Silencing the Bomb Read online

  YIELD (TONS OF TNT EQUIVALENT) COUNTRIES OF LESSER PRIOR NUCLEAR EXPLOSION TEST EXPERIENCE AND/OR DESIGN SOPHISTICATION (ADVANCES ACHIEVABLE IN THE SPECIFIED YIELD RANGES ALSO INCLUDE ALL OF THOSE ACHIEVABLE AT LOWER YIELDS) COUNTRIES OF GREATER PRIOR NUCLEAR EXPLOSION TEST EXPERIENCE AND/OR DESIGN SOPHISTICATION (ITEMS IN COLUMN TO LEFT, PLUS)

  Subcritical experiments (permissible under the CTBT) • Equation-of-state studies • Limited insights relevant to designs for boosted fission weapons

  • High-explosive lens tests for implosion weapons

  • Development and certification of simple, bulky, relatively inefficient unboosted fission weapons (e.g., gun-type weapon)

  < 1 ton (likely to remain undetected) • Building experience and confidence with weapons physics experiments • One-point safety tests

  • Validation of some unboosted fission weapon designs

  • Address some stockpile and design code issues

  1–100 tons (may not be detectable, but strongly location dependent without evasion) • One-point safety tests • Develop low-yield weapons (validation of some unboosted fission weapon designs with yield well below a kiloton)

  • Pursue unboosted designs • Possible overrun range for one-point safety tests

  100 tons–1 kiloton (likely to be detected without evasion; reduced probability of detection with evasion, but strong location dependence) • Pursue improved implosion weapon designs • Proof tests of compact weapons with yield up to 1 kiloton

  • Gain confidence in certain small nuclear designs • Validate some untested implosion weapon designs

  • Assess stockpile issues and validate some design codes

  1–10 kilotons (unlikely to be concealable) • Begin development of low-yield boosted fission weapons • Development of low-yield boosted fission weapons

  • Eventual development and full testing of some implosion weapons and low-yield thermonuclear weapons • Development and full testing of some implosion weapons and low-yield thermonuclear weapons

  • Eventual proof tests of fission weapons with yield up to 10 kilotons • Proof tests of fission weapons with yield up to 10 kilotons

  > 10 kilotons (not concealable) • Eventual development and full testing of boosted fission weapons and thermonuclear weapons or higher-yield unboosted fission weapons • Development and full testing of new configurations of boosted fission weapons and thermonuclear weapons

  • Pursue advanced strategic weapons concepts (e.g., EMP)

  Source: National Academies Report of 2012, Table 4-3.

  The conclusion of the 2012 report indicates that while much can be accomplished by various nations testing at yields greater than 10 kilotons (bottom row), these explosions can be readily detected. Smaller explosions between 1 and 10 kilotons are also unlikely to be concealed. Countries intent on acquiring and deploying modern, two-stage thermonuclear weapons would not be able to have confidence in their performance without multi-kiloton testing.

  Note in Table 16.1 that the development of low-yield lightweight boosted fission weapons is possible only for yields of 1 to 10 kilotons for countries with little or no testing experience.

  Table 16.1 indicates that proof tests of compact weapons with yields up to 1 kiloton are possible with tests of 0.1 to 1 kiloton by the three most experienced nuclear states. That yield range is likely to be detected in the absence of evasion. Evasive testing via the decoupling scenario is strongly dependent upon the location of an explosion. The Russian and Chinese test sites are well monitored down to very small levels, and neither country contains enough salt at those sites for a significant decoupled test in a large underground cavity.

  Subcritical experiments called hydrodynamic tests, which involve no nuclear yield, are permitted under the CTBT (first row of Table 16.1). They can be used to test the properties of plutonium at very high shock pressures. The United States and Russia each stated that experiments conducted after 1996 were of zero yield and hence permitted under the terms of the CTBT. Each country observed the preparation and conduct of those experiments by the other in Nevada and Novaya Zemlya, probably by satellite imagery and other national technical means. No seismic waves were detected close to those times from the announced experiments at Novaya Zemlya.

