Diss. ETH No. 17527 Development of a Method for Xenon Determination in the Microstructure of High Burn-up Nuclear Fuel A dissertation submitted to the SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH for the degree of Dr. sc. ETH presented by MATTHIAS ISTVAN HORVATH Dipl. Phys. ETH born 24 August 1974 citizen of Châtillon (FR), Männedorf (ZH) - Switzerland citizen of Hungary accepted on the recommendation of Prof. Dr. D. Günther, examiner Prof. Dr. A. Wokaun, co-examiner Prof. Dr. Ch. Heinrich, co-examiner Dr. Ch. Hellwig, co-examiner 2008 II III Acknowledgements As many major work, this thesis could not have been performed and written, without the help and support of numerous people. This is especially true since this work was carried out at PSI and some experiments also at ETH combining different fields of research. I would like to send a special thank to my thesis advisor, Prof. Dr. Detlef Günther, and my supervisor Dr. Christian Hellwig for their support of my work at ETH and PSI. I am grateful to Dr. Marcel Guillong, with whom I got into the "world of LA-ICP-MS", and who’s experience was a great benefit. I would also to thank the members of the groups of Dr. Ines Günther-Leopold (Isotope and Element Analysis), Dr. Didier Gavillet (Surface and Solid State Materials), Daniel Kuster (Hot Cell Experiments), Dr. Johannes Bertsch (Core Safety Material Behavior) at PSI, and the trace element group of Prof. Dr. Detlef Günther at ETH. Without their support and the possibility using their infrastructure, this thesis could not be realized. I also want to appreciate and thank for the collaboration with the team of the Ion Beam labo- ratory Laboratory of the Hahn Meitner Institute in Berlin Germany (ISL-HMI). Especially my thank goes to Dr. Jörg Opitz-Coutureau and Dr. Eric Strub. In case of the implantations, I very appreciated the assistance and advises, and therefore like to thank to Dr. Hans-Joachim Matzke. Another collaboration I want to mention and thank is the institute of polymer materials at ETH, especially to Christian Sailer, with whom I have performed various extrusion experiments. I appreciated also the fruitful exchanges of knowledge between our Lab of Material Behavior (LWV) and the Laboratory of Reactor Physics and Systems Behavior (LRS), especially with Dr. Antonino Romano, Prof. Dr. Rakesh Chawla, Dr. Stefano Caruso, Martin Zimmermann and Hannu Wallin. I want also to acknowledge the financial support for this project, which was halfway financed by the department of Nuclear Energy and Safety Research (NES) of PSI, and by swissnuclear. A very special thank goes to my office mate Paul Blair for many fruitful discussions and mo- ments in our office. I am indebted to the people, which made my stay at and outside PSI more comfortable: Röbi, Manuel, Sebastiano, Rossella, Li, Fatima, Juan, Peter, Javier, Felix, Elsa, Moshe, Raluca, Roberto, Botond, Hansjörg, Ammandine and many others. A very special thank goes to my parents for their support and patience, especially at the end of the thesis. IV I want to dedicate this work to my grandmother, Kovács Margit and to an old friend of our family, Lengyel Béla, who have inspired me in my childhood for the interest of natural sciences. Contents Acknowledgements III Abstract IX Zusammenfassung ................................... XI List of publications XV List of abbreviations XVII 1 Introduction 1 1.1 Nuclear fission .................................. 1 1.2 Nuclear fuel ................................... 3 1.3 The high burn-up structure ........................... 4 1.4 Motivation .................................... 7 1.5 Aim of the study ................................. 7 1.6 Gaseous- and fluid inclusion studies: state of the art .............. 8 2 Background to nuclear processes 15 2.1 Nuclear fission in reactors ............................ 15 2.2 Safety issues ................................... 20 2.3 Fission gases (FG) ................................ 22 3 Experimental methods 27 3.1 Laser ablation ICP-MS .............................. 27 V VI Contents 3.1.1 Inductively coupled plasma mass spectrometry (ICP-MS) . 30 3.1.2 Fundamentals in LA-ICP-MS ...................... 34 3.1.3 Experimental setup ........................... 37 3.2 Scanning electron microscopy (SEM) ...................... 40 3.3 Electron probe micro analysis (EPMA) ..................... 42 3.3.1 Experimental setup ........................... 43 3.3.2 Performed experiments on nuclear fuel . 43 3.4 Secondary ion mass spectrometry (SIMS) .................... 44 3.4.1 Analytical applications of SIMS ..................... 45 3.4.2 SIMS experiments on nuclear fuel .................... 48 3.5 Optical microscope instrumentation ....................... 50 4 Quantification Strategies for LA-ICP-MS 53 4.1 Introduction ................................... 