RADIATION SHIELDING OF FUSION SYSTEMS by Andrew Davis A thesis submitted to The University of Birmingham for the degree of DOCTOR OF PHILOSOPHY School of Physics and Astronomy The University of Birmingham April 2010. University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. Abstract This thesis discusses the development, benchmarking and applications of activation dose analysis methods for fusion devices. The development and code logic of the Mesh Coupled Rigorous 2 Step (MCR2S) system is discussed. Following the development of the code, appropriate benchmarking studies were performed on the Frascati neutron generator, and revealed that the code was able to predict shutdown gamma ray dose rates to within ±3% of experimentally determined values, for decay times between 3×105 and 107 seconds. The development of the Ion Cyclotron Resonance Heater (ICRH) with regards to neu- tronics is discussed. The ICRH went through a number of design stages and shutdown gamma ray doserates were determined for each stage. It was determined that of all the designs analysed only one of them, the first concept design for the internally matched design did not meet the shutdown dose criteria. This was due to a flaw in the system design, brought about by a lack of consideration towards nuclear design. The ITER Light Imaging Detection and Ranging (LIDAR) system was subjected to a full shutdown nuclear analysis. It was found that the design of the LIDAR system sup- plied did not meet the ITER required shutdown gamma ray doserate limit of 100 µ Sv hr−1, however use of the MCR2S system highlighted the components that contributed most to the shutdown gamma ray doserate and were shown to be the mirror holder and the laser beam pipe. Future designs should include additional shielding around the beam pipe. Authors Contribution The author of this thesis designed and wrote a computer program called MCR2S, based on the Rigorous 2 Step (R2S) method, that couples the radiation transport program MCNP to the nuclear inventory code FISPACT that facilitates high resolu- tion activation analysis. The technical aspects of this code are described in Chapter 4. Fusion appropriate benchmarking was performed to validate the code for fusion neutronics calculations in two cases, one idealised case to compare MCR2S against a different code that performs similar analysis and one case from a well defined fusion neutronics experiment. The simulations performed and results of the benchmarking studies are described in Chapter 5. The author performed nuclear analysis, including neutron and photon transport, nuclear heating and activation calculations on a number of Ion Cyclotron Resonance Heating (ICRH) designs for ITER. This involved creation of the MCNP model from CAD drawings and the subsequent use of MCNP and FISPACT to perform the analysis. The method used and results of the simulations performed are described in Chapter 6. A shutdown dose analysis was performed on the ITER Laser Imaging Detection and Ranging (LIDAR) system. The model was created by S Zheng, but the author performed neutron transport and MCR2S analysis. The results of the simulations performed are described in Chapter 6. The author was fortunate enough to present the results of ICRH analysis as a poster presentation at the TOFE meeting in San Francisco, the results of ICRH and LIDAR analysis at the IAEA meeting on Fusion Safety. The second case resulted in a collaborative publication in the proceedings of the meeting. The results of the benchmarking of MCR2S were published in the peer reviewed journal Fusion Engi- neering and Design with the reference Fus. Eng. and Des., vol. 85, no. 1, pp. 8792, 2010. “Adam, the first man, didn’t know anything about the nucleus but Dr. George Gamow, visiting professor from George Washington University, pretends he does. He says for example that the nucleus is 0.00000000000003 feet in diameter. Nobody believes it, but that doesn’t make any difference to him. He also says that the nuclear energy contained in a pound of lithium is enough to run the United States Navy for a period of three years. But to get this energy you would have to heat a mixture of lithium and hydrogen up to 50,000,000 degrees Fahrenheit. If one has a little stove