# Comprehensive Nuclear-Test-Ban Treaty: Issues and Arguments

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/crs%3ARL34394

## Record

- **Collection:** Congressional research report
- **Document type:** CRS Report
- **Published:** March 12, 2008
- **Citation:** RL34394

## Text

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Prepared for Members and Committees of Congress

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The Comprehensive Nuclear-Test-Ban Treaty would ban all nuclear explosions. It was opened for
signature in 1996. As of March 2008, 178 nations had signed it and 144 had ratified. To enter into
force, 44 specified nations must ratify it; 35 have done so. The Senate rejected the treaty in 1999;
the Bush Administration opposes it. The United States has observed a nuclear test moratorium
since 1992.
There have been many calls worldwide for the United States and others to ratify the treaty. Many
claim that it would promote nuclear nonproliferation; some see it as a step toward nuclear
disarmament. Several measures have been introduced in Congress regarding the treaty; it might
become an issue in the presidential election.
The U.S. debate involves arguments on many issues. To reach a judgment on the treaty, should it
come up for a ratification vote in the future, Senators may wish to balance answers to several
questions in a net assessment of risks and benefits.
Can the United States maintain deterrence without testing? The treaty’s supporters hold that U.S.
programs can maintain existing, tested weapons without further testing, pointing to 12 annual
assessments that these weapons remain safe and reliable, and claim that these weapons meet any
deterrent needs. Opponents maintain that there can be no confidence in existing warheads because
many minor modifications will change them from tested versions, so testing is needed to restore
and maintain confidence. They see deterrence as dynamic, requiring new weapons to counter new
threats, and assert that these weapons must be tested.
Are monitoring and verification capability sufficient? “Monitoring” refers to technical capability;
“verification” to its adequacy to maintain security. Supporters hold that advances in monitoring
make it hard for an evader to conduct undetected tests. They claim that any such tests would be
too small to affect the strategic balance. Opponents see many opportunities for evasion, and
believe that clandestine tests by others could put the United States at a serious disadvantage.
How might the treaty affect nuclear nonproliferation and disarmament? Supporters claim that the
treaty makes technical contributions to nonproliferation, such as limiting weapons programs;
some supporters believe that nonproliferation requires progress toward nuclear disarmament, with
the treaty a key step. Opponents believe that a strong nuclear deterrent is essential for
nonproliferation, that nonproliferation and disarmament are unrelated, and that this nation has
taken many nonproliferation and disarmament actions that the international community ignores.
This report presents a detailed, comprehensive discussion of the treaty’s pros and cons from a
U.S. perspective. It contains an appendix outlining relevant history. It will be updated periodically
with views from protagonists. CRS Report RL33548, Comprehensive Nuclear-Test-Ban Treaty:
Background and Current Developments, by Jonathan Medalia, tracks current developments.

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Introduction ..................................................................................................................................... 1
Can the United States Maintain Deterrence Under the CTBT?....................................................... 2
Can the United States Maintain the Nuclear Weapons Enterprise Without Testing? ................ 4
Can the United States Maintain Existing Warheads Without Testing?...................................... 9
Does Deterrence Require New Warheads That Must Be Tested? ........................................... 12
Do U.S. Warheads Require New Surety Features? Is Nuclear Testing Needed to Add
Them? .................................................................................................................................. 14
Does the Treaty Provide Adequate Protection Against Cheating? ................................................ 16
What Does the Treaty Ban?..................................................................................................... 17
How Capable Is the CTBT Monitoring Regime?.................................................................... 19
Monitoring Systems and Methods .................................................................................... 19
Additional Evasion Scenarios ........................................................................................... 34
Would Clandestine Testing Confer Military Advantages? ...................................................... 36
What Risks Does a Nation Run if It Is Caught Cheating? ...................................................... 39
The CTBT, Nuclear Nonproliferation, and Nuclear Disarmament................................................ 40
The Treaty’s Technical Contributions to Nonproliferation ..................................................... 42
“Nuclear Umbrella,” New Weapons, and Nonproliferation.................................................... 42
The CTBT and the NPT’s “Grand Bargain”............................................................................ 44
The CTBT and Nuclear Disarmament .................................................................................... 48
Moratorium and Entry into Force............................................................................................ 50
Conclusion: Alternatives, Packages, and a Net Assessment.......................................................... 52

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Appendix A. History of Nuclear Testing, Test Bans, and Nonproliferation .................................. 56
Appendix B. Abbreviations ........................................................................................................... 64

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Author Contact Information .......................................................................................................... 64

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The Comprehensive Nuclear-Test-Ban Treaty, or CTBT, would ban all nuclear explosions.1 It was
opened for signature in September 1996; as of February 2008, 178 nations had signed it and 144
of them had ratified.2 To enter into force, 44 nations with nuclear reactors must ratify it; so far, 35
of them have ratified and another 7 have signed. The United States signed the treaty in September
1996; the Senate rejected it in October 1999.
Nuclear test bans have a long history (see Appendix A). There has been strong international
support for test ban treaties; U.S. opinion has been divided. Most U.S. Presidents have sought
agreements to limit testing. The Eisenhower Administration devoted great, but unsuccessful,
effort to negotiating a treaty. The Kennedy Administration sought a CTBT; when that proved
nonnegotiable, it achieved the Limited Test Ban Treaty (LTBT) in 1963, which bans nuclear tests
in the atmosphere, under water, and in space. The Nixon Administration negotiated the Threshold
Test Ban Treaty (TTBT) with the Soviet Union in 1974, which limits underground tests to a yield
of 150 kilotons.3 The Ford Administration negotiated the Peaceful Nuclear Explosions Treaty
(PNET) in 1976, which extended the 150-kiloton limit to peaceful nuclear explosions. The Carter
Administration did not pursue entry into force of these two treaties, but sought a CTBT; partly
because of strong opposition within the Administration, no treaty was concluded. The Reagan
Administration rejected the TTBT and PNET because of verification concerns, but in 1987 began
to negotiate new verification protocols. The George H.W. Bush Administration concluded
negotiation of these protocols; the Senate approved the two treaties in 1990, and they entered into
force in that year. President Bush also signed into law a provision implementing a nine-month
moratorium on nuclear testing starting in October 1992. President Clinton extended the
moratorium; he had initially thought to pursue a test ban treaty of limited duration and permitting
a low explosive yield, but in 1995 he opted for a CTBT of zero yield and unlimited duration. The
George W. Bush Administration has continued the moratorium but has not pursued the CTBT.
U.S. interest in the CTBT waned after 1999, but has since reemerged. In the wake of 9/11 and the
rise of nuclear programs in Iran and North Korea, the risk of nuclear proliferation has become
more stark; some claim the treaty would curb that risk. An op-ed in January 2007 by Henry
Kissinger, Sam Nunn, William Perry, and George Shultz called for steps toward eliminating
nuclear weapons, including ratification and entry into force of the CTBT.4 The Administration is
pursuing the Reliable Replacement Warhead (RRW), which it argues would make nuclear testing
less likely; some envision a CTBT-RRW bargain. Scientists around the world have made progress
in detecting nuclear explosions, and U.S. scientists have made progress in maintaining nuclear
weapons without testing; both topics were of concern in the 1999 debate. Others hold that
monitoring capability is insufficient and that new weapons requiring testing are needed.
International pressure for the treaty has continued through U.N. General Assembly votes and

1
For treaty text, see http://www.state.gov/www/global/arms/treaties/ctb.html. For CTBT developments, see CRS
Report RL33548, Comprehensive Nuclear-Test-Ban Treaty: Background and Current Developments, by Jonathan
Medalia.
2
For status of signatures and ratifications, see http://www.ctbto.org/.
3
One kiloton is equivalent to the explosive force of 1,000 tons of TNT; for comparison, the yield of the Hiroshima
bomb was 15 kilotons.
4
George Shultz, William Perry, Henry Kissinger, and Sam Nunn, “A World Free of Nuclear Weapons,” Wall Street
Journal, January 4, 2007, p. 15.

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international conferences. The treaty might be an issue in the presidential campaign.5 Several bills
and resolutions in the 110th Congress call for ratification of the CTBT.6
Opinions on the treaty reflect contending views on how to obtain security; the role of nuclear
weapons; nuclear nonproliferation and its relationship, if any, to nuclear disarmament; and
international relations generally. (1) Some opponents would revoke the U.S. signature of the
treaty and resume testing to maintain U.S. nuclear weapons, weapons expertise, and the
credibility of the nuclear deterrent, and to develop new weapons. (2) Some supporters and
opponents prefer to maintain the moratorium because of concern for political and international
ramifications, but would test if necessary to fix a warhead problem. (3) Some supporters favor the
treaty on grounds that it has significant value for nonproliferation and can help the United States
monitor nuclear testing by other nations. (4) Others favor the CTBT as a step toward abolition of
nuclear weapons. While many people of all stripes favor abolition of nuclear weapons as an
ultimate goal, those in the fourth group see abolition as a realistic if long-term possibility and
believe that the CTBT is a critical step toward reaching that goal. These views are on a
continuum, with overlaps and shades of gray between positions. Still others feel the treaty would
make little difference in restraining weapons development because technical advances enable
such development without testing, or that it would make little difference in countering nuclear
proliferation as a stand-alone measure. While the United States has observed a nuclear test
moratorium since 1992, few appear to hold it as their preferred position; instead, the treaty’s
supporters accept the moratorium as better than a return to testing, and opponents accept it as
better than the CTBT.
This report seeks to present information that may help Members understand many CTBT issues
and to assess whether, on balance, the United States is better off with or without the CTBT. It is
organized around three aspects of how the treaty might affect U.S. security that were prominent in
the 1999 debate: the CTBT and deterrence; monitoring and verification; and implications for
nuclear nonproliferation and disarmament. In the public debate since 1999, CTBT supporters
have written extensively on all aspects of the treaty, while opponents have written much less. To
provide balance, CRS has obtained many comments from people representing all perspectives. As
a result, this report contains a substantial amount of new material.

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During the Cold War, the United States and Soviet Union engaged in an arms competition, often
called an “arms race” or “action-reaction cycle.” This competition was dynamic. The United
States built submarines carrying ballistic missiles; the Soviet Union followed suit. The Soviet
Union built deeply buried bunkers for its leaders; the United States built very high yield weapons
5

See “2008 Presidential Candidates’ Responses to Seven Key National Security Questions,” Council for a Livable
World, August 16, 2007, at http://www.clw.org/elections/2008/presidential/
2008_presidential_candidates_questionnaire_responses/.
6
These include Section 3122 of S. 1547, the FY2008 national defense authorization bill, as passed by the Senate but
not included in the final legislation; H.Res. 68, recognizing the dangers posed by nuclear weapons and calling on the
President to engage in nonproliferation strategies designed to eliminate these weapons of mass destruction from United
States and worldwide arsenals; and H.Res. 882, expressing the sense of the House that the Senate should initiate a
bipartisan process to give its advice and consent to CTBT ratification.

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to destroy them. Scores of such examples could be listed. Despite this effort, U.S. and Soviet
nuclear strategies and programs resulted in a rough parity between the two sides, and the Cold
War passed into history with no nuclear or conventional war between them.
While deterrence has had many permutations over the years, most in the United States supported
it during the Cold War for want of a better alternative. To be sure, some argued that the United
States should seek superiority, while others held that a minimum deterrent sufficed. Others
reluctantly supported deterrence as an interim measure, arguing that while it purports to reduce
the risk of nuclear war, that very outcome could be expected if a low probability per year is
aggregated over many years. Despite these differing views, Congress supported the forces to
implement a deterrent strategy over many decades. The capability to deter the Soviet Union was
by far the most stressing case, so it was seen as more than sufficient to deter other threats.7 In that
environment, nuclear testing served many purposes. Nuclear tests were mainly conducted for
weapons development, but also for safety, weapons physics, stockpile confidence, and
certification of modifications. Tests also served to maintain skills in weapons science,
engineering, and manufacturing, and to demonstrate the credibility of the U.S. deterrent.
With the end of the Cold War and the Soviet Union, the “comfort” of dealing for four decades
with a single more-or-less predictable adversary ended, to be replaced by considerable
uncertainty. R. James Woolsey, in his 1993 nomination hearing to be Director of Central
Intelligence, said “Yes, we have slain a large dragon, but we live now in a jungle filled with a
bewildering variety of poisonous snakes. And in many ways the dragon was easier to keep track
of.”8
Despite this changed situation, there remains wide, but not universal, agreement in the United
States on the need to maintain a nuclear deterrent for the foreseeable future. Lawrence Korb and
Max Bergmann of the Center for American Progress wrote, “To maintain an effective deterrent,
the United States must continue to possess conventional and nuclear forces capable of quickly
and decisively destroying these regimes,” referring to “extreme regimes ... such as Iran and North
Korea.”9 Sidney Drell and James Goodby, in an Arms Control Association report, “estimate that a
U.S. strategic force of some 500 operationally deployed warheads would be more than adequate
for deterrence. ... this force level would be enough to provide a degree of flexibility in a fluid
security environment.” A responsive force of 400 to 500 warheads would supplement this force.10
The Administration’s Nuclear Posture Review of 2001 stated that with the end of the Cold War,
“U.S. nuclear forces still require the capability to hold at risk a wide range of target types. This
capability is key to the role of nuclear forces in supporting an effective deterrence strategy
relative to a broad spectrum of potential opponents under a variety of contingencies.”11

7

For information on U.S. nuclear policies, see CRS Report RL34226, Nuclear Weapons in U.S. National Security
Policy: Past, Present, and Prospects, by (name redacted).
8
U.S. Congress. Senate. Select Committee on Intelligence. Nomination of R. James Woolsey. S.Hrg. 103-296, 103rd
Congress, 1st Session, 1993, p. 76.
9
Lawrence Korb and Max Bergmann, Restoring American Military Power: Toward a New Progressive Defense
Strategy for America, Center for American Progress, December 2007, p. 17.
10
Sidney Drell and James Goodby, What Are Nuclear Weapons For? Arms Control Association, revised and updated
October 2007, p. 15.
11
U.S. Department of Defense. Nuclear Posture Review [Excerpts] Submitted to Congress on 31 December 2001, p. 7,
available at http://www.globalsecurity.org/wmd/library/policy/dod/npr.htm.

