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Nuclear Power Systems for Space Applications

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Nuclear Power Systems for Space Applications Aristotle University of Thessaloniki Master Program in Computational Physics Nuclear Power Systems for Space Applications Department of Nuclear and Elementary Particles Physics Laboratory of Atomic and Nuclear Physics Professor: Christos Eleftheriadis Dimitrios Chatzipanagiotidis Acknowledgments The presented work is for my thesis in master degree in Computational Physics at Aristotle University of Thessaloniki. This effort combines my two favorite fields of interest, Nuclear Physics and Space Physics. Firstly, I want to thanks my supervisor, Professor Christos Eleftheriadis, who help and support me all those years from my bachelor degree until now for my thesis with his unique way of teaching and explain Nuclear Physics. Also, I want to thanks Professor Pavel Tsvetkov of Texas A&M University Engineering as he offered to help and guide me for my thesis about RTG. Finally, I would like to thanks my family and my friends for supporting me in my life all these years. Dimitrios Chatzipanagiotidis, Thessaloniki, October 2019 Abstract As the solar energy for space applications put some significant limitations about missions be- yond Jupiter and planetary surface rovers, the use of nuclear energy is the future of space explo- ration. Plutonium 238 is the most desirable fuel for Radioisotopes Thermoelectric Generators (RTG) but is limited on the planet and the production is a highly cost procedure. New techniques of Plutonium 238 production are developed in order to enable new space missions. Other radio- isotopes can be used instead of Plutonium 238, like Strontium 90, but the shielding considera- tions or the half-life make them undesirable for space applications. Although Plutonium 238 offer great designs of power sources still we have some limitations about the amount of power that can be produces by those devices and the profile of a space mission. The next step is the energy from fission reactions. Small fission reactors have been designed form the early years of space exploration but not used due to the safety restrictions but also because RTG provided enough power for the missions of that era. The last years the demands of further exploration of planets and moons or deep space missions with more precise instrumentation and advanced propulsion systems leading to designs of higher power sources that use fissionable radioisotopes like Ura- nium. The design of space fission reactors requires precise simulation with Monte Carlo tech- niques to predict the power and the life time of the energy source. One major problem of these designs is the movable parts that control the fission reactions as increase instability that is unde- sirable in space missions. A solution to this problem is the design of subcritical cores with external neutron source that increase the safety and doesn’t require movable control parts. There are 3 main fuels that considered for the design of a subcritical core and evaluated in this thesis. A suit- able neutron source discussed as well. Also, the energy conversion systems are very important and the two concepts are a steady no movable conversion via thermocouples and a movable based on stripling cycle machine. Index 0 Introduction ......................................................................................................................................................................... 1 1 History of RTG ...................................................................................................................................................................... 4 1.1 Early Steps .................................................................................................................................................................... 4 1.2 First Flights of RTG ........................................................................................................................................................ 5 1.3 Outer Planet Missions .................................................................................................................................................. 7 1.4 Future of RTG ............................................................................................................................................................. 10 2 Physics of RTG .................................................................................................................................................................... 13 2.1 Main Idea of RTG ........................................................................................................................................................ 13 2.2 Radioactivity ............................................................................................................................................................... 14 2.3 Thermal power production from radioisotopes ........................................................................................................ 17 2.4 Heat Conversion Systems ........................................................................................................................................... 20 3 Plutonium 238 .................................................................................................................................................................. 24 3.1 Discovery of Plutonium .............................................................................................................................................. 24 3.2 RTG with Plutonium 238 ............................................................................................................................................. 26 3.2 Artificial Plutonium ..................................................................................................................................................... 32 4 Proper Radioisotopes for RTG ........................................................................................................................................... 37 4.1 Basic Characteristics of Radioisotopes ....................................................................................................................... 37 4.2 Limits of Radioisotopes .............................................................................................................................................. 38 4.3 Fission Radioisotopes and Space Fission Reactors ..................................................................................................... 40 5 Power requirements for space applications .................................................................................................................... 47 5.1 Space applications with Nuclear power systems ....................................................................................................... 47 5.2 Power Requirements .................................................................................................................................................. 49 5.3 Specific Missions Overview ........................................................................................................................................ 51 5.3.1 Opportunity rover ............................................................................................................................................... 51 5.3.2 Deep Space 1 ........................................................................................................................................................ 52 5.3.3 InSight Mission .................................................................................................................................................... 53 5.3.4 Juno ..................................................................................................................................................................... 54 5.3.5 Psyche ................................................................................................................................................................. 55 5.3.6 Europa Clipper ..................................................................................................................................................... 56 6 Subcritical Reactor with External Source ......................................................................................................................... 58 6.1 Basic concept of subcritical reactor ........................................................................................................................... 58 6.2 External neutron source ............................................................................................................................................. 58 6.3 Subcritical Module ..................................................................................................................................................... 62 1 Introduction Space exploration is an exciting journey for humanity. The attempt of this journey provides benefits to society all these years from the first rocket launch, Bumper 2 in 1950 at altitude of 250 miles (higher than the International Space Station’s orbit) to measure the atmosphere’s tem- perature and cosmic rays. Space exploration has a great contribution on creation of new indus- tries, evolution of technology, research in fundamental physics and peaceful connections with other nations in order to satisfied this global curiosity for the unknown. Space probes are spacecrafts with instruments that designed to take measurements and col- lect data from
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