of this temperature installed at Stanford, it would burn everything alive within a radius of 10,000 miles and broil all the fish in the Pacific Ocean. If you could go as fast as nuclear particles generally do, it wouldn’t take you more than one ten-thousandth of a second to go to Miller’s where you could meet Gamow and get more details.” -George Gamow ‘Gamow interviews Gamow’ Stanford Daily, 25 Jun 1936. In Helge Kragh, Cosmol- ogy and Controversy: The Historical Development of Two Theories of the Universe (1996), 90. The author would like to extend his sincerest gratitude to; Thankyou to both of my supervisors, Drs Pampin and Norman, for without whom this thesis would not have been possible. To Dr R Pampin, at the Neutronic and Nuclear Data section of the Culham Centre for Fusion Energy, whose help, support and understanding have been invaluable. To Dr P I Norman, at the University of Birmingham, School of Physics and Astronomy, for giving me the opportunity to follow my dream. And to Dr M J Loughlin, now at ITER, for giving me a good start. To my colleagues at CCFE, all of whom have understood my lack of understanding; especially Dr D Ward, Dr R Forrest, Dr S Newton, Dr S Zheng and Mr L Packer. I also have to thank Mrs W Coombes and Ms K Samson, for without whom I doubt this thesis would have been completed. I would also like to thank my family, friends and peers for the experiences of the past few years. And to my best friend and partner Jenny, who has been wonderful and understanding throughout. This work was funded by the United Kingdom Engineering and Phys- ical Sciences Research Council Contents 1 Introduction 1 1.1 Nuclear Fusion . 1 1.2 Physics of Plasmas . 4 1.2.1 Confinement of Plasmas . 5 1.2.2 Production of neutrons by plasmas . 6 1.3 Magnetically Confined Fusion . 7 1.4 Inertially Confined Fusion . 10 1.5 ITER . 10 1.5.1 Geometry of ITER . 11 1.5.2 Upper, Equatorial and Divertor Ports . 11 1.5.3 Heating Systems . 13 1.5.4 Magnets . 17 1.5.5 Vacuum Vessel . 19 1.5.6 Blanket . 19 1.5.7 Plasma Diagnostics . 21 1.5.8 Divertor . 22 1.5.9 Cooling . 23 1.6 Thesis Outline . 24 2 Radiation Effects and Shielding 26 2.1 Radiation Transport . 26 2.1.1 Neutron Physics . 26 2.1.2 Gamma Ray Physics . 30 2.1.3 Boltzmann Transport Equation . 33 2.1.4 Monte Carlo Methods . 34 2.1.5 Deterministic methods . 35 2.2 Radiation Effects on Materials . 36 2.2.1 Atomic Displacement . 36 2.2.2 Transmutation . 37 2.2.3 Radiation Heating . 39 2.2.4 Engineering Effects . 40 2.2.5 Optical Effects . 41 2.2.6 Electrical Effects . 42 2.3 Biological Effects of Ionising Radiation . 43 2.3.1 Effects of Ionising Radiation . 43 i 2.3.2 Absorbed Dose . 44 2.3.3 Effective Dose Equivalent . 44 2.3.4 Limits on Dose and Dose Rate . 46 2.3.5 Maintenance Ports Dose Rate Limits . 47 2.3.6 Bioshield Dose Rate Limits . 48 2.4 Radiation Shielding . 48 2.4.1 Stages in Radiation Shielding Design . 50 2.4.2 Neutron Shielding . 53 2.4.3 Photon Shielding . 54 2.4.4 Charged Particle Shielding . 55 2.5 Radiation Fields in ITER . 56 2.5.1 Neutron Field . 56 2.5.2 Prompt Gamma ray Field . 57 2.5.3 Shutdown Gamma ray field . 60 2.5.4 Shutdown Neutron Field . 61 3 Computational Methods 62 3.1 Radiation Transport . 62 3.1.1 Monte Carlo N Particle (MCNP) . 63 3.1.2 MCNP Nuclear Data . 73 3.2 Nuclide Inventory . 74 3.2.1 FISPACT . 76 3.2.2 EAF Data Libraries . 76 3.2.3 Modelling Pulsed Irradiations . 77 4 Activation Source Generator for MCNP 79 4.1 Introduction . 79 4.1.1 FISPACT Contact Dose . 80 4.1.2 Direct One Step Method . 83 4.1.3 The Rigorous 2 Step method . 85 4.2 Mesh tally Coupled Rigorous 2 Step . 87 4.2.1 MCR2S Input . 89 4.3 MCR2S Activation Subroutine . 95 4.4 MCR2S Data Processing . 97 4.5 MCR2S MCNP Source Subroutine . 98 4.5.1 Treatment of voids in MCR2S . 101 4.5.2 The effect of mesh resolution . 103 4.6 Sources of uncertainty in MCR2S . 105 5 MCR2S Benchmark 108 5.1 MCR2S and Attila ASG comparison . 108 5.2 Frascati Neutron Generator Benchmarking . 122 5.2.1 The Frascati Neutron Generator . 122 5.2.2 Characterisation of FNG source neutrons . 123 5.2.3 Experimental Campaign 1 . 124 ii 5.2.4 Experimental Campaign 2 . 134 6 ITER Port Plug Nuclear Analysis 145 6.1 Port Plug Nuclear Requirements . 145 6.2 The ITER ICRH Systems .