Advancements in moltres for time-dependent multiphysics molten salt reactor modeling

Molten Salt Reactors (MSRs) are advanced reactors noted for strong passive safety features. They present unique challenges in multiphysics reactor modeling & simulation arising from strong temperature reactivity feedback, delayed neutron precursor flow, and turbulent heat transport in fuel salt regions. Simulating the complex multiphysics interactions in MSRs requires robust, flexible, and highly scalable multiphysics software. Many MSR designs also still retain control rods which can complicate time-dependent reactivity-initiated transient simulations on reactor software relying on neutron diffusion theory. This work builds on existing capabilities in Moltres, a MOOSE-based MSR simulation software, to tackle these challenges and support efforts towards MSR deployment. This work verified and validated existing multiphysics coupling capabilities in Moltres in two comparative studies. In both studies, Moltres showed good agreement with other MSR simulation tools involving coupled neutronics and thermal-hydraulics problems. This work also introduces a turbulence model in Moltres to support future MSR analyses involving turbulent delayed neutron precursor and temperature transport. Lastly, this work introduces a novel hybrid SN-diffusion method for accurate control rod modeling in time-dependent MSR simulations. The hybrid method combines the strengths of both approaches by generating transport corrections using the SN method near control rods. The SN and neutron diffusion solvers are coupled through an adaptive boundary coupling algorithm. This algorithm allows the solver to adapt to the transport correction parameters and preserve smooth neutron flux gradients across the interface. In 1-D, 2-D, and 3-D k-eigenvalue simulations, the hybrid method produced accurate control rod worth estimates, relative to reference neutron transport solutions and experimental data, at approximately four times the computational cost of the neutron diffusion method. The hybrid method also performed well in a time-dependent rod drop simulation by reproducing expected trends observed in experimental data. Analysis of its computational performance indicated the possibility of further optimizations beyond its current implementation. With the hybrid method’s spatial resolution and efficient computational performance, Moltres could enable accurate and cost-effective simulations of asymmetric transients in MSRs.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Nuclear, Plasma, Radiolgc Engr

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Park, Sun Myung

Contributors dc:contributor

• Huff, Kathryn D.
• Munk, Madicken
• Uddin, Rizwan
• Kozlowski, Tomasz
• Fischer, Paul

• multiphysics
• control rod modeling
• molten salt reactor
• neutron transport
• reactor physics
• reactor analysis

Statement dc:rights

• Copyright 2025 Sun Myung Park

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129365

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129365