Ceci N’est Pas une Bombe Toward a Verifiable Definition of a Nuclear Weapon

Nuclear nonproliferation and arms-control and agreements place restrictions on the possession of nuclear weapons or nuclear explosive devices—and, yet, existing treaty definitions of “nuclear weapon” or “nuclear explosive device” are vague or ambiguous, while the Nuclear Non-ProliferationTreaty famously avoided defining the term altogether. This may pose a challenge to any future treaty seeking to confirm the authenticity of, account for, keep track of, and verifiably dismantlenuclear weapons. Some partial definitions of a nuclear weapon have emerged and evolved over time, for example, in the five nuclear-weapon-free-zone treaties or in the 2015 Glossary of Key NuclearTerms agreed by the Working Group of the P5 nuclear weapon states. The Glossary describes a nuclear weapon as a “weapon assembly that is capable of producing an explosion and massive damageand destruction by the sudden release of energy instantaneously released from self-sustaining nuclear fission and/or fusion.” Used in a treaty, this definition would pose the problem of how an inspector could know by observation or measurement if a weapon or device is “capable of producing an explosion and massive damage and destruction” or is capable of “self-sustaining nuclear fission and/or fusion.” To confirm that a weapon or device has such properties, an inspector would need to know what a device is “designed to do” or “capable of doing,” and thus presumably would need access to currently classified weapon-design information. This paper reviews some of the existing definitionsof nuclear weapons, highlighting their strengths and weaknesses, and implications for verification if used as part of future nuclear arms-control or prohibition treaties. It considers also the important problem of defining what is not a nuclear weapon, i.e., artifacts that would be permitted under an agreement but whose nature may be difficult to ascertain by an inspector. It is possible that any strictly verifiable definition will require declassifying additional information about nuclear warheadsthat is currently considered secret.