Simulation of evolving thermal conductivity in lithium ceramic breeder materials for nuclear fusion

Sanjeev, Megha and Murphy, Samuel (2024) Simulation of evolving thermal conductivity in lithium ceramic breeder materials for nuclear fusion. PhD thesis, Lancaster University.

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Abstract

The effect of defects on heat transfer through plasma facing components must be predicted in order to make decisions about the materials which will be chosen and estimate their potential lifespan. The breeder blanket is particularly important for its three essential jobs: breed tritium in situ, defend the more fragile reactor components, and effectively transfer heat for eventual electricity generation. The thermal conductivity is a measure of the effectiveness of heat transfer through a material and can be calculated using atomistic simulation methods. This work focuses on a leading ceramic breeder material, Li2TiO3. It is expected that the inevitable radiation damage to the breeder blanket from the high-energy neutrons escaping the fusion plasma will affect heat transfer in the material. In this thesis, the high anisotropy in the thermal conductivity of Li2TiO3 is shown, with the z-directions displaying much lower thermal conductivity than x or y. The mechanisms for accommodating non-stoichiometry in Li2TiO3 are investigated, and its effect on the thermal conductivity in scenarios of 1% Li excess and 1% Li loss. It is found that while there is a significant decrease in the thermal conductivity at room temperature, at higher temperatures the impact of deviations from stoichiometry is limited. The effect of voids and porosity is investigated, predicting that increasing porosity leads to a decrease in thermal conductivity. This is in good agreement with previous experimental observations. However, we do no observe the increase in thermal conductivity at high temperatures that is observed in some experiments. Therefore, we argue that this increase is a consequence of sintering or some other modification of the experimental sample rather than a fundamental change in the heat conduction mechanism in the crystal matrix. From these results we hope to contribute to estimates on the lifetime of a Li2TiO3 breeder blanket.