53 4.2 Quantification approaches ............................ 53 4.3 Direct injection of xenon calibration gas ..................... 56 4.4 LA-ICP-MS on ZrO2 and non-irradiated UO2 samples . 60 4.4.1 Samples and preparation procedure ................... 60 4.4.2 Optimization of LA-ICP-MS ....................... 61 129 4.5 Implantation of Xe into ZrO2 and UO2 ceramics . 72 4.5.1 Depth-profile measurement of the implantation with TOF-ERDA . 75 4.5.2 TGA measurement on UO2 samples ................... 77 4.5.3 LA-ICP-MS on the implanted samples . 78 4.6 Comparison of gas injection and implanted samples for quantification . 82 4.7 Transparent plexiglass with Xenon bubbles ................... 86 4.7.1 Extrusion of PMMA 6N under Xe atmosphere . 92 4.7.2 LA-ICP-MS on PMMA 6N with Xe inclusions . 93 4.8 Additional concepts ............................... 98 4.9 Discussion and conclusions ............................ 99 Contents VII 5 Quantification of Fission Gases in Nuclear Fuel 101 5.1 Samples .....................................101 5.2 SEM and EPMA on nuclear fuel . 104 5.2.1 Instrumentation .............................104 5.2.2 Results ..................................106 5.2.3 Discussion and Conclusions for EPMA . 111 5.3 SIMS on nuclear fuel ...............................113 5.3.1 Introduction ...............................113 5.3.2 Experimental ...............................113 5.3.3 Results ..................................114 5.3.4 Discussion and conclusions for SIMS . 116 5.4 Quantification of pellet average nuclear burn-up using ICP-MS . 118 5.4.1 Sample preparation . 118 5.4.2 Experimental ...............................118 5.4.3 Results ..................................119 5.4.4 Discussion and conclusions for ICP-MS . 121 5.5 Xe quantification in nuclear fuel using LA-ICP-MS . 122 5.5.1 Experimental ...............................122 5.5.2 Xe quantification in fuel using LA-ICP-MS in single laser shot method . 122 5.5.3 Xe quantification in fuel using LA-ICP-MS in single hole drilling mode . 131 5.5.4 Conclusions for LA-ICP-MS . 144 5.6 Summary .....................................147 6 Conclusions and Outlook 149 6.1 Conclusions ....................................149 6.2 Outlook .....................................151 A Ion current monitoring for implantation 153 A.1 ZrO2 samples ...................................153 A.2 UO2 samples ...................................156 VIII Contents B List of plots of isotopic composition using single hole ablation 159 C Burn-up approximations on the measured high burn-up fuel sample 161 List of Tables 165 List of Figures 171 Bibliography 171 Curriculum Vitae 193 Contents IX Abstract In nuclear fuel, in approximately one quarter of the fissions, one of the two formed fission products is gaseous. These are mainly the noble gases xenon and krypton with isotopes of xenon contributing up to 90% of the product gases. These noble fission gases do not combine with other species, and have a low solubility in the normally used uranium oxide matrix. They can be dissolved in the fuel matrix or precipitate in nanometer-sized bubbles within the fuel grain, in micrometer-sized bubbles at the grain boundaries, and a fraction also precipitates in fuel pores, coming from fuel fabrication. A fraction of the gas can also be released into the plenum of the fuel rod. With increasing fission, and therefore burn-up, the ceramic fuel material experiences a transformation of its structure in the "cooler" rim region of the fuel. A subdivision occurs of the original fuel grains of few microns size into thousands of small grains of sub-micron sizes. Additionally, larger pores are formed, which also leads into an increasing porosity in the fuel rim, called high burn-up structure. In this structure, only a small fraction of the fission gas remain in the matrix, the major quantity is said to accumulate in these pores. Because of this accumulation, the knowledge of the quantities of gas within these pores is of major interest in consideration to burn-up, fuel performance and especially for safety issues. In case of design based accidents, i.e. rapidly increasing temperature transients, the behavior of the fuel has to be estimated. Various analytical techniques have been used to determine the Xe concentration in nuclear fuel samples. The capabilities of EPMA and SIMS have been studied and provided some qualitative information, which has been used for determining Xe-matrix concentrations. First approaches combining these two techniques to estimate pore pressures have been recently reported. How- ever, relevant Xe isotope concentrations in fission gas inclusions have not been reported yet. The aim of this work was focused on quantitative analysis of Xe isotope concentrations