  Tests that involve a very tiny nuclear release equivalent to a few pounds (1 kg) of chemical explosive—called hydronuclear—are not permitted under the treaty. During the moratorium on testing in the early 1960s, the United States detonated hydrodynamic explosions in Nevada. It wanted to make sure that its weapons were “one-point safe” —that an accidental blow would generate at most a tiny nuclear yield. Those tests demonstrated that they were one-point safe. Presumably the other major nuclear powers ascertained before they signed the CTBT that their weapons were one-point safe as well. It is unclear if India, Pakistan, and North Korea, which did not sign the CTBT, have weapons that are one-point safe.

  In 1994 Kathleen Bailey, a defense analyst, wrote an open technical report titled “Hydronuclear Experiments: Why They Are Not a Proliferation Danger.” I have included quotes from her paper here because they indicate that neither hydronuclear nor hydrodynamic experiments can be used to develop advanced nuclear weapons. (In 2014 Bailey and her husband Robert Barker, a former weapons scientist, who have long opposed limitations on nuclear testing, stated that the United States should unsign and renounce its participation in the CTBT.)

  Bailey’s report was part of the debate in the United States about what yields should be banned under the CTBT as it was being negotiated. She stated, “If a country pursues boosted fission weapons or thermonuclear secondaries [in which the energy from a primary fission reaction compresses and ignites a secondary nuclear fusion reaction], HNEs [hydronuclear explosions] will be an ineffective tool.” She went on to say, “Also, HNEs cannot be used to optimize the advanced designs used by existing nuclear weapons states; they are far too low in energy to confirm that boosting will occur in boosted designs, much less provide useful information for staged thermonuclear weapons. They cannot accurately project the neutron multiplication rate at the time a device explodes.”

  Some CTBT critics claim that Russia continues to perform hydronuclear tests and, if so, that gives them a large advantage. Bailey’s 1994 article indicates, however, how little can be learned from those very low yield tests. Can any country develop advanced, lightweight nuclear weapons by such tiny tests and be confident that they will work at yields of say 10 or 100 kilotons? The answer is no.

  COMMENTS AT A FORUM HELD BY THE HERITAGE FOUNDATION

  Soon after the 2012 NAS report was published, the Heritage Foundation, a conservative research think tank based in Washington, DC, released a transcript of an open forum “Comprehensive Test Ban Treaty: Questions and Challenges.” Paul Robinson, a former director of the Sandia weapons lab; John Foster, a former head of Livermore; and Thomas Scheber, a former director of strategic policy in the Department of Defense each spoke and took questions. The quotes that follow are from that transcript.

  Robinson said, “Now, whereas one could not accuse that first [2002] report of being an intellectually deep or well-balanced study, I believe you can say that about this report [2012]. It is very much improved, they cover a much larger set of issues, and on some of them they do a very good job. I still have some I find fault with, as you will see. But, it does make far more interesting reading in its thoroughness, and, indeed, I’m proud to say that this group took up the primary issue of this treaty as being foremost about the defense of the country and our national security, and it tried to keep that uppermost…. I believe they [the 2012 NAS committee] have done an honest job.”

  Each of the three, however, had specific criticisms of the 2012 report. It should be remembered that most experts are familiar either with weapons or with verification. The expertise of Robinson, Foster, and Scheber relate to weapons, not verification. They make a number of comments about verification that are decades behind current capabilities.

  Robinson
said, “One curious weakness in judgment that I’ll point out here is the extensive discussions in the report, based on the assumption that if a nation wanted to clandestinely carry out evasive tests, it would choose to do so within its nuclear test site. Now, this is exactly the opposite of what our intelligence community believes; an evader would never attempt to go to the area that we’re most heavily monitoring to carry out such an explosion, but certainly countries with large territorial masses would likely find very remote areas in which to conduct their tests, not only because of the ability of great secrecy there, but because they’re the farthest from any U.S. monitoring systems.”

