AN ABSTRACT OF THE THESIS OF Robert J. Aldridge for the degree of Master of Science in Nuclear Engineering presented on May 29, 2013. Title: Scaling Study of the Depressurized Conduction Cooldown Event in the High Temperature Test Facility Using RELAP5-3D/ATHENA Abstract approved: ________________________________________________________________________ Brian G. Woods In 2008, the Department of Energy (DOE) and Nuclear Regulatory Commission (NCR) decided that the Next Generation Nuclear Plant (NGNP) would be the Very High Temperature Reactor (VHTR). In support of the licensing and validation effort of the VHTR, Oregon State University was tasked with designing, building, and operating a thermal hydraulic test facility, the High Temperature Test Facility (HTTF). It is expected that the HTTF will provide data on the systemic response of the Modular High Temperature Gas Reactor (MHTGR) during the Depressurized Conduction Cooldown (DCC) event to validate safety analysis codes and the safety concept of the VHTR. The objective of this thesis was to determine the ability of the HTTF to model the DCC event compared to the MHTGR. To do this, a thermal hydraulic systems code, RELAP5-3D/ATHENA, was used to compare the systemic response of the MHTGR and HTTF during the DCC event. Two phases of the DCC event were modeled, the molecular diffusion phase and natural circulation phase. Each phase was modeled as a Separate Effects Test (SET) and as an Integral Effects Test (IET). For each test, the radial temperature profile, peak fuel temperature as a function of time, time to peak fuel temperature, air front velocity, time to onset of natural circulation, and natural circulation flow rates were compared to the MHTGR response. This thesis also provides an analysis of the scaling distortions inherent to the HTTF. ©Copyright by Robert J. Aldridge May 29, 2013 All Rights Reserved Scaling Study of the Depressurized Conduction Cooldown Event in the High Temperature Test Facility Using RELAP5-3D/ATHENA by Robert J. Aldridge A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented May 29, 2013 Commencement June 2013 Master of Science thesis of Robert J. Aldridge presented on May 29, 2013. APPROVED: ________________________________________________________________________ Major Professor, representing Nuclear Engineering ________________________________________________________________________ Head of the Department of Nuclear Engineering and Radiation Health Physics ________________________________________________________________________ Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes the release of my thesis to any reader upon request. ________________________________________________________________________ Robert J. Aldridge, Author ACKNOWLEDGEMENTS I would like to thank my advisor, Dr. Brian Woods, for his guidance and direction on this project. His support and willingness to answer my questions and the suggestions he gave to improve my work were invaluable. I would also like to acknowledge Dr. Andrew Klein, who was able to take me on as a research assistant during the summer of 2012. Also, I would like to thank Dr. Wade Marcum for use of his post-processing scripts that I adapted for my needs. Also, in no particular order, thanks to Joshua Graves, J.J. Utberg, Wesley Deason, Brian Hallee, and Philip Jensen for being around to answer questions, bounce ideas off of, and be great, encouraging friends throughout this process. I would like to thank all of my former teachers, professors, and mentors. Without them nurturing and developing my natural curiosity, I would not be where I am today. I would also like to express my appreciation for my parents, Jim and Becky, for their generous financial support throughout my college and graduate education. Last but not least, I would like to acknowledge my grandfather, Claude, for always telling me to work hard and do my best. I sincerely miss you, and I wish you and grandma were around to see the man I have become. I hope I would have made you proud. TABLE OF CONTENTS Page 1. INTRODUCTION .......................................................................................................... 1 1.1 Research Objectives .................................................................................................. 5 1.2 Analysis Assumptions ............................................................................................... 6 1.3 Analysis Limitations ................................................................................................. 7 1.4 Motivation ................................................................................................................. 8 1.5 Overview of Following Chapters .............................................................................. 9 2. LITERATURE REVIEW ............................................................................................. 10 2.1 The Depressurized Conduction Cooldown (DCC) Event ....................................... 10 2.2 Previous Modeling of the DCC Event .................................................................... 14 2.3 Previous RELAP5 Thermal Hydraulic Modeling ................................................... 23 3. HTTF SCALING .......................................................................................................... 29 3.1 Hierarchal Two-Tiered Scaling Method ................................................................. 29 3.2 H2TS Applied to the HTTF .................................................................................... 34 3.2.1 Air ingress Scaling Analysis ......................................................................................... 35 3.2.2 Single Phase Natural Circulation Scaling Analysis ...................................................... 42 3.3 Scaling Ratio Evaluation ......................................................................................... 46 3.3.1 Designed Scaling Ratios ............................................................................................... 46 3.3.2 Scaling Ratios for the As-Built HTTF .......................................................................... 57 4. DESCRIPTION OF RELAP5-3D MODELS OF THE MHTGR AND HTTF ............ 64 4.1 The MHTGR ........................................................................................................... 64 4.2 The HTTF................................................................................................................ 67 4.3 Validation of Models at Steady-State ..................................................................... 70 5. DCC EVENT RESULTS AND DISCUSSION ............................................................ 73 5.1 SET and IET Molecular Diffusion Phase Simulation ............................................. 73 5.1.1 Molecular Diffusion SET .............................................................................................. 76 5.1.2 Molecular Diffusion IET ............................................................................................... 81 5.2 SET Natural Circulation Phase Simulation ............................................................. 86 6. CONCLUSIONS AND FUTURE WORK SUGGESTIONS ....................................... 94 6.1 Molecular Diffusion SET ........................................................................................ 94 TABLE OF CONTENTS (continued) 6.2 Molecular Diffusion and Natural Circulation IET .................................................. 95 6.3 Natural Circulation Phase SET ............................................................................... 95 6.4 Broader Implications of Work ................................................................................ 96 6.5 Future Work Suggestions ........................................................................................ 96 BIBLIOGRAPHY ............................................................................................................. 98 A. DESIGN NOTEBOOKS ............................................................................................ 104 A.1 MHTGR Design Notebook .................................................................................. 104 A.2 HTTF Design Notebook ....................................................................................... 112 A.3 Material Properties ............................................................................................... 119 A.3.1 Thermal Conductivity ................................................................................................ 120 A.3.2 Volumetric Heat Capacity .......................................................................................... 132 A.4 Decay Heat Curves ............................................................................................... 136 A.4.1 MHTGR ..................................................................................................................... 136 A.4.2 HTTF Molecular Diffusion SET ................................................................................ 140 A.4.3 HTTF Molecular Diffusion and Natural Circulation IET .......................................... 141 A.4.4. Natural Circulation SET ............................................................................................ 147 LIST OF FIGURES Figure Page 1: MHTGR