RADIATION RESISTANT HIGH ENTROPY ALLOYS FOR FAST REACTOR CLADDING APPLICATIONS

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High entropy alloys are a recently developed novel class of materials in which no one element dominates. Instead four or more elements are used in near equal proportions. These alloys have been reported to have a wide range of attractive properties including high strengths at high temperatures, good corrosion resistance and ability to withstand irradiation damage. These properties make HEAs strong candidate materials for use as fuel cladding in sodium cooled fast reactors. These reactors can operate at higher temperatures, using less fuel and are safer than current water and gas cooled reactors.However if HEAs are to be utilised in this highly aggressive environment there are two key needs that must be addressed. The first is to identify promising alloy compositions, manufacture them and characterise their mechanical behaviour. Secondly the mechanisms that lead to the excellent resistance to irradiation damage need to be understood. Through this we will establish whether the irradiation response is universal to all HEAs and devise strategies to predict other potentially better systems to investigate. This grant will use ion irradiations rather than neutrons as ion irradiations are cheaper and faster to carry out and allow for more rapid turn around in alloy development. How the structure of the alloys is changed by irradiation will be studied using advanced microscopy methods and the effect the irradiation has on the mechanical behaviour will be studied using novel micro-mechanical testing methods. Importantly these methods can be used to measure mechanical behaviour at temperatures over 900oC, so the mechanical properties at the operational temperature can be studied in both irradiated and unirradiated conditions. Once the most promising alloys, with the best resistance to irradiation damage, have been identified their resistance to liquid sodium corrosion will be studied. In this way we will develop a novel alloy which can be used as fuel cladding in sodium cooled fast reactors.