IEEE Spectrum - North American - March 2009 - 22

BIG BANG: An
atomic bomb
blast near Bikini
Atoll, one of
1054 nuclear
tests the
united states
conducted
between 1945
and 1992.
Photo: courtesy
of NatioNal
Nuclear security
admiNistratioN/
Nevada site office

warheads. These new weapons would be produced
using state-of-the-art industrial methods that
would vastly simplify manufacturing and maintenance and also drive down costs.
Such arguments for new warheads are compelling-
but also controversial. Critics note that under the
Treaty on the Non-Proliferation of Nuclear Weapons,
or NPT, the United States and other nuclear nations
are obligated to work toward eliminating their nuclear
arsenals. Some even argue that U.S. modernization
efforts, though confined so far to paper studies, have
encouraged North Korea, Iran, and other countries
to redouble their efforts to produce nuclear arsenals
of their own. Proponents of building new warheads
counter that these systems would simply be replacing antiquated weapons and that over time the total
arsenal would continue to shrink.
Geopolitics is an inexact science, to put it mildly.
But physics is not, and as physicists who've been
involved in science and national security policy for
many years, we believe that science and technology
can, in this case at least, tell us all we need to know to
decide this issue. Based on the available data, we are
confident that the current program of stockpile stewardship, with some modifications, can preserve the
U.S. arsenal for the foreseeable future and that it isn't
necessary-and may even be counterproductive-to
pursue new warheads.
What we're not saying is that extending the life span
of the arsenal is going to be easy. To understand why,
you're going to need a quick refresher in nuclear history and technology.

Not surprisingly, nuclear weapons quickly gained a
central role in U.S. national security policy. A vast and
secretive nuclear-weapons complex arose, with the U.S.
Department of Defense dictating the military requirements that guided each new warhead design. Designing,
building, testing, and stockpiling those warheads fell to
the laboratories now operated by the U.S. Department
of Energy (DOE)-namely, Lawrence Livermore,
Sandia, and Los Alamos-and the weapons-production
facilities, including Hanford, Oak Ridge, Rocky Flats,
Y-12, Argonne, Savannah River, and Pantex.
Typically, the labs would produce competing
designs for a new warhead, of which one would be
selected. Los Alamos National Laboratory led the
field: Warheads designed there now make up more
than 80 percent of the active stockpile [see table,
"Warheads Produced at Los Alamos"].
After a design was selected, the first prototypes
would be assembled and tested; based on the test results,
nuclear designers would refine their creations. Once a
design was finalized, the weapons would be built in
quantity at one or more of the DOE production facilities, with the final assembly taking place at the Pantex
plant, near Amarillo, Texas.
The weapons would be deployed to the services
for a typical lifetime of 20 years. (Although the U.S.
Army no longer has nuclear forces, the Navy and
Air Force still do.) At any given time, the number of
weapons deployed or held in reserve depended on
the U.S. government's assessment of threats as well
as its international treaty obligations. For nearly five
decades the United States continued to design, build,
and test nuclear weapons, routinely replacing older
he United States invented nuclear weap- warheads with newer, more advanced ones.
ons during World War II and used the first ones
As in any engineering enterprise, the testing phase
toward the end of that war, in August 1945, when was considered crucial. From July 1945 through
U.S. forces dropped atomic bombs on the Japanese September 1992, the country performed 1054 nuclear
cities of Hiroshima and Nagasaki. They remain the tests. Initially, the detonations occurred above ground,
only nuclear weapons ever used in combat.
at the Pacific atolls of Bikini and Enewetak and also
at the Nevada Test Site in the western United States.
After November 1962, U.S. testing moved underground, at the Nevada site.
Then, in 1992, the U.S. government imposed a moratorium on all nuclear testing, which has since been
extended indefinitely. Three years earlier, production of
the plutonium pits that are at the heart of a warhead had
been shut down at the Rocky Flats facility, in Colorado.
Because Rocky Flats was responsible for the plutonium
pits used in all U.S. warheads, its closure effectively
ended the production of new weapons.
That left nuclear weaponeers with a difficult
engineering challenge: Maintain a reliable U.S.
arsenal, but do it without building or testing new
warheads. The strategy they came up with is called
stockpile stewardship.

urveillance, assessment, and refurbishment
are the cornerstones of the Stockpile Stewardship
Program, which began in 1993. A sprawling endeavor
with activities spread over facilities in seven states
[see map, "Stewards of the Stockpile"], the program cost
U.S. taxpayers about $6.5 billion last year. Compared

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