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At issue, though, is what is needed for deterrence. The aim of deterrence has always been to make
an adversary fear it will suffer unacceptable consequences if it takes certain actions. Many believe
that the U.S.-Soviet deterrent relationship worked during the Cold War because threats were
credible and each side understood the consequences of attacking the other. In the post-Cold War,
post-9/11 world, many questions arise. Who is to be deterred, by what threats? What weapons are
needed to make them credible? Is deterrence dynamic, with constant weapons development
needed to respond to changing threats, or is a modest number of nuclear weapons of existing
designs, together with U.S. conventional forces and economic might, more than sufficient? Are
existing nuclear weapons sufficient to deter North Korea, or are new ones needed that could
destroy underground bunkers where leaders might hide, or is the nation so irrational that it is
beyond deterrence, or is a North Korean nuclear attack wildly implausible? Is a satisfactory
outcome possible through diplomacy? What capabilities are needed to deter Iran or to roll back its
nuclear program? Do nuclear forces have any relevance to deterring terrorists or their state
sponsors?
This report now considers CTBT and nuclear testing issues that link to these broader issues of
deterrence.
•

Without testing, can the United States maintain the facilities and skilled
personnel supporting U.S. nuclear weapons? This question is considered first
because these capabilities are the bedrock on which nuclear weapons rest.

•

Can existing weapons be maintained without testing? This is a necessary criterion
for deterrence under the CTBT, as it would take many years to develop and
deploy new weapons.

•

Does deterrence require new weapons that incorporate new military capabilities,
and is testing required to develop them?

•

Do U.S. weapons need more features for safety and security, and is testing
required to add them? Such features might deter terrorist attempts to seize and
detonate these weapons.

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The nuclear weapons enterprise is here taken to mean the nuclear weapons complex managed by
the National Nuclear Security Administration (NNSA), a semiautonomous agency of the
Department of Energy (DOE) responsible for the U.S. nuclear weapons program;12 scientists,
engineers, and production staff of the complex; and Department of Defense (DOD) agencies that
deal with nuclear weapons. Collectively, they provide the skills and capabilities that support and
would use nuclear weapons.
Whether the United States can maintain this enterprise without nuclear testing has been at issue
for decades. In 1963, the Joint Chiefs of Staff conditioned their support for the LTBT on four
12

The nuclear weapons complex consists of eight sites: Los Alamos, Livermore, and Sandia National Laboratories;
Pantex Plant, Y-12 Plant, Kansas City Plant, and Savannah River Site, which together produce, maintain, and dismantle
nuclear weapons; and the Nevada Test Site, which until 1992 was used to conduct nuclear tests but is now used for
other nuclear weapons-related activities and other purposes.

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“safeguards,” or actions this nation would take within the confines of that treaty. The first three
would help maintain this enterprise: Safeguard A, an aggressive underground nuclear test
program; Safeguard B, technology facilities and programs to attract and retain scientists;
Safeguard C, maintenance of the ability to resume atmospheric testing promptly; and Safeguard
D, improvement of monitoring capability.13 President Kennedy’s assurance to Senators Mansfield
and Dirksen, the majority and minority leaders, that the United States would observe these and
other safeguards14 was instrumental in securing Senate advice and consent to ratification. The
safeguards have been observed over time, though Safeguard C has been modified as the perceived
need for atmospheric tests waned and ended. As Appendix A details, other nuclear test limitation
treaties were negotiated and entered into force between 1974 and 1990.
The Hatfield-Exon-Mitchell amendment, Section 507 of the FY1993 Energy and Water
Development Appropriations Act, P.L. 102-377, mandated a nine-month moratorium on nuclear
testing beginning in October 1992, limited testing thereafter, and directed the President to report
on a plan for achieving a CTBT by September 30, 1996. President Clinton extended the
moratorium several times. In response to the prospect of a permanent halt to testing, Congress, in
Section 3138 of P.L. 103-160, the FY1994 National Defense Authorization Act, and the President,
in Presidential Decision Directive 15, mandated a Stockpile Stewardship Program (SSP) to
maintain U.S. nuclear capabilities in a no-test era.
In 1995, President Clinton announced his decision to seek a zero-yield CTBT. He conditioned the
CTBT on six safeguards: (A) SSP, (B) modern laboratory facilities and nuclear technology
programs to attract and retain scientists, (C) the “basic capability to resume nuclear test
activities,” (D) continued R&D to improve the ability to monitor compliance with the treaty, (E)
continued improvement of intelligence capabilities to provide information on nuclear weapons
programs worldwide, and (F) the understanding that if a key nuclear weapon type could no longer
be certified as safe or reliable, “the President, in consultation with Congress, would be prepared
to withdraw from the CTBT under the standard ‘supreme national interests’ clause in order to
conduct whatever testing might be required.”15 Safeguards A, B, C, and F would help maintain
the nuclear weapons enterprise.
In the 1999 CTBT debate, SSP, as the core of U.S. ability to maintain the nuclear weapons
enterprise without testing, was a major issue. SSP had been in being for a short time, resulting in
uncertainty on its ability to maintain existing weapons. Former National Security Adviser Brent
Scowcroft, former Secretary of State Henry Kissinger, and former Deputy Secretary of Defense
John Deutch questioned whether funding would be maintained and wrote that SSP “is not
sufficiently mature to evaluate the extent to which it can be a suitable alternative to testing.”16
Former Secretary of Defense Caspar Weinberger said, “[i]f we need nuclear weapons, we have to
know that they work. That is the essence of their deterrence.... The only assurance that you have
13

Testimony of General Maxwell Taylor, Chairman, Joint Chiefs of Staff, in U.S. Congress. Senate. Committee on
Foreign Relations, Nuclear Test Ban Treaty, hearings on Executive M, 88th Congress, 1st Session, 1963, pp. 274-275.
14
Letter from President John Kennedy to Hon. Mike Mansfield and Hon. Everett McKinley Dirksen, in address by
Senator Dirksen on the Nuclear Test Ban Treaty, U.S. Congress. Congressional Record, September 11, 1963, p. 1679016791.
15
U.S. White House. Office of the Press Secretary. “Fact Sheet: Comprehensive Test Ban Treaty Safeguards.” August
11, 1995, p. 1.
16
Letter to Hon. Trent Lott, Majority Leader, U.S. Senate, and Hon. Thomas A. Daschle, Minority Leader, U.S. Senate,
October 5, 1999, in U.S. Congress. Senate. Committee on Armed Services. Comprehensive Test Ban Treaty. S.Hrg.
106-490, 106th Congress, 1st Session, 1999 (hereinafter SASC CTBT hearings, 1999), pp. 100-101.

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that they will work is to test them.”17 John Browne, Director of Los Alamos, argued that
Safeguard F was absolutely essential,18 while Weinberger expressed concern that the President
would not exercise it.19 Six former Secretaries of Defense were concerned that an indefiniteduration CTBT could lead to loss of expertise, the topic of President Clinton’s Safeguard B:
Another implication of a CTBT of unlimited duration is that over time we would gradually
lose our pool of knowledgeable people with experience in nuclear weapons design and
testing. Consider what would occur if the United States halted nuclear testing for 30 years.
We would then be dependent on the judgment of personnel with no personal experience
either in designing or testing nuclear weapons. In place of a learning curve, we would
experience an extended unlearning curve.20

Such uncertainties cast doubt for some Senators on the CTBT. Senator Olympia Snowe said,
“there are [SSP] methods that are yet to be proven and we are years or decades away from
knowing whether or not they are reliable.”21 Senator John Warner said, “there are honest
differences on both sides leaving clearly a reasonable doubt, and I come from the old school that
it should be beyond any reasonable doubt if we are going to take a step that affects our vital
security interests for decades to come, indeed possibly into perpetuity as it relates to this cadre of
weapons.”22
The treaty’s defenders tried to give assurance on these points. Secretary of State Madeleine
Albright said, “We have also now said that [the nuclear weapons laboratories] would have $45
billion over a 10-year period to be able to update and keep going all of the various parts of the
stewardship program,” and the United States would “maintain the capability to test again should
the need ever arise.”23 Secretary of Energy Richardson “stress[ed] that the President, in
consultation with Congress, can withdraw from this treaty if a high level of confidence in the
safety and reliability of a nuclear weapon critical to our nuclear deterrent cannot be certified. As
Secretary of Energy, I would not hesitate to so advise the President in the event it becomes
necessary for our country to conduct tests.”24 Senator Carl Levin also emphasized Safeguard F:
if lab directors and other experts ... cannot certify to us 2 years, 4 years, 6 years, 10 years
from now that this is a safe and reliable stockpile, then we are giving everybody notice who
signs this treaty that under our supreme national interest clause we are prepared to withdraw.
So in a sense this treaty is almost a year to year treaty.25

17

U.S. Congress. Senate. Committee on Foreign Relations. Final Review of the Comprehensive Nuclear Test Ban
Treaty (Treaty Doc. 105-28), S.Hrg. 106-262, 106th Congress, 1st Session, 1999 (hereinafter SFRC CTBT hearing,
1999), p. 14.
18
SASC CTBT hearings, 1999, p. 111.
19
SFRC CTBT hearing, 1999, p. 42.
20
Letter from James Schlesinger, Richard Cheney, Frank Carlucci, Caspar Weinberger, Donald Rumsfeld, and Melvin
Laird to The Honorable Trent Lott, Majority Leader, United States Senate, and The Honorable Tom Daschle,
Democratic Leader, United States Senate, in SASC CTBT hearings, 1999, p. 57.
21
SASC CTBT hearings, 1999, p. 43.
22
SFRC CTBT hearing, 1999, p. 52.
23
SFRC CTBT hearing, 1999, pp. 90, 92.
24
SASC CTBT hearings, 1999, p. 107.
25
SASC CTBT hearings, 1999, p. 87.

