Dear Colleagues,

The ever-increasing global demand for energy and the urgency of reducing greenhouse gases to prevent global warming has catalysed a renewed search for clean, viable, safe and sustainable energy sources. Nuclear reactors provide an attractive alternative to fossil fuels in meeting these challenges. New reactors are being designed to increase efficiency, reduce radioactive waste, and improve the safety of operation. However, such nuclear applications usually entail a combination of different extreme conditions, such as high temperatures, high radiation doses, and corrosive environments. The combination of these harsh environments poses considerable challenges, and it requires the use of materials that can withstand such extreme conditions.

As such, the newly designed materials, as well as the currently used ones, need to be tested for changes in their microstructure and mechanical properties after exposure to these harsh conditions. The special nature of the effects of irradiation by energetic particles, including both neutrons and ions, demands the use of advanced characterization and testing techniques to understand the complex changes effected by these processes.

In recent years, small-scale mechanical testing techniques, such as nanoindentation, micro compression testing, micro-tensile testing and others have become increasingly popular in the nuclear materials community for several reasons. Firstly, ion irradiation is being increasingly used as an alternative method of simulating radiation damage in materials, reducing the duration of the radiation experiments by many orders of magnitude. Small-scale testing allows one to assess the mechanical properties of ion-irradiated materials which that otherwise would not be accessible due to limited beam penetration. Secondly, in the case of neutron irradiation, it reduces the amount of active material that one must handle due to reduced sample size. Thirdly, it allows one to target specific microstructural regions of interest, be they individual grain boundaries, oxide layers or phases and orientations. The development of newer technologies has prompted a wave of devices that can perform various types of tests, such as nanoindentation, compression, tension, bending, etc., at the sub-micron to submillimetre scale. However, there are many outstanding issues—such as the grain and sample size, strain rate, temperature, etc.—that affect the results and demand proper analysis in order for the application of these methods to engineer problems to be possible.

Apart from micromechanical testing, it is also imperative to test the materials at a larger scale, as some materials have large grains, which lend themselves better to meso- or mini-scale testing. Such tests can also be used to validate models used to extrapolate test results from the micron scale to the bulk scale. Moreover, when neutron-irradiated materials are tested with the proper safety precautions, they allow full-scale testing, which provides a definitive way to check the engineering properties of irradiated metals and alloys.

In terms of microstructural characterization, a range of advanced techniques are available that facilitate the understanding of the damage phenomena and their underlying processes spanning different length scales. For instance, transmission electron microscopy (TEM) and atom-probe tomography (APT) can be used at the angstrom to ~100 nm scale for obtaining insights into the chemical redistribution of atomic species (through energy dispersive spectroscopy or EDS) and radiation-induced defect structures, voids, bubbles, etc. (through diffraction imaging). At the sub-micron to sub-mm scale, TEM and scanning electron microscopy (SEM), including electron backscatter diffraction (EBSD), can be used to understand the deformation structures and fracture characteristics. In order to obtain statistical information on void or precipitate distributions, diffraction techniques such as small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) techniques are found to be extremely useful.

In light of all these advanced techniques available for the characterization and testing of nuclear materials, authors are invited to send original research papers on subjects including, but not limited to, those suggested in the following list:

• Technique development for mechanical testing including nanoindentation, micromechanical testing, mini- and meso-scale testing, etc.;
• Novel methods of characterization of irradiated and un-irradiated nuclear materials at all scales,involving APT, TEM, SEM, EBSD, EDS, SANS, SAXS, confocal microscopy, etc.;
• New research findings in characterization and testing of nuclear materials in both unirradiated and irradiated conditions at all scales;
• Numerical (finite element, crystal plasticity, dislocation dynamics, molecular dynamics or other methods) and analytical (plasticity-based models, etc.) modelling of small-scale testing or deformation mechanisms.

The editors solicit papers with original research or review papers on these and related topics for publication in this Special Issue on “Advanced Characterization and Testing of Nuclear Materials”.

Dr. Dhriti Bhattacharyya
Dr. Peter Hosemann
Guest Editors

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• characterization
• mechanical properties
• mechanical testing
• micromechanical testing
• nanoindentation
• nuclear materials
• modelling
• small-scale testing
• larger-scale testing
• deformation mechanisms
• radiation damage