Scaling Analysis for the Direct Reactor Auxiliary Cooling System for AHTRs THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Qiuping Lv, B.S. Graduate Program in Nuclear Engineering The Ohio State University 2013 Master's Examination Committee: Prof. Xiaodong Sun, Advisor Prof. Thomas E. Blue Prof. Richard N. Christensen Copyright by Qiuping Lv 2012 Abstract The Advanced High Temperature Reactor (AHTR) or Fluoride Salt Cooled High Temperature Reactor (FHR) is one of the advanced rector concepts that have been proposed for Gen IV reactors. The AHTR combines four main proven nuclear technologies, namely, the liquid salt of molten salt reactors, the coated particle fuel (TRISO particle) of high-temperature gas-cooled reactors, the pool configuration and passive safety system of sodium-cooled fast reactors, and the Brayton power cycle technology. The AHTR is capable of providing very high temperature (750 to 1,000ºC) heat for various industrial processing needs, hydrogen production, and electricity generation. The Direct Reactor Auxiliary Cooling System (DRACS) is a passive heat removal system that was derived from the Experimental Breeder Rector-II (EBR-II), and then improved in later fast reactor designs. The DRACS has been proposed for AHTR as the passive decay heat removal system. The DRACS features three coupled natural circulation/convection loops relying completely on buoyancy as the driving force. In the DRACS, two heat exchangers, namely, the DRACS Heat Exchanger (DHX) and the Natural Draft Heat Exchanger (NDHX) are used to couple these natural circulation/convection loops. In addition, a fluidic diode is employed to restrict parasitic flow during normal operation of the reactor and to activate the DRACS in accidents. ii While the DRACS concept has been proposed, there are no actual prototypic DRACS systems for AHTRs built and tested in the literature. In this report, a detailed modular design of the DRACS for a 20-MWth FHR is first developed. As a starting point, the DRACS is designed to remove 1% of the nominal power, i.e., the decay power being 200 kW. The design process for the prototypic DRACS involves selection of the salts, identification of the reactor core, design of the DHX and NDHX, design of the fluidic diode, design of the air chimney, selection of the loop pipes, and finally determination of the loop height based on pressure drop analysis. FLiBe with high enrichment in Li-7 and FLiNaK have been selected as the primary and secondary salts, respectively. A 16-MWth pebble bed core proposed by University of California at Berkeley (UCB) is adopted in the design. Shell-and-tube heat exchangers have been designed based on Delaware Method for the DHX and NDHX. A vortex diode that has been tested with water in the literature is adopted in the present design. Finally, pipes with inner diameter of 15 cm are selected for both the primary and secondary loops of the DRACS. The final DRACS design features a total height less than 13 m. The design presented here has the potential to be used in the planned small-scale FHR test reactor and will also benefit and guide the DRACS design for a commercial AHTR. Following the prototypic DRACS design is the detailed scaling analysis for the DRACS, which will provide guidance for the design of scaled-down DRACS test facilities. Based on the Boussinesq assumption and one-dimensional formulation, the governing equations, i.e., the continuity, integral momentum, and energy equations are non-dimensionalized by introducing appropriate dimensionless parameters, including the iii dimensionless length, temperature, velocity, etc. The key dimensionless numbers, i.e., the Richardson, friction, Stanton, time ratio, Biot, and heat source numbers that characterize the DRACS system, are obtained from the non-dimensional governing equations. Based on the dimensionless numbers and non-dimensional governing equations, similarity laws are proposed. In addition, a scaling methodology has also been developed, which consists of the core scaling and loop scaling. Due to the importance of the core heat transfer in establishing the DRACS steady state, core scaling is started with, from which the convection time ratio is obtained. The loop scaling is accomplished by utilizing the convection time ratio obtained from the core scaling and by making two assumptions that are related to the power and loop height of the test facility. The consistence between the core and the loop scaling is examined through the reference volume ratio that can be obtained from both scaling processes. The scaling methodology and similarity laws have been applied to obtain a scaled-down low-temperature DRACS test facility (LTDF) and a scaled-down high-temperature DRACS test facility (HTDF). iv Dedication This document is dedicated to my family. v Acknowledgments There are many people I want to thank. First and foremost, I must give my deepest gratitude to my advisor, Prof. Xiaodong Sun, for his guidance, supervision, attention and support throughout my study and research. In addition, I sincerely thank Prof. Richard Christensen and Prof. Thomas Blue for their constructive comments and suggestions during all the research meetings. Helps from Dr. Xia Wang, Dr. Grady Yoder and Dr. Dane Wilson (ORNL), and Dr. Piyush Sabharwall (INL) are greatly appreciated. I also would like to thank my friends and the colleagues in the Ohio State University Nuclear Engineering Program. They have been helpful in improving my English. Special thanks to my wife and my parents for always being understanding and supportive. Finally, the support from the U.S. Department of Energy for our DRACS project is gratefully acknowledged. vi Vita 2009................................................................B.S. in Physics, Nanjing University, China 2009-2010 ......................................................Teaching Assistant, Physics Department, Iowa State University 2010-2011 ......................................................Graduate Fellow, Nuclear Engineering Program, The Ohio State University 2011 to present ..............................................Graduate Research Associate, Nuclear Engineering Program, The Ohio State University Publications 1. X. Wang, Q. Lv, X. Sun, R.N. Christensen, T.E. Blue, G. Yoder, D. Wilson, and P. Sabharwall, “A Modular Design of a Direct Reactor Auxiliary Cooling System for AHTRs,” Transaction of the American Nuclear Society, Vol. 104, 2011 American Nuclear Society Annual Meeting, June 26-30, 2011, Hollywood, FL, pp. 1077-1080. 2. X. Wang, Q. Lv, X. Sun, R.N. Christensen, T.E. Blue, G. Yoder, D. Wilson, and P. Sabharwall, “Scaling Analysis for the Direct Reactor Auxiliary Cooling System for AHTRs,” Transaction of the American Nuclear Society, Vol. 105, 2011 American Nuclear Society Winter Meeting, October 30 – November 3, 2011, Washington, DC, pp. 1027-1030. 3. X. Wang, Q. Lv, X. Sun, R.N. Christensen, T.E. Blue, G. Yoder, D. Wilson, and P. Sabharwall, “Design of a Scaled-down DRACS Test Facility for an AHTR,” Transaction of the American Nuclear Society, Vol. 105, 2011 American Nuclear Society Winter Meeting, October 30 – November 3, 2011, Washington, DC, pp. 1031-1034. vii 4. Q. Lv, X. Wang, I. Adams, X. Sun, R.N. Christensen, T.E. Blue, G. Yoder, D. Wilson, and P. Sabharwall, “Design of a Scaled-down Low-temperature DRACS Test Facility for an AHTR,” Transactions of the American Nuclear Society, Vol. 106, 2012 American Nuclear Society Annual Meeting, June 24-28, 2012, Chicago, IL, pp. 1071-1074. 5. Q. Lv, I. Adams, X. Wang, X. Sun, R.N. Christensen, T.E. Blue, G. Yoder, D. Wilson, and P. Sabharwall, “A MATLAB Code for Thermal Performance Evaluation of a Low- Temperature DRACS Test Facility”, Transaction of the American Nuclear Society, Vol. 107, 2012 American Nuclear Society Winter Meeting, November 11-15, 2012, San Diego, CA, pp. 1374-1377. Fields of Study Major Field: Nuclear Engineering viii Table of Contents Abstract ............................................................................................................................... ii Dedication ........................................................................................................................... v Acknowledgments.............................................................................................................. vi Vita .................................................................................................................................... vii Table of Contents ............................................................................................................... ix List of Tables .................................................................................................................... xii List of Figures .................................................................................................................. xiv Nomenclature ................................................................................................................... xvi Chapter 1: Introduction ....................................................................................................... 1 1.1 Gen IV Reactors ........................................................................................................ 1 1.2 Molten Salt Reactor (MSR) ...................................................................................... 3 1.3 Advanced High Temperature Reactor (AHTR) .......................................................