Nuclear disarmament requires development of a verification mechanism that would provide reliable assurances of the absence of fissile materials available for use in weapons. An effective mechanism would require states to declare their fissile material holdings and make this declaration verifiable. For nuclear-armed states this declaration would be extremely difficult to make. Most importantly, it is well recognized that nuclear-armed states will never provide access to fissile materials in operationally deployed warheads, warhead components, or to materials in classified form. It is, however, possible to design a verification arrangement that would cover all categories of fissile materials, including materials in weapons. This arrangement, "deferred verification," would separate a nuclear complex into two distinct segments. The closed segment will contain materials in weapons and weapon-related activities. No verification activity will take place inside, but the amount of material contained in this segment will be declared with high accuracy. This declaration will be verified when the material is removed from the segment (in unclassified form) to enter the disposition process. The amount of material in the open segment would be declared as well, likely with significant uncertainty. The segment will be open to verification that will seek to close the material balance on the state level by taking the physical inventory in the open segment and analyzing material production and removal records. The lack of access to the closed segment will not interfere with that effort since the amount of material there will be accurately known at every step of the process. With time, the verification program should be able to conclude that the open segment contains no undeclared material. This conclusion will be extended to the state as a whole when all material is removed from the closed segment. One significant feature of the deferred verification approach is that it provides a disarmament mechanism that avoids having to deal with accounting for nuclear warheads, authentication of nuclear weapons, or monitoring of the warhead dismantlement process. This could help simplify the nuclear disarmament process by addressing (or, rather, avoiding) the most challenging verification issues.
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