Computational Methods in Science and Engineering : Proceedings of the Workshop SimLabs@KIT, November 29 - 30, 2010, Karlsruhe, Germany

In this proceedings volume we provide a compilation of article contributions equally covering applications from different research fields and ranging from capacity up to capability computing. Besides classical computing aspects such as parallelization, the focus of these proceedings is on multi-scale approaches and methods for tackling algorithm and data complexity. Also practical aspects regarding the usage of the HPC infrastructure and available tools and software at the SCC are presented

Radiation damage and inert gas bubbles in metals

Inert gases in metals can occur due to ion implantation, from a plasma in a magnetron device or as a result of being by-products of nuclear reactions. Mainly because of the nuclear applications, the properties of the inert gases, helium, argon and xenon in the body centred cubic (bcc) iron crystal are examined theoretically using a combination of molecular dynamics, static energy minimisation and long time scale techniques using empirical potential functions. The same techniques are also used to investigate argon and xenon in aluminium. The primary interest of the work occurred because of He produced in nuclear fission and its effect on the structural materials of a fission reactor. This structure is modelled with perfectly crystalline bcc Fe. In bcc iron, helium is shown to diffuse rapidly forming small bubbles over picosecond time scales, which reach a certain optimum size. In the initial phase of He accumulation, Fe interstitials are ejected. This occurs instantaneously for bubbles containing 5 He atoms and as the more He accumulates, more Fe interstitials are ejected. The most energetically favourable He to vacancy ratios at 0 K, vary from 1 : 1 for 5 vacancies up to about 4 : 1 for larger numbers of vacancies. An existing He bubble can be enlarged by a nearby collision cascade through the ejection of Fe interstitials, allowing more He to be trapped. Ar and Xe in bcc Fe prefer to be substitutional rather than interstitial and there are large barriers to be overcome for the inert gas atoms to diffuse from a substitutional site. Bubbles that form can again be enlarged by the presence of a nearby collision cascade or at very high temperatures. In this case the most energetically favourable vacancy ratios in the bubbles is 1: 1 for Ar and from 0.6: 1 to 0.8: 1 for Xe. For Ar and Xe, bubble formation is more likely as a direct result of radiation or radiation enhanced diffusion rather than diffusion from a substitutional site. Ar in aluminium is also studied. Ar atoms in fcc Al prefer to be substitutional rather than interstitial and evolution into substitutional occurs over picosecond time scales at room temperature. Bubble formation can occur more easily than in bcc iron, mainly because the barriers for vacancy diffusion are much lower but the time scales for bubble accumulation are much longer than those for He. A vacancy assisted mechanism is found which allows Ar to diffuse through the lattice. Finally some preliminary results on the energetics of different geometrical structures of larger Xe bubbles in Al are investigated since experiment has indicated that these can become facetted

Simulating radiation effects in iron with embedded oxide nanoparticles

Alloys used in fission and in future fusion reactors are subjected to extreme conditions including high temperatures, corrosive and intense radiation environments. Understanding the processes occurring at the microscopic level during radiation events is essential for the further development of them. As a prospective candidate material for new reactors, oxide dispersion strengthened (ODS) steels have shown good radiation resistance and the ability to trap He into fine scale bubbles, thus preventing swelling and preserving high-temperature strength. This thesis represents the findings obtained by performing computational studies of radiation effects in pure iron, Y-Ti-O systems and a simplified model of ODS using Molecular Dynamics (MD) and on-the-fly Kinetic Monte Carlo (otf-KMC) techniques. MD studies of radiation damage were carried out in a perfect body-centred cubic (bcc) iron matrix (alpha-Fe) in which yttria nanoparticles are embedded as a simplified model of an ODS steel. The results have shown how the nanoparticles interact with nearby initiated collision cascades, through cascade blocking and energy absorption. Fe defects accumulate at the interface both directly from the ballistic collisions and also by attraction of defects generated close by. The nanoparticles generally remain intact during a radiation event and release absorbed energy over times longer than the ballistic phase of the collision cascade. Also the nanoparticles have shown ability to attract He atoms as a product of fission and fusion reactions. Moreover, studies showed that He clusters containing up to 4 He atoms are very mobile and clusters containing 5 He or more become stable by pushing an Fe atom out of its lattice position. The radiation damage study in the Y-Ti-O materials showed two types of residual damage behaviour: when the damage is localized in a region, usually close to the initial primary knock-on atom (PKA) position and when PKA is directed in the channelling direction and creates less defects compared to the localised damage case, but with a wider spread. The Y2TiO5 and Y2Ti2O7 systems showed increased recombination of defects with increased temperature, suggesting that the Y-Ti-O systems could have a higher radiation resistance at higher temperatures. The otf-KMC technique was used to estimate the influence of the prefactor in the Arrhenius equation for the long time scale motion of defects in alpha-Fe. It is shown that calculated prefactors vary widely between different defect types and it is thus important to determine these accurately when implementing KMC simulations. The technique was also used to study the recombination and clustering processes of post-cascade defects that occur on the longer time scales

