Bicyclus: A statistical fuel cycle simulation framework for nuclear verification

Abstract

Simulation codes are regularly used to model nuclear fuel cycles (NFCs), e.g., in energy transition scenarios. They are, however, not yet established in the context of verifying non-proliferation and disarmament. We present Bicyclus, the first open-source statistical framework tailored to analyse NFCs for such scenarios. Bicyclus combines Cyclus, an existing NFC simulator, with Bayesian inference and Monte-Carlo methods to provide a variety of verification tools. The Bayesian approach is suited to reconstruct past NFC operations, useful for nuclear forensics and nuclear archaeology, while the Monte-Carlo approach can improve the robustness of fissile material estimates and can complement the IAEA's Acquisition Pathway Analysis. We showcase these features in a case study based on a military NFC with intertwined plutonium and HEU production paths. Here, we perform an independent assessment of the fissile material stockpiles. Furthermore, we reconstruct the production history using (synthetic) measurements of produced waste in a nuclear archaeology scenario.