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Irradiation increases the yield stress and embrittles light water reactor (LWR) pressure vessel steels. In this study, we demonstrate some of the potential benefits and risks of using machine learning models to predict irradiation hardening extrapolated to low flux, high fluence, extended life conditions. The machine learning training data included the Irradiation Variable for lower flux irradiations up to an intermediate fluence, plus the Belgian Reactor 2 and Advanced Test Reactor 1 for very high flux irradiations, up to very high fluence. Notably, the machine learning model predictions for the high fluence, intermediate flux Advanced Test Reactor 2 irradiations are superior to extrapolations of existing hardening models. The successful extrapolations showed that machine learning models are capable of capturing key intermediate flux effects at high fluence. Similar approaches, applied to expanded databases, could be used to predict hardening in LWRs under life-extension conditions. [ABSTRACT FROM AUTHOR]

Microstructural evolutions in two variants of the F82H 8 wt%Cr tempered martensitic steel under dual (He+ plus Fe3+) ion irradiations at 500 °C have been characterized by transmission electron microscopy. Emphasis is on understanding the combined effects of displacements per atom (dpa) and the helium/dpa ratio (He/dpa) on cavity evolution and void swelling (f v). The dual ion database includes 231 alloy-dpa-He/dpa conditions for irradiations up to ∼ 82 dpa and 3700 appm helium. We hypothesize that the large "scatter" observed in the f v data is primarily due to local microstructural variations, especially those that shield regions at shallower depths from the effects of injected interstitial atoms, which would otherwise reduce f v. More generally, our hypothesis is that the highest f v data, at a specified dpa and He/dpa, provides the most appropriate estimate of swelling for fusion neutron irradiation conditions. The dose dependence of f v can be described by an incubation dpa i , marking the onset of significant void growth, and a post-incubation swelling rate, f v ' = Δf v /Δdpa. Both dpa i and f v ' decrease with increasing He/dpa. The f v ' data are quantitatively consistent with a simple model for defect partitioning between evolving bubble, void, and dislocation sinks strengths and biases. Most notably, the model correctly predicts both the incubation dpa i , and the subsequent f v ', in spite of the fact that they reflect somewhat different physics. Our analysis also suggests that defect recombination is modest at 500 °C. Along with other considerations, this supports the hypothesis that, even at high dpa rates, dual ion irradiations can be used to reasonably emulate void nucleation and growth for a range of fusion-relevant neutron irradiation service conditions. A companion paper incorporates the results of this study in a reduced-order, data-driven void swelling model. [ABSTRACT FROM AUTHOR]

Recent trends in the aluminum industry toward increasing the recycling rate of aluminum alloys have led to difficulties in controlling the formation of intermetallic compounds (IMCs). The up-to-date investigations have revealed that ultrasonic irradiation is a promising tool to refine and modify the intermetallic compounds formed in the melt before or during casting, and the reported mechanisms include ultrasound-assisted nucleation and fragmentation of compounds. This work presents results concerning the modification effect of ultrasound on model Al 3 Zr compounds with emphasis on the effect of vibration amplitudes. The results reveal that needle-like Al 3 Zr compounds can be significantly modified to thicker shape when amplitude increases from 38 µm to 48 µm, and then change to more rounded shape with the further increase of amplitude. Theoretical consideration and numerical simulation show that in addition to the above-mentioned mechanisms, cavitation-induced heat generation and mircrojet-driven mass transfer are also of prime importance in controlling the morphology and growth of IMCs. • A wide range of ultrasound vibration amplitude is examined. • Needle-like Al 3 Zr compounds can be significantly modified to more rounded shape when amplitude increases. • Behavior of cavitation bubble near compound particle is simulated numerically. • Cavitation-induced heat generation and microjet-driven mass transfer play a prominent role in controlling the morphology and growth of primary Al 3 Zr compounds. [ABSTRACT FROM AUTHOR]

