High-entropy
ceramics is a new class of materials having a great
potential and wide application. The carbide of Ti, Zr, Hf, Ta, Nb
is a typical member of this group. It has been synthesized mostly
through blending, milling, and high-temperature solid-state reaction
of metal carbide precursors for each metal. This route needs extremely
high temperature (2300 °C), which makes it energy and technology
demanding. We have developed a chemical route for high-entropy carbide
powder that needs a synthetic temperature that is several hundred
degrees Celsius lower. A solution of desired metal citrates with an
excess of citric acid was converted into a metal oxide/active carbon
nanocomposite. Starting from a solution enabled ideal mixing of precursors
on a molecular level, allowing us to skip any milling and blending
steps. The nanocomposite was treated in vacuum at 1600 °C, giving
a phase-pure high-entropy carbide. The intermediate compounds and
products were characterized by means of solid-state analysis.
Iodine release modelling of nuclear fuel pellets has major uncertainties that restrict applications in current fuel performance codes. The uncertainties origin from both the chemical behaviour of iodine in the fuel pellet and the release of different chemical species. The structure of nuclear fuel pellet evolves due to neutron and fission product irradiation, thermo-mechanical loads and fission product chemical interactions. This causes extra challenges for the fuel behaviour modelling. After sufficient amount of irradiation, a new type of structure starts forming at the cylindrical pellet outer edge. The porous structure is called high-burnup structure or rim structure. The effects of high-burnup structure on fuel behaviour become more pronounced with increasing burnup. As the phenomena in the nuclear fuel pellet are diverse, experiments with simulated fuel pellets can help in understanding and limiting the problem at hand. As fission gas or iodine release behaviour from high-burnup structure is not fully understood, the current preliminary study focuses on (i) sintering of porous fuel samples with Cs and I, (ii) measurements of released species during the annealing experiments and (iii) interpretation of the iodine release results with the scope of current fission gas release models.
Graphical abstract
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