arXiv subjects

Saya Lee

Publications and source records attributed to Saya Lee.

4 recordsLinked to original sources

arXiv2026

Multiphysics Modelling of the Molten Salt Fast Reactor using NekRS and the Fission Matrix Method

The Molten Salt Fast Reactor (MSFR) has the particularity that the coolant is also the fuel, which tightens the coupling between neutronics and thermal hydraulics as the fuel circulates through the primary system. Therefore, developing computational models to analyze the MSFR requires a multiphysics approach. In this paper, we propose developing a neutronic thermal-hydraulic computational model of the MSFR that uses a reduced-order model to solve the neutronics equations. The principal computational tool chosen for this purpose is the high-fidelity code Cardinal, a wrapping within the MOOSE framework that integrates the Computational Fluid Dynamics code NekRS and the Monte Carlo particle transport code OpenMC. However, we use the Fission Matrix (FM) Method to solve the neutronics equations instead of OpenMC. The FM method can perform fast and still accurate neutronics simulations. It relies on precalculated databases obtained through a Monte Carlo simulation.

physics.comp-ph↗

arXiv2026

Analysis of Fission Matrix Databases using Temperature Profiles obtained from High-Fidelity Multiphysics Simulations

The Fission Matrix method is used to perform fast and still accurate neutronics simulations. It relies on precalculated databases obtained through a Monte Carlo simulation. To represent every state of the reactor, multiple databases are required. The actual state of the reactor is obtained from those databases. In this paper, we analyze the effect of the temperature profiles selected to construct the databases. To do so, the Molten Salt Fast reactor is selected. Two sets of databases are studied: the first uses temperature profiles obtained from high-fidelity Multiphysics simulations with Cardinal, and the second uses uniform temperature profiles. Results showed improved multiplication factor and fission source distribution when the temperature profiles used to generate the databases were similar to those expected when solving the fission matrix.

physics.comp-ph↗

arXiv2025

High-Fidelity Modelling of the Molten Salt Fast Reactor

The Molten Salt Fast Reactor (MSFR) is one of the six GEN-IV reactor designs. In the MSFR, the liquid fuel is the coolant, which moves throughout the primary circuit. This complex phenomenology requires multiphysics modeling. In the present paper, a model of the MSFR is developed in the multiphysics code Cardinal, considering neutronic-thermal hydraulic feedback and the transport of delayed neutron precursors (DNPs) and decay heat precursors (DHPs). OpenMC is used to solve neutronic equations, and NekRS is used to solve mass, momentum, energy, DNPs, and DHPs distribution. A RANS k-t turbulence model is used in NekRS. DNPs and DHPs are modeled using a convective-diffusion equation with modified source terms considering radioactive decay. Cardinal results showed a reasonable behavior for temperature, heat source, velocity, DNPs, and DHPs. However, the current limitations in OpenMC do not allow the modification of delayed neutron source locations. Ongoing efforts look to include this feature in future work to introduce DNP feedback in OpenMC.

physics.comp-ph↗

arXiv2023

High-fidelity simulation of pebble beds: Toward an improved understanding of the wall channeling effect

Wall channeling is a phenomena of interest for Pebble Bed Reactors (PBRs) where flow is diverted into high-porosity regions near the wall. This diversion of flow can have a significant impact on maximum fuel temperatures and core bypass flow. Porous media models that are currently used to model PBRs for design scoping and transient simulation are lacking in their capabilities to model the wall channel effect. Recent efforts at Penn State have produced an improved porous media pressure drop equation that is more capable of modeling the velocity variations caused by the wall channel effect in a porous media model. Several pebble beds were divided into concentric rings of $0.05D_{peb}$, and average flow quantities and porosities were extracted for the ring. A correlation between the form loss coefficient and the local ring porosity was found, allowing for the addition of a correction factor to the form loss term of the KTA equation. The developed correlation was purely empirical, and thus a more thorough understanding of the underlying flow phenomena is desired. This study investigates geometric and flow features that can explain the observed correlation between the form coefficient and the local porosity that was used to generate the improved pressure drop equation. The solid surface area to volume ratio $S_v$ along with the production of Turbulent Kinetic Energy (TKE) is analyzed. A relationship between $S_v$ and the local porosity and an inverse relationship between the negative TKE production and the local porosity were found, pointing to the idea that inertial effects caused by different pore geometry in each ring contribute to the variation of the form constant with the local porosity.

physics.flu-dyn↗