Speaker
Description
Qiang Qi1,2*, Shouxi Gu1, Yingchun Zhang3, Hai-Shan Zhou1,2, Guang-Nan Luo1,2
1Institute of Plasma Physics, Hefei Institutes of Physical Sciences, Chinese Academy of Sciences, Hefei, 230031, China
2Science Island Branch, Graduate School of USTC, Hefei, 230036, China
3School of Materials Science and Engineering, University of Science and Technology Beijing, 30 Xueyuan Road, Haidian District, Beijing 100083, PR China
Lithium-based ceramic tritium breeders are key materials for fusion blankets, producing tritium by neutron-induced lithium transmutation. These pebbles must endure long-term high temperature service in fusion conditions, and their microstructural and property changes impact safety and tritium self-sufficiency.
This work examines the microstructural, phase, and compositional changes in Li4SiO4 pebbles after annealing at 900°C in a 0.1 H2/He atmosphere for various durations, and their effects on deuterium release behavior. Initially, Li4SiO4 pebbles contain Li4SiO4, Li2SiO3, and Li2CO3 phases. Annealing eliminates the Li2CO3 phase, but minor reformation occurs due to CO2 absorption during sampling and storage. Significant oxygen and lithium loss during annealing is undesirable, as it affects tritium breeding and may cause safety issues by blocking gas flow and corroding structural materials. Grain growth and pore coalescence also occur, degrading mechanical performance.
Surprisingly, despite expectations, deuterium release behavior does not deteriorate after 1000 h of annealing. The transformation of closed pores to open pores likely promotes the shift of deuterium release peaks to lower temperatures. The distinct deuterium release behavior between virgin and annealed pebbles is mainly due to carbonate impurities. The high-temperature HDO release peak at 665°C in virgin pebbles is attributed to Li2CO3 decomposition. Drying Li4SiO4 pebbles at 700°C for several hours to remove carbonate impurities is recommended before application. Further neutron irradiation experiments are needed to evaluate tritium release behavior.