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How have President Clinton’s safeguards fared since 1999? Safeguards A and B called for SSP
and facilities and programs to attract and retain scientists. CTBT supporters claim that SSP has
made great progress under NNSA. They cite Thomas D’Agostino, then Acting NNSA
Administrator, who said, “stockpile stewardship is working. This program has proven its ability to
successfully sustain the safety, security and reliability of the stockpile without the need to conduct
an underground test for well over a decade.”26 K. Henry O’Brien, RRW Program Manager at
Lawrence Livermore National Laboratory, called SSP a “dramatic success.”27 SSP has developed
sophisticated computer models of nuclear weapons and explosions, has built some of the world’s
most powerful computers, is building the world’s largest laser, and conducts nonnuclear
experiments. Its surveillance program examines warheads for problems, and its Life Extension
Program (LEP) is designed to correct them by replacing components that are, or are expected to
become, defective. Life-extended W87 warheads have been certified for use in the stockpile.
While the first RRW design, “WR1,” is to replace some W76s, Barry Hannah, Chairman of the
RRW Project Officers Group, called the W76 LEP an “excellent program” that he believes “meets
the Navy’s needs.”28 Richard Garwin, IBM Fellow Emeritus who has been involved with nuclear
weapon issues since 1950, does not “agree with the generally stated assumption that confidence
and the reliability of our existing nuclear weapons will inevitably decline with time as the
weapons age.” Instead, “with the passage of time and the improvement in computing tools, I
believe that confidence in the reliability of the existing legacy weapons will increase rather than
diminish.”29 SSP has permitted 12 annual assessments that the U.S. nuclear stockpile is safe and
reliable. It has permitted design of RRW, as discussed later. NNSA is planning to modernize the
nuclear weapons production complex.30 For FY2001-FY2007, SSP received about $42.2 billion;31
its FY2008 current appropriation is $6.3 billion and its FY2009 request is $6.6 billion.32
CTBT opponents are concerned that without nuclear tests that integrate all phenomena, there is
no experimental basis on which designers can be sure that their understanding of a design
corresponds to what they would learn with a nuclear test. As Kathleen Bailey, former Assistant
Director for Nuclear and Weapons Control, Arms Control and Disarmament Agency, testified in
1998, “Virtual reality cannot replace reality.”33 Without new nuclear test data, in this view,
26
Testimony of Thomas D’Agostino, Acting Administrator, National Nuclear Security Administration, in U.S.
Congress. House. Committee on Appropriations. Subcommittee on Energy and Water Development. Hearing on the
Department of Energy’s FY2008 budget for programs in the National Nuclear Security Administration, 110th Congress,
1st Session, March 29, 2007, transcript by CQ Transcriptions.
27
Personal communication, April 2, 2007.
28
Information provided by Dr. Barry Hannah, SES, Branch Head, Reentry Systems, Strategic Systems Program, U.S.
Navy, telephone conversation, October 23, 2006.
29
U.S. Congress. House. Committee on Appropriations. Subcommittee on Energy and Water Development. Hearing on
nuclear weapon activities, 110th Congress, 1st Session, March 29, 2007. Transcript by CQ Transcriptions.
30
See, for example, U.S. Department of Energy. National Nuclear Security Administration. Office of Defense
Programs. “Report on the Plan for Transformation of the National Nuclear Security Administration Nuclear Weapons
Complex.” January 31, 2007, 31 p, Available at http://www.nnsa.doe.gov/docs/Trans_of_NNSA_WC_2007-31-07.pdf.
31
Data for FY2001-FY2004 are for NNSA annual request documents for FY2003-FY2006; data for FY2005-FY2007
are from U.S. Department of Energy. “FY 2007 Operating Plan by Appropriation,” p. 2, http://www.energy.gov/media/
FY2007OperatingPlanForDOE.pdf. NNSA budget documents list SSP funds as “Weapons Activities.”
32
U.S. Department of Energy. Office of Chief Financial Officer. FY 2009 Congressional Budget Request. Volume 1,
National Nuclear Security Administration. DOE/CF-024, February 2008, p. 71.
33
“Testimony of Kathleen Bailey, Senior Fellow, Lawrence Livermore National Laboratory,” in U.S. Congress.
Senate. Committee on Governmental Affairs. Subcommittee on International Security, Proliferation, and Federal
Services. The Comprehensive Test Ban Treaty and Nuclear Nonproliferation, S. Hrg. 105-699, 105th Congress, 2nd
Session, 1998, p. 26.

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ȱ

stewardship tools are unvalidated, so certifications are political statements and it is not possible to
be certain that the stockpile is safe and reliable.34 Supporters say that the computer models are
valid because they fit a vast array of experimental data, notably including the results of the U.S.
nuclear test program; critics respond that while the performance of an individual electronic
component can be validated through repeated testing, a nuclear explosion is an integrated event
that cannot be predicted by analyzing the performance of individual components. It is a different,
and easier, exercise to fit computer models to past tests, they argue, than to see how well a
computer model predicts the outcome of a future test.
SSP rests on skilled personnel. CTBT opponents point to concerns raised by Carol Burns of Los
Alamos National Laboratory: “In 2006, NNSA indicated that about 40% of nuclear weapons
program technical staff members were eligible for retirement.” She noted a decline in production
of students with doctoral degrees in nuclear science, and pointed to a drop in doctoral degrees
earned at U.S. universities in radiochemistry and nuclear chemistry from 33 in 1968 to 4 in
2003.35 Opponents see problems with LEPs. As Ambassador Linton Brooks, then Administrator
of NNSA, said in 2005, “it is becoming more difficult and costly to certify warhead
remanufacture. The evolution away from tested designs resulting from the inevitable
accumulations of small changes over the extended lifetimes of these systems [i.e., warheads]
means that we can count on increasing uncertainty.”36 John Foster, former Director of Defense
Research and Engineering, raised other concerns:
The Stockpile Stewardship Program has been a lifesaver for the nuclear weapons labs. It has
attracted and maintained scientists and engineers and provided new world-class tools for
understanding nuclear weapon performance and advancing weapon science. But I have three
salient concerns. First, U.S. nuclear weapon pit production was stopped in 1989, leading
quickly to a halt in weapons production. The capability to produce nuclear weapons has
atrophied since then. Second, we have not conducted underground nuclear tests since 1992
and we are running risks regarding the safety, reliability and performance of the stockpile.
Third, periodic surveillance of the aging stockpile has revealed the necessity to initiate Life
Extension Programs to refurbish several warhead types. This process introduces new
materials and components into the warheads, which introduces the possibility of “birth
defects” that raise risks.37

Supporters claim that Safeguard C, the “basic capability to resume nuclear test activities,” has
been met, as NNSA reduced the time needed to conduct a nuclear test from 36-plus months to 24
months.38 Opponents respond that without nuclear testing, the capability to test declines as skills
34

This view provided by Kathleen Bailey, former Assistant Director for Nuclear and Weapons Control, U.S. Arms
Control and Disarmament Agency, personal communication, April 20, 2007.
35
“Testimony of Dr. Carol J. Burns, Group Leader, Nuclear and Radiochemistry, Los Alamos National Laboratory,
Before the U.S. House of Representatives, Committee on Homeland Security, Subcommittee on Emerging Threats,
Cybersecurity and Science and Technology, Hearing on H.R. 2631, the Nuclear Forensics and Attribution Act,”
October 10, 2007, pp. 2-4, http://homeland.house.gov/SiteDocuments/20071010175138-84437.pdf.
36
“Statement of Ambassador Linton F. Brooks, Administrator, National Nuclear Security Administration, U.S.
Department of Energy, Before the Senate Armed Services Committee, Subcommittee on Strategic Forces,” April 4,
2005.
37
Personal communication, October 22, 2007.
38
A 2003 NNSA report stated, “Over the past several years the NNSA conducted reviews of the 24- to 36-month test
readiness posture [i.e., the time between a presidential decision to conduct a nuclear test and the actual conduct of that
test] that the NNSA has maintained since Fiscal Year 1996. ... From these reviews, NNSA concluded that because of a
loss of expertise and degradation of some specific capabilities, the U.S. would more likely require about 36 months to
test, with less confidence in being able to achieve the 24-month end of the range. Furthermore, as time passes without
(continued...)

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ȱ

atrophy, procedures become outdated, and equipment falls into disuse. Safeguards D and E do not
deal with SSP. One cannot prove whether the United States would withdraw from the CTBT, as
per Safeguard F, especially as it has not ratified the treaty. U.S. withdrawal from the Antiballistic
Missile Treaty in 2002 might make the prospect of withdrawal from the CTBT appear more
credible, though critics see prospects for withdrawal dependent on who is President, and thus
uncertain.

Š—ȱ‘Žȱ—’ŽȱŠŽœȱŠ’—Š’—ȱ¡’œ’—ȱŠ›‘ŽŠœȱ
’‘˜žȱŽœ’—ǵȱ
During the Cold War, as noted, deterrence was dynamic, with nuclear moves and counter-moves
by the United States and Soviet Union. Testing was essential for both sides to develop new
weapons. In the 1999 debate, arguments over the treaty and deterrence played a minor, and
predictable, part. Both sides in the debate agreed that maintaining the nuclear deterrent was
crucial. Opponents held that without testing, it would be impossible to do so. As former Secretary
of Defense James Schlesinger testified, “In the absence of testing, confidence in the reliability of
the stockpile will inevitably, ineluctably decline.”39 They questioned whether the United States
could, in 1999 if ever, rely on SSP to maintain weapons. The treaty’s supporters had a different
view. Secretary of State Madeleine Albright said, “Under the treaty, America would retain a safe
and reliable nuclear deterrent.”40 And General Henry Shelton, Chairman of the Joint Chiefs of
Staff, testified:
Senator Levin: What you are telling us is that our top uniformed leadership unanimously
support this Treaty?
General Shelton: I might add, Senator Levin, that we would never say that unless we felt that
we could maintain a credible nuclear deterrent and also a safe and reliable stockpile.41

Since 1999, support has continued for this nation to maintain nuclear weapons as long as it retains
them. There are three main approaches for so doing. Supporters of the Reliable Replacement
Warhead (RRW) program and supporters of the Life Extension Program (LEP) each argue that
their approach will reduce the likelihood of testing while the other will increase it. In contrast,
others believe that neither RRW nor LEP can provide sufficient confidence in the safety and
reliability of current warheads without nuclear testing; they therefore see testing as necessary.
RRW, as a funded program, began in the FY2005 Consolidated Appropriations Act, P.L. 108-447;
it was described as a “program to improve the reliability, longevity, and certifiability of existing
(...continued)
further action, the 36-month posture is viewed as increasingly at risk.” U.S. Department of Energy. National Nuclear
Security Administration. Report to Congress: Nuclear Test Readiness. April 2003, p. 5. In contrast, NNSA said that in
FY2005 it “[a]chieved a 24-month [test] readiness posture.” U.S. Department of Energy. Office of the Chief Financial
Officer. FY 2007 Congressional Budget Request. Volume 1, National Nuclear Security Administration. DOE/CF-002,
February 2006, p. 95. However, the FY2009 NNSA request plans to “maintain a minimum readiness posture of 24 to
36 months.” U.S. Department of Energy. FY 2009 Congressional Budget Request. Volume 1, National Nuclear
Security Administration, p. 147.
39
SASC, CTBT hearings, 1999, p. 59.
40
SFRC, CTBT hearing, 1999, p. 72.
41
SASC, CTBT hearings, 1999, pp. 23-24.

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weapons and their components.”42 In the FY2006 National Defense Authorization Act, P.L. 109163, Congress set as an objective that the program “further reduce the likelihood of the
resumption of underground nuclear weapons testing.” The first proposed RRW, WR1, would be
used in place of some W76 warheads on Trident II submarine-launched ballistic missiles. WR1s
would be designed to meet post-Cold War requirements, such as enhanced safety, increased ease
of manufacture, and high confidence without nuclear testing. However, the FY2008 Consolidated
Appropriations Act, P.L. 110-161, eliminated RRW funds, leaving its prospects unclear. An issue
for any future CTBT debate is which approach—RRW or LEP—is less likely to require nuclear
testing in the long term.43
NNSA claims that RRW will make the need for testing unlikely because of steps to increase
confidence. For example, RRW designers used high margins, basically building in more
performance than is needed, to make material deterioration or design or manufacturing defects
less likely to degrade warhead performance below the minimum required. They argued that they
could do so because the design was unconstrained by technologies and design choices made
decades ago. They view added margin as the single most important goal of the design. Another
basis for confidence is that the design stayed close to past experience. Lawrence Livermore
National Laboratory, which designed the nuclear components of WR1, states that components
very similar to those of the WR1 were nuclear tested in the past. For this and other reasons, “there
is direct nuclear test proof that the [WR1] design will perform properly.”44
NNSA and its labs have expressed concerns that, over the long term, minor changes to current
warheads through repeated LEPs will introduce defects and make it harder to maintain reliability,
possibly requiring nuclear testing. They argue that LEPs replace defective or deteriorated
components with replicas. As Thomas D’Agostino said, “The W76 LEP and the life extension
approach is an exact rebuild of what we’ve had in the Cold War stockpile. We try to mimic the
manufacturing processes exactly the way it was done 30 years ago.”45 The concern is that
components and manufacturing processes cannot be replicated precisely, pushing the warhead
beyond the design envelope validated by nuclear testing.46 This problem could result in defects in
life-extended warheads that could cause them to fail.
LEP supporters question whether RRW will provide high confidence. As Steven Fetter of the
University of Maryland said, “Like most other warheads, RRW will have, or could be expected to
have, birth defects or reliability problems that would be discovered and corrected soon after the
warhead was deployed. No one can say whether the unreliabilities introduced by these birth
defects would be greater or smaller than the unreliabilities that would crop up in the existing
warheads due to their age.”47 They thus doubt that a new-design RRW can be certified without
42

U.S. Congress. Committee of Conference. Making Appropriations for Foreign Operations, Export Financing, and
Related Programs for the Fiscal Year Ending September 30, 2005, and for Other Purposes, conference report to
accompany H.R. 4818, 108th Congress, 2nd Session, H.Rept. 108-792, 2004, p. 951.
43
For more detail, see CRS Report RL33748, Nuclear Warheads: The Reliable Replacement Warhead Program and
the Life Extension Program, by Jonathan Medalia.
44
Information provided by Lawrence Livermore National Laboratory, September 19, 2006.
45
Testimony of Thomas D’Agostino to House Appropriations Committee, Subcommittee on Energy and Water
Development, March 29, 2007.
46
On this point, see George Miller, Paul Brown, and Carol Alonso, Report to Congress on Stockpile Reliability,
Weapon Remanufacture, and the Role of Nuclear Testing, Lawrence Livermore National Laboratory Report UCRL53822, October 1987, Chapter 3, “Weapon Remanufacture,” pp. 25-30.
47
Arms Control Association, “The Future of U.S. Nuclear Weapons: The Weapons Complex and the Reliable
(continued...)

