The Radiative Heat Transfer Properties of Molten Salts and Their Relevance to the Design of Advanced Reactors DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Ethan Solomon Chaleff Graduate Program in Nuclear Engineering The Ohio State University 2016 Dissertation Committee: Dr. Thomas Blue (Advisor) Dr. Xiaodong Sun Dr. Marat Khafizov Dr. Wolfgang Windl Copyright by Ethan Solomon Chaleff 2016 Abstract Molten salts, such as the fluoride salt eutectic LiF-NaF-KF (FLiNaK) or the transition metal fluoride salt KF-ZrF4, have been proposed as coolants for numerous advanced reactor concepts. These reactors are designed to operate at high temperatures where radiative heat transfer may play a significant role. If this is the case, the radiative heat transfer properties of the salt coolants are required to be known for heat transfer calculations to be performed accurately. Chapter 1 describes the existing literature and experimental efforts pertaining to radiative heat transfer in molten salts. The physics governing photon absorption by halide salts is discussed first, followed by a more specific description of experimental results pertaining to salts of interest. The phonon absorption edge in LiF-based salts such as FLiNaK is estimated and the technique described for potential use in other salts. A description is given of various spectral measurement techniques which might plausibly be employed in the present effort, as well as an argument for the use of integral techniques. Chapter 2 discusses the mathematical treatments required to approximate and solve for the radiative flux in participating materials. The differential approximation and the exact solutions to the radiative flux are examined, and methods are given to solve radiative and energy equations simultaneously. A coupled solution is used to examine radiative heat transfer to molten salt coolants. A map is generated of pipe diameters, wall temperatures, ii and average absorption coefficients where radiative heat transfer will increase expected heat transfer by more than 10% compared to convective methods alone. Chapter 3 presents the design and analysis of the Integral Radiative Absorption Chamber (IRAC). The IRAC employs an integral technique for the measurement of the entire electromagnetic spectrum, negating some of the challenges associated with the methods discussed in Chapter 1 at the loss of spectral information. The IRAC design is validated by modeling the experiment in Fluent which shows that the IRAC should be capable of measuring absorption coefficients within 10%. Chapter 4 contains a parallel effort to experimental techniques, whereby information on absorption in salts is pursued using the Density Functional Theory code VASP. Photon-electron interactions are studied in pure salts such as LiF and are shown to be broadly transparent. Transition metal Fluoride salts such as KF-ZrF4 are shown to be broadly opaque. The addition of small amounts of transition metal impurities is studied by insertion of Chromium into the salt mixtures, which causes otherwise transparent salts to exhibit absorption coefficients significant to heat transfer. The spectral absorption coefficient for FLiNaK with Chromium is presented as is the average absorption coefficient as a function of impurity concentration. Chapter 5 discusses experimental efforts undertaken at The Ohio State University. Challenges with the constructed experimental apparatus are discussed and suggestions for future improvement on the technique are included. Finally, Chapter 6 contains broad conclusions pertaining to radiative transfer in advanced reactors. __________ ______ iii Dedication This document is dedicated to the American taxpayers who have generously funded my research to this point. It is a debt that I do not take for granted, and a debt that I intend to repay. iv Acknowledgments While rowing down a river, it’s sometimes easy to lose sight of the current behind you. I want to take this moment to acknowledge and thank the largely unseen forces which helped to ease my progress in life; acknowledge the societal and cultural advantages I earned solely by product of my birth. I am not unaware of how privileged and fortunate my journey has been and continues to be, nor am I unaware of how many others my journey is inaccessible to. That knowledge does not absolve in any way my responsibility or desire to make this a better world for all. Yet it is not only fortunate circumstance that has brought me to this moment. As well, there is an incredibly bounty of specific people who have aided me along the way that I want and need to thank. First and foremost, I want to thank my parents for providing me with endless and unquestionable love, a quality education, and the incredible gift of never wanting for anything truly necessary. The love you have both given me has been a reassuring constant at every difficult stage of my life. I want to thank my grandfather, Julian, who inspired my interest in engineering and nurtured it throughout my life. To my grandmother Frieda, in addition to your love and the respite from my parents, you and the life you lived have taught me how to see the world in an egalitarian way. I want to thank my siblings, Michael, Aaron, and Lauren, for helping to form me into the person I have v become, and my cousins for doing their best to prevent that. To all my aunts and uncles who gave me the wonderful experience of being in a large and loving family, thank you. I have been in school for many years, and so the list of people I need to thank from the world of academia is similarly long. First I want to thank Dr. Thomas Blue, who originally saw something in me which I did not see in myself, who encouraged me to forge on when I wanted to give up. You have been a calm, understanding and guiding influence in my academic pursuits. Thank you to Dr. Wolfgang Windl, for your guidance and patience in explaining physics and math to a mechanical engineer. Thanks to Dr. Sandip Mazumder for serving on my candidacy committee and helping to guide my education and research. Thank you to Michael Eades, for all your help through my graduate career and constant motivation and advice. You have always kept my career and future on your mind, helping me in ways I didn’t fully appreciate at the time. Thanks to Ben Reinke, Tim Garcia, Nik Antolin, and all the other students I have had the pleasure of working with. Thanks to all the wonderful faculty at Case Western Reserve University, specifically Dr. Alexander and Dr. Barnhart, for your time, patience and high expectations I strived to meet. Thanks to Jim Drake for teaching me how to work with my hands and how to be a real engineer. Finally, thank you to every person who provided me with answers, assurance, advice, belays, carpools, meals, beer, friendship, and pizza. I couldn’t have done it without all this help and more, and I still can’t believe that I did. This research was performed using funding received from the Department of Energy Office of Nuclear Energy University Programs. vi Vita March 3, 1990 ................................................................................ Born, Summit, NJ, USA May, 2008 ............................................... Solomon Schecter Day School, West Orange, NJ May, 2012 ........................B.S. Mechanical Engineering, Case Western Reserve Univeristy May, 2015 ........................................ M.S. Nuclear Engineering, The Ohio State University 2013................................. Ohio Space Grant Consortion Fellow, The Ohio State University 2013-2016 .................................................. DOE-NEUP Fellow, The Ohio State University Publications Ethan Chaleff, Piyush Sabharwall, Thomas Blue. “Radiation Heat Transfer in the Molten Salt FLiNaK,” Nuclear Technology. October, 2016 Michael Eades, Ethan Chaleff, Thomas Blue. “Effects of Xe-135m on Steady State Xenon Worth in Thermal Molten Salt Reactors,” Progress in Nuclear Energy. September, 2016 Ethan Chaleff, Thomas Blue, “Measurement of the Radiative Absorption Coefficient of FLiNaK” Transactions of American Nuclear Society, November, 2016 Ethan Chaleff, Michael Eades, Justic Flanders, Xiaodong Sun, Thomas Blue. “Space Molten Salt Reactor for Colonization-Level Surface Power.” Transactions of American Nuclear Society, Washington, DC Fields of Study Major Field: Nuclear Engineering vii Table of Contents Abstract ................................................................................................................................ ii Dedication ........................................................................................................................... iv Acknowledgments................................................................................................................v Vita..................................................................................................................................... vii Publications ........................................................................................................................ vii Fields of Study ................................................................................................................... vii Table of Contents .............................................................................................................. viii List of Tables ...................................................................................................................