The expanded compositional freedom afforded by high-entropy alloys (HEAs) represents a unique opportunity for the design of alloys for advanced nuclear applications, in particular for applications where current engineering alloys fall short. This review assesses the work done to date in the field of HEAs for nuclear applications, provides critical insight into the conclusions drawn, and highlights possibilities and challenges for future study. It is found that our understanding of the irradiation responses of HEAs remains in its infancy, and much work is needed in order for our knowledge of any single HEA system to match our understanding of conventional alloys such as austenitic steels. A number of studies have suggested that HEAs possess ‘special’ irradiation damage resistance, although some of the proposed mechanisms, such as those based on sluggish diffusion and lattice distortion, remain somewhat unconvincing (certainly in terms of being universally applicable to all HEAs). Nevertheless, there may be some mechanisms and effects that are uniquely different in HEAs when compared to more conventional alloys, such as the effect that their poor thermal conductivities have on the displacement cascade. Furthermore, the opportunity to tune the compositions of HEAs over a large range to optimise particular irradiation responses could be very powerful, even if the design process remains challenging.

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h i g h l i g h t sDense iodide sodalite prepared by HIP of hydrothermally synthesised powders. Sodalite was free from leachable secondary phases. Leach tests indicate self-arresting congruent dissolution. a b s t r a c tAn iodide sodalite wasteform has been prepared by Hot Isostatic Pressing of powder produced by hydrothermal synthesis. The wasteform was free of leachable secondary phases which can mask leaching mechanisms. Leaching is by congruent dissolution and leach rates decrease as Si and Al accumulate in the leachate. Differential normalised leach rates are 0.005-0.01 g m À2 d À1 during the 7-14 day period. This indicates that sodalite dissolution in natural groundwater, already saturated in these elements, will be very low. Crown

Various two terminal electrode geometry configurations are commonly employed to probe the electrical properties of materials with the key consideration being how current flows through the sample. Here, finite element modeling is used to simulate the dc electrical response of an electrically homogeneous sample (based on single crystal SrTiO3) using two terminal electrode geometries based on full surface, top‐bottom macro‐contacts as is commonly used when characterizing bulk ceramics or large single crystals and top‐bottom and top‐top micro‐contacts that are used to characterize thin films and local intra‐ and inter‐granular regions in ceramics. Well‐known equations for macro‐ and micro‐contacts are used to calculate the conductivity of the sample and are compared to the intrinsic values to determine their accuracy. A geometric factor returns accurate bulk conductivity values when there is homogeneous current flow whereas the spreading resistance equation gives the most accurate conductivity values for heterogeneous current flow. When micro‐contacts are used, the response is dominated by a small region of high current density in the vicinity of the contact, providing local electrical properties. Interference can occur when regions of high current density overlap, providing a less resistive route for current flow, thus reducing the applicability of the spreading resistance equation. For top‐top micro‐contacts at small separations, the conductivity is overestimated. The accuracy of the spreading resistance equation increases as the contact separation increases and is within 10% error when they are separated by eight times the micro‐contact radius. Convergence of the error to values lower than 10% becomes increasingly difficult and requires excessively large (and experimentally challenging) separation distances. For example, to obtain a result with an error below 5% requires separations in excess of 28 times the micro‐contact radius. Confinement occurs when the sample size limits the ability of the current to spread out from a micro‐contact, thus increasing the resistance. As the sample shape and dimensions can limit current flow, a geometric factor can sometimes be used to determine accurate conductivity values. In some cases, interference can counter‐balance confinement to yield fortuitously accurate conductivity values.

A novel multicomponent alloy, V2.5Cr1.2WMoCo0.04, produced from elements expected to favour a BCC crystal structure, and to be suitable for high temperature environments, was fabricated by arc melting and found to exhibit a multiphase dendritic microstructure with W-rich dendrites and V-Cr segregated to the inter-dendritic cores. The as-cast alloy displayed an apparent single-phase XRD pattern. Following heat treatment at 1187 °C for 500 hours the alloy transformed into three different distinct phases -BCC, orthorhombic, and tetragonal in crystal structure. This attests to the BCC crystal structure observed in the as-cast state being metastable. The radiation damage response was investigated through room temperature 5 MeV Au + ion irradiation studies. Metastable as-cast V2.5Cr1.2WMoCo0.04 shows good resistance to radiation induced damage up to 40 displacements per atom (dpa). 96 wt% of the as-cast single-phase BCC crystal structure remained intact, as exhibited by grazing incidence Xray diffraction (GI-XRD) patterns, whilst the remainder of the alloy transformed into an additional BCC crystal structure with a similar lattice parameter. The exceptional phase stability seen here is attributed to a combination of self-healing processes and the BCC structure, rather than a high configurational entropy, as has been suggested for some of these multicomponent "High Entropy Alloy" types. The importance of the stability of metastable high entropy alloy phases for behaviour under irradiation is for the first time highlighted and the findings thus challenge the current understanding of phase stability after irradiation of systems like the HEAs.

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Highlights 60,000 asymptomatic individuals were assessed for SARS-CoV-2 antibody responses Increased Spike IgG correlates with antibody diversity and ACE2 binding inhibition COVID-19 patients had lower antibody responses compared with high asymptomatic responders Individuals can mount diverse immune responses to COVID-19 without symptoms