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ȱ

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testing. Robert Peurifoy, a former vice president at Sandia National Laboratories, stated, “The
present nuclear weapon stockpile contains 8 or so nuclear weapon types. That population has
enjoyed perhaps 100 successful yield tests. These weapons have benefitted from a test base of
perhaps 1,000 yield tests conducted during the 40 or so years when nuclear testing was allowed.
Is the DoD really willing to replace tested devices with untested devices?”48
LEP’s supporters argue that current warheads are reliable, as evidenced by 12 stockpile
assessments, and that LEP can keep them reliable for many years without testing. While problems
emerge, solutions do as well, and LEP supporters argue that SSP has been keeping at least even in
this race. RRW supporters agree that SSP is making progress; an NNSA official stated, “Each
year, we are gaining a more complete understanding of the complex physical processes
underlying the performance of our aging nuclear stockpile.”49 Further, say LEP advocates, current
warheads stay within design parameters validated by nuclear tests. In this view, SSP and LEP can
maintain margins through careful remanufacture to minimize changes. They also state, to general
agreement, that margins for some warheads could be increased in certain ways with no change to
a warhead.50 While RRWs, as new designs, are likely to have “birth defects,” LEP supporters
claim such defects have been wrung out of existing designs.
Some, however, doubt that either LEP or RRW can be assessed as reliable, in the case of RRW
because it will never be tested and in the case of LEPs because small changes will undermine
confidence in reliability.51 In this view, SSP has enabled only political assessments rather than
technical ones. Since SSP emerged after the moratorium on testing began, these critics hold that
its tools were never validated with nuclear tests dedicated to that purpose, so they could lead to
false conclusions. Accordingly, in this view, NNSA will not know for sure if SSP, and thus RRW
or LEP, work until it conducts nuclear tests. With confidence in the U.S. nuclear arsenal—by the
United States, its friends, and its foes alike—central to deterrence, in this view, the United States
must conduct nuclear tests regardless of political concerns because only testing can maintain
confidence.52
This section has discussed three views: RRW is less likely to require testing than LEP; LEP is less
likely to require testing than RRW; and the United States can have confidence in neither RRW nor
LEP without testing. One could argue a fourth view, that both RRW and LEP are unlikely to need

(...continued)
Replacement Warhead,” press briefing, Washington, DC, April 19, 2007.
48
Personal communication, September 24, 2006.
49
“Statement of Thomas P. D’Agostino, Deputy Administrator for Defense Programs, National Nuclear Security
Administration, Before the House Armed Services Committee, Subcommittee on Strategic Forces,” April 5, 2006, p. 1.
50
One such change involves a revised means of dealing with the boost gas, a mixture of tritium and deuterium gases
injected into the pit to increase its explosive energy. A study found, “Primary yield margins can be increased by
appropriate changes specific to each stockpile system. These include changes to initial boost-gas composition, shorter
boost-gas exchange intervals, or improved boost-gas storage and delivery systems. These modifications have been
validated by nuclear test data for the appropriate systems, and they would not place burdens on the maintenance or
deployment of the systems by the military.” National Academy of Sciences, Committee on Technical Issues Related to
Ratification of the Comprehensive Nuclear Test Ban Treaty, Technical Issues Related to the Comprehensive Nuclear
Test Ban Treaty, Washington, National Academy Press, 2002 (hereinafter NAS report), p. 31 See also JASON report
JSR-99-305, Primary Performance Margins, McLean, VA, MITRE Corporation, 1999, p. 2.
51
Information provided by Robert Barker, former Assistant to the Secretary of Defense for Atomic Energy, November
29, 2006.
52
Information provided by Kathleen Bailey, November 28, 2006.

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testing. This view could lead to a mixed LEP-RRW force. As Henry O’Brien of Lawrence
Livermore National Laboratory stated, “Our best approach for a small stockpile and complex
would be to retain a couple of the better current weapon types (i.e., those with relatively higher
margins, more advanced safety and security technologies, and more sustainable materials), and
replace the rest with a small number of RRW types.”53

˜ŽœȱŽŽ››Ž—ŒŽȱŽšž’›ŽȱŽ ȱŠ›‘ŽŠœȱ‘ŠȱžœȱŽȱŽœŽǵȱ
CTBT opponents argue that the ability to maintain existing weapons without testing through LEP,
even if it can be done, misses the point. Deterrence, as they see it, requires continuing to hold at
risk assets that enemy leaders prize. However, they argue, current nuclear warheads have many
limitations.
•

Current warheads, which were designed during the Cold War, were given high
yield to destroy hard targets like Soviet missile silos. But that yield, in this view,
could cause the United States to refrain from using these weapons out of concern
for inflicting massive civilian casualties in the target area and beyond. As a 2006
Defense Science Board study stated, “weapons that are not seen as useable and
effective by potential adversaries cannot be an effective, reliable deterrent.”54

•

Current warheads, if exploded near the Earth’s surface, would leave much
residual radiation that would contaminate large areas and kill many people,
barring the United States from using them, the treaty’s opponents believe.

•

The radiation output of current warheads, they argue, differs from that needed for
such missions as destroying chemical or biological agents or generating
electromagnetic pulse.

•

Current warheads cannot destroy key targets that enemy leaders would value
highly, such as hardened and deeply buried bunkers where weapons of mass
destruction, key communications nodes, or the leaders themselves might hide.

WR1 shares these limitations. For example, it would have about the same yield as the W76 it
would replace, and would use a reentry body55 that cannot penetrate the ground.
CTBT opponents see deterrence as dynamic, so that it continues to require new military
capabilities that can only be embodied in new weapons that could only be developed with nuclear
testing. The Threat Reduction Advisory Committee, an expert panel advising DOD, stated that
one reason to test would be “[t]o support certification—prior to quantity production—of new
nuclear weapons, should the decision be made that a new weapon design requiring testing is the
only option to achieve a needed capability.” It provided examples of weapons requiring “tailored
physics package design for nuclear effects for new missions,” including:

53

Personal communication, November 7, 2007.
U.S. Department of Defense. Office of the Under Secretary of Defense for Acquisition, Technology, and Logistics.
Defense Science Board. Report of the Defense Science Board Task Force on Nuclear Capabilities. December 2006.
Report summary, p. 15, original emphasis.
55
A reentry body, also called a reentry vehicle or aeroshell, is the cone-shaped device that contains a single warhead
and protects it from heat and other stresses as it reenters the atmosphere on the way to its target.
54

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ȱ
•

Earth-penetrating warheads with reduced collateral effects to defeat hard, deeply
buried targets;

•

Warheads to defeat chemical or biological sites ... while simultaneously
neutralizing released chem-bio agents;

•

Reduced residual radiation warheads.56

The 9/11 attacks brought concerns about nuclear terrorism to the fore, and raised questions about
the link between nuclear weapons and deterrence of rogue states and terrorists. According to the
Nuclear Posture Review of December 2001,
Greater flexibility is needed with respect to nuclear forces and planning than was the case
during the Cold War. The assets most valued by the spectrum of potential adversaries in the
new security environment may be diverse and, in some cases, US understanding of what an
adversary values may evolve. Consequently, although the number of weapons needed to hold
those assets at risk has declined, US nuclear forces still require the capability to hold at risk a
wide range of target types.57

The treaty’s opponents see another value in testing. According to Vice Admiral Robert Monroe
(USN, Ret.), former Director of Defense Nuclear Agency, “an ongoing underground nuclear test
program adds immensely to the credibility of the U.S. deterrent. Conversely, failure to test
virtually destroys the credibility of our nuclear forces. A nation which lacks the strength to test
nuclear weapons will almost surely lack the strength to use them.”58
CTBT supporters hold that current nuclear weapons suffice for deterrence; no adversary leader
would gamble that they would not work, or that the United States would not use them if severely
provoked. At the same time, supporters see nuclear weapons as most unlikely to be used,
regardless of their characteristics or yield, because of the norm that has built up since 1945
against their use. Current nuclear weapons deterred a Russian or Chinese nuclear attack during
the Cold War, it is argued, and will continue to do so, especially as the probability of such attack
must be judged as remote. U.S. conventional forces, the treaty’s supporters claim, deter threats
from other nations. Use of these forces is credible, they can be precisely targeted, and they would
create very much less collateral damage than nuclear weapons.
Further, it is argued, adversaries could readily counter new U.S. nuclear capabilities. Nuclear
weapons to destroy chemical or biological weapons could be defeated by placing the weapons
deep underground; even earth penetrator weapons could not destroy them because the heat and
radiation of the blast would not reach down that far. More simply, the weapons could be moved to
nondescript buildings in cities or to caves in rural areas; U.S. intelligence, in this view, could
locate few if any sites. Earth penetrators could be defeated by deeper burial, greater hardening,
tunneling under a mountain, or dispersing assets to secret aboveground locations.

56

Threat Reduction Advisory Committee. Nuclear Deterrent Transformation Panel. Underground Nuclear Testing:
Issues Regarding Resumption, approved for limited distribution, October 2003, updated for general distribution, March
2005, p. 6.
57
Nuclear Posture Review [Excerpts], submitted to Congress on 31 December 2001, at http://www.globalsecurity.org/
wmd/library/policy/dod/npr.htm.
58
Personal correspondence, November 26, 2007, and January 29, 2008.

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ȱ

The treaty’s proponents see several congressional actions as implying that Congress would not
support testing to develop new weapons. In the last several years, Congress terminated the
“bunker buster” Robust Nuclear Earth Penetrator (RNEP)59 and the Advanced Concepts Initiative,
widely but erroneously thought to be developing a “mini-nuke.” It specified in the FY2006
National Defense Authorization Act that an objective of the RRW program was to further reduce
the likelihood of a return to testing. It eliminated FY2008 funding for RRW.

˜ȱǯǯȱŠ›‘ŽŠœȱŽšž’›ŽȱŽ ȱž›Ž¢ȱŽŠž›Žœǵȱ œȱžŒ•ŽŠ›ȱ
Žœ’—ȱŽŽŽȱ˜ȱȱ‘Ž–ǵȱ
While there are several definitions, surety is here taken to include safety, security, use control, and
use denial. Safety involves protecting a warhead against accidental detonation; security is handled
through a layered approach that includes everything from warhead features to physical security;
use control permits authorized persons to use a warhead only at the direction of the national
command authority; and use denial prevents any unauthorized use of a nuclear weapon. Surety
has always been the most important characteristic in nuclear weapons design, and its technology
has constantly improved, such as with several generations of permissive action links that require a
user to enter a code in order to arm the weapon, and with various safety enhancements. During
the Cold War, nuclear testing was routine, so the question of whether testing was essential for
incorporating these features was moot.
In 1999, CTBT opponents argued that new surety features could and should be added to U.S.
warheads, and could only be added through nuclear testing. In 1997, Siegfried Hecker, then
Director of Los Alamos, testified that “with a CTBT it will not be possible to make some of the
potential safety improvements for greater intrinsic warhead safety that we considered during the
1990 time frame.”60 Robert Barker, former Assistant to the Secretary of Defense for Atomic
Energy, said in 1999, “Of the nine types of weapons that will remain in the inventory only three
types have all three of the most modern safety features while three types have only one such
feature. These safety deficiencies will remain as long as we cannot conduct the necessary nuclear
tests.”61 Secretary of Energy Richardson, in contrast, stated, “Seven years after our last
underground test our stockpile of nuclear weapons is safe and reliable. Three times since 1996 the
Secretary of Energy and the Secretary of Defense have certified this to the President.... Our
nuclear deterrent will continue to be safe and reliable under the Comprehensive Test Ban
Treaty.”62
Also at issue was the need for new surety features. Sidney Drell, emeritus professor of physics at
Stanford University, said in 1999,
I did not support the CTBT then [in 1990]. I thought of some further safety improvements. I
presented some arguments.
59
For a discussion of congressional handling of RNEP, see Jonathan Medalia, “Water Power: Why Congress Zeroed
“Bunker Buster” Appropriations,” Comparative Strategy, no. 26, 2007, pp. 231-248.
60
S.S. Hecker, “Answers to Senator Kyl’s questions,” attachment to letter from S.S. Hecker, Director, Los Alamos
National Laboratory, to Honorable Jon Kyl, September 24, 1997, in U.S. Congress. Senate. Committee on
Governmental Affairs. Subcommittee on International Security, Proliferation, and Federal Services. Safety and
Reliability of the U.S. Nuclear Deterrent. Senate Hearing 105-267, 105th Congress, 1st Session, 1997, p. 84.
61
SASC CTBT hearings, 1999, p. 175.
62
“Prepared Statement by Secretary Bill Richardson,” in SASC CTBT hearings, 1999, p. 109.

