of the project's product. A typical project often
ends with deployment of a new process, sometimes throughout the
DOE complex. Several projects discussed in this article typify this
Most work in the Superblock
falls into one of two categories. It is related either to the stewardship
of our nation's arsenal of nuclear weapons or to finding safe ways
to dispose of surplus plutonium components from the Cold War. Physicist
Booth Myers, deputy program leader for Programmatic Operations,
oversees this work.
Behind the scenes, other
activities support the ongoing work. Under the direction of engineer
Alan Copeland, deputy program leader for Facility Operations, a
staff of about 80 maintains the equipment and assures that all operations
are carried out safely and securely. Health physicists, industrial
hygienists, fire safety personnel, security professionals, and health
and safety technicians are constantly reviewing procedures that
control work in the Superblock. Any proposed new operation receives
special attention. Detailed procedures that ensure safety and security
are prepared before any new operation proceeds.
With the end of nuclear testing
in 1992, most of the DOE's production facilities closed or had their
operations cut back severely. The only other site in the DOE complex
with facilities comparable to those in the Superblock is Los Alamos
National Laboratory. The Nuclear Materials Technology Program is
responsible for keeping the Plutonium Facility fully operational
to ensure that work related to plutonium for the Stockpile Stewardship
Program can proceed without interruption.
How Dangerous Is Plutonium?
the nuclear material in the Superblock is plutonium, a dense,
gray metal. Yes, plutonium is dangerous. But it is by no means
the world's most dangerous substance. Many common chemicals
are at least as hazardous, if not more so.
naturally in trace quantities in uranium ore. But most plutonium
is produced from irradiation of uranium in nuclear reactors.
Plutonium is heavy, weighing 75 percent more than lead and
nearly 20 times more than water. There are 18 different isotopes
of plutonium, all of which are unstable and decay into other
elements by emitting various types of radiation. Because of
the radioactivity, a piece of plutonium is warm to the touch.
Plutonium-239 is an essential fuel for nuclear weapons and
is the form of plutonium most often used at Livermore. When
it decays, plutonium-239 emits a helium nucleus (two protons
and two neutrons, also called an alpha particle) to become
uranium-235, which then decays further, eventually into an
isotope of lead. The alpha particle from plutonium-239 travels
only a short distance before grabbing two electrons to become
harmless helium. This range of the danger is just an inch
or two in air. Alpha particles are easily shielded; they cannot
penetrate a sheet of paper or even the thin dead layer of
The danger from swallowing plutonium is not much greater
than from other heavy metals such as lead or mercury. Very
little plutonium is absorbed by the body. Most of it passes
out in feces. In fact, accidentally swallowing a small amount
of parathion, a widely used agricultural insecticide, would
more likely result in death than ingesting a somewhat larger
amount of plutonium.
The real danger from plutonium is from
inhalation. If small particles of it or its oxide are inhaled
into a person's lungs, they may become trapped there. Without
any protective skin, the cells that line the lung can be damaged
by the decaying plutonium, eventually resulting in lung cancer
and perhaps death after many years. Inhaling chlorine gas
would produce about the same effect.
Workers in the Superblock
who handle plutonium are keenly aware of its hazards. Keeping
it outside the body is the aim of the many health and safety
rules that govern the handling of plutonium.
Caution is always the watchword
when working with or around fissile materials. A criticality incident,
where a critical mass could produce a burst of radiation, would
be the most serious safety problem for workers. A greater threat
to the public would be a fire spreading contamination off the Laboratory
site. As discussed in the box below, another danger from handling
plutonium is breathing it. All manner of safety systems and work
control procedures come together to protect workers in the Superblock's
Radioactive Materials Area as well as the general public from any
of these dangers. Considerable protection is also provided to prevent
the theft of materials.
Depending on the specific
work being done, there are 25 different sets of criticality controls
to provide protection. Individual workers likely know four or five
such controls that cover their authorized activities. Work controls
cover handling of fissile material, industrial hazards, fire, and
Virtually all handling of
plutonium is done in a glovebox to protect workers from any airborne
particles. The air pressure in the glovebox is slightly lower than
the pressure in the room, which is lower than in the hall, and so
on. This pressure control assures that the flow of air is always
directed inward to contain and capture any plutonium that might
escape the glovebox in an accident. A complex air handling system
is needed that includes electrical power, fans, and a complete backup
system. A filtration system prevents leakage of any potentially
dangerous material into the atmosphere.
