Oak Ridge National Laboratory (ORNL) has identified a number of previously reported technical factors impacting the implementation of safeguards for Molten Salt Reactors (MSRs), which include: (1) the homogeneous mixture of fuel, coolant, fission products (FPs), and actinides; (2) continuous variation of isotopic concentrations in the fuel salt, including removal (passive or active) of FPs, rare earth elements, and noble metals; (3) the potential for online reprocessing whereby some fraction of the inventory can be removed while the reactor is operational; (4) unique refueling schemes, including the ability to continuously feed the core with fresh fissile or fertile material; and (5) the need for measurements to occur in high-radiation, high-dose, high-temperature environments. These factors necessitate the use of advanced modeling and simulation for tracking the isotopic masses and signatures (i.e., chemical, elemental, isotopic, and radiation) throughout the reactor and associated auxiliary processing, and importantly, tracking must be accomplished as a function of time as the fuel salt evolves during reactor and fuel cycle operations. Determining what needs to be measured, what can be observed, and where to make the measurement(s) are the first steps towards the development of the safeguards technology for the MSR family of reactors. This paper presents insight into the necessity of advanced modeling and simulation methods and tools, highlighting the tight coupling between the reactor and fuel cycle operations and the resulting fuel inventory and associated signatures. This paper also demonstrates the importance of a comprehensive understanding of the MSR and fuel cycle technologies, as well as the safeguards approaches and technologies that need to be applied. Using ORNL-developed tools designed to model dynamic, complex systems such as salt-fueled MSRs (e.g., source term accountancy), several scenarios are presented that demonstrate the data and modeling fidelity required and highlights the physical behavior of the critical factors identified above, illustrating the need to capture the tight coupling between MSR behavior and safeguards assessments. A preliminary evaluation of the implications for safeguards technology development is also presented.
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