Neutron hardening and embrittlement of pressure vessel steels is due to a high density of nanometer scale features, including Cu-rich precipitates which form as a result of radiation enhanced diffusion. High-energy displacement cascades generate large numbers of both isolated point defects and clusters of vacancies and interstitials. The subsequent clustering, diffusion and ultimate annihilation of primary damage is inherently coupled with solute transport and hence, the overall chemical and microstructural evolutions under irradiation. In this work, we present atomistic simulation results, based on many-body interatomic potentials, of the migration of vacancies, solute and self-interstitial atoms (SIA) in pure Fe and binary Fe-0.9 and 1.0 at.% Cu alloys. Cu diffusion occurs by a vacancy mechanism and the calculated Cu diffusivity is in good agreement with experimental data. Strain field interactions between the oversized substitutional Cu solute atoms and SIA and SIA clusters are predominantly repulsive and result in both a decreased activation energy and diffusion pre-factor for SIA and small (N < 5) SIA cluster migration, which occurs by three-dimensional motion. The Cu appears to enhance the reorientation of the SIA clusters to different <111> directions, as well as the transition from <110> to mobile <111> configurations. The migration behavior of …

The Spallation Neutron Source (SNS) project is a collaborative effort between Brookhaven, Argonne, Jefferson, Lawrence Berkeley, Los Alamos and Oak Ridge National Laboratories. Los Alamos is responsible for the design of the linac for this accelerator complex. The code PARMILA, developed at Los Alamos is widely used for proton linac design and beam dynamics studies. The most updated version includes superconducting structures among others. In recent years, some other codes have also been developed which primarily focuses on the studies of the beam dynamics. In this paper, we compare the simulation results and discuss physics aspects of the different linac design and beam dynamics simulation codes.

An alternative approach is described to evaluate the statistical nature of the breakup of shaped charge liners. Experimental data from ductile and brittle copper jets are analyzed in terms of velocity gradient, deviation of {Delta}V from linearity, R/S analysis, and the Hurst exponent within the coupled map lattice model. One-dimensional simulations containing 600 zones of equal mass and using distinctly different force-displacement curves are generated to simulate ductile and brittle behavior. A particle separates from the stretching jet when an element of material reaches the failure criterion. A simple model of a stretching rod using brittle, semi-brittle, and ductile force-displacement curves is in agreement with the experimental results for the Hurst exponent and the phase portraits and indicates that breakup is a correlated phenomenon.

Advances in computational capability and modeling techniques, as well as improvements in experimental characterization methods offer the possibility of directly comparing modeling and experiment investigations of irradiation effects in metals. As part of a collaboration among the Instituto de Fusion Nuclear (DENIM), Lawrence Livermore National Laboratory (LLNL) and CIEMAT, single and polycrystalline {alpha}-Fe samples have been irradiated with 150 keV Fe-ions to doses up to several dpa. The irradiated microstructure is to be examined with both transmission electron microscopy (TEM) and positron annihilation spectroscopy (PAS). Concurrently, we have modeled the damage accumulation in Fe under these irradiation conditions using a combination of molecular dynamics (MD) and kinetic Monte Carlo (KMC). We aim to make direct comparison between the simulation results and the experiments by simulating TEM images and estimating positron lifetimes for the predicted microstructures. While the identity of the matrix defect features cannot be determined from TEM observations alone, we propose that both large self-interstitial loops, trapped at impurities within the material, and small, spherical nanovoids form.

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