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˜–™›Ž‘Ž—œ’ŸŽȱžŒ•ŽŠ›ȬŽœȬŠ—ȱ›ŽŠ¢DZȱ œœžŽœȱŠ—ȱ›ž–Ž—œȱ

ȱ

First of all, the Department of Defense had zero interest. It wanted to spend no money on
making them. Second, some of the problems have been retired. Others have been altered by
handling procedures in the Navy, and they have satisfied themselves and the Department of
Defense that the safety requirements are safe and sound now.63

Others took the opposite view. Bailey and Barker argued, “Given the increasing threat of
terrorism, it would seem prudent to ensure that U.S. nuclear weapons are as safe, secure, and
invulnerable to unauthorized use as possible.”64
In the wake of 9/11, surety has become even more important. As Linton Brooks said in 2005, “We
now must consider the distinct possibility of well-armed and competent terrorist suicide teams
seeking to gain access to a warhead in order to detonate it in place.”65 The prompt response,
adding physical security, has been costly. Added use-denial features could reduce the burden on
guard forces.
Surety features, it is argued, would enhance deterrence, though in a different way than during the
Cold War. One form of nuclear attack would be for suicide terrorists to seize a U.S. nuclear
weapon and detonate it in place; another would be for terrorists to seize a U.S. nuclear weapon,
dismantle it, and use its fissile material to build a weapon. It is difficult at best to deter terrorists
by threatening to use nuclear weapons to destroy a city or training camp in response to a terrorist
nuclear attack; they might view U.S. nuclear use as desirable if it turned many nations against the
United States. Instead, it is hoped, enhanced surety features would deter attack by creating an
unacceptable consequence, namely a high probability of failure. In addition, if such attacks were
to occur, enhanced surety might defeat them.
Weapon designers and NNSA argue that the WR1 design shows that surety features can be added
without testing, and see RRW as essential to obtaining them. Livermore states that the relaxation
of weight constraints for WR1, for example, has allowed a design that incorporates revolutionary
advances in safety and security without nuclear testing.66 In contrast, according to NNSA
testimony, “[m]ajor enhancements in security are not readily available through system retrofits
via the LEP approach.”67
CTBT supporters dismiss enhanced surety as an argument for testing. They see current weapons
as safe enough, as shown by 12 assessments and the absence of accidental U.S. nuclear
detonations. They see a goal of as much surety as possible as a recipe for unending generations of
weapons to add new features. They also see scenarios involving terrorist seizure and detonation
of U.S. warheads as far-fetched because of physical security measures, and feel that such
measures could be enhanced to add surety if needed. They doubt that new surety features that can
be added only by testing are so critical as to warrant testing.
63

SASC CTBT hearings, 1999, p. 180.
Kathleen Bailey and Robert Barker, “Why the United States Should Unsign the Comprehensive Test Ban Treaty and
Resume Nuclear Testing,” Comparative Strategy, no. 22, 2003, p. 132.
65
“Statement of Ambassador Linton F. Brooks, Administrator, National Nuclear Security Administration, U.S.
Department of Energy, Before the Senate Armed Services Committee, Subcommittee on Strategic Forces,” April 4,
2005.
66
Information provided by Lawrence Livermore National Laboratory, personal communication, May 10, 2007.
67
“Statement of Thomas P. D’Agostino, Acting Under Secretary for Nuclear Security and Administrator, National
Nuclear Security Administration, U.S. Department of Energy, Before the Committee on House Armed Services [sic],
Subcommittee on Strategic Forces,” March 20, 2007, p. 4.
64

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CTBT opponents favor the most surety possible in light of the terrorist threat, and hold that more
surety features can be added with testing than without. While it is possible to add guns, gates, and
guards, so doing would be very costly. They maintain that current warheads are not as safe and
secure as possible, and argue that their surety can only be increased through testing. While RRW
offers more advanced surety features than do current warheads, CTBT opponents hold that the
United States can never know if these features will work without testing. They see testing as
needed also to reveal if new surety features on existing warheads or RRWs would impact
performance.

˜Žœȱ‘Žȱ›ŽŠ¢ȱ›˜Ÿ’ŽȱŽšžŠŽȱ›˜ŽŒ’˜—ȱ
Š’—œȱ‘ŽŠ’—ǵȱ
Monitoring and verification have been central to the debate and negotiations on nuclear test bans
for a half-century.68 While the terms are often used interchangeably, there is a difference.
Monitoring involves looking for indicators that a nuclear test has taken place. It is a dynamic
contest between hiders and seekers, with CTBT supporters showing that monitoring capability is
improving and treaty opponents raising doubts about that capability and claiming that evasion
capability is improving.
Verification, literally “truth making,” involves deciding whether a nation is in compliance with its
treaty obligations. At issue is not perfect verification but effective verification. In 1988, Paul
Nitze offered a widely-used definition: by effective verification, “[w]e mean that we want to be
sure that, if the other side moves beyond the limits of the treaty in any militarily significant way,
we would be able to detect such violation in time to respond effectively, and thereby deny the
other side the benefit of the violation.”69 Thus monitoring is a technical activity that provides
data, while verification uses the data to form judgments on compliance. It is for this reason that
the CTBT establishes an International Monitoring System and leaves it to individual nations to
determine whether a nation has violated the treaty.
Monitoring capability, the military value of clandestine tests, and effective verification are linked.
If, as a hypothetical example, tests above 0.1 kiloton had significant military value and the
threshold of detection was 10 kilotons, the CTBT could not be effectively verified, but it could be
if the numbers were reversed. Thus CTBT opponents claim the threshold for detection is high and
that for military value is low; supporters make the opposite claim. Accordingly, the following
section examines what the treaty bans; describes several monitoring technologies and arguments
about their capabilities and weaknesses; considers whether clandestine testing would confer
military advantages; and discusses risks a nation might run if it is caught cheating.
The public 1999 debate on ratification did not go into detail on the technical ability to monitor the
CTBT. For example, no scientists with primary expertise in a monitoring technology testified in
68

For discussions of test ban monitoring and verification issues up to the early 1960s, see Harold Karan Jacobson and
Eric Stein, Diplomats, Scientists, and Politicians: The United States and the Nuclear Test Ban Negotiations, Ann
Arbor, University of Michigan Press, 1966, 538 p.; and Benjamin Greene, Eisenhower, Science Advice, and the
Nuclear Test-Ban Debate, 1945-1963, Stanford, CA, Stanford University Press, 2007, 358 p.
69
U.S. Congress. Senate. Committee on Foreign Relations. The INF Treaty. S.Hrg. 100-522, pt. 1, 100th Congress, 2nd
Session, 1988, part 1, p. 289.

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Senate hearings on the treaty. However, members and staff received extensive classified briefings
from scientists from the national laboratories and from the intelligence community.70 Since 1999,
scientists have made many advances in detection capability that have been widely published. The
most important technical report on monitoring was prepared in 2002 by the National Academy of
Sciences (NAS).71 It is generally favorable to the treaty. Two other overviews of technical
progress prepared in 2007 also favor the treaty.72 Many journal articles discuss specific technical
advances. In contrast, few if any unclassified technical reports rebut claims of progress in
monitoring. Nevertheless, CTBT opponents have developed many arguments, so any future
debate on monitoring is likely to be less lopsided than one might infer from the imbalance in
writing.

‘Šȱ˜Žœȱ‘Žȱ›ŽŠ¢ȱŠ—ǵȱ
Article I of the CTBT sets out the treaty’s basic obligation: “Each State Party undertakes not to
carry out any nuclear weapon test explosion or any other nuclear explosion....” The treaty does
not define “nuclear explosion.” Yet it is physically possible to conduct tiny nuclear explosions
that cannot be detected without cooperative measures. For example, the United States conducted
several dozen “hydronuclear” tests, many releasing fission energy equivalent to less than a gram
of high explosive, during the 1958-1961 nuclear test moratorium.73 As discussed later, some see
the prospect of undetected tests of very low yield as a concern. As a result, a point of contention
in the 1999 debate was whether the treaty barred very low yield tests. Some CTBT critics argued
that Russian and U.S. definitions of zero differed. Senator Richard Shelby referenced “public
statements from the Russian First Deputy Minister of Atomic Energy that Russia intends to
continue to conduct low-yield hydronuclear tests and does not believe that these constitute
nuclear tests prohibited by the treaty.”74 In this view, then, Russia might conduct militarily useful
low-yield nuclear tests and still consider itself as observing the CTBT.
Administration officials responded that all parties understood the treaty was zero yield. Under
Secretary of State John Holum said that the treaty “does ban any nuclear test explosion or any
other nuclear explosion, and in the negotiating record it is very clear that that means there cannot
be any critical yield from a nuclear event. You can do things that do not go critical; you cannot do
things that do.”75 76 Ambassador Stephen Ledogar, who retired from the Foreign Service in 1997
70
Personal communication, Bureau of Verification, Compliance, and Implementation, U.S. Department of State,
January 25, 2008.
71
NAS report.
72
David Hafemeister, “Progress in CTBT Monitoring Since Its 1999 Senate Defeat,” Science and Global Security 15,
2007, pp. 151-183; and Raymond Jeanloz, “Comprehensive Nuclear-Test-Ban Treaty and U.S. Security,” paper
prepared for delivery at conference, “Reykjavik Revisited: Steps Toward a World Free of Nuclear Weapons,” Hoover
Institution, Stanford University, October 24-25, 2007.
73
Robert Thorn and Donald Westervelt, “Hydronuclear Experiments,” Los Alamos National Laboratory, LA-10902MS, UC-2, February 1987, p. 4-5.
74
SFRC CTBT hearing, 1999, p. 56.
75
SFRC CTBT hearing, 1999, p. 99.
76
This paragraph explains terms and concepts relevant to the question of what is a nuclear explosion. A fissile material
is one whose atoms split (fission) when struck by a neutron regardless of its speed; uranium-235 and plutonium are the
fissile materials used in atomic bombs. Each nuclear fission releases a tiny amount of energy, as well as two or three
neutrons. A self-sustaining nuclear chain reaction occurs if the number of neutrons produced by fission equals the
number of neutrons that escape the material or are absorbed within it without causing further fissions. “Criticality” is
the point at which this chain reaction occurs; a “critical mass” is the amount of fissile material just enough to support
(continued...)

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ȱ

and was the chief negotiator for the CTBT under Presidents Reagan, Bush, and Clinton,
elaborated:
As the name suggests, the treaty imposes a comprehensive ban on all nuclear explosions, of
any size, in any place. I have heard some critics of the treaty seek to cast doubt on whether
Russia, in the negotiating and signing of the treaty, committed itself under treaty law to a
truly comprehensive prohibition of any nuclear explosion, including an explosion or
experiment or event of even the slightest nuclear yield. In other words, did Russia agree that
hydronuclear experiments which do produce a nuclear yield, although usually very, very
slight, would be banned and that hydrodynamic explosions, which have no yield because
they do not reach criticality, would not be banned.
The answer is a categoric “yes.” The Russians as well as the rest of the P-5 [China, France,
Russia, the United Kingdom, and the United States, the permanent five members of the U.N.
Security Council] did commit themselves. That answer is substantiated by the record of the
negotiations at almost any level of technicality and national security classification that is
desired and permitted. More importantly, for the current debate, it is also substantiated by the
public record of statements by high level Russian officials as their position on the question of
thresholds evolved and fell into line with the consensus that emerged.77

The issue remains unresolved. In a 2007 letter, the State Department stated:
the Department of State is not aware of any international agreement on what “zero” yield
means. During the negotiation of the Treaty, the P-5 reached an understanding that
subcritical nuclear experiments would not be prohibited under the Treaty. The United States
also made clear that, in its view, supercritical nuclear explosive-driven device tests would be
prohibited under the Treaty. However, there was no agreement among the P-5 that criticality
would be the basis for determining which activities would be permitted under the CTBT and
which activities would not be permitted. Therefore, it is left to the individual State Party to
decide for itself whether a test that produced more than a zero yield would violate the
Treaty.78

(...continued)
criticality. The amount of material for a critical mass depends on many factors, such as shape, density, impurities that
absorb neutrons, and use of material to reflect neutrons back into the fissile material. A nuclear reactor is an example of
a critical chain reaction; it releases energy in a controlled manner. In contrast, a chain reaction in which the number of
neutrons generated increases over time is said to be supercritical; an atomic bomb exemplifies a supercritical chain
reaction, releasing a vast amount of energy in a tiny fraction of a second. The energy released is expressed as yield. It is
typically measured in kilotons, where one kiloton equals the energy released by the explosion of 1,000 tons of TNT;
modern nuclear weapons typically have yields in the range of tens to hundreds of kilotons. In contrast, several types of
experiments producing little to no nuclear yield have been conducted over the years. Hydronuclear experiments were
conducted during the 1958-1961 nuclear test moratorium. They initially used less than a critical mass of fissile
material; as the amount of this material was stepped up toward criticality from one experiment to the next, some of
these experiments resulted in the release of tiny amounts of energy from fission, even as little as a gram of TNT
equivalent or less. Hydrodynamic experiments implode a pit (the first stage or “trigger” of a nuclear weapon) in order
to examine how the pit behaves; these experiments use non-fissile material as a surrogate for fissile material, so they
cannot become critical. Subcritical experiments examine how plutonium behaves when subjected to a spike in pressure,
such as when struck by an explosive-driven metal plate. The plutonium is configured in a way, such as by its shape and
quantity, that it cannot go critical.
77
SFRC CTBT hearing, 1999, pp. 16-17.
78
Enclosure, in letter from Jeffrey T. Bergner, Assistant Secretary, Legislative Affairs, U.S. Department of State, to
The Honorable Jon Kyl, United States Senate, August 9, 2007.

