Superlattice Structure and Precipitates in O⁺ and Zr⁺ Ion Coimplanted SrTiO₃: A Model Waste Form for ⁹⁰Sr

Abstract

There are high yields of 90Sr radionuclide present in the spent fuels from nuclear power plants. Permanent disposal of the nuclear waste requires immobilization of the highly radioactive materials. We investigate strontium titanate as a model waste form for 90Sr. Coimplantation with O+ and Zr+ ions, followed by annealing at 1423 K, was performed to simulate 90Sr to 90Zr decay. The microstructures were examined using a state-of-the-art aberration-corrected scanning transmission electron microscope (STEM) with a spatial resolution of better than 0.1 nm. At low Zr concentrations, we observe formation of a ZrO-Sr superlattice structure. Ab initio calculations indicate that this atomic configuration is energetically favorable. At higher Zr concentrations, we observe precipitates of ZrO2 with a coherently strained interface or a monolayer of disordered interfacial structure. Chemical and charge effects in the model waste form of 90SrTiO3 are discussed.

Percolation of Ion-Irradiation-Induced Disorder in Complex Oxide Interfaces

“…Similarly, the STO side of the interface also exhibits strong diffraction disks, despite some distributed damage, consistent with past observations. 47,58 Correlative STEM-EELS chemical analysis of the interface, shown in Figure 3B, reveals the gradual breakup of the crystalline film upon transitioning from the interface into the bulk, resulting in three distinct regions (labeled 1−3). Region (1) consists of a ∼3 nm region of LMO that is strongly diffracting and highly chemically ordered on both the La and Mn sublattices.…”

Milestone Report - M4FT-15OR03120218 - A Literature Search on the Effects of the Decay of ⁸⁵Kr to ⁸⁵Rb on Long-term Storage Options

“…The Rb + would become part of the metal matrix as an interstitial particle either as an ion or metal after gaining an electron from the metal through conduction, probably the conduction band. From a study of transmutation effects on crystalline materials potentially used for nuclear waste, it was determined that, even in these non-conducting materials, electrons were available from neighboring atoms or from the unoccupied conduction band and, at relatively high concentrations of the decaying atom, some defects were likely because of the changes in atomic volume (Jiang et al 2012;Jiang et al 2014;Van Ginhoven et al 2010. At the low concentrations expected for the decay of 85 Kr to 85 Rb, the electrons might be extracted from the conduction band while little effect is expected on the overall crystal structure of the vapor deposited metal.…”

“…As indicated in Section 3.2, there are effects on the sorbent material resulting from the transmutation of one atom into another (Jiang et al 2012;Jiang et al 2014;Van Ginhoven et al 2010. The charge can be compensated though transfer of electrons from the Fermi band or from a multivalent atom with available oxidation states, e.g., Fe(II) and Fe(III).…”

Nanoparticle Precipitation in Irradiated and Annealed Ceria Doped with Metals for Emulation of Spent Fuels

“…The microstructure of the irradiated fuel is complex due to various factors, including the presence of various fission product precipitates, β-decay induced changes in charge imbalance, − increase in oxygen potential, temperature gradient, irradiation-enhanced GB migration, and lattice disorder produced by elastic collisions with high-energy neutrons and energetic daughter nuclide recoils in the damage cascade process. There is a long history of effort devoted to characterization of spent nuclear fuels.…”