The Comprehensive Nuclear Test Ban Treaty Technical Issues for the United States (2012) / Chapter Skim
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4 POTENTIAL TECHNICAL ADVANCES FROM NUCLEAR-EXPLOSION TESTING
4 POTENTIAL TECHNICAL ADVANCES FROM NUCLEAR-EXPLOSION TESTING
Pages 95-118
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From page 95... ...
These specifically include changes in the nuclear programs of other NPT-acknowledged Nuclear Weapon States, the lack of a definition of "nuclear explosion" in the CTBT text, the probability of detection, the implications for those hoping to avoid detection, and the feasibility of evasion for avoiding detection. With those basics established, we update the comparison used in the 2002 Report of the potential threats posed by ratification of the CTBT given the possibility of clandestine tests versus the threats posed by a possible return to global full-yield nuclear-explosion testing.
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From page 96... ...
that other advanced weapons States will also use science-based approaches in maintaining and possibly adapting their nuclear weapons. Such activities may be quite extensive, but under a test ban, weapons deployable with confidence will be limited to designs that fall within the range of previously tested designs.1 Here we present a synopsis of how the four other Nuclear Weapon States (NWS)
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From page 97... ...
has not been used for testing since 1975. Russia continued testing at its Arctic test site near Matochkin Strait on Novaya Zemlya until 1990 (Khalturin et al., 2005)
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From page 98... ...
, particularly weapons intended for tactical use on the battlefield. Russia no longer sees itself as capable of defending its vast territory and nearby interests with conventional forces…The combination of new warhead designs, the estimated production capability for new nuclear warheads, and precision delivery systems…open up new possibilities for Russian efforts to threaten to use nuclear weapons to influence regional conflicts" (Congressional Commission, 2009)
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From page 99... ...
. China China, like the other recognized Nuclear Weapon States under the NPT, has observed a moratorium on nuclear-explosion testing since 1996, when China last tested at the Lop Nor nuclear-explosion test facility.
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From page 100... ...
. Finding 4-1: The Nuclear Weapon States have been able to maintain their nuclear weapons programs under a nuclear-explosion-test moratorium and are likely to be able to make nuclear weapons modifications that fall within the design range of their test experience without resorting to nuclear-explosion testing.
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From page 101... ...
Conversely, Russia and China also have a sophisticated science base for understanding nuclear weapons and are likely to be able to make nuclear weapons modifications (at least those that fall within the design-range of their test experience) without resorting to testing.
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From page 102... ...
of high-explosive equivalent.5 A related issue is the relevance or usefulness of such tests. These questions are considered here, under the assessment that hydronuclear tests, or very low-yield testing in general, are potentially of value primarily to experienced Nuclear Weapon States.
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From page 103... ...
Public statements indicate that perhaps an average of six "non-explosive" nuclear weaponrelated experiments are conducted there annually, and it is clear that considerable resources have been devoted to maintaining the northern test site (RIA Novosti, 2006)
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From page 104... ...
Finding 4-3: Based on Russia's extensive history of hydronuclear testing, such tests could be of some benefit to Russia in maintaining or modernizing its nuclear stockpile. However, it is unlikely that hydronuclear tests would enable Russia to develop new strategic capabilities outside of its nuclear-explosion test experience.
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From page 105... ...
To evaluate the evader's risk, we use the example of seismic monitoring and the same statistical approach that was used in assessing the probability of detection, where we quote the device yield11 that would be detectable 90 percent of the time. For instance, for the specific case of using the IMS network threshold of mb = 3.4 in Asia, Europe and North Africa, the probabilities of detecting an explosion in hard rock are given in Table 4-1 below (see also Chapter 2, Table 2-1, and Box 2-1 on magnitude-yield relations)
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From page 106... ...
For instance if an evasive tester has 90 percent confidence of evading detection on one test, there will be only 81 percent confidence for evading detection on 2 tests and only 73 percent confidence of evading detection on 3 tests, etc. Historically, Nuclear Weapon States have conducted multiple nuclear-explosion tests to
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From page 107... ...
In these cases, a State might be willing to accept the risk level presented by one test only.14 Evasive Underground Testing The 2002 Report addressed clandestine scenarios for evasive nuclear-explosion testing and concluded that only two warrant serious discussion: cavity decoupling -- reducing the size of the seismic signal created by an explosion by muffling the explosion in a large underground cavity, and mine masking -- concealing a nuclear explosion by conducting a nuclear-explosion test in a region that has frequent, large chemical explosions associated with mining operations.15 The 2010 committee again concludes that these are the only evasion scenarios that warrant serious technical exploration at the present time. The understanding of decoupling is supported by a very small test base, which is mainly derived from chemical explosions and has not changed appreciably in the past 10 years.
