Modeling the Multi-Isotopic Separation in a Gas Centrifuge and Enrichment Cascades

Possibility of nuclear warfare and the misuse of nuclear technology are pressing issues of the modern times. Despite best attempts by the International Atomic Energy Agency (IAEA) to limit the use of nuclear energy to peaceful purposes, there are looming threats of nuclear proliferation on a regular basis. Therefore, it is essential to be able to understand the science and model the technology behind the production of such weapons of mass destruction and to recognize any potential threats in a timely manner. To that goal, this work looks to build upon and refine the studies that have been conducted to model the gas centrifuges used in the development of fuel required to operate power reactors as well as create nuclear weapons. Such fuel is obtained by enriching the fissile uranium-235 isotope from the uranium hexafluoride (UF6) gas mixture inside the high-speed centrifuges.
This research focuses on the study of fluid flow and isotopic diffusion of the UF6 gas inside the rotor volume of a gas centrifuge. The primary objective is to develop a numerical model to simulate the concentration gradients of the different uranium isotopes present in the gas mixture. Previous work in this topic has primarily looked at the separation of two isotopes, U-235 and U-238; however, uranium also consists of the U-232, U-234, and U-236 isotopes that can affect the separative capability of the machine. Therefore, a two-dimensional multi-isotope separation model has been created by solving the diffusion transport equations using finite element analysis. The new 2-D model is unique to its counterparts in the past as it provides a holistic view of isotope transport inside the machine for any arbitrary number of isotopes that may be present in the gas mixture. In addition to the development of the multi-isotope model, this work also looks to refine the mass flow solution, specifically by evaluating the ideal distribution shapes of the sources of mass, momentum, and energy. This ensures that the simulated mass flow is the best representation of reality as well as provides the researcher with options to model the flow as desired. To ensure that the developed numerical models provide accurate results, verification measures including sensitivity analysis and uncertainty quantification are performed. Finally, the work is extended from a single centrifuge to cascades of centrifuges to simulate gas centrifuge enrichment plants (GCEPS) and to be able to identify any proliferation threats. Thus, the last section of the dissertation highlights how the IAEA can benefit from the glossary of existing as well as newly developed models and studies during verification of declared nuclear material.