Nuclear reaction analysis as a tool for the 3He thermal evolution in Li2TiO3 ceramics

Li2TiO3 ceramic is one of the promising solid breeding candidates for fuel generation in deuterium-tritium Fusion reactors. The Tritium (T) release characteristics consist of a complex combination of gas diffusion stages inside the solid. Considering that this ceramic will produce high concentration of gaseous transmutation products (H-3 and He-4) when exposed to high-energy neutrons, there are considerable interests in studying He-3 thermal evolution for the fundamental understanding of the light ion behavior in breeder blanket materials under reactor conditions. He-3 atoms used to simulate the He-4 incorporation were implanted by a 600 keV ion beam at a fluence of 10(17) at/cm(2) and the He-3(d,alpha)H-1 nuclear reaction analysis (NRA) technique was subsequently used to study depth profiles evolution after different thermal annealing treatments. The release experiments showed that He-3 outgassing is not effective at room temperature, remaining quite negligible till 300 degrees C. After this temperature, the He-3 content in the sample reduces steadily with increasing the annealing temperature, and less than 5% of the initial He-3 concentration was found at 900 degrees C after an isochronal annealing, without significant depth-profile broadening. Scanning and transmission electron microscopies characterization highlight the microstructural changes of the implanted and annealed ceramic within the nuclear cascades zone. The correlation of results obtained by electron microscopy and NRA technique leads to the conclusion that the helium release is governed by a transport mechanism that involves rapid migration/diffusion through interconnected gas cavities and resulting microcracks before reaching grain boundaries and opened pores. (C) 2014 Elsevier B.V. All rights reserved.