Indian and Pakistani Nuclear Tests Show Importance of Test Ban Treaty
India took the world by surprise by announcing it had conducted a series of nuclear explosions in mid-May 1998. Pakistan responded with its own test series two weeks later. These events have raised concerns in some quarters about the verifiability of the Comprehensive Test Ban Treaty, or CTBT. In fact, the Indian and Pakistani nuclear tests show that, although the CTBT monitoring system -- like all monitoring systems -- has limits, it is remarkably good. Under the CTBT, the international community will be able to detect the nuclear explosions of greatest concern.
No Advance Warning
The US Government had no advance warning that the Indian explosions were imminent. While this raises questions about US intelligence, this is not a failure of the CTBT monitoring system. The treaty does not prohibit preparations for nuclear tests or other test site activities. The United States was a major proponent of this position at the CTBT negotiations in Geneva. The Clinton Administration wanted to preserve the ability to conduct subcritical nuclear experiments at the Nevada Test Site.
Nevertheless, prior warning of test preparations can be very helpful. The ability of national intelligence means to detect preparations for nuclear tests can be used to dissuade nations from carrying out their plans and also can be used as evidence to support a request for an on-site inspection under the CTBT. Intelligence reports indicated in December 1995 that India was preparing to conduct nuclear tests. This led to US intervention, international attention, and an Indian denial that any tests were planned.
In fact, India had completed the major test site preparations that are most visible from space in 1995 or earlier (in the case of drilling the test shafts, years before), easing its task of concealing subsequent preparations for its recent test series. The fault in this case lies not so much with technical intelligence (satellite photos, etc), but unjustified complacency in the US intelligence community that India would not conduct nuclear tests. According to press reports, the Indian government decided to conduct the tests 30 days before actually doing so.
What does this mean for CTBT? One should not assume that US intelligence will no longer be able to spot nuclear test preparations. The United States has the most sophisticated national intelligence means in the world, and it serves as a powerful deterrent to cheating under the CTBT. To be sure, the United States missed an important opportunity to prevent the Indian tests by failing to predict them. But Indian preparations were detected in 1995, and a nation going from no test site activity to drilling shafts will be more easily noticed than was India's recent activity.
Detection After the Fact
The purpose of the CTBT verification system is to detect nuclear explosions of militarily significant yields. 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. 1 kiloton = 1,000 tons). The May 11 series was detected in near-real time by some 50 seismic stations that are part of the prototype International Monitoring System (IMS), as called for by the CTBT. Similarly, numerous stations quickly detected the Pakistani test series (May 28: five explosions claimed, one 30-35 kilotons, four low yield; May 30: reportedly one test, 15-18 kilotons).
Independent seismologists estimate the total yield of the May 11 Indian series to be in the range of 10 to 25 kilotons, and the Pakistani series to be 2 to 15 kilotons and a few kilotons, respectively. Confusion about the actual yields of the explosions should not cloud that fact that if India or Pakistan had wanted to hide its test series from the world it would not have succeeded. This system works, and will get better with time as more monitoring stations are added to the network.
Subkiloton Explosions
On May 13, 1998, India announced it had conducted a second series of two tests with low yields between 200 and 600 tons. There is no independent confirmation that this series actually took place. If it did occur, evidence suggests that the announced yields may be too high. Since the time and location of the alleged explosions are known, regional stations should have registered a corresponding seismic signal for any event over a few hundred tons or so. Yet no seismic signals were recorded. For comparison, non-nuclear seismic events have been detected near the Russian test site on Novaya Zemlya with magnitudes equivalent to explosions as little as 10 tons of TNT. In the Indian case, the CTBT monitoring system has played the important role of establishing an upper bound for these explosions.
Rather than a failure of the CTBT monitoring system, the May 13 series demonstrates the already acknowledged limitations of seismic detection. The goal of any verification system is not to catch all possible violations, but to catch the most significant ones. The lower the nuclear yield of the explosion, the harder it is to detect by seismic means. At very low levels -- one kiloton globally and for many areas 100 tons or less -- confidence of detection drops off.
However, explosions at this level have limited potential to prove advanced weapons designs, such as boosted or two-stage thermonuclear devices. Before the recent Indian nuclear explosions, the world assumed that New Delhi had a workable fission bomb. The next important technological step is a fission device that uses a mixture of deuterium-tritium gas to "boost" or enhance the nuclear yield of the device by 10 to 20 times. This allows a dramatic reduction in weight for a given yield, enabling the development of powerful warheads small enough to be placed on ballistic missiles. Once a nation has taken this step, the door is open to developing two-stage thermonuclear weapons. But experimenting with boosting requires nuclear tests of a few hundred tons and confirming a ten-fold increase in yield would require tests in the kiloton range, which the IMS could detect. Detecting such tests, and thus preventing the development of more advanced weapons, is the central security value of the CTBT.
Thus the Indian experience proves the point: under the CTBT, the international community will be able to detect the nuclear explosions of greatest concern. In a resource-limited world, there is no choice but to deploy a cost-effective monitoring system, and that means setting priorities.
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, it can still be picked up in other ways. For example, test site preparations were in fact uncovered in 1995, and surface disturbance from the May 13 test series may be visible from space. Moreover, a violator cannot be confident that human intelligence activities would not reveal testing activity.
Nevertheless, efforts should be made to improve the ability to discover very low yield nuclear tests. These tests are unlikely to be of use to the five original nuclear powers and are unlikely to be successful in states that have already signed the Non-Proliferation Treaty (NPT), where improved safeguards should provide warning signs of such tests. The countries of primary concern are India, Pakistan, and Israel. One useful step would be for those nations that have test sites to build confidence that no prohibited activities are being conducted by making their activities more transparent. For Indian and Pakistan, greater test site openness is an important confidence-building measure that could be implemented right away.
Better Off with the CTBT
The bottom line question for the US Senate is this: Are we better off with the CTBT in force or not? Regardless of the CTBT, the United States will continue to monitor the nuclear activities of other nations, including India and Pakistan. But with the CTBT, the United States will gain access to over 200 additional monitoring stations worldwide that it would not otherwise have, including in South Asia. And with US ratification of the treaty and its entry into force, the United States will also be able to seek on-site inspections to clarify ambiguous events. The US ability to detect and identify clandestine nuclear explosions will be better with the CTBT in force than without it.
No Need for US Nuclear Testing
The Indian and Pakistani nuclear explosions in no way affect US testing requirements. Although the legal impediment to US testing has been removed (the United States had previously been barred by legislation from conducting nuclear tests unless another nations did so), the recent tests do not introduce any security threat that calls for US testing in reply. Nor has it eliminated the overwhelming reluctance of the American public to get back into the testing business. A national poll conducted after the Indian explosions found 73 percent of the American public supporting the CTBT (with only 16 percent opposed). Therefore, we continue to be in a world where the United States is not conducting nuclear explosive tests. A CTBT that makes the same constraint binding on everyone else is strongly in our interest.
The Indian and Pakistani nuclear tests are a wake-up call for those who question the importance of the CTBT to US security. The United States must take the lead in locking in the test ban regime before other nations follow India and Pakistan's path. But 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. In the interest of US national security, the United States Senate must consent to ratification of the CTBT without delay.
June 15, 1998
