Radiation damage in the bulk and at the surface (original) (raw)
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High-energy radiation damage in zirconia: Modeling results
Zirconia is viewed as a material of exceptional resistance to amorphization by radiation damage, and consequently proposed as a candidate to immobilize nuclear waste and serve as an inert nuclear fuel matrix. Here, we perform molecular dynamics simulations of radiation damage in zirconia in the range of 0.1-0.5 MeV energies with account of electronic energy losses. We find that the lack of amorphizability co-exists with a large number of point defects and their clusters. These, importantly, are largely isolated from each other and therefore represent a dilute damage that does not result in the loss of long-range structural coherence and amorphization. We document the nature of these defects in detail, including their sizes, distribution and morphology, and discuss practical implications of using zirconia in intense radiation environments.
Use of massively parallel molecular dynamics simulations for radiation damage in pyrochlores
Journal of Materials Science, 2007
DL_POLY_3 is a general purpose molecular dynamics (MD) simulation package designed to simulate systems of the order of tens of millions of particles and beyond by efficiently harnessing the power of modern computer clusters. Here we discuss the package design, functionality and report on performance and capability limits. We then report the application of DL_POLY_3 to study radiation cascades in Gd2Ti2O7 and Gd2Zr2O7, potential materials for high-level radioactive waste storage and discuss problems associated with the analysis of the cascades. We see little direct amorphisation but rather the start of a transition to the fluorite structure which is more pronounced for the Zr than the Ti compound.
Molecular dynamics simulations of irradiation cascades in alpha-zirconium under macroscopic strain
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2013
Numerous computer simulation studies have been performed on the radiation damage of zirconium. In contrast to most of the work in the literature which has focused on the effects of temperature and recoil energy on defect production and defect clustering, we have developed a computational model to consider the influence of elastic strain field on the formation of defects and their clusters, as strain is commonly present in a real reactor environment. In this work, irradiation induced displacement cascades in alphazirconium experiencing a macroscopic strain have been studied by molecular dynamics (MD) simulations using a many-body interatomic potential. The external strain mainly affects the size of defect clusters rather than the total number of defects. The sizes of interstitial and vacancy clusters respond differently to the external strain conditions.
Uncovering the hidden damage in irradiated zirconia
Zirconia is viewed as a material of exceptional resistance to amorphization by radiation damage, and consequently proposed as a candidate to immobilize nuclear waste and serve as an inert nuclear fuel matrix. Here, we perform molecular dynamics simulations of radiation damage in zirconia in the range of 0.1-0.5 MeV energies with full account of electronic energy losses. We find that the lack of amorphizability co-exists with a large number of point defects and their clusters. These, importantly, are largely isolated from each other and therefore represent a dilute damage that does not result in the loss of long-range structural coherence and amorphization. We document the nature of these defects in detail, including their sizes, distribution and morphology, and discuss practical implications of using zirconia in intense radiation environments.
Molecular dynamics simulation of defect production in collision cascades in zircon
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 2005
Defect production in collision cascades in zircon has been examined by molecular dynamics simulations using a partial charge model combined with the Ziegler-Biersack-Littmark potential. U, Zr, Si and O recoils with energies ranging from 250 eV to 5 keV were simulated in the NVE ensemble. To obtain good statistics, 5-10 cascades in randomly chosen directions were simulated for each ion and energy. The damage consists of mainly Si and O Frenkel pairs, a smaller number of Zr Frenkel pairs, and Zr on Si antisite defects. Defect production, interstitial clustering, ion beam mixing and Si-O-Si polymerization increase with PKA mass and energy.
Journal of Physics: Condensed Matter, 2003
Zircon has been proposed as a nuclear waste form to safely encapsulate weapons-grade plutonium. In order to study the impact of self-irradiation damage in zircon on its aqueous durability, we performed a hydrothermal experiment (2 M CaCl 2 solution, 600 • C, 100 MPa) with several variably radiation-damaged, i.e. amorphized, zircon samples. We found an anomalous increase in the alteration rate at two critical concentrations of amorphous domains. The first dramatic increase sets in when the amorphous domains form interconnected clusters in the structure. The second increase is related to the percolation of fast diffusion pathways consisting of nano-sized regions of depleted matter that are formed during strongly overlapping α-recoil events, as seen by molecular-dynamics simulations and small-angle x-ray scattering measurements. The two percolation thresholds provide model benchmarks for the safety performance of a zircon waste form.
Atomistic simulation of collision cascades in zircon
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006
Defect production in energetic collision cascades in zircon has been studied by molecular dynamics simulation using a partial charge model combined with the Ziegler-Biersack-Littmark potential. Energy dissipation, defect accumulation, Si-O-Si polymerization and Zr coordination number were examined for 10 keV and 30 keV U recoils simulated in the constant NVE ensemble. For both energies an amorphous core was produced with features similar to that of melt quenched zircon. Disordered Si ions in this core were polymerized with an average degree of polymerization of 1.5, while disordered Zr ions showed a coordination number of about 6 in agreement with EXAFS results. These results suggest that nano-scale phase separation into silica-and zirconia-rich regions occurs in the amorphous core.
Atomistic simulations of resistance to amorphization by radiation damage
Physical Review B, 2006
We use molecular-dynamics simulations to study processes related to resistance to amorphization by radiation damage. We simulate high-energy radiation events in SiO 2 , GeO 2 , TiO 2 , Al 2 O 3 , and MgO, and find that simulation results match the experiments. We discuss the difference between the damage that the structures along this series can support. We find that for the same material, activation barriers for damage recovery can strongly depend on the degree of structural damage. We observe that the effect of resistance to amorphization is primarily governed by the relaxation processes at the time scales of several picoseconds. On this time scale, we observe two distinct relaxation processes, reversible elastic deformation around the radiation cascade and recovery of the in-cascade damage of high topological disorder. Finally, we discuss how resistance to amorphization is related to interatomic interactions and to the nature of the chemical bond.
CSaransh : Software Suite to Study Molecular Dynamics Simulations of Collision Cascades
Journal of Open Source Software
The micro-structural properties of materials change due to irradiation. The defects formed during the displacement cascades caused by irradiation are the primary source of radiation damage (Björkas, Nordlund, & Caturla, 2012; Stoller, 2012). The number of primary defects produced, defect cluster size distribution, and defect cluster structures after a collision cascade can be studied using Molecular Dynamics simulations. These results determine the long term evolution of the micro-structural changes in the material (
Journal of Nuclear Materials, 2006
Kinetic Monte Carlo is used extensively in the field of radiation effects to understand damage accumulation and growth under irradiation. These calculations require previous knowledge on the formation of these defects, the relative stabilities of the different types of defects, their interactions and their mobilities. Many of these parameters can be extracted from molecular dynamics calculations using empirical potentials or from ab initio calculations. However, the number of parameters necessary for a complete picture is rather large. Kinetic Monte Carlo can be used as a tool to isolate those parameters that most influence the outcome of the calculations. In this paper, we focus on one aspect: the form of the damage after the collision cascade. We describe the effect of the form of the cascade as obtained from molecular dynamics simulations on damage accumulation. In particular, we demonstrate that the form of the cascade drastically changes the nucleation and growth of helium-vacancy clusters, possible precursors of voids and bubbles. Finally, we point to those open questions that need to be resolved to develop a truly predictive kinetic Monte Carlo model.