decide that there are no military requirements for new designs that would justify the costs or other impacts of the changes. In any case, whether arising from a CTBT or not, such a constraint on the introduction of new designs would lead to aging of the stockpile, with possible impact on the safety or reliability of U.S. nuclear weapons unless effectively counteracted by programs of surveillance, repair, and remanufacture as needed. A further set of negative impacts that has been asserted concerning a constraint on new designs is the resulting inability to extend certain safety improvements to weapons not now so equipped and the inability to optimize nuclear weapons for additional specialized missions. Potential positives of U.S. commitment to a CTBT, on the other hand, include limiting further development of the nuclear-weapon capabilities of potential adversaries; reducing the competitive incentive for acquisition or improvement of nuclear weapons by such states; supplementing U.S. capabilities for the detection and attribution of nuclear explosions by others; and increasing the global credibility of U.S. non-proliferation policy and the strength of the non-proliferation regime. Weighing these pros and cons obviously entails political judgments as well as technical ones.
This committee was not asked to address the full range of issues—political as well as technical—germane to a “net assessment” of whether the United States would be better off with a CTBT in force than without it; and we have not tried to do so. But we believe that our analysis of some of the key technical issues in such a determination, as enumerated above, will be helpful to those who must make it. In what follows, we first summarize briefly what the CTBT says and requires, before turning to the three specific issues in our charge—U.S. nuclear-weapon capabilities under a CTBT, the verifiability of the treaty, and effects of a CTBT on the capabilities of countries of potential concern.
The Comprehensive Nuclear Test Ban Treaty obligates all parties not to conduct “any nuclear weapon test explosion or any other nuclear explosion” in any environment (i.e., in the atmosphere, underwater, underground, or in space) and to refrain from encouraging or helping any other state to carry out such explosions (Article I). The treaty primarily affects the five treaty-designated Nuclear-Weapon States (China, France, Russia, the United Kingdom, and the United States) since the 180 Non-Nuclear-Weapon States Party to the Nuclear Non-Proliferation Treaty (NPT) are already prohibited from nuclear testing (and from developing and producing nuclear weapons, even if without testing) by the NPT. The four states that are not parties to the NPT (Cuba, India, Israel, and Pakistan) would not be able to test if they signed the CTBT but so far only Israel has signed.
Although “nuclear explosion” is not defined in the treaty, Senate testimony by the Secretary of State, the Under Secretary, and the U.S. CTBT negotiator states explicitly that the negotiating record makes clear that all explosions with nuclear yields greater than zero are prohibited.1 The Nuclear-Weapon States agreed that, while tests with nuclear yields greater than zero (including “hydronuclear tests”) were prohibited, weapons-related experiments producing no nuclear yield, including subcritical experiments involving fissile materials and hydrodynamic tests of weapon assemblies without fissile materials, were not banned by the treaty. Similarly, it was understood that the treaty does not cover nuclear reactors, which obtain energy from controlled