Ewing, R.

Lang, M.

Palomares, R.

Park, C.

Popov, D.

Tracy, C.

Trautmann, C.

Zhang, F.

GSI Repository

In situ defect annealing of swift heavy ion-irradiated CeO2 and ThO2* Raul I. Palomares1,#, Cameron L. Tracy2, Fuxiang Zhang2, Changyong Park3, Dmitry Popov3, Christina Trautmann4,5, Rodney C. Ewing6, Maik Lang1, 1University of Tennessee, Knoxville, TN, U.S.A.; 2University of Michigan, Ann Arbor, MI, U.S.A.; 3Geophysical La-boratory, Carnegie Institution of Washington, Argonne, IL, U.S.A.; 4GSI Helmholtzzentrum & Technische Universität Darmstadt, Germany; 6Stanford University, Stanford, CA, U.S.A.Ceria (CeO2) and thoria (ThO2) are isostructural ana-logues to typical nuclear fuels, such as UO2. During reac-tor operation, nuclear fuels are exposed to intense radia-tion fluxes and temperature gradients. These conditions, in particular fission fragment- and fast neutron-fluxes, generate nanoscale defects and induce adverse effects such as swelling and redox reactions [1]. Such modifica-tions can degrade materials properties relevant to fuel performance. In this study [2], a hydrothermal diamond anvil cell (HDAC) and synchrotron x-ray diffraction (XRD) con-figuration was used to investigate the defect annealing kinetics in swift heavy ion-irradiated CeO2 and ThO2 at ambient pressure. Swift heavy ions were used to simulate the effect of ionizing fission-fragment irradiation because of the similarity in specific kinetic energies (>1 MeV/nucleon) and energy deposition mechanisms. Polycrystalline CeO2 and ThO2 cold-pressed pellets were irradiated at room temperature at the M2-beamline of the UNILAC of GSI with 945 MeV 197Au ions to a fluence of 2.5×1013 ions-cm-2. After irradiation, the sam-ples were transferred into one of two holes that were drilled into a rhenium gasket (Fig. 1) for use with an HDAC. In order to monitor the recovery kinetics of ion-induced defects in CeO2 and ThO2, the samples were isochronally annealed for 20 minutes per step in 50-75 K temperature steps from 300-1075 K at beamline 16-BM-D of the Advanced Photon Source, U.S.A.. After each heat-ing step, the samples were quenched to ambient tempera-ture and allowed to equilibrate for 20 minutes. Upon reaching stable temperature, diffraction patterns were recorded. Fig. 1: The HDAC sample chamber as imaged by light microscopy (left) and x-ray absorption (right). Fig. 1: Fig. 2: The relative change in the unit cell parame-ter, a, from the unirradiated value, a0, as a function of isochronal annealing temperature. The inset shows the differential curves of the data. Irradiation induces unit cell expansion due to the accu-mulation of isolated point defects which can agglomerate into defect clusters. As a material is heated, these defects are annealed and the unit cell parameter begins to recover. The annealing data indicate that the materials recover at different rates. The differential curves show one defect recovery stage in ThO2 while there exist two in CeO2 within the temperature regime investigated (Fig. 2 inset). Material recovery was attributed [2] to the relaxation of heterogeneous microstrain, and the recombination and annihilation of anion defects (a & c, Fig. 2). This is fol-lowed by cation vacancy migration in CeO2 (b, Fig. 2). The discrepancy in kinetics can be attributed to the redox behavior exhibited by CeO2 under energetic irradiation [1]. These results suggest that cation electronic configura-tion plays a significant role in not only the defect produc-tion behavior, but also the defect recovery mechanisms of the fluorite-structure oxides.  References [1] C.L. Tracy et al., Redox response of actinide materials to highly ionizing radiation. Nat Commun, 2015. 6: p. 6133. [2] R.I. Palomares et al., In Situ Defect Annealing of Swift Heavy Ion Irradiated CeO2 and ThO2, under review  ____________________________________________ * This work was supported as part of the Materials Science of Acti-nides, an Energy Frontier Research Center funded by the US DOE Office of Science, Office of Basic Energy Sciences under Award Num-ber DE-SC0001089.. # rpalomar@utk.edu APPA-MML-MR-06 GSI SCIENTIFIC REPORT 2014258 DOI:10.15120/GR-2015-1-APPA-MML-MR-06

In situ defect annealing of swift heavy ion-irradiated CeO$_2$ and ThO$_2$

http://repository.gsi.de/record/183992/files/APPA-MML-MR-06.pdf

In situ defect annealing of swift heavy ion-irradiated CeO $_2$ and ThO $_2$

Abstract

Similar works

Full text

Available Versions

GSI Repository

In situ defect annealing of swift heavy ion-irradiated CeO2_22​ and ThO2_22​

Abstract

Similar works

Full text

Available Versions

GSI Repository

In situ defect annealing of swift heavy ion-irradiated CeO $_2$ and ThO $_2$