based on current materials, technologies, and manufacturing processes. This does require, however, the provision of adequate resources to provide not only the needed manufacturing capability and capacity but also for the associated engineering R&D and systems integration capabilities, on an ongoing basis.
It is important that a rigorous, highly disciplined process be instituted for controlling changes in the nuclear components. Such a process must discourage deviations from the original specifications. Before adopting deviations that are judged necessary, they must be analyzed thoroughly for potential performance impacts. In the long term, the process must also protect against performance degradations due to cumulative effects of multiple small changes in materials and/or processes that may be introduced in the course of periodic refurbishment operations. The required change-control process must begin with a thorough documentation of the original design and manufacturing specifications. Any subsequent deviations must be thoroughly documented. The resulting audit trail should make it possible to include consideration of possible cumulative effects in judging the acceptability of any proposal for further change. In order to avoid the introduction of interference effects between nuclear and non-nuclear components, prudence dictates that a similar discipline be practiced in regard to any changes in design or location of non-nuclear components situated in proximity to the nuclear subsystem.
Confidence in the safety and reliability of stockpiled nuclear weapons depended far more on activities in the first five categories just described than on nuclear testing even when numbers and kinds of nuclear tests were essentially unconstrained. (The sixth category did not play a large role in the past, because weapons were generally replaced by new tested designs before cumulative changes could become a concern.) Most U.S. nuclear tests were focused on the development of new designs; the other major roles of testing were exploring weapon physics and investigating weapon effects. The so-called stockpile confidence tests were limited to only one per year and-with two exceptions (involving weapon types retired soon after the tests)-they involved new-production units, so they would better be described as “production verification” tests. Even in the absence of constraints on nuclear testing, no need was ever identified for a program that would periodically subject stockpile weapons to nuclear tests.
Stockpile stewardship by means other than nuclear testing, then, is not a new requirement imposed by the CTBT. It has always been the mainstay of the U.S. approach to maintaining confidence in stockpile safety and reliability. The fact that older nuclear designs are no longer being replaced by newer ones means, however, that the average age of the nuclear subsystems in the stockpile will increase over time beyond previous experience. (The average age will eventually reach a maximum that depends on the rate at which weapons are remanufactured or retired.) This means that the enhanced surveillance activities that are part of the current SSP will become increasingly important. But that would be so whether nuclear testing continued or not. Nuclear testing would not add substantially to the SSP in its task of maintaining confidence in the assessment of the existing stockpile.
An important component of the Stockpile Stewardship Program is the development of a broad spectrum of advanced diagnostic tools in support of the surveillance function. These tools are intended to yield a more complete understanding of weapon performance and potential failure modes for nuclear as well as non-nuclear components and subsystems. This effort represents a continuation of the traditional knowledge-based approach to problem solving in the nuclear-weapon program, albeit at a significantly accelerated rate of progress. The SSP can already point to significant successes in that regard, as seen, for example, in the implementation of numerous new, relatively small-scale, measurement and analysis techniques ranging from new bench-top