Effect of Iodine and Strontium Ion Implantation on the Microstructure of Cubic Zirconia
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Effect of Iodine and Strontium Ion Implantation on the Microstructure of Cubic Zirconia Sha Zhu, Lumin Wang, Shixin Wang and Rodney C. Ewing Department of Nuclear Engineering and Radiological Sciences University of Michigan, Ann Arbor, MI 48109-2104, USA ABSTRACT 200 keV iodine and 400 keV strontium ions have been implanted into YSZ in order to study the effects of fission product incorporation in YSZ as an inert fuel matrix. The ion implantation was conducted at room temperature. The ion fluences reached 1×1021 ions/m2 which gives peak displacement damage levels of ~ 290 dpa for I ion implantation and ~ 200 dpa for Sr ion implantation. The peak concentration reaches ~26 at. % for implanted I ions and ~11.6 at.% for Sr ions. Cross-sectional transmission electron microscopy (TEM) was completed to investigate the microstructure changes caused by the implantation. No evidence of amorphization was detected in both samples although a high density of defect clusters was observed by TEM. Cross-sectional TEM revealed formation of iodine containing voids in Iimplanted samples and crystalline precipitates of a few tens of nanometers in Sr-implanted samples after annealing of the implanted sample at 1000°C for 0.5 to 2 hours. The void size increased with increasing annealing time. The nano-crystalline precipitates in Sr-implanted YSZ are isometric SrZrO3 (a≅0.41 nm). The orientation relation between the matrix and precipitates, as determined by selected area diffraction pattern, was: [011]YSZ // [ 1 11]SrZrO3 and [200]YSZ // [110]SrZrO3. INTRODUCTION Inert matrix fuel is one of possible options studied in recent years for the elimination of excess plutonium arising from nuclear power plants and dismantled nuclear weapons. Such a strategy would allow direct disposal without reprocessing after once-through burn-up. Among all the candidate materials, yttria stabilized cubic-zirconia is of interest based on its high solubility for actinides, high chemical durability and its exceptional stability under radiation [1-6]. Because the incorporation of fission and other transmutation products in zirconia during the burn-up may significantly affect the radiation response and chemical durability of the material, the solubility of the fission product nuclides in the inert fuel matrix at both high temperature (reactor fuel conditions) and low temperature (repository conditions) are important. Of special interest are the long-lived radionuclides, 135Cs, 129I and 90Sr, that can make significant contributions to radiation exposure. There have been limited studies on the behavior of I, Cs and Sr in cubic zirconia. In previous publications we have reported the amorphization of Cs-implanted YSZ due to relative larger cation radii and low mobility of Cs [7]. In this paper, we present results on the effects of Sr and I ion implantation on the microstructure. Because ion beam implantation can introduce ions as extra interstitials with radiation damage, the technique somewhat simulates the effects of fission product incorporation in the zirconia stru
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