Characterization of swift heavy ion irradiation damage in ceria
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Ram Devanathanb) Nuclear Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA
Janne Pakarinenc) Fuel Materials Group, Institute for Nuclear Research Center (SCKdCEN), B-2400 Mol, Belgium
Jian Gan Nuclear Fuels & Materials Division, Idaho National Laboratory, Idaho Falls, Idaho 83415, USA
Daniel Severin GSI Helmholtzzentrum, 64291 Darmstadt, Germany
Christina Trautmann GSI Helmholtzzentrum, 64291 Darmstadt, Germany; and Technische Universität Darmstadt, 64287 Darmstadt, Germany
Todd R. Allen Engineering Physics Department, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA (Received 10 October 2014; accepted 23 January 2015)
Swift heavy ion induced radiation damage is investigated for ceria (CeO2), which serves as a UO2 fuel surrogate. Microstructural changes resulting from an irradiation with 940 MeV gold ions of 42 keV/nm electronic energy loss are investigated by means of electron microscopy accompanied by electron energy loss spectroscopy showing that there exists a small density reduction in the ion track core. While chemical changes in the ion track are not precluded, evidence of them was not observed. Classical molecular dynamics simulations of thermal spikes in CeO2 with an energy deposition of 12 and 36 keV/nm show damage consisting of isolated point defects at 12 keV/nm, and defect clusters at 36 keV/nm, with no amorphization at either energy. Inferences are drawn from modeling about density changes in the ion track and the formation of interstitial loops that shed light on features observed by electron microscopy of swift heavy ion irradiated ceria.
I. INTRODUCTION
The safety and reliability of current and future generations of nuclear reactors can be advanced if the behavior of fuels and cladding materials during normal operation and accident scenarios is well understood. Nuclear fission results in fission fragments with a mass of the order of 100 amu and kinetic energy around 100 MeV. As these particles slow down, they create damage tracks in the material. Radiation damage in fuel, typically UO2, has a negative influence on thermal conductivity,1 fuel pellet integrity,2 and fission product retention.3 Examination of Contributing Editor: Joel Ribis a) Address all correspondence to this author. e-mail: [email protected] b) C.A. Yablinsky and R. Devanathan contributed equally to this work c) This work was performed while C.A. Yablinsky and J. Pakarinen were at Engineering Physics Department, University of Wisconsin-Madison, 1500 Engineering Drive, Madison, WI 53706, USA DOI: 10.1557/jmr.2015.43 J. Mater. Res., 2015
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nuclear fuel irradiated in a reactor suffers from the drawbacks that it usually takes a long time to accumulate damage and the fuel cannot be examined right away because of high radioactivity. There are only a few radiological facilities where nuclear fuel can be examined. Given the extensive radiological controls needed to handle irradiated UO2 , there is considerable interest in the use of
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