All fissile material must
be accounted for. Following any operation that causes plutonium
debris, such as cutting or machining, the waste crumbs are brushed
into a tray and weighed. The weight for all material–both usable
and residue–must be within a gram of the total weight prior to cutting.
This system of weights and records, maintained by a dedicated computer
network, verifies that all the Laboratory's plutonium can be accounted
for at any time, day or night.
A two-person surveillance
system is required when an operation involves more than a specified
quantity of plutonium. The issue again is accountability. Two workers
must together open the work room, and both must stay in the room,
each within sight of the other at all times. If a visitor happens
to be present, a fourth person must watch the visitor.
All Superblock workers must
participate in the Laboratory's Personnel Security Assurance Program.
It is aimed at assuring the highest levels of reliability and personal
responsibility in all plutonium workers.
Implementation over the past
year and a half of an integrated safety management system has increased
attention to safety throughout the Laboratory. A similar program
was put in place in the Superblock a full year ahead of the rest
of the Laboratory, in the fall of 1998.
All of these procedures are
only as good as the people implementing them. Says Copeland, "It
takes a long time to get a skilled technician up and running in
the Plutonium Facility. Acclimation and training take at least 12
to 18 months. At the same time, people tend to stay. We have very
Bill Poulos, a trained fissile material handler, weighs a machined
plutonium part in a glovebox in the Plutonium Facility's Radioactive
Materials Area. He is using a certified balance that is part
of the plutonium accountability system. Virtually all handling
of plutonium is done in a glovebox such as this one.
In the Superblock, work on
stockpile stewardship includes nonnuclear testing of components
of weapons that are now sitting in the stockpile (including fundamental
physics and engineering experiments on plutonium) and investigating
technologies for remanufacture of plutonium parts in nuclear weapons.
Every year, the Livermore and Los Alamos national laboratories provide
the technical basis for certification to the U.S. president that
the nuclear weapons for which they are responsible are safe and
reliable. Much of the research in the Superblock contributes to
this annual process.
With no new weapons being
designed to replace aging weapons in the stockpile, concern focuses
on what is happening to existing weapons as they get older. Inside
the Plutonium Facility, a "spiked" alloy of plutonium has been created
that accelerates the metal's aging process.
Pyrochemist Karen Dodson
leads the work on production of spiked plutonium, which incorporates
more of the isotope plutonium-238 than would normally be found in
weapons–grade plutonium, 7.5 percent rather than the typical 0.036
percent. Because plutonium-238 is more radioactive, the spiking
process accelerates the formation of defects that occur within the
metal during alpha decay of plutonium. The new alloy ages more quickly,
on the equivalent of 16 years for every year of actual aging, which
makes it perfect for experiments on plutonium decay. Information
from experiments with the spiked alloy will be compared with and
will supplement results generated from tests with naturally aged
To produce the spiked alloy,
plutonium-238 oxide is reduced to metal and combined with standard
weapons-grade plutonium in molten salt. The metal is purified by
electrorefining, and salt residues are filtered and/or scrubbed
with calcium to recover all of the plutonium before disposal. The
metal is then cast into "cookies" that are rolled, heat-treated,
and machined to produce test samples for gas-gun experiments, tensile
testing, examination by transmission electron microscopy, and other
experiments (see "Plutonium Up Close . . . Way Close," in this issue). Equipment for machining the samples
was cold tested (that is, without plutonium) before actual machining
of the spiked alloy began. This year, Dodson will be producing additional
spiked plutonium alloys with varying amounts of plutonium-238.
Subcritical tests of plutonium
at the Nevada Test Site are another key feature of the DOE's Stockpile
Stewardship Program. Subcritical experiments, which are tests that
by design cannot create a fission chain reaction, provide a better
understanding of the fundamental nature of plutonium and how aged
plutonium affects the performance of a weapon (see S&TR,
Are Music to Their Ears").
Engineer James Sevier oversees
the production of plutonium samples in the Superblock for subcritical
tests. Certified fissile material handlers cast a log of plutonium
alloy and then slice it into disks that are machined and finished
into the size and shape required for a particular test. The samples
may also be heat-treated and put through a rolling mill to produce
the grain structure needed. Says Sevier, "The resulting material
looks and more or less behaves like weapons plutonium. The physicists
who design a test must certify that the samples they have asked
for do not contain enough material in the right geometry to go critical."
