Abstract
Time is running out for the Comprehensive Test Ban Treaty (CTBT). Submitted to the Senate for ratification almost two years ago by the Clinton administration, the treaty has sat on the desk of Foreign Relations Committee Chair Jesse Helms, a conservative Republican from North Carolina, ever since. Chairman Helms refuses even to allow debate on the issue.
Helms says he will not consider the CTBT until the Clinton administration also sends him protocols to the Anti-Ballistic Missile Treaty and the Kyoto Climate Change Treaty, both of which he opposes. For its part, the administration has refused Helms's demands, but–after declaring the CTBT to be a key priority two years running–has failed to mount any significant effort to win Senate ratification for the treaty. The CTBT remains trapped in a political box.
It is too bad that Helms and his Republican colleagues continue to see the test ban treaty as a partisan issue rather than what it really is: a useful tool that serves Republican aims as well as U.S. goals. While attacking or ignoring the treaty, Republicans in Congress have spent valuable legislative time on the alleged spread of ballistic missiles to “rogue” regimes and the apparent leakage of U.S. nuclear weapons design information to China.
Yet any nation seeking to develop a high-yield nuclear warhead small enough to put on top of a long-range ballistic missile would have to conduct nuclear tests to ensure that the design actually worked. Thus the CTBT would reduce the very threat the GOP says it is so concerned about.
As for China, to the extent that Beijing has already incorporated U.S. secrets into its warhead designs, it would have had time to test them before halting its nuclear testing in 1996. But additional tests would certainly take China further down this road.
Another U.S. security objective–stopping a nuclear arms race between India and Pakistan–would be well-served by the treaty. Although neither nation has signed it, both have declared moratoria on further tests–in large part because of the international norm against testing embodied by the treaty. But even if India and Pakistan sign the treaty this year, they are unlikely to ratify it if the United States has not done so.
An international CTBT conference is scheduled in October to seek ways to accelerate the treaty's entry into force. Of the five original nuclear weapon powers–the United States, Russia, Britain, France, and China–only Britain and France have so far ratified. If the other three ratify by October, the conference could focus on the major holdouts, India, Pakistan, and North Korea. (The treaty specified that 44 nuclear-capable states must ratify before the treaty can enter into force.) But if Russia, China, and especially the United States have not ratified by October, it will be difficult to later create pressure on the non-ratifiers.
A matter of self-interest
The United States has not conducted a nuclear test explosion since 1992. In support of U.S. nonproliferation and arms control objectives, the United States has been leading the international community toward a global ban on nuclear tests since 1993, an effort that originated with a bipartisan congressional initiative in 1992.
The secretaries of Defense and Energy have once again certified, as recently as last December, that the U.S. nuclear stockpile remains safe and reliable. As a technical matter, the United States can indefinitely maintain nuclear weapons with its stewardship programs, without fission-yield tests.
Given these realities, the logic of the CTBT is hard to beat. A global ban on nuclear test explosions imposes a barrier to the development of many types of nuclear weapons, especially those intended to meet the volume and weight constraints of missile delivery. The United States, which conducted 1,030 nuclear tests, already has such weapons; its security interests are best served by keeping other nations from developing and testing them.
While tacitly acknowledging the lack of any current requirements for nuclear test explosions, test ban opponents raise worst-case “what if” scenarios to suggest that a “prudent” approach to maintaining nuclear deterrence requires an ever present option to test, and thus the avoidance of any binding treaty commitment.
In reality, America's deterrent can be sustained without nuclear explosive tests. This conclusion is supported by the three nuclear weapons laboratories; by numerous independent weapons experts; by the Joint Chiefs of Staff and four former chairmen (Colin Powell, John Shalikashvili, David Jones, and William Crowe); and by the Defense Department.
And if the United States ever chose to exercise the “option” to resume underground nuclear test explosions, it would pay a very high political cost. Russia and China would certainly respond in kind, the treaty would unravel, and the global nonproliferation regime would be in tatters.
But what if the United States needed to resume nuclear testing in 10 or 15 years? Test ban opponents suggest that this small risk means we should opt out of the treaty now. We disagree. While it is difficult to conceive of future security threats likely to require nuclear testing as the most appropriate response, if such a serious threat did emerge the United States could withdraw from the treaty.
