Deferred verification: the role of new verification technologies and approaches

Researchers have recently proposed a new approach to nuclear-arms-control verification, dubbed “deferred verification.” The concept forgoes inspections at sensitive nuclear sites and of nuclear weapons or components in classified form. To implement this concept, a state first divides its nuclear program 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. Essentially no inspections take place in the closed segment. In contrast, inspectors have access to the open segment, which includes in particular the civilian nuclear sector. The fissile-material inventory in the open segment is known with less accuracy, but uncertainties can be reduced over time using nuclear-archaeology methods. Deferred verification relies primarily on established safeguards techniques and avoids many unresolved verification challenges, such as the need for information barriers for warhead confirmation measurements. At the same time, deferred verification faces some unique challenges. Here, we explore some of these challenges and offer possible solutions; to do so, we examine possible noncompliance strategies in which a state would seek to withhold a higher-than-declared inventory.