In epithelia, tight junctions (TJs) create a primary barrier to the diffusion of solutes through the paracellular pathway. Although TJ-related molecules are present in the epidermis, the precise mechanisms underlying TJ functions in this tissue remain unclear. In this study, we use an ultraviolet (UV) B-irradiated murine skin model, in which the epidermal barrier function has been perturbed, to demonstrate a correlation between the expression patterns of TJ-related molecules and the epidermal permeability of TJs. Occludin remained localized in the upper epidermis, regardless of UVB irradiation (0.15 J per cm2). ZO-1 was localized in the upper portion of normal epidermis, and within 3–4 days of UVB irradiation, it was expressed throughout the upper epidermis and their expression coincided with epidermal thickening. Protein expression of claudin-1 and occludin did not alter until 3 and 4 days after UVB irradiation, respectively and thereafter expression remained elevated above pre-irradiation levels. An in vivo epidermal permeability assay revealed that tight junction-barrier function was perturbed by UVB irradiation, whereby biotinylated markers clearly permeated the stratum granulosum 3–5 days after irradiation. These results suggest that TJ-related molecules play important roles in epidermal barrier function in murine skin and show that changes in their expression patterns are associated with epidermal barrier perturbation after UVB irradiation. Specifically, it appears that epidermal barrier recovery is accelerated by the increased production and dense localization of occludin in the cell–cell contact region of the stratum granulosum. [ABSTRACT FROM AUTHOR]

Abstract: Data on irradiation hardening and embrittlement of 8–10Cr normalized and tempered martensitic steel (TMS) alloys has been compiled from the literature, including results from neutron, spallation proton (SP) and He-ion (HI) irradiations. Limitations of this database are briefly described. Simple, phenomenological–empirical fitting models were used to assess the dose (displacement-per-atom, dpa), irradiation temperature (T i) and test temperature (T t) dependence of yield stress changes (Δσ y), as well as the corresponding dependence of sub-sized Charpy V-notch impact test transition temperature shifts (ΔT c). The Δσ y are generally similar for SP and neutron irradiations, with very high and low helium to dpa ratios, respectively. Further, the Δσ y trends were found to be remarkably consistent with the T i and dpa hardening-dependence of low alloy steels irradiated at much lower doses. The similar T i and (low) dose dependence of Δσ y and ΔT c, as well as an analysis of paired ΔT c–Δσ y datasets, show that embrittlement is typically dominated by a hardening mechanism below about 400°C. However, the corresponding hardening-Charpy shift coefficient, C c =ΔT c/Δσ y ≈0.38±0.18°C/MPa is lower than that for the fracture toughness reference temperature, T 0, with ΔT 0/Δσ y ≈0.58±0.1°C/MPa, indicating that sub-sized Charpy tests provide non-conservative estimates of embrittlement. The C c increases at T i >400°C, and ΔT c >0 are sometimes observed in association with Δσ y ⩽0, indicative of a non-hardening embrittlement (NHE) contribution. Analysis of limited data on embrittlement due to thermal aging supports this conclusion, and we hypothesize that the NHE regime may be shifted to lower temperatures by radiation enhanced diffusion. Possible effects of helium on embrittlement for T i between 300 and 400°C are also assessed based on observed trends in C c. The available data is limited, scattered, and potentially confounded. However, collectively the database suggests that there is a minimal NHE due to helium up to several hundred appm. However, a contribution of helium to NHE appears to emerge at higher helium concentrations, estimated to be more than 400–600appm. This is accompanied by a transition from transgranular cleavage (TGC) to intergranular fracture (IGF). IGF generally occurs only at high Δσ y. Synergistic combinations of large Δσ y and severe NHE, due to helium weakening of grain boundaries, could lead to very large transition temperature shifts in first wall and blanket structures at fusion spectrum dose levels above 50–75dpa and in SP irradiations at much lower doses. [Copyright &y& Elsevier]

