Design of a Sodium-cooled Epithermal Long-term Exploration Nuclear Engine By Peter Yarsky B.S. Nuclear Engineering and Engineering Physics Rensselaer Polytechnic Institute, 2002 SUBMITTED TO THE DEPARTMENT OF NUCLEAR ENGINEERING IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR A DEGREE OF MASTER OF SCIENCE IN NUCLEAR ENGINEERING AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY September 2004 © 2004 Massachusetts Institute of Technology. All rights reserved. Author Peter Yarsky Department of Nuclear Engineering June 28, 2004 Certified by Professor Andrew C. Kadak Thesis Advisor Certified by Professor Michael J. Driscoll Thesis Reader Accepted by Professor Jeffrey A. Coderre Chairman, Department Committee on Graduate Students ii Design of a Sodium-cooled Epithermal Long-term Exploration Nuclear Engine By Peter Yarsky Submitted to the Nuclear Engineering Department on June 28, 2004 in partial fulfillment of the requirements for a degree of Master of Science in Nuclear Engineering at the Massachusetts Institute of Technology. Abstract To facilitate the mission to Mars initiative, the current work has focused on conceptual designs for transformational and enabling space nuclear reactor technologies. A matrix of design alternatives for both the reactor core and the power conversion unit were considered. Based on a preliminary screening of technologies using simplified analyses, a conceptual design was established for more detailed design work. The boiling sodium Rankine cycle was selected for the power conversion unit, and the reactor core is an ultra high power density core with highly enriched uranium fuel. The sodium Rankine cycle has many advantages, lending to a highly efficient radiator and compact reactor core. The sodium- cooled, epithermal long-term exploration nuclear engine (SELENE) is designed to be scalable to meet many differing mission requirements. The SELENE core is a comprised of Nb-1Zr clad, lead bonded, UC plates in a honeycomb pattern. The fuel plates are arranged into a rectangular grid, roughly 25cm on each end. The fuel is in two zones, one is 97 a/o enriched in 235U and the other is 70 a/o enriched in 235U. The core is a fast spectrum reactor, BeO reflected, and ex-core controlled. Three designs are proposed, the first is for a 10 MWth / 1.0 MWe Low Temperature (1300 K) system (SELENE-10-LT) and the second for a 10 MWth / 1.2 MWe High Temperature (1500 K) system (SELENE-10-HT) and the third for a 27 MWth / 2.6 MWe system (SELENE-30). All of these designs utilize essentially the same system architecture. Three designs are proposed so that low power variants can be used to verify the technology and develop experience. The reactor systems may then by uprated to a higher power level. The system lifetime is 9 effective full power months, corresponding roughly to a single trip from Earth to Mars and back. Thesis Supervisor: Dr. Andrew C. Kadak Title: Professor of the Practice, Nuclear Engineering iii Table of Contents 1.0 INTRODUCTION........................................................................................................9 1.1 BACKGROUND....................................................................................................................................9 1.2 SCOPE OF THE CURRENT WORK ..................................................................................................11 1.3 ORGANIZATION OF THIS THESIS .................................................................................................12 2.0 ARGON BRAYTON CYCLE...................................................................................... 13 2.1 METHODOLOGY ..............................................................................................................................13 2.2 THEORY.............................................................................................................................................14 2.3 RESULTS.............................................................................................................................................16 2.4 DISCUSSION ......................................................................................................................................18 3.0 THERMIONIC POWER CONVERSION................................................................. 21 3.1 SINGLE LAYER DESIGN..................................................................................................................21 3.2 DUAL LAYER DESIGN.....................................................................................................................23 3.3 DIRECT CONTACT SINGLE LAYER...............................................................................................24 3.4 COMPARISONS..................................................................................................................................25 3.5 CONCLUSIONS ..................................................................................................................................25 4.0 SIMPLIFIED SODIUM RANKINE CYCLE ............................................................. 27 4.1 SIMPLE RANKINE CYCLE SPECIFICATIONS ................................................................................27 4.2 IDEAL ANALYSIS ..............................................................................................................................27 4.3 REAL ANALYSIS................................................................................................................................31 4.4 HIGH TEMPERATURE CYCLE ........................................................................................................31 4.5 DISCUSSION ......................................................................................................................................32 5.0 RADIOISOTOPE DOPING TO PREVENT COOLANT FREEZING................... 33 5.1 RADIOISOTOPES ..............................................................................................................................33 5.2 ANALYSIS...........................................................................................................................................33 5.3 CALCULATIONS ................................................................................................................................35 5.4 CONCLUSIONS ..................................................................................................................................36 6.0 HEU FUELED ULTRA HIGH POWER DENSITY CORE .................................... 37 6.1 DESIGN CHANGES ..........................................................................................................................37 6.2 CORE SIZE.........................................................................................................................................38 6.3 CORE LIFE STUDIES ........................................................................................................................39 6.4 CONTROL MECHANISM ..................................................................................................................39 6.5 VOID REACTIVITY...........................................................................................................................40 6.6 CONCLUSIONS ..................................................................................................................................40 7.0 SUMMARY AND SELENE OVERVIEW.................................................................. 43 8.0 SODIUM RANKINE CYCLE..................................................................................... 47 8.1 BASIC CYCLE.....................................................................................................................................47 8.2 TWO-PHASE FLOW IN MICRO GRAVITY......................................................................................50 8.3 VAPOR SEPARATION .......................................................................................................................50 8.4 JET PUMP ...........................................................................................................................................50 9.0 THERMAL HYDRAULIC ANALYSIS ...................................................................... 51 9.1 AVERAGE CHANNEL FINITE ELEMENT METHODOLOGY......................................................51 9.2 LIQUID REGIME...............................................................................................................................54 9.3 TWO-PHASE REGIME......................................................................................................................57 iv 9.4 VAPOR REGIME................................................................................................................................59 9.5 SELENE-10-LT...............................................................................................................................60 9.6 SELENE-10-HT..............................................................................................................................61 9.7 SELENE-30......................................................................................................................................62 10.0 REACTOR PHYSICS AND BURNUP....................................................................... 65 10.1 REACTIVITY LIMITED BURNUP.....................................................................................................68 10.2 BURNABLE