JASON report JSR-95-320: Nuclear Testing
NUCLEAR TESTING
Summary and Conclusions
Sidney Drell, Chair
John Cornwall
Freeman Dyson
Douglas Eardley
Richard Garwin
David Hammer
John Kammerdiener
Robert LeLevier
Robert Peurifoy
John Richter
Marshall Rosenbluth
Seymour Sack
Jeremiah Sullivan
Fredrik Zachariasen
JSR-95-320
August 3, 1995
(UNCLASSIFIED)
Cleared for release August 4, 1995
JASON
The MITRE Corporation
7525 Colshire Drive
McLean, VA 22102-3481
(703) 883-6997
JASON Nuclear Testing Study
SUMMARY AND CONCLUSIONS
We have examined the experimental and analytic bases for understanding the
performance of each of the weapon types that are currently planned to
remain in the U.S. enduring nuclear stockpile. We have also examined
whether continued underground tests at various nuclear yield thresholds
would add significantly to our confidence in this stockpile in the years
ahead.
Our starting point for this examination was a detailed review of past
experience in developing and testing modern nuclear weapons, their
certification and recertification processes, their performance margins
(Defined as the difference between the minimum expected and the minimum
needed yields of the primary) and evidence of aging or other trends over
time for each weapon type in the enduring stockpile.
CONCLUSION 1:
The United States can, today, have high confidence in the safety,
reliability, and performance margins of the nuclear weapons that are
designated to remain in the enduring stockpile. This confidence is based
on understanding gained from 50 years of experience and analysis of more
than 1000 nuclear tests, including the results of approximately 150
nuclear tests of modern weapon types in the past 20 years.
Looking to future prospects of achieving a Comprehensive Test Ban Treaty
(CTBT), a stated goal of the United States Government, we have studied a
range of activities that could be of importance to extending our present
confidence in the stockpile into the future. We include among these
activities underground experiments producing sub-kiloton levels of nuclear
yield that might be permitted among the treaty-consistent activities under
a CTBT.
Three key assumptions underlie our study:
(1) The U.S. intends to maintain a credible nuclear deterrent.
(2) The U.S. remains committed to the support of world-wide
non-proliferation efforts.
(3) The U.S. will not encounter new military or political circumstances in
the future that cause it to abandon the current policy --- first announced
by President Bush in 1992 --- of not developing any new nuclear weapon
designs.
CONCLUSION 2:
In order to maintain high confidence in the safety, reliability, and
performance of the individual types of weapons in the enduring stockpile
for several decades under a CTBT, whether or not sub-kiloton tests are
permitted, the United States must provide continuing and steady support
for a focused, multifaceted program to increase understanding of the
enduring stockpile; to detect, anticipate and evaluate potential aging
problems; and to plan for refurbishment and remanufacture, as required.
In addition the U.S. must maintain a significant industrial infrastructure
in the nuclear program to do the required replenishing, refurbishing, or
remanufacturing of age-affected components, and to evaluate the resulting
product; for example, the high explosive, the boost gas system, the
tritium loading, etc. Important activities in a stockpile stewardship
program that will sustain a strong scientific and technical base,
including an experienced cadre of capable scientists and engineers, are
described in the body of this study.
The proposed program will generate a large body of technically valuable
new data and challenging opportunities capable of attracting and retaining
experienced nuclear weapons scientists and engineers in the program. This
is the intent of DOE's currently planned stockpile stewardship
program.(See the 1994 JASON Report JSR-94-345 on "Science Based Stockpile
Stewardship".) For the success of this program, the management of the
three weapons laboratories (LANL, LLNL, SNL) must motivate, support, and
reward effort in an area that has lost some of its glamor and excitement
in the absence of new nuclear design and test opportunities.
Nevertheless, over the longer term, we may face concerns about whether
accumulated changes in age-affected weapons components, whose replacements
might have to be manufactured by changed processes, could lead to
inadequate performance margins and reduced confidence in the stockpile.
Enhancements of performance margins will add substantially to long-term
stockpile confidence with or without underground tests. To cite one
example, we can adjust the boost gas fill or shorten the time interval
between fills. (This is discussed more fully in the classified text.)
CONCLUSION 3:
The individual weapon types in the enduring stockpile have a range of
performance margins, all of which we judge to be adequate at this time.
In each case we have identified opportunities for further enhancing their
performance margins by means that are straightforward and can be
incorporated with deliberate speed during scheduled maintenance or
remanufacturing activities. However greatest care in the form of
self-discipline will be required to avoid system modifications, even if
aimed at "improvements", which may compromise reliability.
This brings us to the issue of the usefulness, importance, or necessity of
reduced-yield (less than 1 kiloton) underground tests for maintaining
confidence in the weapon types in the U.S. stockpile over a long period of
time.
