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A nonlinear dynamic model for the two-fluid molten-salt breeder reactor (MSBR) system is presented. This work is partly inspired by a preliminary dynamic model of the concept studied at Oak Ridge National Laboratory (ORNL). The core heat transfer model has been revised to accurately reflect the design exemplified in ORNL-4528—the last report on the two-fluid design. A brief description of the reactor system and the effects of reactor poisons and a discussion of temperature feedback mechanisms are presented. This background information is followed by an overview of the modeling approach and a discussion of the revised lumped parametrization, along with detailed descriptions of the modeling methodology and model limitations. All equations and parameters used in the model are presented to aid in model reproduction and adaptation for other molten-salt reactor designs. Model stability is analyzed by observing the uncontrolled response to reactivity perturbations. Simulations illustrate stable behavior at all power levels investigated. Temperature-induced feedback effects lead to stable dynamics for both large and small reactivity transients. Stable and smooth changes in the various nodal temperatures are also observed. The frequency response of the system indicates no dynamics problems at all operating power levels and is consistent with the transient response. Characteristic features in the frequency response plots due to feedback effects are also discussed. Finally, the load-following capability of the MSBR system is studied for various ramp rates of the power demand in the final heat sink. The temperatures in all salt-containing parts of the system are observed to vary about an average during the load-following maneuver. It is observed that the MSBR system exhibits a self-regulating behavior, minimizing the need for external controller action for load-following operations. [ABSTRACT FROM AUTHOR]

Several molten-salt reactor (MSR) concepts are currently being developed by private vendors and national organizations. Molten-Salt Reactor Experiment (MSRE) is the only MSR that operated for several years, for which the performance was well documented in the literature. Experimental data from MSRE serve as the standard for developing models and tools for MSR analysis. MSRE underwent several design changes from conception to construction to operation. Model validation requires the use of parameters consistent with those that existed during the various measurements. The paper therefore presents a brief discussion of the parameters that evolved over time, and details of sources for all the parameters used in the modeling. This report is part of a series of papers on modeling MSR dynamics. The goal here is to validate the modeling approach by comparing simulation results with experimental data. For this purpose, two nonlinear dynamic models are developed. The first model uses a one-region one-dimensional representation of the core. The second reproduces the nine-region core model developed by Oak Ridge National Laboratory for MSRE studies. The dynamics are analyzed by simulating transients during normal power operation. The frequency response of the models is also evaluated. Both models show excellent agreement with experimental data for both U-235 and U-233 fuels. Some apparent discrepancies in experimental data are reported and their consequences discussed. The one-region model is modified to simulate reactivity excursions resulting from operational anomalies, and the results are presented. This modeling approach can be applied to other MSR systems provided valid system parameters. [ABSTRACT FROM AUTHOR]

• Open-source plant-level dynamic model of commercial-scale molten-salt reactor. • Primary side coupled with OTSG and a reheated-regenerative Rankine cycle BOP. Xenon poison effect accounted. • Frequency response with different boundary conditions on the model shows need for accounting secondary-side dynamics for I&C related studies. • Results suggest that self-regulating characteristics emanating from feedbacks can be leveraged to engineer control systems offering a great deal of autonomy. Ongoing research by the authors has led to a dynamic modeling approach that was verified against experimental data from the Molten-Salt Reactor Experiment (MSRE). These lumped-parameter models, characterizing the reactor dynamics, are nonlinear and represent changes in mass, energy, and temperature in all parts of the reactor plant. The reactivity feedback effects due to changes in temperature and Xe-135 concentration are taken into account. These models can be used to study both the time and frequency response to perturbations caused during normal operating conditions and during anomalies resulting from failure of certain sub-systems. A plant-level dynamic model of a representative molten salt reactor system developed based on the same methodology is presented here. A once-through steam generator providing superheated steam and reheated-regenerative Rankine cycle balance-of-plant system are coupled to the plant model. Results from simulation are presented for various transients and the resulting response of the plant is analyzed. Frequency response of the plant is also presented for various boundary conditions on the secondary side. Modeling results suggest that the inherent temperature-related feedbacks result in load-following characteristics that can be leveraged to engineer control systems offering a great deal of autonomy. [ABSTRACT FROM AUTHOR]