High-level nuclear waste glasses are subject to radiation-induced degradation over very long time scales. In such glasses, bond-breakage and atom displacements occur by both radiolysis (principally from energetic beta-decay electrons) and ballistic mechanisms involving collision cascades initiated by energetic fission nuclei and recoil of alpha-emitting actinide nuclei [1]. This study investigates collision-cascade-induced alteration of the glass network in a simplified sodium borosilicate model nuclear waste glass, using molecular dynamics (MD) codes and efficient topological assessment algorithms. Collision cascades were initiated ballistically (4 keV initial kinetic energy, dissipated elastically) and carried out using MD codes incorporating both two-body Buckingham and three-body Stillinger-Weber potentials verified in the GULP atomistic simulation package. Network topologies of the initial and resulting altered glass structures were determined by enumerating the primitive-ring-based local cluster atom complement at each atom site. The topological description is seen to provide a revealing assessment of network structural changes in the simulated radiation environment that can be potentially related to observable macroscopic changes, such as swelling, viscosity changes, and radiation-induced devitrification.

The effect of seawater on thermal behavior of conventional and nanophased carbon/epoxy composites was investigated in this study. Composites were fabricated with 1 wt.%, 2 wt.%, and 3 wt.% nanoclay by vacuum assisted resin transfer molding (VARTM) process and compared with neat samples with and without exposure to seawater. Thermal characterization was performed by the dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). Samples exposed to the seawater for 30- and 60-day periods revealed that samples with nanoclay retained better thermal properties compared to the neat samples. Storage modulus was reduced by 6.28%, 6.76%, 6.15%, and 7.05% for neat, 1 wt.%, 2 wt.%, and 3 wt.% nanoclay infused samples, respectively, after the samples were exposed to seawater for 60 days . From TGA results, it was observed that the thermal stability is not related to nanoclay content and conditoning. Optical microscope (OM) and scanning electron microscope (SEM) studies revealed no significant change in surface morphology in the 30-day conditioning samples.

Systematic first-principles calculations based on density functional theory were performed on a wide range of Ln2TiO5 compositions (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy and Y) in order to understand the correlation between structural, elastic and electronic properties. A complete set of elastic parameters including elastic constants, Hill’s bulk moduli, shear moduli, Young’s moduli and Poisson’s ratio, were calculated. All Ln2TiO5 are ductile in nature, and analysis of densities of states and charge densities suggests that the oxide bonds are highly ionic.

Hierarchical modeling based on atomistic and continuum simulations were established to describe the fundamental characteristics of plastic deformation in irradiated materials. Typical irradiation defects of a self-interstitial atom (SIA) loop and vacancy loop are considered. At first atomic models, including a SIA loop and a vacancy as well as a straight dislocation loop in single crystals were constructed. Constant strain is applied to each model and the equilibrium configuration under deformation is calculated by a molecular statics simulation. Maximum shear stresses in various radii of irradiated defects are stored in a database for the continuum mechanics analysis. Then local interaction events between glide dislocation and irradiation defects were introduced through crystal plasticity finite element analysis. In this model the effect of radiation hardening was considered by referring to the experiment. We found that softening after the first yield event is caused by annihilation of irradiation defects resulting from unfaulting of the radiation defects.

Defects inside oxide ceramics of magnesium oxide (MgO) and sapphire (Al2O3) were formed using femtosecond laser irradiation. The laser irradiance in these ceramics forms various defects classified as dislocations, twins, or nano cracks near the focal point due to the increase of temperature and successive generation of shockwave within several picoseconds. The morphology of defects mainly depends on the crystal structure; dense dislocations inside MgO with a rock-salt type structure, and nanocracks, dislocations, or twins in sapphire with a corundum structure. The TEM analysis revealed that the dense dislocations formed on the two slip planes {110} to form a cross-shaped pattern when the laser beam focused on the (100) plane in MgO. In case of sapphire crystal, cracks propagated from the focal point that has an amorphous structure along R-planes {11-02}, which had the lowest fracture surface energy. The nano crack transformed into the aligned void and dislocation structure during the heat treatment over 1573K, which is one of the crack healing effect.