Plutonium test pieces are
also used in experiments on the Los Alamos gas gun. And various
alloys of plutonium, including spiked ones, will soon be used in
Livermore's new, more powerful two-stage gas gun, JASPER (for Joint
Actinides Shock Physics Experimental Research), at the Nevada Test
Site (see S&TR,September
Gas-Gun Experiments"). The JASPER facility will be coming on
line this year. Shock experiments help scientists determine the
properties of materials at high pressures, temperatures, and strain
steps in producing "cookies" of a spiked plutonium alloy are
shown here, culminating in machinist Paul Benevento's work in
a glovebox (photo at lower left). The spiked alloy has an increased
percentage of the more radioactive plutonium-238, which accelerates
the material's aging process. Experiments on aging plutonium
are a critical part of Livermore's stewardship of the U.S. nuclear
Tests that shake, drop, heat,
and cool samples of fissile materials take place inside the Superblock's
Hardened Engineering Test Building. These tests are designed to
duplicate as nearly as possible the likely environments for a weapon
during its lifetime, known as its stockpile-to-target sequence.
Such tests have been performed on weapons and their components since
the early days of the nuclear weapons program. Mock high explosives
and other carefully engineered materials stand in for many real
substances to prevent potentially dangerous interactions with fissile
Livermore engineers and technicians
have performed several such tests as a service to Los Alamos. In
1999, Livermore vibration tested parts of Los Alamos's W76 weapon.
In the spring of 2000, it shock tested part of the B61 bomb. This
year, it is performing thermal and vibration tests of the W88 weapon.
These tests at Livermore are a "critical step in the certification
process," according to Sefcik.
Says Myers, "One version
of the B61 bomb must penetrate the earth before it detonates, so
it encounters severe shock. Our 4-meter-high drop test machine can
simulate that tremendous shock." For this kind of test, mock high
explosive is wrapped around a plutonium pit inside an aluminum case.
The case has flanges that simulate the mounting to a warhead case.
It is mounted to the test fixture, which in turn is mounted to the
drop machine's carriage. When the test unit is dropped, the speed
of its fall usually depends just on gravity. (Although in the testing
of Los Alamos's B61, carefully arranged bungee cords pull the test
fixture downward to create acceleration and velocities greater than
those that could be achieved by gravity.) The unit comes down onto
a chunk of steel that is suspended on hydraulic cylinders—to isolate
the rest of the machine from the shock pulse. The steel is layered
with felt to calibrate the shock pulse to known shock data for the
The test is performed just
once with plutonium in the mock warhead, but practice runs assure
that velocities, shock pulse, and other parameters are properly
Before the shock test, the
plutonium pit is radiographed. Afterward, the whole test assembly
is radiographed to ensure there are no broken pieces. Then it is
disassembled, and the pit is radiographed alone to see what changes,
if any, occurred during the test. In the case of the B61, no change
or damage resulted from the test. Says Alan Brooks, project engineer
for these environmental tests, "Los Alamos's design work was indeed
Some of the experimental
work includes disassembly of a weapon to determine its continued
safety and reliability. The plutonium pit is taken out for analysis
and is often subjected to destructive testing. Because no new weapons
are being produced, reassembly of the weapons may be required, and
then a newly manufactured pit is needed.
The traditional method for
manufacturing a pit includes casting a disk (blank) of plutonium,
rolling and pressing it to the right size and overall shape, and
machining it into its final shape. This was the process predominantly
used at the Rocky Flats pit manufacturing plant in Colorado before
it shut down in the early 1990s. While effective at producing parts,
this method was expensive, generated considerable waste, and required
a large amount of plutonium to be recycled in the plant. An alternative
approach being developed in the Superblock is to cast the parts
to their near-final shape in a precision mold, which avoids the
rolling, pressing, and extensive machining. This process also reduces
waste generation in the machining process and thus the amount of
plutonium that must be recycled.
Gerard Martinez of Los Alamos (left) and Richard Ring of Livermore
remove the B61 test object from its shipping container. (b)
The B61 test object is mounted on the carriage of the shock
machine for a drop test. The shock test is part of the annual
stockpile certification process.