˜—›Žœœ’˜—Š•ȱŽœŽŠ›Œ‘ȱŽ›Ÿ’ŒŽȱ

ŗŞȱ

˜–™›Ž‘Ž—œ’ŸŽȱžŒ•ŽŠ›ȬŽœȬŠ—ȱ›ŽŠ¢DZȱ œœžŽœȱŠ—ȱ›ž–Ž—œȱ

ȱ

˜ ȱŠ™Š‹•Žȱ œȱ‘Žȱȱ˜—’˜›’—ȱŽ’–Žǵȱ
˜—’˜›’—ȱ¢œŽ–œȱŠ—ȱŽ‘˜œȱ
Because of concerns that states parties to the CTBT could cheat and thereby change the strategic
balance, the ability to monitor the treaty has always been an integral part of the debate over the
treaty. Monitoring has always been more difficult for underground nuclear tests than for tests in
other environments. Radioactive particles in the atmosphere (fallout) are readily detectable in
trace amounts. Sound waves in the oceans travel great distances. Tests in space can be detected by
national technical means. It is for this reason that the LTBT banned tests only in the atmosphere,
in space, and under water. Accordingly, much of this section focuses on detection, and evasion of
detection, of underground tests. This section presents a technical background and contending
views for several monitoring technologies.
The treaty contains complex provisions in an effort to monitor compliance with its basic
obligation of conducting no nuclear explosions. It establishes a Comprehensive Nuclear-Test-Ban
Treaty Organization (CTBTO) that would begin operation upon the treaty’s entry into force. Its
elements are a Conference of States Parties; an Executive Council to promote implementation of,
and compliance with, the treaty; and a Technical Secretariat for monitoring. The secretariat is
deploying an International Monitoring System (IMS) to detect nuclear tests;79 an International
Data Center (IDC) to analyze data and disseminate the results to member states; and a Global
Communications Infrastructure to transmit data to, and reports from, the IDC. The treaty provides
for on-site inspections (OSIs) if 30 of the 51 Executive Council members approve. In 1996, the
signatory states established a Preparatory Commission for the CTBTO to implement the
organization, the IMS, and the IDC, and to prepare for OSIs, so that the CTBTO would be fully
operational upon the treaty’s entry into force.
The treaty calls for the IMS to have 321 stations worldwide to monitor signals that might indicate
a nuclear explosion: 170 seismic stations to monitor seismic waves in the Earth; 11 hydroacoustic
stations to monitor underwater sound waves; 60 arrays of infrasound detectors to monitor very
low frequency sound waves in the atmosphere; and 80 radionuclide stations to detect radioactive
particles that a nuclear explosion might produce; as well as 16 radionuclide laboratories to
analyze radioactive samples. Of the seismic stations, 50 are to be primary stations to provide data
to IDC continuously and in real time, while 120 are to be auxiliary stations to provide data when
requested by the IDC. As of November 26, 2007, 37 primary seismic stations, 76 auxiliary
seismic stations, 10 hydroacoustic stations, 37 infrasound arrays, 47 radionuclide stations, and 9
radionuclide laboratories had been certified. That is, they are completed and meet the technical
requirements of the Preparatory Commission. They transmit data automatically and continuously
to the IDC, excepting for the auxiliary stations and the radionuclide laboratories, which transmit
data as requested by the IDC.80
The United States has operated its own system to detect nuclear tests since the 1940s. The present
system, the U.S. Atomic Energy Detection System (USAEDS), is operated by the Air Force
Technical Applications Center (AFTAC). AFTAC states that USAEDS is a “global network of
79

For a map of IMS stations, at http://www.ctbto.org see Verification Regime > Monitoring Facilities > Map of
Facilities.
80
Information provided by Annika Thunborg, Chief, Public Information, Comprehensive Nuclear-Test-Ban Treaty
Preparatory Commission, personal communication, November 26, 2007.

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nuclear event detection sensors” including underground, underwater, atmospheric, and space
sensors.81 NNSA provides technical support for satellite- and ground-based nuclear explosion
monitoring. Other organizations are conducting research on nuclear explosion monitoring as
well.82 While 21 USAEDS seismic stations were part of IMS as of August 200783 (i.e., they
provide data to IDC), USAEDS also has other capabilities, such as detectors on satellites, that are
not part of IMS. USAEDS and IMS are to some extent complementary. USAEDS, as a national
system, focuses on areas of concern to the United States; IMS, as an entity of an international
treaty, maintains a worldwide detection network so no nation feels singled out for special
monitoring attention. IMS makes available to all states signatories, including the United States,
data from its network; some data are from sites that the United States could not access. Further,
IMS data may be more credible to some of those nations than data from USAEDS. The former
come from a transparent, internationally-controlled system, while USAEDS data might be less
convincing to Executive Council members if they suspected that the United States was releasing
information selectively or if the sensors and resulting data were unfamiliar and thus difficult for
some council members to interpret. As the State Department said, “In the case of the DPRK
[North Korean] test, several countries have noted that the combination of IMS and IDC data and
analysis with U.S. national data and analysis provided them with greater confidence in assessing
the event than would have been the case with the U.S. data and analysis alone.”84 In addition to
IMS and USAEDS, academic institutions and national governments operate thousands of other
seismic stations worldwide.85 Some of these stations may feed information to IDC on an ad hoc
basis.
There is general agreement that IMS will be able to detect most nonevasive tests at 1 kiloton or
less. C. Paul Robinson, then director of Sandia National Laboratories, said in 1999, “The
detection threshold that was used informally by treaty negotiators as an unofficial target for the
IMS was about 1 kiloton, non-evasively tested, in environments other than outer space. Although
IMS coverage will not be uniform over the entire globe, it is expected to generally achieve that
informal target.”86 A National Academy of Sciences report places the threshold for nonevasive
underground tests at “significantly better than 1 kt [kiloton]” and says, “For most of Europe, Asia,
and Northern Africa, the detection threshold is down in the range from 30 to 60 tons [i.e., 0.03 to
0.06 kilotons] in hard rock.”87 The detection of the 2006 North Korean nuclear test, with a yield
the United States placed at less than a kiloton,88 by IMS and non-IMS stations supports the claim
of a low detection threshold for nonevasive underground tests.
81
U.S. Air Force. Intelligence, Surveillance, and Response Agency. “Fact Sheet: Air Force Technical Applications
Center.” June 2007. http://www.afisr.af.mil/library/factsheets/factsheet.asp?id=10309.
82
These organizations include the Air Force Research Laboratory, the Army’s Space and Missile Command, the Office
of Naval Research, the Special Geology Program of the U.S. Geologic Survey, and the U.K. Atomic Weapons
Establishment’s Forensic Seismology Group. In addition, other organizations are conducting research relevant to
nuclear explosion monitoring. Information provided by Bureau of Verification, Compliance, and Implementation, U.S.
Department of State, personal communications, February 1 and 4, 2008.
83
Letter from Jeffrey T. Bergner, Assistant Secretary, Legislative Affairs, U.S. Department of State, to The Honorable
Jon Kyl, United States Senate, August 9, 2007, enclosure, answer to question 2.
84
Ibid., answer to question 9.
85
See, for example, Incorporated Research Institutions for Seismology, “Stations & Instrumentation,” available at
http://www.iris.edu/stations/.
86
SASC CTBT hearings, 1999, p. 131.
87
NAS report, p. 42.
88
U.S. Office of the Director of National Intelligence. Public Affairs Office. “Statement by the Office of the Director
of National Intelligence on the North Korea Nuclear Test,” ODNI news release no. 19-06, October 16, 2006.

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Ž’œ–’ŒȱŽŒ‘—˜•˜¢ȱ
Seismology has been used for decades to detect and differentiate between earthquakes and
explosions, though it is very difficult for seismology to differentiate between conventional and
low-yield nuclear explosions. Earthquakes and explosions generate many types of seismic waves
that propagate through the Earth. Various techniques are used to obtain more information from
these waves. For example, seismic arrays are typically groups of 5 to 30 seismometers spread out
over several square kilometers linked to a central point.89 Because of the distance between
seismometers, seismic waves from an event arrive at each seismometer at slightly different times.
These differences can be used to calculate the direction from which the waves arrived. This
technique has been in use for decades.
Other techniques also help extract information. Some seismic waves are teleseismic, detected
even at distances over 9,000 km.90 For example, an IMS station in South America detected
seismic waves from the 2006 North Korean nuclear test.91 Some teleseismic waves travel along
the Earth’s surface, while others travel through the interior. Of the latter, some are shear waves;
an earthquake generates them strongly as the two sides of a fault slide past each other. Others are
pressure waves; an explosion generates them strongly as the pressure of an explosion radiates
outward. The appearance of shear and pressure waves on a seismogram differs, giving a clue
whether an event is an earthquake or explosion. Another difference is that the first waves from an
explosion arrive suddenly, while those from an earthquake build up over a short time. More
recently, regional seismic waves have come into use to differentiate between earthquakes and
explosions. These waves are generally observed at distances of up to 2,000 km; they can often be
detected even when teleseismic waves from an event cannot be.
The direction from which seismic waves from an event arrive at multiple seismic stations around
the world can be used to determine the approximate location of the event. The magnitude of
seismic waves can also be used to calculate the yield of an explosion, though with considerable
uncertainty. The CTBT limits the area of an OSI to 1000 sq. km,92 and the CTBTO Preparatory
Commission stated that in the case of the North Korean nuclear test, “analysis of all available
data allowed for the identification of a potential inspection area of considerably less than 1000
square kilometers” despite the low yield of the explosion.93
Contending views. CTBT critics point to “decoupling” as a method of evading seismic
detection. It dates from the late 1950s.94 This technique involves setting off a blast in an
underground cavity large enough to absorb the force of the blast elastically, thus muffling the
resulting seismic signal. Critics point to a 1966 decoupling experiment conducted in a salt dome
in Mississippi in which a 0.38 kiloton explosion generated a seismic signal that appeared to be

89

NAS report, p. 40.
NAS report, p. 39.
91
“The CTBT Verification Regime Put to the Test—The Event in the DPRK on 9 October 2006,” Comprehensive
Nuclear-Test-Ban Treaty Preparatory Commission, 2007, available at http://www.ctbto.org/press_centre/
featured_articles/2007/2007_0409_dprk.htm.
92
Protocol to the Treaty, Part II, On-Site Inspections, Section A, General Provisions, Paragraph 3.
93
CTBTO Preparatory Commission, “The CTBT Verification Regime Put to the Test.”
94
See Jacobson and Stein, Diplomats, Scientists, and Politicians, pp. 151-154.
90

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ȱ

from an explosion one-seventieth as large.95 Larry Turnbull of the Central Intelligence Agency
said,
In judging whether this evasion scenario is credible, both the feasibility of constructing a
large cavity and of containing the debris from the nuclear explosions must be examined ...
construction of large cavities in both hard rock and salt is feasible, with costs that would be
relatively small compared to effort to produce the material for a nuclear device ... containing
both particulate and gaseous debris is feasible in salt, and more difficult—though not
impossible—in hard rock. Therefore, we judge that the cavity decoupling evasion scenario to
be credible and should be factored into any underground CTB monitoring.96