Thin films nano-crystalline zirconia of ~ 300 nm thick were deposited on Si substrate, and the samples were irradiated with 2 MeV Au+ ions at temperatures of 160 and 400 K, up to fluences of 35 displacements per atom. The films were then studied using glancing incidence x-ray diffraction, Rutherford backscattering, secondary ion mass spectroscopy and transmission electron microscopy. During the irradiation, cavities were observed to form at the zirconia/silicon interface. The morphology of the cavities was found to be related to the damage state of the underlying Si substrate. Elongated cavities were observed when the substrate is heavily damaged but not amorphized; however, when the substrate is rendered amorphous, the cavities become spherical. As the ion dose increases, the cavities then act as efficient gettering sites for the Au. The concentration of oxygen within the cavities determines the order in which the cavities getter. Following complete filling of the cavities, the interface acts as the secondary gettering site for the Au. The Au precipitates are determined to be elemental in nature due to the high binding free energy for the formation of Au-silicides.

The austenitic stainless steels so-called, the EHP steels with the extra high purity, are developed for improving the reliability of nuclear equipments materials used in the heavily corrosive irradiation environments. By considering the impurities segregation mechanism, the major impurities included in the EHP steels is controlled less than 100ppm by the new melting technology. It is two-step refining process composed of CCIM and EB for effectively removing both non-volatile and volatile harmful elements. The risk to cracking on melting and welding processes is also effectively minimized by enhancing both the eutectic point and the metallic bonding at grain-boundaries. In the EHP steels, it is possible to select the appropriate composition of Ni and Cr for stabilizing austenitic phase and enhancing corrosion resistance. The characteristics of the welding joints are as good as those of the base metal because the same filler metal is sed without the formation of residual delta ferrite. The resistance to IGC and SCC of the EHP steels is markedly improved by minimizing the refining effects, except for type 316 steels with Mo. The welding technique and the chemical composition range are selected for standardizing the EHP.

We have performed density-functional theory (DFT) calculations of phase stability, formation energies of radiation defects in tungsten-based binaries W-Ta and W-V. These alloys are candidate for DEMO divertor applications because of their high melting point and expected improved ductility and fracture toughness in comparison with tungsten. We have identified the lowest energy intermetallic compounds, which should form at low temperatures, and calculated the effective inter-atomic interactions. Using Monte-Carlo calculations, we calculated the temperature of order-disorder phase transformations for these alloys. The predicted temperature of order-disorder phase transformations is relatively low and at high temperature it is found that the short-range order is present for both alloys. Ab-initio calculations also show that vanadium atoms strongly trap self-interstitial atom defects in W-V alloys, whereas Ta atoms in W-Ta alloys have very little effect on either the formation energy or thermally activated mobility of self-interstitial atom defects.

Adhesive strength between V-4Cr-4Ti type alloys and an yttrium oxide layer formed by a plasma spray technique was evaluated by a laser shock spallation method, which uses a pulse laser to generate a shock wave to create tensile stress inside the specimen. There was no significant dependence of the adhesive strength on the alloying elements examined, such as yttrium, silicon and aluminum. Detailed observation of the exfoliation behavior was carried out to identify the weakest interface of the coating layer. Several modes of exfoliation behavior were categorized after cross-sectional observation. There was some uncertainty of the adhesive strength of the layer evaluated by the laser shock method, due to the thickness of the coating layer. The typical adhesive strength between the alloy and yttrium oxide layer was evaluated to be approximately 400 MPa.

The effect of energetic oxygen bombardment of the TiO2 rutile {110} surface is studied by means of molecular dynamics simulations using a variable charge potential. A random selection of O atoms and O2 molecules are incident successively and normally onto the surface. At an energy of 5 eV the surface becomes saturated with oxygen until covered with between 1 and 2 monolayers of adatoms. As the fluence further increases Ti atoms are pulled out from the bulk and become surrounded by the O atoms forming well-defined atomic clusters on the surface which then desorb. At bombardment energies of 400 eV, the O atoms penetrate into the bulk and voids form whose surfaces are decorated with oxygen atoms. As the O fluence further increases the surface is sputtered and the voids then intersect the surface forming a very rough topography.