Treaty opponents question whether the United States would actually withdraw under any circumstances, given the high political cost. That argument misses the point. The price of resuming tests is already high; ratification would only marginally increase it. In contrast, a U.S. failure to ratify the treaty would almost surely doom it.
Technical and political restraints
A global ban on nuclear explosions will affect nations differently, depending on their technological level and the resources available to them.
Relatively simple pure fission weapons can be designed and built without full-scale nuclear tests, as demonstrated by South Africa and Pakistan (which was understood to be nuclear-capable well before its May 1998 tests).
Even without nuclear explosive testing, a technically sophisticated proliferator could have confidence that a conservatively designed weapon would work. But considerable uncertainty would persist about its yield, and the design would not approach the optimum in terms of its yield-to-weight or yield-to-volume ratios, reducing its effectiveness for missile delivery. Moreover, the yield of an untested pure fission weapon intended for longer range missile delivery probably would be limited to a few tens of kilotons.
The greatest strategic impact of the treaty would be on more sophisticated devices–single-stage boosted fission weapons and two-stage high-yield thermonuclear weapons. In a boosted weapon, the yield of a given amount of plutonium or highly enriched uranium is increased by a burst of additional energetic neutrons from fusion reactions in deuterium-tritium gas injected into the center of the core immediately prior to detonation.
Because deuterium-tritium ignition does not begin until the fission energy release has reached at least 100 tons of TNT equivalent, non-nuclear testing with surrogate materials cannot definitively determine that the boost phase of a nuclear device will operate as designed.
In a staged thermonuclear device, radiation from a fission or boosted fission primary is partly trapped and re-radiated within a heavy metal case to heat and compress a “secondary” component composed of fission and fusion materials. Radiation implosion of the secondary, and ignition of the fusion fuel of a modern, staged, high-yield thermonuclear weapon can be verified experimentally only with nuclear explosive testing beginning at around 10-20 kilotons. This is the primary technical reason why the CTBT remains both an important arms control and nonproliferation measure.
To put it differently, a proliferant cannot accurately predict nuclear yield without verifying the accuracy of the computational modeling for the explosive disassembly phase of the weapon. For this, it needs higher yield nuclear testing–or access to historical nuclear test data or nuclear test-calibrated codes.
Given that, full-scale nuclear explosive tests are desirable for all but the lowest technology designs–not only to certify the yield of fully engineered devices, but also to improve the predictive power of nuclear weapons design codes and to optimize designs with respect to yield-to-weight and yield-to-volume constraints.
From a political perspective, the CTBT is already an important instrument of geostrategic restraint. We can credit the CTBT–even though it is not yet in force–for cementing the global norm against nuclear testing. And we can assume that that norm induced India and Pakistan to keep their test series short, to quickly declare moratoria on further tests, and to say they intended to sign the CTBT. In regard to India and Pakistan, the treaty has proved its value.
Is the ban verifiable?
According to a September 1998 letter that Senators Trent Lott, Helms, and John Kyl sent to President Clinton, “As the recent Indian nuclear tests demonstrated, the CTBT is not adequately verifiable. According to the New York Times, the international monitoring system set up to verify compliance with the treaty only detected one of the five nuclear tests conducted by India.”
This is a common misreading of the events of last May. In fact, the Indian and Pakistani nuclear tests show that, although the CTBT monitoring system has limits, it is remarkably good. Under the treaty, the international community will be able to reliably detect seismic events and identify those nuclear explosions of greatest concern.
The U.S. government had no warning that the May 1998 Indian explosions were imminent. While this raises questions about U.S. intelligence efforts, it was not a failure of the CTBT monitoring system. The treaty permits preparations for nuclear tests or other test-site activities. (The United States was a major proponent of this permissive stance, because it wanted to preserve an unconstrained ability to conduct subcritical and other weapons-related nuclear experiments at the Nevada Test Site.)
The purpose of the CTBT verification system is to detect and identify–and thereby deter–nuclear explosions that would allow a treaty party to gain a significant military advantage over parties that continue to comply with the treaty. On May 11, 1998, India announced it had conducted a series of three simultaneous explosions (a 200-ton low-yield device, a 12-kiloton fission device, and a 43-kiloton thermonuclear device.) The May 11 event was detected by some 50 seismic stations that are part of the prototype International Monitoring System (IMS), as called for by the CTBT.
