Deferred Verification: The Role of New Verification Technologies and Approaches

Researchers at UNIDIR have recently proposed a fundamentally new approach to nuclear arms-control verification, dubbed “deferred verification.” The concept forgos inspections at sensitive nuclear sites and inspections of nuclear materials or components in classified form. To implement this concept, a state first divides its territory into a closed segment and an open segment. The total fissile material inventory in the closed segment, which includes the weapon complex, is known and declared with very high accuracy. No inspections ever take place in the closed segment. In contrast, inspectors have access to sites, facilities, and materials in the open segment, which includes in particular the civilian nuclear sector, all operational fissile-material production facilities, and all waste materials. The fissile material inventory in the open segment is known with less accuracy, but uncertainties can be reduced over time using methods of nuclear archaeology. Deferred verification relies primarily on established safeguards techniques and avoids many hard and so far unresolved verification challenges, including for example the need for information barriers often envisioned for warhead confirmation measurements. At the same time, however, deferred verification faces some unique challenges in the context of agreements on fissile material cutoff, deep weapon reductions, and weapon program elimination. Here, we explore some of these challenges and offer possible verification mechanisms to address them while maintaining the strengths of the concept; to do so, we examine possible strategies a state might pursue in a deferred-verification regime to evade detection of noncompliance, in particular, scenarios in which a state would seek to withhold a higher-than-declared nuclear warhead and fissile material inventory.