The irradiation behaviour in two different precipitation hardening types of Ni-base alloys with the ultra high purity grade (EHP), namely, the γ’ type and G phase type was investigated by multi-ion beam techniques simulated to the irradiation conditions in fuel cladding tubes used in sodium cooled FBRs. Single ion-beam irradiation tests were conducted up to 90 dpa (by Fe3+ or Ni3+) at 673 K. Triple ion-beam irradiation tests were conducted up to 90 dpa (by Ni3+, 90 appmHe and 1350 appmH) at 823K. The irradiation behaviour was examined by and the microscopic observation by TEM to the distribution of dislocations, cavities and voids. The behaviour was compared with those of PNC316. The dominating irradiation defects in EHP(γ’) alloy at 673 K by single ion-beam are Frank loops, perfect unfaulted loops and line dislocations. Whereas, those of EHP(WSi) alloy are the irradiation-induced γ’ (Ni3Si) precipitates along {111} planes. Those dominating defect structures at 823 K by triple ion-beam are classified as followings, bimodal distributions in EHP(γ’), bubbles in EHP(WSi) and voids in PNC316. From those results, the excellent irradiation properties of EHP(WSi) alloy is clarified as the inhibition effects of secondary irradiation defects.

The corrosion behavior of three martensitic/ferritic oxide dispersed strengthened (ODS) steels with different chromium contents (respectively 9, 14 and 18wt %) has been studied in hot and concentrated nitric acid. Immersion and electrochemical tests have been carried out in different experimental conditions (temperature and nitric acid concentration). In each case, the corrosion kinetics has been characterized by mass loss measurement of samples (immersion tests) and the electrochemical behavior by linear sweep voltammetry techniques. The dependency of the corrosion rate with the chromium content in the steel, the nitric acid concentration and the temperature, has been quantitatively established and qualitatively discussed.

We report evidence for graphene layer rearrangements in heavy ion interactions with carbon onions at 140 MeV and 70 MeV per nucleon kinetic energies. Graphene layer rearrangements have been recently predicted in spherical and cylindrical multi-layer graphene systems. The implications of graphene layer rearrangement on the tribological performance of multi-layer nano-carbons in extreme environments are discussed.

In advanced nuclear applications, high temperature and a corrosive environment are present in addition to a high dose radiation field causing displacement damage in the material. In recent times it has been shown that Nanostructured Ferritic Alloys (NFA’s) such as advanced Oxide Dispersion Strengthened (ODS) steels are suitable for this environment as they tolerate high dose irradiation without significant changes in microstructure or relevant mechanical properties.

Ion beam irradiation is a fast and cost effective way to induce radiation damage in materials but has limited penetration depth. Therefore, small scale mechanical testing such as nanoindentation and micro compression testing in combination with FIB based sample preparation for micro structural characterization has to be performed allowing a full assessment of the materials’ behavior under radiation environment. In this work two different ODS materials have been irradiated using proton and combined proton and He beams up to 1 dpa at different temperatures. Nanoindentation and LEAP measurements were performed in order to assess the changes in properties of these alloys due to irradiation. The same techniques were applied to intermetallic nanostructured alloys in order to investigate the effectiveness of the metal-intermetallic interface to provide defect sinks for He and radiation damage. It was found that irradiation can cause the formation of intermetallic particles even at room temperature while increasing the material strength significantly.

Mineral samples of varying petrology, exposed to ion irradiation and subsequently immersed in water or exposed to a humid environment, show up to 60% depletion of specific surface atoms (Mg, Ca, K, and Na) — a depletion that is enhanced 26,000x compared to unirradiated surfaces. Surface depletions of irradiated minerals exposed to water were measured using X-ray photoelectron spectroscopy. Irradiations were performed with 4 keV Ar+ ions at fluences from 1014 – 1019 ion cm-2; samples were subsequently exposed to liquid water or humid air (35º C and 70% RH). Analyses were done before irradiation, after irradiation, and after exposure to water, allowing identification of changes in composition due solely to ion irradiation or combined with water exposure. Before water exposure, we observe no significant change in stoichiometry of the minerals for ion fluences <1018 ions cm-2. We find incongruent depletion of 60% Mg for forsterite after exposure to humidity or three minutes (or more) water immersion. Augite undergoes reduction in the surface concentration of approximately 30% Mg, 40% Ca, and 55% Na after 1.9 x 1017 Ar cm-2 and immersion in HPLC water (pH: 6.8) for three minutes. Depth profiles of the irradiated, water exposed, minerals show that the depth of the depleted region is on the order of the ion range, ~15nm. In addition, preliminary results for albite, anorthoclase, and microcline in water show significant depletions of Na, Na and K, and K, respectively, from the mineral surface.

