The nuclear inspectors at International Atomic Energy Agency (IAEA) routinely employ environmental sampling (ES) as a verification method to strengthen safeguards. The environmental swipe samples collected at various locations in Gas Centrifuge Enrichment Plants (GCEPs) can detect undeclared nuclear material and activities at a declared facility based on isotopic ratios. Even though ES is highly effective in detecting the changes in enrichments and their deviations from the declared values, it cannot explain the cause of those changes. Several potential explanations can be employed as possibilities for particles detected above or other than the declared enrichment. These include changes to the design of the enrichment cascades, unintentional failures of the machines, or deliberate misuse by the facility operators such as addition of undeclared feed. The primary objective of this work is to understand how these factors affect the enrichments produced by a cascade and quantify anticipated multi-isotopic concentrations for each case. The focus is given to cascades enriching uranium between 5-19.75% 235U, commonly referred in the U.S. as HALEU. The high assay enrichment has gained momentum in the last few years with increasing focus on the development and implementation of advanced nuclear reactors. This study will analyze the isotopic signatures in HALEU as well as Low Enriched Uranium (LEU) cascades and highlight any potential differences that may require modifications of the current safeguard measures. Two scenarios that include enrichment of natural uranium (NU) feed to 19.75% 235U in a single cascade compared to a two-step process will be investigated. Next, an intentional operator violation and an accidental machine failure for both enrichment levels will assess the differences in isotopic concentrations. A non-ideal squared-off cascade model developed at the University of Virginia is used to determine flow rates and isotopic concentrations of the UF6 gas. The analysis is performed using the Iguaçu machine operated at 600 m/s rotor speed.
Year
2022
Abstract