CTBT supporters respond that while decoupling works for very low yield explosions, it is much
harder for larger ones. The National Academy of Sciences (NAS) report raised ten difficulties in
conducting a decoupled test, such as constructing a cavity clandestinely, predicting the signals
from the test, ensuring that the yield of the device is not greater than planned, and containing
radionuclides. It finds, “Accepting the possibility of a cavity decoupled test, we conclude that
such an underground nuclear explosion cannot be reliably hidden if its yield is larger than 1 or 2
kilotons.”97
CTBT critics believe that decoupling could be concealed. Kathleen Bailey, former Assistant
Director for Nuclear and Weapons Control, Arms Control and Disarmament Agency, and Robert
Barker, former Assistant to the Secretary of Defense for Atomic Energy, reject the claim that the
earth and rock removed to create a cavity would be an indicator of decoupling: “In India, where
the very test site used had been closely observed, no such activity was detected prior to a nuclear
test.”98 CTBT advocates respond that this example is not a valid indicator of U.S. capability to
detect the excavation for decoupling because the test was not decoupled, and a decoupled test
would require excavation of far more material. For example, a cavity 37 meters in radius would
be needed to decouple a 3-kiloton device, with a volume of 212,175 cubic meters. In contrast, a
shaft 10 feet in diameter and 600 feet deep, possible dimensions for a non-decoupled 3-kiloton
test, has a volume of 1,327 cubic meters.99 CTBT opponents reply that excavated material may
not be observed by satellites if someone wants to hide the fact that digging is occurring. Material
could be removed when satellites are not overhead, or it could be moved underground in existing
tunnels. Aqueous excavation could be used to create large cavities in salt domes. In particular,
according to the State Department, “Iran presents particular challenges from a seismic detection
perspective. Iran’s vast numbers of salt domes offer an effective decoupling environment, making
detection particularly difficult in the absence of close-in sensors.”100
95

NAS report, p. 46.
Larry Turnbull, Central Intelligence Agency, “U.S. Monitoring Goals for the Comprehensive Test Ban Treaty,”
address to the Council on Foreign Relations, March 16, 1998, in SASC CTBT hearings, 1999, p. 204; see also p. 200.
97
NAS report, pp. 47-48.
98
Bailey and Barker, “Why the United States Should Unsign the Comprehensive Test Ban Treaty and Resume Nuclear
Testing,” p. 135.
99
Source for radius of a spherical cavity for full decoupling: “The Soviet Union carried out a partially decoupled test of
about 8 to 10 kt in 1976, in a cavity (in salt) of mean radius 37 m (sufficient to fully decouple about 3 kt).” NAS report,
p. 46. Source for dimensions of a shaft: According to one report, “[underground] tests are conducted in vertical drill
holes up to 10 feet in diameter and from 600 ft to more than 1 mile deep.” U.S. Congress. Office of Technology
Assessment. The Containment of Underground Nuclear Explosions. OTA-ISC-414, October 1989, p. 16. Note that the
diameter of the shaft depends on the drilling equipment used, not on the yield of the device.
100
Letter from Jeffrey T. Bergner, Assistant Secretary, Legislative Affairs, U.S. Department of State, to The Honorable
Jon Kyl, United States Senate, August 9, 2007, enclosure, answer to question 9.
96

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ȱ

Supporters of the treaty point to numerous advances in seismological capability that would help
monitor the CTBT. Foremost is the ongoing rollout of the IMS; many of its seismic (and other)
stations around the globe provide data to IDC in real time. As the IMS is an international system,
many of its stations are in areas that the United States could not access, such as in Iran. Further, it
is important that the seismic stations will contribute regional as well as teleseismic data because
regional data is of particular value in detecting low-yield tests and decoupling. One source states,
“Regional waves enhance the ability to detect cavity decoupling because higher frequency waves
are more observable at regional distances and decoupling is smaller at higher frequencies ...
compared to teleseismic waves ...”101 Regional stations have proven more valuable than was
expected; according to U.K. seismologists,
When the IMS was negotiated, the rationale for auxiliary seismic stations [those that provide
data only when interrogated, not on a continuous basis, to the International Data Center] was
that these stations would improve the ability of the IMS to locate seismic events, and to more
finely characterize the seismic source. With the ongoing deployment of the IMS,
seismologists have discovered that the auxiliary stations are of particular value for
identifying the source of a seismic signal as an earthquake or explosion because they pick up
certain seismic waves that can be used in identification. In addition, it has turned out that
having many seismic stations, such as those in individual national or university networks,
complements the IMS stations and increases the availability of data.102

CTBT supporters note that other signatures in addition to characteristics of seismic waves help
differentiate between earthquakes and explosions. Finding that the epicenter of an event is more
than 10 km deep rules out an explosion, as does finding the epicenter at sea in the absence of
hydroacoustic waves indicative of an explosion. Other characteristics specific to local geology aid
determining whether an event is an earthquake or explosion. The CTBTO Preparatory
Commission states that IMS stations around the world detected the North Korean nuclear test of
2006, and IMS was able to locate the test to well under 1000 square km. As another indicator, the
seismic record shows a clear difference between that explosion and an earlier earthquake.
According to seismologists Paul Richards and Won-Young Kim,
The seismogram of 9 October [2006, the North Korean test] has three important features.
First, it shows an impulsive onset of compressional waves ... characteristic of an explosion.
Second, peaks indicative of shear waves in the [Earth’s] crust, which would be typical of an
earthquake, are very weak ... And third, short-period ‘Rayleigh waves’ are apparent. They ...
are known to be excited only by sources at a depth not much more than about 3 or 4 km,
which is much shallower than typical earthquakes.103

Critics point to evasive tactics and weaknesses in seismic monitoring that open prospects for
clandestine testing. Yield can be calculated from the magnitude of seismic waves. Yet many
factors affect the intensity of seismic signals in addition to the yield of a nuclear device. The NAS
report states, “[regional] waves are dependent on local properties of the Earth’s crust and
uppermost mantle—which can vary strongly from one region to another.”104 For example, a
device detonated in soft rock can have ten or more times the yield as one detonated tamped (fully
101

Hafemeister, “Progress in CTBT Monitoring Since Its 1999 Senate Defeat,” p. 160.
Information provided by seismologists at the U.K. Atomic Weapons Establishment, personal communication,
October 11, 2007.
103
Paul Richards and Won-Young Kim, “Seismic Signature,” Nature Physics, January 2007, p. 5. For a seismogram of
the North Korean test, see CTBTO Preparatory Commission. “The CTBT Verification Regime Put to the Test.”
104
NAS report, p. 39.
102

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coupled) in hard rock, yet the seismic signals from each can indicate the same apparent yield
because soft rock transmits seismic energy much less efficiently than does hard rock.105 An
evader, knowing this from the unclassified literature, would consider this difference in selecting a
test site. While CTBT supporters note that regional seismic signals can aid in detecting loweryield nuclear detonations, opponents reply that Russia and China did not permit IMS stations to
be located within hundreds of kilometers of their nuclear test sites, at Novaya Zemlya and Lop
Nor, respectively. The closest IMS station is 1,112 km from Novaya Zemlya, and 783 km from
Lop Nor. In contrast, the three IMS stations closest to the Nevada Test Site (NTS) are at distances
of 249, 380, and 417 km.106 The State Department observes,
There is no doubt that we would be better off if we had close-in seismographs around Lop
Nor and Novaya Zemlya. If IMS were allowed to install three seismographs surrounding Lop
Nor at the distances similar to those surrounding the NTS, it would be much easier not only
to detect smaller events, but also to identify the nature of smaller events and to determine a
better location as well as the origin time.107

Iran has numerous salt domes many hundred of miles from the IMS station near Teheran. Critics
argue that Iran could easily create cavities for decoupling by using water to dissolve salt. It has
extensive experience in drilling for oil, which is often found near salt deposits. As such, it is
argued, it is well equipped to excavate cavities for decoupling. Further, much of Iran is
seismically active, making it easier for Iran to conduct a test during an earthquake to mask the
explosion’s signals. Others respond that hiding a test in an earthquake requires holding the test in
readiness, possibly for years, for the “right” earthquake to come along, and it may still be possible
to distinguish signals from an earthquake from those of an explosion.
Other techniques can also reduce seismic signals from underground nuclear tests. Don Linger,
Senior Scientific Advisor, Advanced Systems Concepts Office, Defense Threat Reduction
Agency, and former director of the Defense Nuclear Agency’s nuclear effects testing program,
provided the following information.108
One technique for reducing seismic signals is “geologic preconditioning.” A nuclear test in
hard rock will fracture or microfracture the surrounding rock to distances of several hundred
meters, fragmenting it and changing the shock propagation and attenuation characteristics.
As a result, a test conducted underground in a hard rock geology region in which a previous
nuclear test was conducted will in effect be conducted in fragmented rock, which absorbs
much more energy than undisturbed rock, weakening the seismic signal. This attenuation
was observed in experiments using 100 tons of chemical explosive, conducted by the U.S.
Departments of Defense/Defense Nuclear Agency (now the Defense Threat Reduction
Agency) in a series of tests in Kazakhstan during the closing of the former Soviet Nuclear
Test site in 1993 to 2002. Moreover, the Russian test site at Novaya Zemlya, which is
comprised mainly of similar hard rock, has similar regions of preconditioned hard rock
created by previous tests that could be used to muffle seismic signals of clandestine tests.
This is a proven technology, clearly understood by the testing community.

105

NAS report, pp. 41-42.
U.S. Department of State. Bureau of Verification, Compliance, and Implementation. “Response to Medalia
Questions of 27 Nov [2007].” January 14, 2008. Hereinafter “Response to Medalia Questions.”
107
“Response to Medalia Questions.”
108
Information provided by personal interview and emails, December 3-13, 2007.
106

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A second technique to reduce seismic signals, “radiation spectrum tuning,” is to reduce the
radiation coupling of the nuclear device to the ground. The amount of energy that a nuclear
device deposits into the surrounding geology is very sensitive to specifics of its radiation
output spectrum, and strongly affects the manner in which the blast is coupled to the ground,
causing large changes in the ground shock and seismic signature. Radiation spectrum is
entirely different than yield. For a given test cavity, a 10-kiloton weapon with energy
concentrated in the thousand-electron-volt range will produce a significantly lower seismic
signal than a 10-kiloton weapon with electromagnetic energy concentrated in the tens-ofmillion-electron-volt range. Nuclear explosives have been designed with different energy
spectra. For example, the U.S. Plowshare program of nuclear explosives for peaceful
purposes, and the parallel Soviet program, developed nuclear explosive devices with energies
concentrated in a part of the electromagnetic spectrum different than that of typical nuclear
weapons.

CTBT proponents respond that geologic preconditioning may be of use to Russia or China, which
have a “stockpile” of cavities left by nuclear test explosions, and possibly to India and Pakistan,
which may have a few small cavities, but not to other nations. Opponents dismiss this argument
because they view the prospect of Russian or Chinese covert testing as the greatest threat.
Proponents, in turn, reply that the decoupling capability of geologic preconditioning would vary
greatly depending on specifics of the surrounding rock and the extent of its fracturing, which
would be extremely difficult to determine. Regarding radiation spectrum tuning, proponents ask if
modifications to the test device that would be needed to reduce the seismic signature would
interfere with the purpose of, and results from, the test so much as to diminish its value
significantly.
Seismic monitoring entails other arguments. Critics state that the ability to detect lower-yield tests
increases many-fold the number of seismic events that must be analyzed as possible nuclear tests.
Supporters reply that improved seismic detection and data analysis capability rule out most such
events as possible explosions, and that low-yield tests are of little military significance. Critics
respond that low-yield explosions have military significance, as discussed below, and that it
would be easier for IDC to miss a low-yield explosion among thousands of low-magnitude
earthquakes than to miss a higher-yield explosion. Supporters retort that the North Korean test of
October 2006 was clearly detected even though it had a yield of less than a kiloton; critics counter
that it was not conducted evasively.

ŽŽŒ’˜—ȱ˜ȱ›Š’˜ŠŒ’ŸŽȱŠœŽœȱ
Nuclear explosions generate a great variety of radioactive atoms, or radionuclides, some of which
are gases. Of special interest are radioactive isotopes of noble gases, such as argon-37, krypton85, xenon-131, and xenon-133. The background level of these gases is extremely low. Because
noble gases are chemically inert, they do not bond with the rocks and soil surrounding an
underground nuclear explosion. As a result, they work their way to the surface and disperse into
the atmosphere, where they may be detected thousands of miles away. For example, the
Automated Radioxenon Sampler/Analyzer, in use by IMS, concentrates and measures minute
quantities of the isotopes of radioactive xenon.109 Once a detection system has accumulated a data
archive of background levels of radioactive noble gases, a spike above that level can indicate a
109

“Breakthrough Systems to Detect Nuclear Explosions Worldwide,” Pacific Northwest National Laboratory, press
release, July 24, 1998, at http://www.pnl.gov/news/1998/Bnw98_24.htm. See also Hafemeister, “Progress in CTBT
Monitoring Since Its 1999 Senate Defeat,” p. 168.

