DESIGN, CONSTRUCTION, AND DEMONSTRATION OF A NEUTRON BEAMLINE AND A NEUTRON IMAGING FACILITY AT A MARK-I TRIGA REACTOR by Aaron E. Craft 1 Copyright by Aaron E. Craft 2012 All Rights Reserved i A thesis submitted to the Faculty and the Board of Trustees of the Coloado School of Mines in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Nuclear Science and Engineering). Golden, Colorado Date _____________________ Signed: _____________________ Aaron E. Craft Signed: _____________________ Dr. Jeffrey C. King Thesis Advisor Golden, Colorado Date _____________________ Signed: _____________________ Dr. Jeffrey C. King Assistant Professor and Interim Director Nuclear Science and Engineering Program Signed: _____________________ Dr. Michael J. Kaufman Professor and Head Department of Metallurgical and Materials Engineering ii ABSTRACT The fleet of research and training reactors is aging, and no new research reactors are planned in the United States. Thus, there is a need to expand the capabilities of existing reactors to meet users’ needs. While many research reactors have beam port facilities, the original design of the United States Geological Survey TRIGA Reactor (GSTR) did not include beam ports. The MInes NEutron Radiography (MINER) facility developed by this thesis and installed at the GSTR provides new capabilities for both researchers and students at the Colorado School of Mines. The facility consists of a number of components, including a neutron beamline and beamstop, an optical table, an experimental enclosure and associated interlocks, a computer control system, a multi-channel plate imaging detector, and the associated electronics. The neutron beam source location, determined through Monte Carlo modeling, provides the best mixture of high neutron flux, high thermal neutron content, and low gamma radiation content. A Monte Carlo n-Particle (MCNP) model of the neutron beam provides researchers with a tool for designing experiments before placing objects in the neutron beam. Experimental multi- foil activation results, compared to calculated multi-foil activation results, verify the model. The MCNP model predicts a neutron beamline flux of 2.2*106 ± 6.4*105 n/cm2-s based on a source particle rate determined from the foil activation experiments when the reactor is operating at a power of 950 kWt with the beam shutter fully open. The average cadmium ratio of the beamline is 7.4, and the L/D of the neutron beam is approximately 200±10. Radiographs of a sensitivity indicator taken using both the digital detector and the transfer foil method provide one demonstration of the radiographic capabilities of the new facility. Calibration fuel pins manufactured using copper and stainless steel surrogate fuel pellets provide additional specimens for demonstration of the new facility and offer a comparison between digital and film radiography at the new facility. Comparison of the radiographs taken by the two methods reveals that the digital detector does not produce high quality images when compared to film radiography. iii TABLE OF CONTENTS ABSTRACT ............................................................................................................................. iii LIST OF FIGURES .................................................................................................................. vi LIST OF TABLES .................................................................................................................... ix NOMENCLATURE ....................................................................................................................x LIST OFABBREVIATIONS .................................................................................................... xi ACKNOWLEDGEMENTS...................................................................................................... xii DEDICATION ........................................................................................................................ xiii 1 INTRODUCTION ...............................................................................................................1 2 BACKGROUND .................................................................................................................3 2.1 History of Neutron Radiography ...................................................................................3 2.2 Fundamentals of Neutron Imaging ................................................................................6 2.3 Neutron Beams ........................................................................................................... 12 2.4 Neutron Sources .......................................................................................................... 14 2.4.1 Radioisotope Sources ........................................................................................... 14 2.4.2 Accelerator-Based Systems .................................................................................. 15 2.4.3 Nuclear Reactors .................................................................................................. 17 2.4.4 The United States Geological Survey TRIGA Reactor ......................................... 19 2.5 Neutron Imaging Techniques and Detection Methods.................................................. 21 2.5.1 Direct Imaging Methods....................................................................................... 22 2.5.2 Indirect Imaging Methods .................................................................................... 23 2.5.3 Dynamic Neutron Radioscopy.............................................................................. 25 2.5.4 Computed Tomography ....................................................................................... 29 2.6 Radiographic Artifacts and Image Processing.............................................................. 30 2.6.1 Nonuniformity ..................................................................................................... 30 2.6.2 Acquisition System Defects ................................................................................. 30 2.6.3 Beam Hardening .................................................................................................. 31 iv 2.7 Neutron Imaging Applications .................................................................................... 32 3 MAJOR FACILITY SUBSYSTEMS................................................................................. 35 3.1 Neutron Beamline ....................................................................................................... 35 3.1.1 Beamline Design and Control .............................................................................. 35 3.1.2 Selection of the Beamline Source Location .......................................................... 38 3.1.3 Installation of the Neutron Beamline .................................................................... 41 3.1.4 Gas Pressure Control System ............................................................................... 43 3.2 Radiation Beamstop .................................................................................................... 44 3.2.1 Beamstop Modeling and Design ........................................................................... 44 3.2.2 Construction of the Beamstop .............................................................................. 50 3.3 Experiment Station ...................................................................................................... 51 3.3.1 Optical Table and Vibration Isolation ................................................................... 51 3.3.2 Experiment Enclosure .......................................................................................... 53 3.3.3 Motorized Sample Stage ...................................................................................... 56 3.4 Neutron-Sensitive Multi-Channel Plate Detector ......................................................... 57 3.5 Computer Control System ........................................................................................... 60 4 MCNP MODEL OF THE BEAMLINE ............................................................................ 66 4.1 Experimental Verification of the Beamline Model ....................................................... 70 5 CHARACTERIZATION AND DEMONSTRATION OF THE NEW FACILITY ............. 75 5.1 Characterization of the New Beamline ........................................................................ 75 5.2 Demonstration of the New Neutron Radiography Capabilities ..................................... 78 6 SUMMARY AND CONCLUSIONS ................................................................................. 90 7 RECOMMENDATIONS FOR FUTURE WORK .............................................................. 92 REFERENCES ......................................................................................................................... 95 APPENDIX A – MCNP Model of the Neutron Beamline ........................................................ 101 APPENDIX B – Procedures for the Neutron Imaging Facility ................................................. 109 APPENDIX C – 50.59 Review for a Neutron Imaging Facility at the GSTR ........................... 121 v LIST OF FIGURES Figure 2.1. Qualitative representation of x-ray and neutron cross-sections. .................................. 6 Figure 2.2. Qualitative representation of x-ray and neutron cross-sections