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Here, we review recent computational findings focused on the behavior of transmutation elements (TEs) in Tungsten (W). W is chosen as one of the most promising materials for the divertor armor and plasma facing components in future fusion reactors. However, W in exposure of fusion neutrons can cause the transmutation reaction and produce TEs, such as rhenium and osmium. The presence of TEs can change chemical component of materials, and therefore inevitably influence the microstructure and properties of W materials. Multiscale simulation methods have been employed to investigate the dissolution, diffusion and radiation induced precipitation of TEs, as well as their effects on the behaviors of hydrogen isotopes in W. This systematic review can provide an insightful understanding to estimate the influence of TEs on the properties and performance of W-based materials. Image 1 • There are strong attractive interactions between TEs and point defects in W. • Interstitial diffusion is the dominating diffusion route for TEs in irradiated W. • The presence of radiation-induced defects will facilitate the aggregation of TEs. • The presence of Re will significantly affect the retention of H in W. [ABSTRACT FROM AUTHOR]

Abstract Detailed analysis was carried out on proton and a neutron irradiated Nb-containing Zr-alloy to study the evolution of dislocation loop size and densities as well as the formation and evolution of irradiation-induced precipitation/clustering. The results obtained here have been contrasted against previously published work on a Nb-free Zr-alloy [1, 2] to investigate the mechanistic reason for the improved resistance to irradiation-induced growth of Nb-containing Zr alloys. The combined use of bright field scanning transmission electron microscopy, ultra-high-resolution energy dispersive spectroscopy and atom probe tomography analysis provides evidence of evenly distributed radiation-induced Nb clusters that have formed during the early stage of proton irradiation and Fe-rich nano-rods near Fe-containing second phase particles. The former seems to have a profound effect on loop and subsequent loop formation, keeping loop size small but number density high while loops seem to initially form at similar dose levels compared to a Nb-free alloy but loop line density does not increase during further irradiation. It is hypothesized that the formation of the Nb nano-precipitates/clusters significantly hinders mobility and growth of loops, resulting in a small size, high number density and limited ability of loops to arrange along basal traces compared to Nb-free Zr-alloys. It is suggested that it is the limited loop arrangement that slows down loop formation and the root cause for the high resistance of Nb-containing Zr-alloys to irradiation-induced growth. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

The current work combines the Cluster Dynamics (CD) technique and CALPHAD-based precipitation modeling to address the second phase precipitation in cold-worked (CW) 316 stainless steels (SS) under irradiation at 300–400 °C. CD provides the radiation enhanced diffusion and dislocation evolution as inputs for the precipitation model. The CALPHAD-based precipitation model treats the nucleation, growth and coarsening of precipitation processes based on classical nucleation theory and evolution equations, and simulates the composition, size and size distribution of precipitate phases. We benchmark the model against available experimental data at fast reactor conditions (9.4 × 10 −7 dpa/s and 390 °C) and then use the model to predict the phase instability of CW 316 SS under light water reactor (LWR) extended life conditions (7 × 10 −8 dpa/s and 275 °C). The model accurately predicts the γ′ (Ni 3 Si) precipitation evolution under fast reactor conditions and that the formation of this phase is dominated by radiation enhanced segregation. The model also predicts a carbide volume fraction that agrees well with available experimental data from a PWR reactor but is much higher than the volume fraction observed in fast reactors. We propose that radiation enhanced dissolution and/or carbon depletion at sinks that occurs at high flux could be the main sources of this inconsistency. The integrated model predicts ∼1.2% volume fraction for carbide and ∼3.0% volume fraction for γ′ for typical CW 316 SS (with 0.054 wt% carbon) under LWR extended life conditions. This work provides valuable insights into the magnitudes and mechanisms of precipitation in irradiated CW 316 SS for nuclear applications. [ABSTRACT FROM AUTHOR]