Declassification of the Number of Devices and Amount of Plutonium in
Nuclear Tests

The Department of Energy has declassified additional information about
the total number of nuclear tests and the number of nuclear explosive
devices in each nuclear test. The Department of Energy also has
declassified the total quantity of plutonium expended in all U.S.
nuclear weapon tests (atmospheric and underground).

From 1963 to 1992, there were 63 tests that involved more than one
nuclear explosive device. See attached listing for exact details.

Certain tests had as many as 6 nuclear explosive devices and were
conducted in a single vertical shaft. Other tests had two or more
drilled shafts separated by considerable distance with one device in
each hole.

While reviewing the number of tests with multiple detonations, the
Department found a few errors in its list of 204 previously unannounced
nuclear tests. Certain tests with multiple devices were found not to
conform to the Threshold Test Ban Treaty test definition and should have
been counted as additional tests rather than as tests with multiple
devices. The revised total number of U.S. tests is 1054, i.e., three
additional tests.

The total quantity of plutonium expended in all U.S. nuclear
tests is 3.4 metric tons.

On December 7, 1993, the Department of Energy declassified
information identifying a number of previously unannounced tests at the
Nevada Test Site. At the time of that announcement the Secretary of
Energy promised declassification of additional information on those
tests at a later date, if review provided assurance that proliferation
constraints would not be jeopardized. Additionally, a review of the
accuracy of the historical information was to be accomplished. Both
reviews have been completed.

A test is defined in the Threshold Test Ban Treaty as:

The term "underground nuclear weapon test," hereinafter "test,"
means either a single underground nuclear explosion conducted at a test
site, or two or more underground nuclear explosions conducted at a test
site within an area delineated by a circle having a diameter of 2
kilometers and conducted within a total period of time of 0.1 seconds.
The yield of a test is the aggregate yield of all explosions in the
test.

Many of the tests with multiple devices were done in that way to
reduce costs. A large part of the cost of testing involves drilling the
vertical shafts. To save money, sometimes more than one device was
placed in a shaft. In other instances, several single test devices were
arrayed in separate emplacement holes around a set of common central
facilities to minimize construction costs for utilities, ground-zero
buildings or diagnostic facilities.

Some tests, as defined by the Threshold Test Ban Treaty
definition, were in fact two separate holes drilled close to each other
with a device in each hole and were fired simultaneously. The reasons
for relative proximity and timing were operational in nature.

The quantity listed here is based on the evaluation of the records
available, some of which are very old. The quantity may be updated in
the future after re-evaluation of the methodology used originally.

As part of the Secretary of Energy's Openness Initiative, the
Department of Energy is declassifying information regarding the number
of devices detonated in tests. As a result, the American public will
have information that further describes the extent of the United States
testing program. It is hoped that release of this information will
encourage other nuclear weapon nations to declassify similar
information.

The public will know the exact location of each detonated device
in terms of coordinates on the Nevada Test Site and depth of burial.

This information will assist in studies related to the migration
of radioactivity.

The Public. The public will have access to more information
regarding the U.S. nuclear testing program.

Public Interest Organizations. Stakeholders include
environmental, safety and health groups, historians, archivists,
researchers, scientists, and industrial workers, as well as State and
Federal personnel. With this declassification, those interested in
oversight of nuclear weapons testing related activities will have
additional information regarding the number of devices in nuclear
weapons tests. Public interest organizations which have expressed such
an interest include (but are not limited to): Energy Research
Foundation, Environmental Information Network, Friends of the Earth,
Greenpeace, League of Women Voters, Military Production Network,
National Association of Atomic Veterans, National Security Archive,
Natural Resources Defense Council, Nevada Desert Experience, Physicians
for Social Responsibility, Plutonium Challenge, Sierra Club, and the
Western States Legal Foundation.

Freedom of Information Act Requesters. Documents with information
on tests with multiple devices can now be released.

Historians and Researchers. Historians will have more information
on the U.S. nuclear testing program.

Health Researchers. More information regarding certain tests will
be available to health researchers which may aid their epidemiological
studies.

Q. Why is a test defined in such a way to include the detonation of
multiple devices?

A. The definition of a test was carefully constructed in the Threshold
Test Ban Treaty in order to prevent a nation from conducting a test
above the 150 kiloton limit and claiming that it was really two or more
tests with yields of less than 150 kilotons.

Q. How does information revealed about the U.S. nuclear testing
program compare with what is known about other nuclear weapon states
testing programs?

A. Because of the Openness Initiative, the public knows far more about
the U.S. testing program than that of any other nuclear weapon state
testing program. The United States sees no national security threat in
revealing this information and encourages other nuclear weapon states to
reveal more information on their respective testing efforts.

Q. Why did you revise the total number of U.S. tests to 1,054 which is
an increase of three?

A. As part of the review the Department promised in December, we
determined that three tests originally considered as part of an
announced test with multiple detonations should have been defined as
additional tests according to the definition of the Threshold Test Ban
Treaty.

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