A conceptual model for “inherent reliability” for nuclear weapons

Many people, when thinking about different stages of a particular device's life vis-à-vis defectiveness, use the notion of the “bathtub curve” as a model. However this model is not fully applicable for the class of systems referred to as one-shot or single-shot systems. Key attributes of these systems are outlined in [1]: they typically stay in dormant storage until called upon for one-time use. Common examples of one-shot devices are air-bags in vehicles, fire suppression systems, certain types of safety features in nuclear power plants, missiles, thermal batteries, and some stand-by systems. This paper will focus on a particular example of one-shot systems, nuclear weapons, but the concepts presented are relevant for one-shot devices in general. A new model will be proposed as an alternative to the bathtub curve for one-shot systems. The new model includes two regimes: birth defect dominated and time-dependent dominated. A short discussion of why a bathtub curve might mistakenly be inferred is included. Finally, the relationship between inherent and estimated reliability will be described in the context of this model.