  The 2012 report, in fact, did not state that any country would conduct nuclear explosions only at an existing test site. What is different today from 2002 is that data are now available in near real time from numerous seismic stations in Russia, China, Mongolia, and the now independent countries of Central Asia. For sixty years the United States had sought greater monitoring capabilities in those areas. Their use greatly improves verification throughout various countries of concern to the United States. If stations in one country were unplugged at the time of a suspect event, it would be even more suspect. From his statements, Robinson clearly is not familiar with the present capabilities and how much verification has improved for countries of concern to the United States.

  Foster stated, “If we look at the National Research Council report, we see that it talks a lot about detection. Detection is quite different from verification.” That statement is no longer correct. Previously, many people thought that to identify an event it needed to be about three times larger than that needed for detection. That criterion was correct when data were only available at large (teleseismic) distances. Once regional seismic data became available, it was no longer correct.

  A previous standard rule was that data from at least four seismic stations were needed for detection and the determination of a good location. Today, good data from one or two regional stations can be used. An example of this is an earthquake of magnitude 2.8 that occurred near the Russian test site at Novaya Zemlya on June 26, 2007. High-frequency P and S waves at the seismic arrays in northern Norway and Spitsbergen were sufficient to identify the event as an earthquake. To obtain a better location, recordings of the 2007 event were cross-correlated with those of previous larger nuclear explosions. Had it been a fully coupled nuclear explosion, its yield would have been about 0.04 kilotons, or 40 tons.

  Robinson said, “[W]e in the U.S. labs requested that the permitted test level [under a CTBT] should be set to a level which is in fact lower than a one-kiloton limit, which would have allowed us to carry out some very important experiments, in our view, to determine whether the first stage of multiple stage devices was indeed operating successfully…. [T]oday others may be carrying out such experiments without detection, while the U.S. is forbidden to do so.”

  Debate raged in the United States for nearly twenty years about the determination of Soviet yields near the 150-kiloton limit of the Threshold Treaty. Setting a threshold under the CTBT near the lower limit of detection would be a mistake. Picking a zero nuclear yield was a better choice because debate likely would have gone on for decades about the yields near the lower limit of a very low threshold treaty.

  Robinson repeated an old saw: “[T]he ‘Little Boy’ device, which was first exploded over Hiroshima, had never been previously tested.” He did not state that the bomb was extremely heavy and not appropriate for most delivery systems, especially those of Egypt, India, Iran, North Korea, and Pakistan.

  Robinson also stated, “Lastly, the CTBT for the first time takes a major step in drastically changing diplomacy of security treaties by surrendering major strategic defense decisions to an international body—a subgroup of the United Nations.” In fact, the treaty prohibits the Comprehensive Test Ban Treaty Organization (CTBTO) from reaching conclusions about the nature of a detected event. The CTBTO merely provides for the collection and distribution of data; the United States makes its own determinations. The experience with the five tests by North Korea from 2006 to 2016 indicates that many countries concluded within hours that each of those events was a nuclear explosion.

  FINAL WORDS ON DECOUPLED NUCLEAR TESTING: THE VERIFICATION GAUNTLET

  The CTBT report of 2012 states:

  Evaluation of the cavity-decoupling scenario as the basis for a militarily significant nuclear test program therefore raises a number of different technical issues for a country considering an evasive test:

  1. Is there access to a region with appropriate geology for cavity construction?

  • Is that geological medium nearly homogeneous on a scale of hundreds of meters [yards]?

  • Can cavities of suitable size, shape, depth and strength be constructed clandestinely in the chosen region?

  2. For a cavity in salt formed by solution mining:

  • Is enough water available?

  • Can it be pumped out and the brine disposed clandestinely—eight times the cavity volume, plus the final brine fill?

  • How should the very limited experience with conducting decoupled nuclear explosions in salt be taken into account?

  • Can decoupling factors as high as 70 be attained for yields much larger than sub-kiloton (i.e. larger than the 1966 Sterling test)?

  • Can the layered properties of rock sequences for bedded salt be dealt with?

  3. For a cavity in hard rock:

  • Can mined rock be disposed of clandestinely?

  • Can a country afford the price of mining a large cavity in hard rock?