Chemical disorder in ion-irradiated SiC and GaN has been examined by means of transmission electron microscopy. Radial distribution functions obtained by a quantitative analysis of electron diffraction intensities revealed that homonuclear bonds, which do not exist in the crystalline state, are formed in both ion-irradiated specimens. The origin of the homonuclear bonds is quite different between SiC and GaN. The constitute elements mix on the atomic-scale in amorphous SiC, while phase separation induced by irradiation is attributed to the formation of self-bonded Ga atomic pairs in amorphous/nanocrystalline GaN.

The paper presents a rate-independent dislocation growth and defect annihilation mechanism to capture the pre- and post-yield material behavior of FCC metals subjected to different doses of neutron radiation. Based on observation from molecular dynamics simulation and TEM experiments, the developed model is capable of capturing the salient features of irradiation induced hardening including increase in yield stress followed by yield drop and non-zero stress offset from the unirradiated stress-strain curve. The key contribution is a model for the critical resolved slip resistance that depends on both dislocation and defect densities which are governed by evolution equations based on physical observations. The result is an orientation-dependent nonhomogeneous deformation model which accounts for defect annihilation on active slip planes. Results for both single and polycrystalline simulations of OFHC copper are presented and are observed to be in reasonably good agreement with experimental data. Extension of the model to other FCC metals is straightforward and is currently being developed for BCC metals giving its way for generation of new materials.

We present in this text a new experimental tool to study the mixing of atoms under irradiation. Based on physics of x ray diffraction, the specular reflectivy of x ray was used to estimate the Auto Correlation Function associated with the electron density gradient. The accuracy of the ACF is around 1 nanometer and does not evolve with the thickness of the probed layer. Thus, this point allows accurately measuring the broadening of the electron density gradient spreading induced by irradiation. Such an accurate profile extracted over a large range of fluences (about 3 decades) would lead to the determination of the functional dependence of this spreading with the fluence. This could allow pointing out the main mechanisms triggering the atomic mixing over large distances when atomic mixing occurring in thermal spikes is washed out.

Nanostructured ferritic alloys (NFA) are Fe-Cr based ferritic stainless steels containing an ultrahigh density of very stable Y-Ti-O nanofeatures (NFs) that provide dispersion strengthening and radiation damage resistance for candidate Generation IV and future fusion reactor materials. This work is a small and focused part of a larger collaboration to produce large best practice NFA heats. The powders analyzed were rapidly solidified from a melt containing Fe-14%Cr, 3%W, 0.4%Ti and 0.2%Y by gas atomization in Ar, Ar/O, and He atmospheres. Note this represents a different processing path from conventional NFA production where metallic powders are mechanically alloyed with Y2O3 by ball milling. Electron probe microanalysis (EPMA), atom probe tomography (APT), transmission electron microscopy (TEM) and small angle neutron scattering (SANS) were used to characterize the powders in the as-atomized, ball milled and ball milled and annealed conditions. EPMA showed the Y is heterogeneously distributed and phase separated in all the as atomized powders, but attritor milling for 20 to 40 h is required to mix the Y. Milling also creates a significant quantity of O as well as N contamination. Subsequent powder annealing treatments, typically at 1150°C, result in the precipitation of a high density of NFs. All the annealed powder variants show a bimodal grain size distribution, but TEM and APT show NFs in both large and small grains. Reducing O content added during milling of the Ar atomized powders increased the precipitate size and decreased the number density, adversely affecting the hardness.