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Measurement and Analysis of the Resolved Resonance Cross Sections of the Natural Hafnium Isotopes

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Measurement and Analysis of the Resolved Resonance Cross Sections of the Natural Hafnium Isotopes CORE Metadata, citation and similar papers at core.ac.uk Provided by University of Birmingham Research Archive, E-theses Repository MEASUREMENT AND ANALYSIS OF THE RESOLVED RESONANCE CROSS SECTIONS OF THE NATURAL HAFNIUM ISOTOPES by TIMOTHY CHRISTOPHER WARE A thesis submitted to The University of Birmingham for the degree of DOCTOR OF PHILOSOPHY School of Physics and Astronomy College of Engineering and Physical Sciences The University of Birmingham June 2010 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties.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 Hafnium is a ductile metallic element with a large neutron absorption cross section. It can be used in reactor control rods to regulate the fission process. The NEA High Priority Request List for nuclear data presents a need for improved characterisation of the hafnium cross section in the resolved resonance region. This thesis presents new resonance cross section parameters for the six natural hafnium isotopes. Cross section measurements, supported by the NUDAME and EUFRAT projects, were performed at the IRMM Geel GELINA time-of-flight facility. Capture experiments were conducted on the 12 m, 28 m and 58 m flight paths using C6D6 detectors and transmission experiments were performed at flight paths of 26 m and 49 m using a 6Li glass detector. The samples used were metallic natural hafnium discs of various thicknesses and hafnium oxide powders, with differing isotopic enrichments. Data analysis was performed using the least square fitting REFIT code, which was updated during this work. The use of isotopically-enriched samples enabled previously unrecorded resonances to be allocated to the correct isotope. The resulting evaluated data files extend the upper energy limits of the resolved resonance regions for the 174Hf, 176Hf, 177Hf, 178Hf, 179Hf and 180Hf isotopes, relative to the current European recommended evaluation (JEFF3.1), to 250 eV, 3 keV, 1 keV, 3 keV, 1 keV and 3 keV respectively. The natural hafnium resonance integral calculated from the new resonance parameters is 1.2% lower than the integral corresponding to the JEFF3.1 evaluated hafnium data. Comparison of calculated to experimental k-effective values for appropriate zero-power reactor assemblies show improvement over the JEFF3.1 data. - ii - “An experiment is a question which science poses to Nature and a measurement is the recording of Nature’s answer.” - Max Planck (1858-1947) - iii - In loving memory of my Grandad, who showed pride in my every achievement in a way only a grandfather can. - iv - ACKNOWLEDGMENTS Throughout my PhD research, I have received important contributions, as well as help in many small ways, from many people, for which I express my deepest gratitude. Firstly, I thank my industry supervisor, Christopher Dean; not least for conceiving and laying the foundations of my project, but for imparting his expert knowledge of the nuclear data field, for sharing my learning experience and for his continuing advice, often into the later hours, be it in the office on a cold Winfrith evening or over a cold beer on a balmy Provence night. Thank you to Mick Moxon, for freely giving me his time and (many years worth of) advice that have allowed me to develop my understanding of resonance analysis. He has also given me the privileged opportunity to co-author his REFIT code. Many thanks to all at Serco, including Richard Hiles, Dave Hanlon, Glynn Hosking, John Lillington, Chris Maidment, Ray Perry, Paul Smith, the IT team and all those that provided the diverse conversations in the tea room. Thanks are also due to Ian Giles for his support of my work. I am grateful to my University supervisor, David Weaver for academic guidance, as well as fielding numerous emails and expenses claims. Together with Paul Norman, I thank David for accepting me onto the PTNR MSc course and bringing me into the world of nuclear physics. Thank you to Peter Schillebeeckx, Alessandro Borella, Stefan Kopecky, André Moens, Arjan Plompen, Peter Rullhusen, Peter Siegler and Ruud Wynants for supporting, preparing and undertaking the hafnium measurements and instructing me in time-of-flight techniques and - v - data reduction. I thank all the staff at the Neutron Physics Unit for making me most welcome during my visits. The measurements were supported by the European Commission within the Sixth Framework Programme through NUDAME (EURATOM contract no. FP6-516487) and the Seventh Framework Programme through EUFRAT (EURATOM contract no. FP7-211499). I thank Natalia Janeva and her colleagues of the Institute of Nuclear Research and Nuclear Energy, Sofia, Bulgaria for kindly loaning the enriched hafnium samples, without which many of the measurements used in my analysis would not have taken place. Thank you to Gilles Noguère and his colleagues at CEA Cadarache for providing the results of their average parameter studies of hafnium. Thanks to Yaron Danon and Mike Trbovich of RPI and Jack Harvey of ORNL for kindly supplying data. Thank you to the NEA Databank staff for the distributing the REFIT code and scanning the Harwell measurement printouts. From the School of Physics, I thank Norma Simpson and Anna Jenkin for answering all manner of questions, Andrew Davis and Louise Evans for sharing the PhD experience and Stuart Wilson, for his MSc thesis detailing the modification of application data libraries. Some special mentions: to my Mum, my Dad, David and Julie for their unconditional support throughout, plus the free board-and-lodge whilst I was writing up; to the growing number I can call my family for always talking an interest; and to my many friends for giving me a life outside work and the distractions of archery, DIY and occasional pint or two. Finally, a special thank you to my fiancée and best friend, Mel; for her love, her counsel and her unwavering support, throughout her MChem, teaching training and all that the last five years have brought us. - vi - TABLE OF CONTENTS 1. INTRODUCTION..................................................................................................................1 1.1. Motivations for This Work......................................................................................1 1.1.1. Properties and Uses of Hafnium...............................................................1 1.1.2. Present Status of Hafnium Cross Section Data ........................................2 1.2. Structure of This Thesis...........................................................................................4 1.3. Statement of the Author’s Contribution ..................................................................5 2. NEUTRON CROSS SECTIONS ...........................................................................................6 2.1. General Description of Cross Sections....................................................................6 2.2 Representation of Cross Sections by Resonance Parameters ...................................9 2.3 Storage of Resonance Parameters...........................................................................14 2.4 Specifics of Hafnium Cross Sections .....................................................................16 3. HAFNIUM CROSS SECTIONS MEASUREMENTS ........................................................20 3.1 Principles of Neutron Time-of-Flight Measurements ............................................20 3.1.1 Neutron Transmission Measurements .....................................................21 3.1.2 Neutron Capture Measurements ..............................................................22 3.2 Experimental Considerations..................................................................................23 3.2.1 Background Correction ...........................................................................23 3.2.2 Dead Time Correction .............................................................................24 3.3 High Resolution Cross Section Measurements at GELINA...................................25 3.3.1 The GELINA Time-of-Flight Facility.....................................................25 3.3.2 Capture Measurement Set-up ..................................................................28 3.3.3 Natural and Isotopically-Enriched Hafnium Capture Measurements......30 3.3.4 Data Reduction ........................................................................................33 3.4 Natural Hafnium Transmission Measurement........................................................37 3.5 Previous Measurements Used In This Work ..........................................................39 3.5.1 ORNL 1963 Transmission Measurements ..............................................39 3.5.2 Harwell 1973 Capture Measurements .....................................................40 3.5.3 ORNL 1982 Capture Measurements .......................................................41 3.5.4 Geel 2001 Transmission Measurements..................................................42 3.5.5 RPI 2003 Transmission and Capture Measurements...............................43 - vii
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