Simulation and analysis of xenon removal system through gas sparging in molten salt reactor

Chen, Jiaqi

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https://hdl.handle.net/2142/122144 Copy

Description

Title

Simulation and analysis of xenon removal system through gas sparging in molten salt reactor

Author(s)

Chen, Jiaqi

Issue Date

2023-11-28

Director of Research (if dissertation) or Advisor (if thesis)

Brooks, Caleb S.

Doctoral Committee Chair(s)

Brooks, Caleb S.

Committee Member(s)

• Kozlowski, Tomasz
• Smith, Kyle C.
• Stubbins, James F.

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear, Plasma, Radiolgc Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Molten Salt Reactor
• Xenon
• Gas Sparging

Abstract

In the quest for a sustainable and climate-resilient future, the global aim has shifted towards achieving net-zero greenhouse gas emissions. In this context, nuclear energy is viewed as an important component in realizing carbon neutrality in both an efficient and economical way. This perspective has piqued significant interest in advanced reactor technologies in recent years including the molten salt reactors (MSRs). Recent research of MSRs includes both solid-fueled and liquid-fueled MSR designs. Liquid-fueled MSRs stand out due to their unique characteristics, such as inherent safety against core melting, capabilities for online refueling, and fuel processing. By removing undesirable fission gases, especially xenon-135, fuel utilization can be enhanced, and the reactor becomes more adaptable to load-following operations. The latter is becoming increasingly attractive due to the increase of intermittent generations on the grid. For molten salt thermal breeder reactors, xenon removal becomes even more crucial to optimize the breeder ratio. Among several processing methods, the xenon removal system employing helium sparging has received significant attention, forming the central theme of this thesis. The proposed xenon removal system includes a bubble generator for helium injection into the primary loop, a removal pipeline to provide contact time between the phases, a bubble separator to eliminate introduced bubbles, and additional off-gas processing components for subsequent radioactivity management. A good understanding of the complex two-phase flow and species transfer dynamics in the xenon removal system is necessary for the design and assessment of a prototypical system. This study utilizes CFD simulations with a Eulerian two-fluid model coupled with species transport to study this complicated flow mechanism. The aim is to extend the limited experimental data on the xenon removal system to derive reduced-order models for design analysis. Sensitivity studies are conducted in order to provide estimations of uncertainties within the CFD simulations and the reduced-order models. A one-dimensional species transport model is derived for the removal pipeline using weighted averaged of the governing equations and inputs form the CFD simulations. An engineering correlation of the bubble separator is constructed using data generated by the CFD simulation, which can predict the separator efficiency across various flow scenarios and geometric configurations. Integrating the component models developed based on the CFD simulations, system-level models for both the Molten Salt Reactor Experiment (MSRE) and the Molten Salt Demonstration Reactor (MSDR) are developed using Simulink. These models aim to analyze xenon migration at the plant level within MSRs, which is required to design the xenon removal system. The steady-state and transient xenon poison worth in the MSRE is simulated using the system-level model and compared with available data in the literature. Good agreement is found between the simulation and the experiment and the Simulink model is considered validated. Following this, the model is adapted for the MSDR, a reactor with a 750 MWt capacity, designed based on the MSRE. Simulations are performed to design a preliminary xenon removal system that could satisfy the criteria posed by load-following operation and fuel utilization improvement. The viability of this prototypical removal system is evaluated by performing a supplementary cost-benefit analysis, where the system is shown to be economical in the context of today’s U.S. energy market.

Graduation Semester

2023-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Jiaqi Chen

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