  • Can uncertainties in rock properties and in orientations and magnitudes of principal stresses be dealt with?

  • Can the presence of joints and faults be detected and dealt with?

  • Can flow of water into the cavity—in either hard rock or salt—be dealt with?

  • Can cavities that depart significantly from a spherical shape be used?

  • Should a decoupling factor no larger than 10 to 20 be assumed?

  4. Can collapse of a cavity during construction and in a decoupled test be avoided?

  • Can surface deformation potentially detectable by interferometric synthetic aperture radar (InSAR) both during and after construction and following the test be minimized?

  5. Can radionuclides be fully contained from a decoupled explosion?

  • Take into account that noble gases can be detected today at much smaller concentrations than a decade ago.

  • Take into account that radionuclides have leaked from many previous nuclear explosions in hard rock at Novaya Zemlya and Eastern Kazakhstan and the few in granite at the Nevada Test Site.

  6. Can the site be chosen to avoid seismic detection and identification, given the detection thresholds of modern monitoring networks and their capability to record high frequency regional signals?

  • Can the limited practical experience with nuclear tests in salt, and very low-yield chemical explosions in hard rock, be extrapolated to predict the signals associated with nuclear testing in cavities in hard rock?

  • Can the size of a test be made small enough to deal with future advances in detection and identification capabilities?

  7. Is there such a region that is suitably remote and controllable, and that can handle the logistics of secret nuclear weapons testing?

  • Can secrecy be successfully imposed on all of the people involved in the crosscutting technologies of a clandestine test program, and on all who need to know of its technical results?

  • Can the tester avoid compromising security by conducting a nuclear test in a region containing a hostile ethnic group or a civil war? Can the test be conducted outside one’s own territory?

  8. Can nuclear explosions of large enough yield be carried out secretly, and repeated as necessary, to support the development of a deployable weapon?

  • Can those carrying out a decoupled test be sure that the yield will not be larger than planned, and thus only partially decoup
led?

  • Can a minimum of drill holes, cables, and specialized equipment be used and yet obtain necessary information about the characteristics of nuclear device(s)?

  • Can the site be cleaned up before an on-site inspection team arrives?

  9. Can a clandestine test in a mining area be hidden in one of a series of ongoing large chemical explosions?

  • Can suitable rock for a decoupled test be found below coal, other minerals, and sedimentary rock in which large chemical explosions are used in mining?

  This verification gauntlet faces a country wanting to conduct a decoupled nuclear explosion with confidence it would not be detected and identified. As stated earlier, Russia and China are unlikely to be able to deploy new types of strategic nuclear weapons that fall outside the design range of their nuclear explosion test experience without several multi-kiloton tests to build confidence in their performance. Each already conducted tactical nuclear explosions prior to signing the CTBT.

  The 2012 report stated that yields of 0.1 to 1 kilotons are likely to be detected without evasion and at reduced probability with evasion (but with a strong location dependence). The probabilities of nuclear explosions’ being detected and identified are even better for decoupled explosions at the test sites of Russia at Novaya Zemlya, China at Lop Nor, North Korea, and India. Because salt is not present in sufficient thicknesses at any of those sites, decoupled tests would have to be conducted in hard rock.

  Weapons designers would want to collect a variety of data from a clandestine decoupled nuclear explosion in addition to merely knowing that it detonated and generated an approximate yield. This goes against having only a sparse set of recording instruments. Before 1996 the United States used huge amounts of instrumentation and large cranes to emplace nuclear devices underground (figure 16.1).

  FIGURE 16.1

  Signal cables and test device being lowered down a test hole in Nevada. Photo credit: Department of Energy.

  Source: Office of Technology Assessment, 1988.

  High-level administrators of the weapons labs who were members of the two Academies studies were not proponents of decoupled testing. The 2012 report found that yields of nuclear explosions that are fully coupled and that might not be detectable are very small. Russian scientists stated to me that the partially decoupled explosion at Azgir in Kazakhstan in 1976 was their only nuclear test utilizing decoupling. I know of no other Russian decoupled nuclear test.