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Řśȱ

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release from a nuclear reactor or nuclear explosion. Computer models of global atmospheric
conditions in the days before a spike can then be worked backwards to provide a general location
of the source.
At entry into force of the CTBT, the IMS is to have 80 radionuclide stations around the world; all
are to monitor radioactive particles and upon the treaty’s entry into force 40 of them would have
capability to monitor radioactive noble gases. Sixteen laboratories would analyze samples from
these stations. The CTBTO PrepCom states: “The relative abundance of different radionuclides in
these [air] samples can distinguish between materials produced by a nuclear reactor and a nuclear
explosion.... The presence of noble gases can indicate if an underground explosion has taken
place.”110
Contending views. The treaty’s supporters claim that the 2006 North Korean nuclear test shows
the value of noble gas monitoring and the capability of the IMS. An IMS radionuclide system at
Yellowknife, Northwest Territories, Canada, collected samples two weeks after the test that, upon
analysis, indicated a trace amount of xenon-133. By comparing this amount to data in its archive,
analysts were able to determine that the level was elevated. By examining wind currents for the
preceding two weeks, and data on releases from the Chalk River Laboratories, a Canadian nuclear
research site several thousand kilometers southeast of Yellowknife, analysts were able to conclude
that the xenon-133 was “consistent with a release from the location and time of the DPRK
event.”111
Opponents see numerous ways to evade detection of radioactive noble gases. They recognize that
noble gases will reach the surface if there is no effort at containment, but believe containment can
work. They point to a statement by Donald Barr, a retired Los Alamos radiochemist with over 50
years of nuclear testing and related experience: “Deep burial of a nuclear device, combined with
gas blocking techniques, virtually eliminates the seepage of noble gases to the surface, though
some such gases might occasionally be detected, but only at the surface above the detonation
point.”112 Burying a nuclear test device at greater depth than would be typically used for
containment would also delay the time when these gases would reach the surface, providing more
time for radioactive decay to reduce the amount reaching the surface. Certain geologies, such as
salt domes, would more readily seal the cavity, blocking the escape of these gases.
CTBT supporters point to experimental data to buttress their claim that it is very difficult to
contain noble gases following an underground nuclear explosion because they rise to the surface
through faults or fractures, especially during periods of low barometric pressure.113 Opponents
would note that the experiment in question used surrogate gases (sulfur hexafluoride and helium3), not argon and xenon. Further, the report stated that the decay of argon-37 to chlorine-37 “will
limit the sampling ‘window’ during which surface detection is possible,” and that “selecting the
timing of a challenge inspection to include the arrival of weather fronts may be necessary to

110

Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty, “Verification Technologies:
Radionuclide,” at http://www.ctbto.org, link to “Verification Regime” > “Monitoring Technologies” > “Radionuclide.”
111
P.R.J. Saey et al., “A Long Distance Measurement of Radioxenon in Yellowknife, Canada, in Late October 2006,”
Geophysical Research Letters, vol. 34, L20802, doi: 10.1029/2007FL030611, October 16, 2007, p. 5 of 5.
112
Personal communication, November 21, 2007.
113
C.R. Carrigan et al., “Trace Gas Emissions on Geological Faults as Indicators of Underground Nuclear Testing,”
Nature, vol. 382, August 8, 1996, pp. 528-531.

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optimize the possibility of detection.”114 An evader, knowing this, might try to delay inspections
beyond the time such a front is due to arrive.

ŽŽŒ’˜—ȱ˜ȱ›Š’˜ŠŒ’ŸŽȱ™Š›’Œ•Žœȱ
Underground nuclear explosions may vent radioactive particles (fallout) into the atmosphere,
where they may travel for thousands of miles, depending on wind, rain, particle size, and other
factors. Fallout analysis has provided a clear indication of a nuclear test for many decades. For
example, the United States learned of the first Soviet nuclear test (an atmospheric test) in 1949,
and learned much about the design of the first Soviet thermonuclear device in 1953, through
collection and analysis of these particles.115 The ease of detecting fallout particles was a main
reason why the United States, Soviet Union, and United Kingdom were able to negotiate the
LTBT in 1963, and worldwide protests against fallout were a main impetus for the treaty.
Contending views. CTBT supporters assert that containment of radioactive debris from a
nuclear test is difficult, and many techniques are learned through trial and error. Geologic
features, such as faults, can provide a path through which debris can vent. Certain types of soil or
rock are better for containment than others. Underground water, turned to steam by an explosion,
generates a great deal of pressure. Depth of burial must be adequate. Elaborate methods must be
used to prevent debris and gases from escaping through the shaft dug for the test.116 Despite
extensive experience with contained underground tests beginning in the 1950s, many U.S.
underground tests through 1970 released radioactive material.117 CTBT supporters therefore argue
that it would be difficult for Russia or China, and much more so for first-time testers, to have high
confidence that they could contain a clandestine test.
CTBT opponents respond that Russia and China would have high confidence in their ability to
contain a nuclear test because of their test experience. Opponents point to a U.S. example.
Following the “Baneberry” test of 1970, which vented a large radioactive cloud, the United States
took further steps to contain underground tests, and of the 386 post-Baneberry tests conducted at
the Nevada Test Site through 1992, only 2 resulted in accidental release of radioactivity detected
outside the test site.118 Even nations without nuclear test experience could learn much about
containment from the open literature, and could make containment more likely by burying the test
device more deeply, examining geologic characteristics in selecting a test site, and building a
large margin of error into containment techniques.
The treaty’s supporters point to data on Soviet nuclear tests at Russia’s only nuclear test site,
Novaya Zemlya in the Arctic Ocean, to show the difficulty of containment. Using the period
beginning in 1971 so as to be comparable to U.S. post-Baneberry tests, 30 underground tests were
conducted from 1971 to 1990, with data unclear for two. Of the other 28, 10 vented radioactive
gases offsite, another 7 vented such gases onsite only, 1 vented radioactive gases and debris
114

Ibid., p. 531.
Richard Rhodes, Dark Sun: The Making of the Hydrogen Bomb, New York, Simon and Schuster, 1995, pp. 370-372,
524.
116
For a detailed discussion of containment, see Office of Technology Assessment. The Containment of Underground
Nuclear Explosions, pp. 31-55.
117
U.S. Department of Energy. Nevada Operations Office. United States Nuclear Tests, July 1945 through September
1992, DOE/NV-209, rev. 15, December 2000, pp. 2-63.
118
Department of Energy, United States Nuclear Tests, pp. 64-88.
115

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offsite, and 10 were contained. The treaty’s opponents counter that there was a sharp
improvement in containment. Of the 28 tests, for the period 1971 through August 1978, 10 of 16
tests vented offsite, 1 vented onsite, and 5 were contained; for September 1978 through 1990, 6
vented onsite only, 1 vented offsite (both gases and particles), and 5 were contained.119

—Ž›Ž›˜–Ž›’Œȱœ¢—‘Ž’ŒȱŠ™Ž›ž›Žȱ›ŠŠ›ȱǻ —Ǽȱ
This technique was developed in the early 1990s to study ground deformation around
earthquakes. In it, a satellite-borne radar sends out microwave radar beams to a swath of ground
some 100 km wide, and records, pixel by pixel, what is in effect the distance between the satellite
and each point on the ground.120 If another radar picture of the same terrain is taken later from
nearly the same point in space,121 one image can be digitally subtracted from the other, with any
difference shown as bands of color that reveal ground motion. According to the technical
literature, InSAR can detect ground deformation of less than 1 cm122 and can take pictures
through many types of clouds. Because it does not use visible light, it can take pictures night or
day. This technique has also been used to detect ground deformation due to oil and gas reservoirs
and to measure the stability of retaining walls around a reservoir in London.123
While IMS does not use satellite monitoring techniques, the CTBT (Article IV, section A,
paragraph 5) permits the use of national technical means. According to David Hafemeister,
professor emeritus of physics at California Polytechnic State University, “InSAR is now a widely
adopted technology, available to all CTBT States Parties at reasonable prices from commercial
vendors.”124 The depression formed by an underground nuclear test—assuming the rock or
ground above the test does not collapse into the cavity left by the test, leaving a clearly visible
crater—may be 1 to 2 km across and one to several cm deep.125
Contending views. CTBT advocates hold that InSAR complements other monitoring
techniques. It can monitor large areas for subsidence. It can localize a suspicious site, even with a
test of yield less than 1 kiloton (depending also on other factors such as depth of burial and
geology) to within 100 meters, thus helping to guide an OSI.126 It can discriminate between an
earthquake and an explosion based on changes in ground deformation revealed by InSAR; an
earthquake produces a more or less linear pattern caused by the two sides of a fault sliding past
each other, while an explosion produces a roughly circular depression. It can help find
119

Vitaly Kjalturin et al., “A Review of Nuclear Testing by the Soviet Union at Novaya Zemlya, 1955-1990,” Science
and Global Security, no. 13, 2005, pp. 40-42.
120
For brief descriptions of InSAR, see Gabriele Rennie, “Monitoring Earth’s Subsurface from Space,” S&TR, April
2005, pp. 4-11; and U.S. Department of the Interior. U.S. Geologic Survey. “Using Satellites to Monitor Deformation:
Radar Interferometry,” updated October 11, 2007, at http://volcanoes.usgs.gov/insar/more_insar.html.
121
The U.S. Geologic Survey states, “It isn’t possible to steer a satellite accurately enough to return it to exactly the
same point in space on different orbits, but it’s relatively easy to get within a few hundred feet and then do the
necessary geometric corrections.” Ibid.
122
Rennie, “Monitoring Earth’s Subsurface from Space,” p. 5.
123
On the latter point, see European Space Agency, “Groundmotion: Service Examples,” at http://www.eomd.esa.int/
booklets/booklet183.asp.
124
Hafemeister, “Progress in CTBT Monitoring Since Its 1999 Senate Defeat,” p. 169.
125
Paul Vincent et al., “New Signatures of Underground Nuclear Tests Revealed by Satellite Radar Interferometry,”
Geophysical Research Letters, vol. 30, no. 22, November 2003, p. SDE 1-1.
126
Hafemeister, “Progress in CTBT Monitoring Since Its 1999 Senate Defeat,” p. 171.

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construction of a decoupling cavity, as ground above the cavity may subside slightly. The wide
availability of InSAR data would arguably make a request for an OSI based on this data more
convincing to the CTBTO Executive Council.
Critics respond that InSAR requires before-and-after pictures of the same piece of ground in order
to detect slight subsidence. If only an “after” picture is available, the technique is thought to work
only for nuclear tests of 20 kilotons of yield or so, a level that seismic techniques can easily
locate, rendering InSAR superfluous. The State Department points to other limitations.
NASA, [Lawrence Livermore National Laboratory], Canadian Space Agency, and European
Space Agency all have InSAR systems and should have libraries of data covering much of
the world, at least up to middle latitudes. However, in some areas where there is rugged
terrain, terrain shadowing will likely cause large areas to be uncovered. Additionally, one
would need to have “before” images that are fairly recent to do an accurate comparison. If
significant changes have occurred in the terrain (other than those caused by the test) by wind,
rain or other natural factors, the “before” image will not be useful in constructing an InSAR
image. Furthermore, this is complicated by the fact that the subsidence may not occur until
some time after the test, perhaps years. So, whereas libraries do exist, without specific
tasking, they’re unlikely to be good enough.

Further, “It is particularly noteworthy that no evidence of subsidence was observed by the InSAR
technique after the North Korean test.” For these and other reasons, State concludes, “the
potential of InSAR in assisting detection of a nuclear explosion is limited and cannot be
considered a useful technique in many test scenarios.”127
Critics assert that subsidence could occur too late to aid an OSI. They also argue that some very
low yield tests, the kind an evader is most likely to attempt, conducted at Nevada Test Site did not
form depressions,128 and that deep burial and certain geologies (e.g., deep inside a granite
mountain) may preclude subsidence. Supporters reply that InSAR is of value if it helps deter
evasion, and that it may reduce the value and increase the difficulty of clandestine tests by forcing
a would-be evader to dig deeper and use smaller nuclear devices in order to avoid detection by
InSAR.

ŽŽŒ’—ȱŒ˜••ŠŽ›Š•ȱŽŸ’Ž—ŒŽȱ
A nuclear test requires much preparation. The testing nation must survey the site to d

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/crs%3ARL34394. Public record. Not legal advice.