Study on Effects of Heavy Ion Irradiation on CeO2 by Using Synchrotron Radiation X-Ray Absorption Spectroscopy -as a Sim
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1043-T09-02
Study on Effects of Heavy Ion Irradiation on CeO2 by Using Synchrotron Radiation X-Ray Absorption Spectroscopy -as a Simulation Study for Radiation Damage in High-Burnup Light Water Reactor FuelsHirotaka Ohno1, Daiju Matsumura2, Yasuo Nishihata2, Jun'ichiro Mizuki2, Norito Ishikawa3, Takeshi Sonoda4, Motoyasu Kinoshita4, and Akihiro Iwase1 1 Osaka Prefecture University, Sakai, 599-8531, Japan 2 Japan Atomic Energy Agency, Sayo, 679-5148, Japan 3 Japan Atomic Energy Agency, Tokai-mura, 319-1195, Japan 4 Central Research Institute of Electric Power Industry, Komae, 201-8511, Japan ABSTRACT CeO2 thin films were irradiated with 200MeV Xe ions. Effects of the irradiation were studied by using Extended X-ray Absorption Fine Structure (EXAFS) measurement at SPring8 synchrotron radiation facility. EXAFS spectra for the irradiated thin films near the Ce K-edge show that the coordination number for oxygen atoms around Ce atom decreases and that the CeO Debye-Waller factor increases by the irradiation. The atomic distance between oxygen atom and Ce atom does not vary within the accuracy of EXAFS measurement. The effect of high density electronic excitation on the structure of CeO2 is discussed. INTRODUCTION High-burnup extension of light-water reactor nuclear fuel is quite useful for the reduction of the total amount of spent fuel and the fuel cycle costs. The structure of high-burnup nuclear fuel pellets is, however, strongly modified by fission products (FPs) with energies around 100 MeV[1], which may influence the fuel performance. As the values of electronic stopping power, Se, for such FPs are very large, the effect of high-density electronic excitation on the lattice structure of a nuclear fuel has to be considered as well as the effects of elastic collisions and inert gas accumulation. This study has been performed to evaluate the effects of high energy FPs on the lattice structure of simulation material CeO2 by means of Extended X-ray Absorption Fine Structure(EXAFS) spectroscopy near Ce K-edge at a synchrotron radiation facility. EXPERIMENT Specimens used in the present experiment were CeO2 thin films 300 nm thick. They were prepared on Al2O3 substrates by using RF magnetron sputtering method. The thin CeO2 films were irradiated at room temperature with 200MeV Xe14+ ions up to 1.0 x 1014/cm2 using the tandem accelerator at JAEA-Tokai. After the irradiation, EXAFS measurements near the Ce Kedge (40.449keV) were carried out at room temperature on the beam line BL14B1 of SPring-8 synchrotron radiation facility. The spectra were obtained using a 19 element germanium detector in fluorescence mode. We note here that because of the high density of Ce atoms in CeO2 lattice, we have to use thin films and not bulk specimens to avoid the self-absorption of X-ray. For
comparison, X-ray diffraction(XRD) measurements were also performed by means of a conventional X-ray diffractometer. RESULTS and DISCUSSION Fig.1 shows the normalized EXAFS spectra near Ce K-edge for CeO2 thin films irradiated with 200 MeV Xe ions. Th
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