Simulación de la evolución de defectos en materiales irradiados de interés en fusión nuclear mediante un método GPU-OKMC

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, leída el 28-11-2022As the current world reliance on fossil fuels proves to have catastrophic environmental consequences, which are only exacerbated with a growing world economy and population, a future clean source of energy is required. The scientific community expects nuclear fusion to fulfill this task, in particular magnetically confined fusion. To achieve this, an experimental fusion reactor, the ITER Project, is underway and shall provide the basis for a future demonstration power plant, known as DEMO. One of the most important challenges in the design of a future nuclear fusion reactor is the choice of materials. Materials are subjected to an intense flux of neutrons and heat in a fusion reactor like ITER or, in a much more pronounced way, DEMO. Under irradiation, a large amount of defects are created and, as aconsequence, the properties of materials are severely degraded, and may cause the reactor components to malfunction or break...Dado que la actual dependencia mundial de los combustibles fósiles muestra ciertas consecuencias catastro cas para el medio ambiente, las cuales son magnificadas a medida que crecen la economía y población mundiales, se necesita una fuente de energía limpia para el futuro. La comunidad científica espera que sea la fusión nuclear la que desempeñe este papel, en particular la fusión por confinamiento magnético. Para ello, un reactor de fusión experimental, el Proyecto ITER, esta en marcha y proporcionará las bases para un futuro reactor de demostración llamado DEMO. Uno de los desafíos principales en el diseño de un futuro reactor de fusión es la elección de los materiales. En efecto, los materiales serán sometidos a un flujo intenso de neutrones y calor en un reactor de fusión como ITER; y, de forma más pronunciada, en uno como DEMO. Esto provocara la creación de una gran cantidad de defectos, por lo que las propiedades de los materiales serán gravemente alteradas, y podrán provocar que los componentes del reactor dejen de funcionar correctamente o, incluso, se quiebren...Fac. de Ciencias FísicasTRUEunpu

Advanced Industrial Materials (AIM) Program: Annual progress report FY 1995

In many ways, the Advanced Industrial Materials (AIM) Program underwent a major transformation in Fiscal Year 1995 and these changes have continued to the present. When the Program was established in 1990 as the Advanced Industrial Concepts (AIC) Materials Program, the mission was to conduct applied research and development to bring materials and processing technologies from the knowledge derived from basic research to the maturity required for the end use sectors for commercialization. In 1995, the Office of Industrial Technologies (OIT) made radical changes in structure and procedures. All technology development was directed toward the seven ``Vision Industries`` that use about 80% of industrial energy and generated about 90% of industrial wastes. The mission of AIM has, therefore, changed to ``Support development and commercialization of new or improved materials to improve productivity, product quality, and energy efficiency in the major process industries.`` Though AIM remains essentially a National Laboratory Program, it is essential that each project have industrial partners, including suppliers to, and customers of, the seven industries. Now, well into FY 1996, the transition is nearly complete and the AIM Program remains reasonably healthy and productive, thanks to the superb investigators and Laboratory Program Managers. This Annual Report for FY 1995 contains the technical details of some very remarkable work by the best materials scientists and engineers in the world. Areas covered here are: advanced metals and composites; advanced ceramics and composites; polymers and biobased materials; and new materials and processes