Radiation stability of long-term annealed bi-phasic advanced ceramic breeder pebbles
Abstract Advanced ceramic breeder pebbles consisting of Li4SiO4 and additions of Li2TiO3 were tested regarding their long-term thermal and to their radiation stability. As-prepared and long-term annealed pebbles were irradiated with accelerated electrons (up to 6 MGy) to investigate the formation of radiation-induced defects and radiolysis products caused by ionizing radiation. By using Raman spectroscopy the formation of significant amounts of radiolysis products can be excluded. Electron spin resonance spectrometry revealed several paramagnetic radiation-induced defects, such as HC2 centres ( SiO 4 3 - and TiO 3 - ), E’ centres ( SiO 3 3 - and TiO 3 3 - ), Ti 3 + centres and peroxide radi…
Formation and accumulation of radiation-induced defects and radiolysis products in modified lithium orthosilicate pebbles with additions of titanium dioxide
Abstract Lithium orthosilicate (Li4SiO4) pebbles with 2.5 wt.% excess of silicon dioxide (SiO2) are the European Union's designated reference tritium breeding ceramics for the Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM). However, the latest irradiation experiments showed that the reference Li4SiO4 pebbles may crack and form fragments under operation conditions as expected in the HCPB TBM. Therefore, it has been suggested to change the chemical composition of the reference Li4SiO4 pebbles and to add titanium dioxide (TiO2), to obtain lithium metatitanate (Li2TiO3) as a second phase. The aim of this research was to investigate the formation and accumulation of radiation-induced …
Overview of the HCPB Research Activities in EUROfusion
In the framework of the EUROfusion’s Power Plant Physics and Technology, the working package breeding blanket (BB) aims at investigating four different BB concepts for an EU demonstration fusion reactor (DEMO). One of these concepts is the helium-cooled pebble bed (HCPB) BB, which is based on the use of pebble beds of lithiated ternary compounds and Be or beryllides as tritium breeder and multiplier materials, respectively, EUROFER97 as structural steel and He as coolant. This paper aims at giving an overview of the EU HCPB BB Research and Development (R&D) being developed at KIT, in collaboration with Wigner-RCP, BUTE-INT, and CIEMAT. The paper gives an outline of the HCPB BB design evolut…
Radiation-induced effects in neutron- and electron-irradiated lithium silicate ceramic breeder pebbles
Abstract Ceramic breeder (CB) pebbles consisting of lithium orthosilicate (Li4SiO4) as the main phase and lithium metasilicate (Li2SiO3) as a secondary phase were analysed with respect to radiation-induced defects and radiolysis products. Therefore, pebbles that were irradiated with neutrons in the so-called HICU experiment ( H igh neutron fluence i rradiation of pebble sta c ks for f u sion) were compared to pebbles irradiated with accelerated electrons and to an unirradiated sample. Fourier transformation infrared spectroscopy was used to investigate changes in the phase composition. Beside an expected increase in the second phase in the neutron-irradiated samples, no further significant …
Influence of chemisorption products of carbon dioxide and water vapour on radiolysis of tritium breeder
Abstract Lithium orthosilicate pebbles with 2.5 wt% excess of silica are the reference tritium breeding material for the European solid breeder test blanket modules. On the surface of the pebbles chemisorption products of carbon dioxide and water vapour (lithium carbonate and hydroxide) may accumulate during the fabrication process. In this study the influence of the chemisorption products on radiolysis of the pebbles was investigated. Using nanosized lithium orthosilicate powders, factors, which can influence the formation and radiolysis of the chemisorption products, were determined and described as well. The formation of radiation-induced defects and radiolysis products was studied with …
X-ray induced defects in advanced lithium orthosilicate pebbles with additions of lithium metatitanate
Abstract Advanced lithium orthosilicate (Li4SiO4) pebbles with additions of lithium metatitanate (Li2TiO3) as a secondary phase have attracted international attention as an alternative solid-state candidate for the tritium breeding in future nuclear fusion reactors. In this research, the generation of radiation-induced defects in the Li4SiO4 pebbles with various contents of Li2TiO3 was analysed in-situ by X-ray induced luminescence technique. After irradiation with X-rays, the accumulated radiation-induced defects in the Li4SiO4 pebbles were studied by electron spin resonance, thermally stimulated luminescence and absorption spectrometry. On the basis of the obtained results, it is conclude…
Investigation of hydrogen and deuterium impact on the release of tritium from two-phase lithium ceramics under reactor irradiation
In the development of fusion energy, an important task is the study and improvement of tritium production technologies. In this case, one of the most promising materials for tritium generation is lithium ceramics. Considering the importance of the task, numerous studies are aimed at solving the problem of determining the parameters and mechanisms of tritium release in lithium-containing materials. This paper presents the results of a study of tritium release processes from two-phase lithium ceramics of Li$_{4}$SiO$_{4}$/Li$_{2}$TiO$_{3}$ during reactor irradiation when hydrogen and deuterium are injected into the chamber with irradiated samples. The mechanisms regularities of the tritium yi…