Nuclear archaeology for heavy-water-moderated plutonium production reactors

There is growing interest in a set of methods and tools that can be used to characterize past fissile material production activities, using measurements and sampling at production and storage sites. This field has been dubbed "nuclear archaeology." The best-established example of nuclear archaeology relies on measurements of the isotope ratios of selected elements in the graphite of graphite-moderated plutonium production reactors. This Graphite Isotope-Ratio Method (GIRM) determines the cumulative neutron fluence through the graphite and thereby estimates the cumulative plutonium production in the reactor. The great limitation of this particular method is that it can only be applied to graphite-moderated reactors, which represent only one class of reactors that have been used for unsafe guarded plutonium production. In this article, we propose to extend this method to non-graphite moderated reactors by analyzing the evolution of relevant isotope ratios in the support structures and other core components of heavy-water moderated reactors. We present results of neutronics calculations for a generic heavy-moderated reactor evaluating the robustness of the method and explore the role of nuclear archaeology for applications in arms-control treaty verification.