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From page 108... ...
Hence, the chance that more faults, cracks and joints would be encountered at the surface of a non-spherical cavity increases the chance that radionuclides could escape and be detected. The shortest dimension of non-spherical openings in hard rock will experience a more intense non-elastic pressure pulse compared with that experienced on the wall of a fully decoupled nuclear explosion of the same size in a spherical cavity.
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From page 109... ...
For a potential evader, the uncertainty in the actual amount of decoupling would present a difficult technical challenge. Mine Masking Masking is intended to hide the occurrence of a nuclear explosion by conducting the test in a region that has frequent, large chemical explosions associated with mining operations: the motivation is that although the nuclear-explosion test might well be recorded, it would be incorrectly identified as just another conventional explosion associated with the mining operations in the region.
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From page 110... ...
will provide a 90 percent global seismic detection limit of about 0.2 kt for a fully coupled nuclearexplosion test in hard rock. In addition, regional monitoring and focused monitoring at known or suspected test sites can detect explosions of much lower seismic yield, as for instance the 5-15 ton detection limit at Novaya Zemlya (see Appendix D)
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From page 111... ...
SOURCE: Committee Table 4-2 indicates that, in principle, fully decoupled underground nuclear-explosion tests in salt cavities might be conducted (e.g., in remote areas of Russia) with yields up to nearly 3 kt with only a 10-percent probability of teleseismic detection by the IMS.
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From page 112... ...
With the breakup of the Soviet Union, Russia no longer contains the many salt domes of the Pre-Caspian Depression in Kazakhstan, and "bedded salt" is less suitable for containing a nuclear explosion than is a cavity in a salt dome -- due to greater likelihood of leakage of radioactive materials. Given the lack of experience anywhere in the world with fully decoupled nuclear explosion testing in mined salt or hard rock, and the likelihood that an evasive tester would probably test at or below the 10 percent detection probability, we find that cavity decoupling as a means of escaping detection by the IMS is decreasingly credible at device yields above 1 kt.
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From page 113... ...
Non-Nuclear Weapon States, or those with limited testing experience, might derive some limited benefit from low-yield or evasive testing -- albeit with a higher risk of exposure. At the other extreme, a return to full-yield nuclearexplosion testing would likely present new strategic threats to the United States (see Box 4-3 below)
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From page 114... ...
Table 4-3 summarizes technical constraints on nuclear weapons development posed by testing with intent to avoid detection by States with various levels of nuclear-explosion test experience: countries with greater prior text experience versus countries of lesser or no test experience. Note that it is assumed here that the States have made the commitment to the risks of clandestine testing and will test only to the level where they could have high confidence that they would escape detection; that is, no detectable indicators of a nuclear explosion.
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From page 115... ...
, possibly with evasive testing to avoid detection, to virtually unconstrained development of new or modified weapons with yields greater than 1 kt, very likely to be detected even with attempts at evasion. For the countries with lesser nuclear-explosion test experience or design sophistication, capabilities range from exploring nuclear weapon physics and gaining experience and confidence with weapons physics experiments at very low yields (< 1 ton)
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From page 116... ...
• Begin development of low-yield • Development of low-yield boosted boosted fission weapons fission weapons • Eventual development and full • Development and full testing of 1 kt–10 kt testing of some implosion some implosion weapons and lowunlikely to be weapons and low-yield yield thermonuclear weapons concealable thermonuclear weapons • Proof tests of fission weapons • Eventual proof tests of fission with yield up to 10 kt weapons with yield up to 10 kt • Eventual development and full • Development and full testing of testing of boosted fission weapons new configurations of boosted and thermonuclear weapons or fission weapons and > 10 kt higher- yield unboosted fission thermonuclear weapons not concealable • Pursue advanced strategic weapons weapons concepts (e.g., EMP)
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From page 117... ...
• Nuclear Weapon States could use low-yield evasive testing to partially validate design codes and modernize their arsenals. • Countries with lesser test experience could build confidence with weapons physics experiments or develop and certify inefficient, unboosted fission weapons that might pose a regional threat.
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