Thermal Management and Neutronics Calculations for Medium to High Power Neutron Production Targets

다국어 초록 (Multilingual Abstract)

Neutron sources can be applied for various purposes from nuclear medicine to material science, and they can be used for power generation and waste transmutation in the form of accelerator driven system in future. Although research reactors are the prime source of neutron generation, they need to address the major issues like proliferation risks, safety, aging, nuclear wastes, etc. These issues limit the future development of reactors as a clean, safe and sustainable solution. Developing accelerator-based production of neutrons can be one of the solutions to overcome the problems associated with research reactors. It is worth mentioning that one of the most critical component in the accelerator complex is the target irradiation system which is composed of different parts. Among all parts in the target irradiation system, there is a component that is bombarded by particles, referred to as the target. Despite all the progress in target technology, this area needs more research for new applications of neutron sources. Target study can be complex as several parameters like geometry, materials, cooling flow, particle interaction, etc. are involved in its design and testing. The cost of target station in an accelerator site is quite considerable, hence the target design as well as its operating condition should be treated properly to prevent any failure. The simulating tools in physics and engineering are employed in design and optimization stages. These simulation tools cover several aspects of target study from neutronics, safety, shielding, radiation protection, material damage to heat transfer. Among these, this thesis is focused on thermal management and neutronics characterization of several target systems for neutron production.
The accelerator technology is well established for different types of applications; a general description of which is explained in Chapter 1. Chapter 2 briefly covers a few different applications of neutron sources. Potential materials for neutron source targets are also reviewed in Chapter 2.
The majority of the beam power loss occurs in the target material. The heat is generated by the interaction of charged particles with target medium. Chapter 3 explains the physics of charged particle interaction with matter. The theory is accompanied by simulation of charged particle interaction with different target materials (as well as different geometry and projectile) in order to obtain the neutron yield and energy deposition in target volume for spallation process. It is also essential to consider an optimal cooling configuration for the targets. The theory of fluid mechanics, stress analysis and the related simulation tools are further discussed in Chapter 3.
An alternative to reactor-based production of 99Mo (as one of the major application of neutron sources) is the accelerator-based method via 98Mo(n,γ)99Mo reaction. Neutrons are produced by bombarding targets with proton (or deuteron) beam. The total beam power considered for this work is 2 kW, and beryllium is selected as target material. The heat transfer analysis was done for two type of coolants; helium and water. Thermal analysis of a multi-channel helium cooled device is performed with the computational fluid dynamics code CFX. Different boundary conditions are taken into account in the simulation process and many important parameters such as maximum allowable solid target temperature as well as uniform inlet velocity and outlet pressure changes in the channels are investigated. The simulation has been carried out for water-cooled beryllium target as well. The temperature distribution in different components is obtained for the target bombarded by protons or deuterons. Stress analysis of the water-cooled beryllium target is also done in this work. The results of the simulation for beryllium target are given in Chapter 4.
The idea of designing a high power (100 kW) portable neutron product target is the main theme of Chapter 5. Such device fits in several laboratories' scope which are planning to use neutron sources. Additionally neutron irradiation can be used for research in material science. Neutronic analysis as well as heat transfer analysis of the liquid metal target are highlighted in Chapter 5. Furthermore it has been tried to improve the primary design of the liquid metal target from fluid mechanics point of view.
Chapter 6 lists and describes the challenges in studying neutron source targets from physics and engineering point of view. The proposal for future works is given in Chapter 6. Chapter 7 concludes the thesis.

목차 (Table of Contents)

• 1.Introduction to applications of accelerators 1
• 1.1 Industrial applications of accelerators 2
• 1.2 Nuclear Medicine 6
• 1.2.1 Radioisotope production in accelerators and reactors: Historical background 6
• 1.2.2 Radioisotopes: Diagnosis and therapy 8
• 1.2.2.1 Medical diagnostics 10
• 1.2.2.2 Medical therapy 11
• 1.2.3 Accelerator-based radioisotope production 12
• 1.2.4 Application of accelerators in beam/hadron therapy 13
• 2. Neutron sources: applications and associate target technology 16
• 2.1 Neutron source for nuclear waste management and power generation 18
• 2.2 Neutron source for medical applications 23
• 2.2.1 Boron Neutron Capture Therapy (BNCT) 23
• 2.2.2 Adiabatic resonance crossing (ARC) for medical radioisotope production 26
• 2.3 Past and current studies on neutron sources 30
• 2.4 Potential materials for neutron source targets 33
• 2.4.1 Liquid metal target system 35
• 2.4.2 Solid target system 37
• 3. Simulation methods: nuclear transport and thermal-hydraulics analysis 40
• 3.1 Interaction of charged particles with matter 41
• 3.1.1 Electromagnetic cascade events 42
• 3.1.2 Hadronic cascade events 44
• 3.1.2.1 Spallation process 45
• 3.1.2.2 Neutron interaction with matter 48
• 3.2 Stopping power and range 49
• 3.3 Nuclear data 52
• 3.4 FLUKA 53
• 3.4.1 FLUKA calculation for neutron yield and energy deposition from proton beams 55
• 3.4.1.1Neutron yield 57
• 3.4.1.2 Energy deposition 62
• 3.4.1.3 Binning modification for low-energy proton beam 72
• 3.4.1.4 Effect of beam shape on energy deposition 72
• 3.4.1.5 Energy distribution 76
• 3.5 Computational fluid dynamics (CFD) 82
• 3.5.1 Application of CFD in target systems 85
• 3.5.2 CFD procedure 90
• 3.5.3 Turbulence 91
• 3.5.4 ANSYS CFX 94
• 3.5.5 Data transfer from FLUKA to ANSYS 97
• 3.6 Fluid–structure interaction analysis (FSI) 98
• 3.6.1 Stress and deformation analysis 99
• 3.6.2 Finite element method (FEM) 100
• 3.6.3 ANSYS static structural analysis 101
• 4. Engineering study of solid target for neutron activators 104
• 4.1 Gas-cooled beryllium target 106
• 4.1.1 Heat transfer and pressure considerations 107
• 4.1.2 Numerical simulation 114
• 4.1.3 Results and discussion 116
• 4.2 Water-cooled beryllium target 123
• 4.2.1 The proton beam case 126
• 4.2.1.1 Stress analysis 132
• 4.2.2 The deuteron beam case 134
• 5. Liquid metal cooled targets 140
• 5.1 Geometry 143
• 5.2 Neutronic analysis 146
• 5.3 CFD analysis 151
• 5.3.1 Results 156
• 5.3.2 Imbalance 158
• 6. General discussion 167
• 6.1 Issues on the physics of the project 168
• 6.2 Issues on engineering aspects of the project 174
• 6.3 Future works 178
• 7. Conclusion 181
• References 187
• Appendix A: Energy deposition profiles for Al, Fe, Ta and Hg targets 200
• Appendix B: Energy balance tables for Al, Fe, Ta and Hg targets 205