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Multiscale Modelling and Materials by Design of interface-controlled Radiation Damage in Crystalline Materials

Final Report Summary - RADINTERFACES (Multiscale Modelling and Materials by Design of interface-controlled Radiation Damage in Crystalline Materials)

Executive Summary:
The RadInterfaces project studies a novel class of nanostructured multilammelar compounds considered to have practical application in the nuclear industry. The aim of the project is to develop a software suite capable of studying these compounds over a vast range of time and length scales from individual atomic interactions to a complete characterization of the mechanical response of the material over the reactor lifetime. These compounds present the very promising property of being self-repairing under the damage sustained by materials under heavy and continual irradiation, and thus present a possibly ground breaking application of nanoscience and functional material design to the nuclear industry. A common goal for materials in nuclear reactors, be they containment vessels or fuel cladding materials, is to exhibit the highest radiation tolerance possible. The emergence of new concepts using nanoscience in the design of bulk structural materials shows promise for providing the breakthroughs needed for future nuclear energy systems. In particular, the design and control of nanostructures and complex defect structures can create self-healing materials for radiation-induced defects and impurities that can yield radiation impervious materials. This concept has the potential to make radiation damage much less critical in design considerations, provided that complete defect absorption and self-healing can be achieved. The realization of this concept presents enormous scientific and technical challenges in the design and fabrication of bulk alloys using concepts developed for manipulating materials at the nanoscale. In reality, this entails expanding emerging capabilities for the synthesis of nanostructured materials at low dimensions (thin films and three-dimensional assemblies of precipitate phases) to true bulk alloys with the requisite thermo-mechanical properties required for reactor operation. In a nuclear reactor the structural materials and the fuel components can undergo significant radiation damage. Most commonly radiation damage occurs via the impingement of neutrons into the material. The neutrons interact with a single atom, the primary knocked-on atom (PKA), leading to a cascade of collisions with other atoms. After the very fast dissipation of the thermal energy spike, the radiation induced damage takes the form of point defects, vacancies and self-interstitials and clusters thereof, within the material. Over time these point defects agglomerate and interact with the existing microstructure, leading to weakening effects such as void swelling and irradiation creep.
Additionally, hydrogen and helium gas can be produced via neutron capture reactions. These gases are insolubile in the metals and alloys used in the nuclear industry, and thus tend to aggregate at voids, dislocation and grain boundaries, further weakening the mechanical properties.
A class of materials have recently been developed which exhibit a tremendous ability to repair the damage associated with the initial cascade from a PKA. The materials are constructed from nanoscale thick layers of immiscible metals deposited in alternating layers via, e.g. physical vapour deposition. The interfaces between the metallic layers serve as almost limitless sinks for the as yet still mobile point defects. Additionally the point defects that are absorbed into the interface interact over a much larger length scale. The point defects themselves, the vacancies and interstitials, are each the anti-defect of the other and annihilate when they come into contact, leaving behind pristine, that is “repaired”, crystal. So that this increased interaction scale leads to increased annihiliation.
In order to utilize the full potential of nanoscience in designing materials for nuclear systems, it is necessary to develop a full physical and chemical understanding of defect production, diffusion, and trapping under extreme conditions of temperature and radiation fluences. Theory, modeling and simulation tools can provide detailed understanding and predictive capability for nanostructured structural and functional materials for the nuclear energy systems. In order to create these materials, novel synthesis techniques spanning the full range from nanoscale to the bulk will be required along with analytical tools to characterize defect structures at the atomistic level.

Project Context and Objectives:
Please see pdf file "4.1 Final publishable summary report" in attachment, pages 2, 3, 4, 5 and 6

Project Results:
Please see pdf file "4.1 Final publishable summary report" in attachment, pages 6 to 19

Potential Impact:
The experimental findings obtained during the three years of work within Radinterfaces project can be expected to have a significant impact on the different areas of investigation involved. The fact that the results have been published in well reputed, in a few cases outstanding, international peer-reviewed journals represents itself an indirect measure of their potential impact on scientific community. A more direct measure of the interest attracted by the subject of study and by the experimental results obtained is given by the outstanding citation report on one of the published papers, namely M. A. Monclús, S. J. Zheng, J. R. Mayeur, I. J. Beyerlein, N. A. Mara, T. Polcar, J. LLorca, J. M. Molina-Aldareguía, APL Materials 1, 052103 (2013). For a few months, it has been indeed one of the five most cited APL Materials papers.
It can be reasonably expected that the scientific evidences regarding the mechanical properties of nanolaminate samples produced by physical vapor deposition will also attract similar interest, probably fostering further progress in the field.
From a technological point of view, the achievement of the capability of depositing nanocomposites of refractory metals by electrochemical methods can be considered a significant breakthrough. A new technology has been set up, providing a new synthetic route to composite materials. It is a valid alternative to molten salts technology, and is in principle extremely versatile due to the possibility of varying almost without limit the chemical system. At the same time, it also represents a definite alternative to aqueous solutions. Therefore, it could give rise to a completely new sector of application for electrochemistry, which is one of the most widespread methodologies in industry. It follows that the new methodology set up can have a disrupting impact on the existing industrial technology.
The software developed here as not only enabled a fundamental investigation into the irradiation and mechanical properties of NMMC materials, but has also resulted in a user-friendly multiscale tool which has already been incorporated into a graduate level mechanical engineering curriculum (ME6202 at the Georgia Institute of Technology). This software package will also be distributed as an open source teaching resource suitable for upper year undergraduate students and graduate students.

List of Websites:
These new NMMC concepts are expected to have considerable impact in the nuclear industry. As a result, the consortium members were able to develop software for fast modelling of the mechanical response of NMMCs.