Precipitation of α′ in Fe Cr alloys under neutron irradiation is thermodynamically driven while being accelerated by radiation-enhanced diffusion. However, similar alloys under ion irradiation at high dose rates (> 10 − 4 dpa/s) fail to exhibit α′ precipitation. Here, the microstructure of an Fe 18Cr alloy under ion or neutron-irradiation at 300 °C at dose rates from ~ 10 − 7 to 10 − 4 dpa/s was analyzed by atom probe tomography. The steady-state composition content of the clusters depends on the ion irradiation dose and dose rate, confirming the contribution of ballistic mixing in diluting the Cr concentration in non-equilibrium α′ precipitates. [ABSTRACT FROM AUTHOR]

Irradiation effects are studied using accelerated-damage experiments in test reactors and charged-particle accelerator facilities. Neutrons and ions create vacancy and self-interstitial defects, in dose unit of displacements per atom (dpa). It is important to understand the effects of irradiation dose rate on microstructural evolution processes, including irradiation enhanced precipitation, to properly interpret results from experiments using accelerated-damage experiments. Here we report on precipitation in Fe-Cu and Fe-Cu-Mn model alloys irradiated at dose rates ranging from ∼10 −10 dpa/s (neutrons) to ∼10 −5 dpa/s (70 MeV Fe ions). Atom probe tomography, small angle neutron scattering, and rate theory models show that precipitation is affected by both dose rate and alloy composition. Higher dose rates: 1) decrease the efficiency of radiation enhanced diffusion, due to increased vacancy-self interstitial recombination; and, 2) increase the rate of ballistic mixing that partly dissolves the precipitate constituents. The key parameter is the rate of ballistic mixing relative to the rate that solutes are reacquired by diffusion. The Mn in the ternary alloy traps vacancies and enhances recombination, leading to very different precipitate evolution kinetics. [ABSTRACT FROM AUTHOR]

Ferritic-martensitic steels are leading candidates for many nuclear energy applications. However, formation of nanoscale α′ precipitates during thermal aging at temperatures above 450 °C, or during neutron irradiation at lower temperatures, makes these Fe-Cr steels susceptible to embrittlement. To complement the existing literature, a series of Fe-9 to 18 Cr alloys were neutron-irradiated at temperatures between 320 and 455 °C up to doses of 20 dpa. In addition, post-irradiation annealing treatments at 500 and 600 °C were performed on a neutron-irradiated Fe-18 Cr alloy to validate the α-α′ phase boundary. The microstructures were characterized using atom probe tomography and the results were analyzed in light of the existing literature. Under neutron irradiation and thermal annealing, the measured α′ concentrations ranged from ∼81 to 96 at.% Cr, as influenced by temperature, precipitate size, technique artifacts, and, possibly, cascade ballistic mixing. [ABSTRACT FROM AUTHOR]

An investigation of the influence of helium on damage evolution under neutron irradiation of an 11 at% Al, 19 at% Cr ODS ferritic PM2000 alloy was carried out in the High Flux Isotope Reactor (HFIR) using a novel in situ helium injection (ISHI) technique. Helium was injected into adjacent TEM discs from thermal neutron 58 Ni(n th ,γ) 59 Ni(n th ,α) reactions in a thin NiAl layer. The PM2000 undergoes concurrent displacement damage from the high-energy neutrons. The ISHI technique allows direct comparisons of regions with and without high concentrations of helium since only the side coated with the NiAl experiences helium injection. The corresponding microstructural and microchemical evolutions were characterized using both conventional and scanning transmission electron microscopy techniques. The evolutions observed include formation of dislocation loops and associated helium bubbles, precipitation of a variety of phases, amorphization of the Al 2 YO 3 oxides (which also variously contained internal voids), and several manifestations of solute segregation. Notably, high concentrations of helium had a significant effect on many of these diverse phenomena. These results on PM2000 are compared and contrasted to the evolution of so-called nanostructured ferritic alloys (NFA). [ABSTRACT FROM AUTHOR]