Similarly, the Pakistani test series (May 28: five explosions claimed, one 30-35 kilotons, four low yield; May 30: reportedly one test, 15-18 kilotons) was quickly detected by numerous stations.
Independent seismologists (see, for instance, Terry C. Wallace, “The May 1998 India and Pakistan Nuclear Tests,” Seismological Research Letters, September 1998) estimate the total yield of the May 11 Indian series as no more than 15 kilotons, and the Pakistani series as about 10 and 5 kilotons, respectively.
Confusion about the actual yields of the explosions should not cloud the fact that if India or Pakistan had wanted to hide their test series from the world, they would not have succeeded. The system works, and it will get better with time as more monitoring stations are added.
On May 13, India announced it had conducted a second series of two tests with yields between 200 and 600 tons. There is no independent confirmation that this sub-kiloton series actually took place. If it did occur, evidence suggests that the announced yields may be too high. Because the time and location of the alleged explosions are known, there should be a corresponding seismic signal registered by regional stations of any event over one hundred tons or so. Yet no seismic signals were recorded.
Rather than a failure of the CTBT monitoring system, the May 13 series, if it took place, merely demonstrates the acknowledged limitations of seismic detection. The affordable and plausible goal of any verification system is not to catch all possible violations, but to detect those that would confer a significant military advantage.
The lower the nuclear yield of an explosion, the harder it is to detect by seismic means. The probability of detecting and identifying very low-yield tests drops off sharply if the explosion is below one kiloton. In some areas, however, explosions of one tenth that size will be detected.
But explosions at that level have limited potential to prove out advanced weapons designs, such as boosted or two-stage thermonuclear devices. To even begin to experiment with boosting requires nuclear tests of a few hundred tons and to confirm, say, a ten-fold increase in yield would require tests in the kiloton range. The latter tests would be detected by the seismic monitoring system.
Although very low-yield explosions may be difficult to detect and identify seismically in some areas, CTBT monitoring also includes hydroacoustic, infrasound, and radionuclide monitoring stations, as well as on-site inspections and the national intelligence means of member states.
If a nuclear explosion falls below the seismic threshold of detection or identification for a given area, it can be picked up in other ways. For example, India's test-site preparations were uncovered in 1995 by U.S. spy satellites. Further, a prospective violator could not be confident that human intelligence would not reveal testing activity.
Moreover, the capabilities to monitor the CTBT go beyond the International Monitoring System. In addition to the system's 170 seismic stations, for example, there are more than 10,000 other seismic stations that provide dense regional coverage. Also, the United States is deploying enhanced capabilities as part of its own national intelligence means that will exceed those of the IMS in important areas.
Treaty opponents raise the possibility that cheaters could conduct an explosion in an underground cavity that would muffle or “decouple” the blast's seismic signal. That's a red herring. Engineering and cost considerations make the decoupling scenario wholly impractical above a few kilotons.
But in reality the prospective evader would be far from certain that decoupled explosions in the low kiloton range would escape detection and subsequent identification as nuclear tests. This is particularly true for states with little or no nuclear test experience. Decoupling is a major technical undertaking, requiring specialized knowledge and equipment and hundreds of skilled personnel.
For example, full decoupling of a 5-kiloton explosion in a salt dome would require a deeply buried cavity with a minimum diameter of 86 meters (282 feet), big enough to contain the Statue of Liberty on its pedestal with room to spare.
Opponents also raise the possibility that a nation might conduct a test in the open ocean, where it would be relatively easy to detect but difficult to determine who did it. To be sure, it is possible that the international community would be unable at first to attribute an open-ocean explosion.
But this does not mean that there would be no risk to the violator. Once a test was detected, the United States and other nations would go to great lengths to figure out who conducted it. Secret operations are always vulnerable to leaks, before and after the fact. The movements of naval vessels and even commercial shipping around the world are monitored by the United States as well as by other naval intelligence services. Reconnaissance satellites scan the oceans, and ship-to-ship and ship-to-shore communications are likewise subject to monitoring.
There is only one reported case of a publicly unattributed open-ocean explosion, the still-unresolved 1979 event in the Indian Ocean. If this method of evasion is so easy, why haven't we seen more of it?
An erosion of confidence?