Plutonium The other major
facet of program work in the Superblock centers on disposal of surplus
plutonium from dismantled U.S. nuclear weapons. Livermore researchers
are continuing the development and demonstration of systems to bisect
weapon pits, remove the plutonium, and convert the material into
either plutonium oxide, which is suitable for disposal by immobilization,
or into mixed oxide fuel for nuclear reactors (see S&TR,
April 1997, "Dealing with a Dangerous Surplus from the Cold War"). The technology for plutonium oxide production
will be transferred to DOE's Savannah River Site. As other DOE sites,
such as Hanford, Rocky Flats, Livermore, and Los Alamos, process
their surplus plutonium, they will ship it to the Savannah River
plant where the oxide feed will be mixed with a ceramic material
to produce inert, puck-shaped disks that immobilize the plutonium
for long-term storage and, ultimately, underground disposal.
The Savannah River plant
is expected to begin the immobilization effort late in this decade.
In the meantime, a way is needed to store the oxide as well as any
other excess plutonium metal from DOE sites. A method of "canning"
plutonium has been developed by British Nuclear Fuels Limited, and
Livermore is working to perfect it. Dodson is leading this effort.
is developing the technology and the hardware to immobilize
DOE's excess plutonium. (a) Plutonium oxide powder is blended
into a ceramic material and then granulated, pressed, and baked
to produce (b) ceramic "pucks" for long-term storage.
the method, processed plutonium oxides or metal are transferred
into a "convenience can," which is itself sealed into an inner and
then an outer can. Both inner and outer cans are laser welded. Says
Dodson, "This canning process eliminates any organic materials that
might react to produce unwanted gases in the package. In addition,
the inner and outer cans are filled with helium that is used to
check for any leaks." The laser welds must meet acceptance criteria
established by the Savannah River Site, or the cans will not be
allowed into storage. That qualification process was just completed
earlier this year.
In another project, workers
in the Superblock are recovering the plutonium from some weapon
parts stored at Rocky Flats and destroying the shapes of the parts.
The plutonium can then be processed and sent to Savannah River.
Needs Plutonium Facility
Plutonium Facility and the Superblock in which it resides are one
of the foundations of the DOE's research on plutonium. The National
Nuclear Security Administration, the recently formed arm of the
DOE for governing the national laboratories, has three missions:
nonproliferation, stockpile stewardship, and meeting the Navy's
needs for reactors. Livermore is home to active programs in two
of these three missions. Says Sefcik, "The DOE's Stockpile Stewardship
Program could not succeed without our Plutonium Facility and the
research we do there. There is only one other plutonium R&D facility
for defense programs in the country, at Los Alamos, and parts of
it are not currently operating. So the experiments we do are key
to certifying the weapons in the stockpile."
"The DOE also has to clean the plutonium out of Hanford, Rocky Flats,
and other DOE sites housing a surplus of plutonium parts. We are
taking the lead in research and development of technologies to dispose
of the material. The Plutonium Facility and other buildings associated
with it in and near the Superblock are essential to cleaning these
sites up and preventing the material from falling into the wrong
are three configurations of the "convenience can" used for storing
plutonium oxide and other excess plutonium metal. These three
configurations are shown, from left, by the first stack of two
cans, second can, and third can. Each convenience can will be
crimp sealed or screw sealed and placed inside an inner can
(fourth one from left), and it is then welded shut. The inner
can is itself placed inside an outer can (fifth from left),
which is also welded shut.
fissile materials, material disposition, Plutonium Facility, plutonium
immobilization, radiography, Stockpile Stewardship Program, subcritical
tests, Tritium Facility.
information contact Joseph Sefcik (925) 423-0671 (firstname.lastname@example.org).
is program leader for the Nuclear Materials Technology Program
at Livermore. He is responsible for the research and development
programs associated with special nuclear materials and for managing
Livermore's Superblock complex. He received his B.S. in applied
and engineering physics from Cornell University and his Ph.D.
in nuclear engineering from the Massachusetts Institute of Technology.
He joined the Laboratory in 1981 to work on issues in nuclear
nonproliferation, export control, and strategic defense. Later,
he participated in the design of thermonuclear devices shot
at the Nevada Test Site and led one of the directed-energy weapons
programs. With the moratorium on nuclear testing, he focused
on applying Laboratory-developed defense technologies to commercial
industry. Before his current assignment, he led the Advanced
Design and Production Technologies (ADAPT) program to bring
modern fabrication and integration technologies into the aging
plants in the DOE complex. Sefcik is the recipient of two Department
of Energy Awards of Excellence and shares an R&D 100 Award for
the development of femtosecond laser materials processing. He
is the author of numerous publications on nuclear nonproliferation,
nuclear design, and directed-energy technology. His current
focus is on nuclear facility safety and security.