For the U.S. stockpile, testing under a 500 ton yield limit would allow
studies of boost gas ignition and initial burn, which is a critical step
in achieving full primary design yield. The primary argument that we
heard in support of the importance of such testing by the U.S. is the
following: the evidence in several cases and theoretical analyses
indicate that results of a sub-kiloton (~ 500 tons) test of a given
primary that achieves boost gas ignition and initial burn can be
extrapolated to give some confidence in the yield of an identical primary
with full boosting. Therefore, if a modified or remanufactured primary is
introduced into the stockpile in the future to correct some aging problem,
such tests on the modified system would add to confidence that the
performance of the new primary is still adequate.
It follows from this argument that the utility to the U.S. of testing at
yields of up to approximately 500 tons depends on such tests being
performed on a continuing basis and yielding reproducible results. If
they are permitted only for a few years, such tests could add to the
theoretical understanding of the boosting process and the reliability of
the computer-codes that attempt to describe it, but would not contribute
directly to the reliability of the weapon in the enduring stockpile in
view of the possible manufacturing changes made at a later date. To gain
evidence as to whether long-term changes in age-affected weapons
components have any impact on boost-performance the tests would have to be
made with the remanufactured weapons themselves.
CONCLUSION 4:
In order to contribute to long term confidence in the U.S. stockpile,
testing of nuclear weapons under a 500 ton yield limit would have to be
done on a continuing basis, which is tantamount to remaking a CTBT into a
threshold test ban treaty. While such ongoing testing can add to long
term stockpile confidence, it does not have the same priority as the
essential stockpile stewardship program endorsed in Conclusion 2, nor does
it merit the same priority as the measures to enhance performance margins
in Conclusion 3. In the last analysis the technical contribution of such a
testing program must be weighed against its costs and its political impact
on the non-proliferation goals of the United States.
CONCLUSION 5:
Underground testing of nuclear weapons at any yield level below that
required to initiate boosting is of limited value to the United States.
However experiments involving high explosives and fissionable material
that do not reach criticality are useful in improving our understanding of
the behavior of weapons materials under relevant physical conditions.
They should be included among treaty consistent activities that are
discussed more fully in the text (of the full report).
This conclusion is based on the following two observations.
a) So-called hydronuclear tests, defined as limited to a nuclear yield
of less than 4 lbs TNT equivalent, can be performed only after making
changes that drastically alter the primary implosion. A persuasive case
has not been made for the utility of hydronuclear tests for detecting
small changes in the performance margins for current U.S. weapons. At
best, such tests could confirm the safety of a device against producing
detectable nuclear yield if its high explosive is detonated accidentally
at one point. We find that the U.S. arsenal has neither a present nor
anticipated need for such re-confirmation. The existing large nuclear
test data base can serve to validate two- and three-dimensional
computational techniques for evaluating any new one-point safety
scenarios, and it should be fully exploited for this purpose.
b) Testing with nominal yields up to a 100-ton limit permits examination
of aspects of the pre-boost fission process. However, this is at best a
partial and possibly misleading performance indicator.
An agreement to limit testing to very low yields raises the issue of
monitoring compliance. We have not made a detailed study of this issue,
but note the following: Cooperative, on-site monitoring would be
necessary, and relevant measurements, including for example neutron
yields, could be made without compromising classified information on bomb
designs.
We have reviewed the device problems which occurred in the past and which
either relied on, or required, nuclear yield tests to resolve.
CONCLUSION 6:
For the weapon types planned to remain in the enduring stockpile we find
that the device problems which occurred in the past, and which either
relied on, or required, nuclear yield tests to resolve, were primarily the
result of incomplete or inadequate design activities. In part, these were
due to the more limited knowledge and computational capabilities of a
decade, or more, ago. We are persuaded that those problems have been
corrected and that the weapon types in the enduring stockpile are safe and
reliable in the context of explicit military requirements.
Should the U.S., in the future, encounter problems in an existing
stockpile design (which we do not anticipate at present) that are so
serious as to lead to unacceptable loss of confidence in the safety,
effectiveness, or reliability of a weapon type, it is possible that
testing of the primary at full yield, and ignition of the secondary, would
be required to certify a specified fix. Useful tests to address such
problems generate nuclear yields in excess of approximately 10 kT. DOE's
currently planned enhanced surveillance and maintenance program is
intended to alert us to any such need that may arise. A "supreme national
interest" withdrawal clause that is standard in any treaty to which this
nation is a signatory would permit the U.S. to respond appropriately
should such a need arise.
CONCLUSION 7:
The above findings, as summarized in Conclusions 1 through 6, are
consistent with U.S. agreement to enter into a Comprehensive Test Ban
Treaty (CTBT) of unending duration, that includes a standard "supreme
national interest" clause. Recognizing that the challenge of maintaining
an effective nuclear stockpile for an indefinite period without benefit of
underground tests is an important and also a new one, the U.S. should
affirm its readiness to invoke the supreme national interest clause should
the need arise as a result of unanticipated technical problems in the
enduring stockpile.