Treaty opponents suggest the nuclear deterrent is still important to U.S. security, and that the test ban will erode confidence in that deterrent. That's another red herring. Continuing confidence in the reliability of U.S. nuclear weapons already in the stockpile was not–and is not–predicated on an ability to conduct fission-yield tests.
From 1965 to 1980, for instance, no underground tests were conducted for the primary purpose of identifying or developing corrections to stockpile problems. According to C. Paul Robinson, director of Sandia National Laboratory, “Historically, only a small fraction of our nuclear tests were for the purpose of evaluating the stockpile's health, because we could depend on a variety of other evaluation techniques.”
Under the stewardship program, Robinson argues, “the introduction of new and improved non-destructive surveillance techniques should provide us the ability to detect problems in the stockpile and to maintain or even improve the safety of our systems.”
The source of concern for the long term, Robinson notes in a November 1997 written response to a query from the Senate Appropriations Committee, has “more to do with whether we will end up unable to correct problems once they are detected, than with a general loss of confidence that might result from the elimination of nuclear testing.”
In fact, the extent of U.S. dependence on nuclear explosive tests to maintain stockpile weapon “reliability” is rather precisely known. A 1996 tri-lab study of the Stockpile Surveillance Program reveals that of some 830 specific “findings” of defects in stockpile weapons from 1958 to 1993, less than one percent were “discovered” in nuclear tests, and all but one of the cases involved weapons that entered the stockpile before 1970 and are no longer in the U.S. nuclear stockpile.
After 1970, one warhead maintenance problem, related to the effect of tritium decay on design yield, was discovered in a stockpile confidence test of the W84 ground-launched cruise missile warhead (now in the “reserve” stockpile). The problem was easily rectified. In fact, according to a January 1996 Sandia document, only 11 of the 387 tests conducted after 1970 were directly related to maintaining the reliability of the existing stockpile.
Thus there is no immediate and compelling link between the success or failure of stockpile stewardship activities designed to “replace” nuclear explosive testing and the continuing safety and reliability of the nuclear stockpile. The real question is what will happen to existing warheads as they are kept in the arsenal beyond their “nominal design life” of 20-25 years.
Non-nuclear tests, warhead inspections, and computations will be used to assess the arsenal as it ages. Worn-out parts can be replaced, if necessary, on a conservative preventive maintenance cycle that preempts the current hand-wringing regarding the “unknown effects” of aging on device performance.
The Energy Department plans to spend $45 billion over the next 10 years to keep the arsenal and its “stewards” in shape. The stewardship program faces challenges, of course, but none are serious. It is true that some facilities, like the National Ignition Facility (NIF), will not be completed for years. But it is also true that NIF is not central to the kinds of surveillance and component replacement activities that will be required to maintain the stockpile.
Will facilities like NIF work as hoped? Maybe, maybe not. But their main purpose is to attract and retain capable scientists at the labs by offering opportunities for challenging scientific and technical work with a strong connection to nuclear weapons science and engineering. Failure of the NIF to achieve ignition would damage some scientific reputations and delay experiments designed to validate the predictive capabilities of new three-dimensional weapon codes. But NIF is clearly of secondary importance to the stewardship effort. The stockpile can be maintained independently of NIF.
Now or … when?
The Indian and Pakistani nuclear tests were a wake-up call. The United States must retake the lead in locking in the test-ban regime while India, Pakistan, and other key states such as China and Russia are open to it. But the Senate and the administration have eaten up valuable legislative time on issues of less importance. Without the advice and consent of the Senate, the treaty cannot go into force and the benefits of the verification system cannot be fully achieved.
Finally, failure by the United States to ratify the CTBT before the 2000 Review Conference of the Nuclear Non-Proliferation Treaty would be an ugly breach of faith with all those nations who, at the behest of the United States, voted for its indefinite extension in 1995 in return for a commitment by the United States and the other original nuclear weapon states to conclude a comprehensive test ban treaty.
Failure to follow through on that promise will stoke perceptions of a lawless and disordered world that fuels proliferation–a perception that the United States and its allies have tried hard to dispel since the crumbling of the old Cold War order.
If the United States, unquestionably the strongest economic and military power in history, cannot bring itself to ensure its security without relying on nuclear explosions, what message does that send to weaker powers in unstable regions who face more plausible threats to their national security? That message is tantamount to a call for proliferation in the next century.