Advancement and verification of Moltres for molten salt reactor safety analysis

Molten salt reactors, a class of advanced nuclear reactors, promise numerous improvements over the current fleet of largely light-water reactors. As the world continues its transition towards low-carbon electricity generation to combat climate change, building molten salt reactors is a potential option in the near-term future for replacing fossil fuel and aging nuclear power plants. At the current state of development, molten salt reactors still require extensive research to become viable. This thesis presents the latest developments in Moltres, a simulation tool for molten salt reactors. These new developments are: the support for coupling the incompressible Navier-Stokes and the delayed neutron precursor looping systems, and a model for simulating decay heat from fission products at steady-state and during transients. This work demonstrates these capabilities through multiphysics simulations of the Molten Salt Fast Reactor concept. This work first verifies the six-group neutron diffusion results from Moltres against continuous-energy Monte Carlo neutron transport results from Serpent 2. The multiplication factors k_eff, delayed neutron fractions beta, temperature reactivity coefficient alpha_T, and the six-group neutron energy spectra from Moltres agreed with the high fidelity simulation results from Serpent 2. The k_eff values have small discrepancies on the order of 100 pcm, which is smaller than the -256.7 pcm discrepancy reported in the literature with the same six-group neutron diffusion approach. The decay heat model showed an expected flattening of the temperature distribution due to the movement of the decay heat precursors throughout the primary coolant loop. This work also demonstrates and verifies steady-state and transient multiphysics simulations of the Molten Salt Fast Reactor. The transient scenarios under study include unprotected instances of reactivity insertion, loss of heat sink, loss of flow, and pump overspeed. This thesis verifies the steady-state and transient results against data from the literature for the same case studies. The steady-state temperature and velocity distributions, and the peak neutron flux showed good agreement with the literature results. Minor differences in the delayed neutron precursor distribution and the in-core delayed neutron fraction were explainable with the differences in the handling of turbulence in the models. In three of the transient results (reactivity insertion, loss of heat sink, and pump overspeed), Moltres reproduced the expected magnitude and pattern of the reactor response to these transient initiators. The loss of flow results showed greater discrepancies that resulted from differences in the fluid dynamics modeling in Moltres and the other models. Through the verification studies, this work has also identified avenues for further Moltres software development.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Nuclear, Plasma, Radiolgc Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2020

Author dc:creator

• Park, Sun Myung

Contributors dc:contributor

• Huff, Kathryn D.
• Kozlowski, Tomasz

• Reactor Physics
• Reactor Safety Analysis
• Multiphysics
• Finite elements
• Molten Salt Reactor
• Molten Salt Fast Reactor
• MOOSE

Statement dc:rights

• Copyright 2020 Sun Myung Park

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/108542

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/108542