New reactor model unlocks deeper insights into molten salt reactor dynamics

New reactor model unlocks deeper insights into molten salt reactor dynamics
by Simon Mansfield
Sydney, Australia (SPX) Apr 28, 2025

Researchers at the University of Shanghai for Science and Technology, working alongside the University of Illinois Urbana-Champaign, have introduced a comprehensive modeling system to better simulate the unique behaviors of liquid-fueled molten salt reactors (MSRs). Designed using Simulink, the new coupled model integrates neutron kinetics, thermal hydraulics, xenon behavior, and void transport, validated against data from the historic Molten Salt Reactor Experiment (MSRE) conducted at Oak Ridge National Laboratory.

Modernizing Reactor Simulation Tools

Traditional analysis platforms, built for solid-fueled reactors, often struggle to capture the dynamic conditions in MSRs. Addressing this gap, the team's new model explicitly incorporates the transport processes of xenon and delayed neutron precursors (DNPs), significantly enhancing the ability to predict reactivity feedback during critical transitions such as pump activations, coast-downs, and control rod adjustments.

"This work helps us better understand how circulating fuel, xenon removal, and void reactivity affect reactor stability and control," said Dr. Jia-Qi Chen, the study's lead author. "It provides a validated model and open-sourced model for analyzing MSR dynamics and supporting future reactor designs."

Through simulations of different operational events, the model illustrated how factors like off-gas system blockages or the loss of gas voids could influence reactor behavior, offering critical data for advancing the safe and adaptable deployment of MSRs in future energy systems.

Capturing the Complexities of Liquid-Fueled Reactors

The development marks a significant advance in understanding the intertwined effects of xenon migration, DNP circulation, and thermal-hydraulic feedback in MSRs. Benchmarking against MSRE data, the model successfully replicated power-to-reactivity frequency responses across a range of conditions, including zero power and outputs up to 8 MW using both U and 5U fuel types. Crucially, it accurately captured the system's resonant frequency near 0.23 rad/s, a value linked to out-of-core DNP flow, and aligned closely with observed reactor gain and phase behavior under various dynamic scenarios.

One of the study's key findings showed that reactor stability increases with operational power due to stronger thermal feedback effects. Conversely, reactors operating at lower powers displayed heightened sensitivity to disturbances caused by void changes and xenon dynamics. The model predicted that losing gas voids could trigger an immediate surge in reactor power, particularly at lower power levels, followed by a gradual decline driven by rising xenon poisoning over subsequent hours. In scenarios simulating off-gas system blockages, a significant xenon buildup was found to reduce power output by over 20% after 30 hours without control rod interventions.

A Platform for the Future of Nuclear Innovation

This research highlights the capability of a well-calibrated lumped-parameter Simulink model to accurately represent the intricate multi-physics behavior of MSRs. Providing a flexible and robust framework, the model offers valuable insights for optimizing control mechanisms, ensuring operational stability, and defining safety margins for next-generation reactor designs. As the global demand for flexible, low-carbon energy continues to grow, this modeling approach lays essential groundwork for the licensing and deployment of advanced molten salt reactor technologies.

Research Report:Validation and application of a coupled xenon-transport and reactor dynamic model of Molten-salt reactor experiment