A Method for Assessing Safeguards Effectiveness and Its Application to State-Level Material Accountancy Verification

A formalism for assessing international safeguards systems at declared facilities is presented and applied to safeguards for detecting diversion from a states fuel cycle. This formalism is aimed at better understanding and documenting the logic of safeguards verification; an example is presented showing how thorny the logic of flow verification and MUF = 0 can be. The proposed formalism has two steps: the first creates a proof logic: a set of statements that proves, at a certain level of abstraction, that the safeguards system is effective. The second step involves analyzing how any idealizations of the proof logic might be compromised in reality, for example through adversary concealment considerations. As an application of this approach, a model of state-level material accountancy verification is then presented, incorporating: locations of declared nuclear materials, nuclear material accounting declarations, physical inventory verifications, distinguishable nuclear material species and substitution possibilities, and three well-defined concepts of flow verification involving containment/surveillance and process flow measurements. It is shown that physical inventories in the state should follow certain rules regarding scope, simultaneity, and sequencing. These rules may be read off of a directed graph defined over the set of locations of nuclear material. The analysis shows that mass balance boundaries should be designed at the state level in specific ways, which in general will have to take into account containment/surveillance and process monitoring possibilities, and the nature of the species of nuclear materials, rather than facility boundaries or pre-existing accounting divisions.