Analysis of and comparison between reprocessing methods in the molten salt breeder reactor

Seifert, Luke

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https://hdl.handle.net/2142/122029 Copy

Description

Title

Analysis of and comparison between reprocessing methods in the molten salt breeder reactor

Author(s)

Seifert, Luke

Issue Date

2023-12-05

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

Munk, Madicken

Committee Member(s)

Kozlowski, Tomasz

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear, Plasma, Radiolgc Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Molten Salt Reactors
• Online Reprocessing
• Batchwise Reprocessing
• Continuous Reprocessing
• MSR
• MSBR
• Mass Balancing

Abstract

Liquid fueled molten salt reactor modeling can be challenging, as the fuel composition varies temporally and spatially. Although these models are challenging, they are important for predicting reactor safety and performance during operation. One of the reasons these models are challenging is the difficulty in capturing different physical phenomena which occur in different time scales. Over short time scales, one of these physical phenomena is the movement of delayed neutron precursors to less important regions of the reactor. For longer time scales, one of these physical phenomena is online reprocessing, which includes adding fresh fuel and removing fission products from the reactor during operation and is the focus of this work. Reprocessing is useful in liquid fueled molten salt reactors because it limits chemical corrosion and improves the neutron economy. Reprocessing can be performed continuously during operation, referred to as online reprocessing, or in batches during outages, referred to as batchwise reprocessing. In order to simulate reprocessing computationally, there are two different mathematical approaches which are commonly implemented in the literature, called batchwise and continuous reprocessing. The continuous reprocessing method is more physically reflective of reactors using a chemically continuous reprocessing scheme. However, there are many works which have implemented batchwise reprocessing methods to simulate a physically continuous reprocessing process. In this thesis, I show that continuous reprocessing and batchwise reprocessing methods are not interchangeable. Using both methods on the same system shows that there are non-trivial differences in the results. I also investigate the computational cost of different reprocessing methods by performing a depletion time step refinement study. In this study, I found that continuous reprocessing allows for significantly larger time steps without large increases in error, which reduces computational cost. However, continuous reprocessing does not necessarily keep the overall mass constant, thus potentially leading to a nonphysical solution. I compare the differences between both methods while determining the effect of this nonphysical mass change caused by continuous reprocessing.

Graduation Semester

2023-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Luke Seifert

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