Revisiting Statistical Aspects of Nuclear Material Accounting

Nuclear material accounting (NMA) is the only safeguards system whose benefits are routinelyquantified. Process monitoring (PM) is another safeguards system that is increasinglyused, and one challenge is how to quantify its benefit. This paper considers PM in the role ofenabling frequent NMA, which is referred to as near-real-time accounting (NRTA). We quantify NRTA benefits using period-driven and data-driven testing. Period-driven testingmakes a decision to alarm or not at fixed periods. Data-driven testing decides as the dataarrives whether to alarm or continue testing. The difference between period-driven and datad-rivenviewpoints is illustrated by using one-year and two-year periods. For both one-year andtwo-year periods, period-driven NMA using once-per-year cumulative material unaccounted for(CUMUF) testing is compared to more frequent Shewhart and joint sequential cusum testingusing either MUF or standardized, independently transformed MUF (SITMUF) data. We showthat the data-driven viewpoint is appropriate for NRTA and that it can be used to comparesafeguards effectiveness. In addition to providing period-driven and data-driven viewpoints, new features include assessingthe impact of uncertainty in the estimated covariance matrix of the MUF sequence andthe impact of both random and systematic measurement errors