Luminescence of X-ray induced radiation defects in modified lithium orthosilicate pebbles with additions of titanium dioxide (original) (raw)
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Fusion Engineering and Design, 1991
Formation and properties of radiation-induced defects and radiolysis products in polycrystaUine powders and ceramic pellets of Li4SiO 4 were studied under the effect of various types of ionizing irradiation (~/quants, accelerated electrons, reactor irradiation), humidity, temperature, impurities in the samples, etc. The content of radiation defects and radiolysis products poorly depends on irradiation type, dose rate, admixture elements. The concentration of defects highly depends on the temperature of irradiation, humidity, granural size. Empirical dependence of radiolysis degree a on the dose was found: a= 5×10-2 × D °5 for "y and electron irradiation (Tra d = 300-350 K) and a = 5×10-3 × D °5 for reactor radiation (Tra d = 700-800 K); a-matrix dissociation degree (in %); D-dose (in MGy). Colloidal litium and silicon, lithium and silicon oxides, and O 2 are the final products of radiolysis. Radiation-induced defects change tritium thermo-extraction parameters, deteriorate mechanical, thermo-physical and electric properties of ceramics.
Fusion Engineering and Design
h i g h l i g h t s • Irradiation temperature affects accumulation of radiation-induced defects (RD) and radiolysis products (RP). • With an increasing content of Li2 TO3 in the advanced pebbles, the concentration of accumulated RD and RP decreases. • The accumulated RD and RP annihilates around 423-773 K. • Mechanical properties of the advanced pebbles practically do not change after irradiation. Advanced lithium orthosilicate (Li4 SiO4) pebbles with additions of lithium metatitanate (Li2 TiO3) as a secondary phase are suggested as a potential source for tritium breeding in future nuclear fusion reactors. The advanced Li4 SiO4 pebbles with different contents of Li2 TiO3 were examined before and after simultaneous action of 5 MeV accelerated electron beam (dose rate: up to 10 MGy h −1) and high temperature (up to 1120 K) in a dry argon atmosphere. The accumulated radiation-induced defects (RD) and radiolysis products (RP) were studied by electron spin resonance (ESR) spectrometry and thermally stimulated luminescence (TSL) technique. The phase transitions were studied with powder X-ray diffraction (p-XRD). The microstructure and mechanical strength of the pebbles, before and after irradiation, were investigated by scanning electron microscopy (SEM) and comprehensive crush load tests. The obtained results revealed that the irradiation temperature has a significant impact on the accumulation of RD and RP in the advanced Li4 SiO4 pebbles, and with an increasing content of Li2 TiO3 , the concentration of accumulated paramagnetic RD and RP decreases. Major changes in the mechanical strength, microstructure and phase composition of the advanced pebbles were not detected after irradiation.
Low-temperature irradiation effects in lithium orthosilicates
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006
The emission spectra of lithium orthosilicates (Li 4 SiO 4) ceramics have been measured in the range of 1.8-5.8 eV under irradiation by 6-30 eV photons or 1-30 keV electrons at 6-300 K. The tunnel recombination phosphorescence, as well as luminescence, stimulated by 1.5-2.5 eV photons has been detected in the sample preliminarily irradiated at 6 or 80 K. The main peaks of thermally stimulated luminescence (TSL) in the irradiated ceramics have been observed at 72, 118 and 265 K. The creation spectra of the 118 K TSL peak, as well as the excitation spectrum of photostimulated luminescence (PSL) span the region of the intrinsic absorption of a lithium orthosilicate (9-30 eV). The intensity of PSL and the TSL peaks in Li 4 SiO 4 ceramics prepared in hydrogen/argon atmosphere is several times lower than that in the mainly investigated Li 4 SiO 4 ceramics prepared in the atmosphere of dry argon. The optical characteristics of Li 4 SiO 4 are compared with the ones known for Li 2 O and SiO 2 . Low-temperature luminescent methods are promising for the investigation of electron-hole processes and radiation defects serving as the traps for tritium released in D-T fusion reactor blanket systems.
Ceramics for fusion reactors: The role of the lithium orthosilicate as breeder
Physica B: Condensed Matter, 2012
Lithium-based oxide ceramics are studied as breeder blanket materials for the controlled thermonuclear reactors (CTR). Lithium orthosilicate (Li 4 SiO 4) is one of the most promising candidates because of its lithium concentration (0.54 g/cm 3), its high melting temperature (1523 K) and its excellent tritium release behavior. It is reported that the diffusion of tritium is closely related to that of lithium, so it is possible to find an indirect measure of the trend of tritium studying the diffusivity of Li þ. In the present work, the synthesis of the Li 4 SiO 4 is carried out by Spray drying followed by pyrolysis. The study of the Li þ ion diffusion on the sintered bodies, is investigated by means of electrical conductivity measurements. The effect of the gray irradiation is evaluated by the impedance spectroscopy method (EIS) from room temperature to 1173 K. The results indicate that the síntesis process employed can produce Li 4 SiO 4 in the form of pebbles, finally the best ion species for the electrical conduction is the Li þ and is shown that the g-irradiation to a dose of 5MGy, facilitate its mobility through the creation of defects, without change in its conduction process.
2018
Several materials have been developed and being investigated for reliable and sustainable breeder candidate material. Lithium meta-titanate (Li2TiO3) and Lithium ortho-silicate (Li4SiO4) are the prominent among the suitable candidate materials for tritium breeders. Indian Lead-Lithium cooled Ceramic Breeder (LLCB) is one of the tritium breeding blanket concept in which Li2TiO3is proposed as the tritium breeder materials in the form of pebble bed for LLCB TBM. Li2TiO3 power was prepared by solid state reaction using LiCO3 and TiO2 followed by ball-milling and calcination. Li2TiO3 pellets and pebbles are prepared from this powder followed by high temperature sintering. Effect of sintering time and temperature on the properties of pebbles has been studied. At every stage of preparation, extensive characterizations are being carried out to meet the desired properties of these materials. The geometry and loading conditions of the breeder blankets makes the analysis complex. For a robust ...
2017
Lithium based ceramics such as Lithium Titanate (Li2TiO3), Lithium Orthosilicate (Li4SiO4) and Lithium Zirconate (Li2ZrO3) are promising solid breeder materials used in the Test Blanket Module (TBM) for the extraction of tritium. These breeders should have good thermal properties especially thermal conductivity as well as good tritium breeding characteristics. The thermal properties of tritium breeders are important for the blanket design. The tritium breeding reaction occurring in the pebble bed is an exothermic reaction liberating a large amount of heat. Thus generated heat is transmitted through the packed pebble bed. With the increase in temperature of the pebble bed the tritium breeding ratio decreases. As a result heat produced must be effectively removed from the pebble bed in order to maintain the required tritium breeding ratio. This can be achieved if the thermal conductivity and heat transfer of the packed bed is high. In this study the pebbles of Li2TiO3, Li4SiO4, LiO2 a...
Ceramics International, 2019
A novel mass production method of lithium titanite (Li 2 TiO 3) tritium breeder ceramic pebbles using polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) assisted granulation method (APG) was proposed. A binder solution of polyvinyl alcohol (PVA) was used to modify the Li 2 TiO 3 precursor powder. The powders with adhesive properties were prilled to form green pebbles (GPs) by spheronization at a low rotation speed and spraying with polyvinyl pyrrolidone (PVP), in several cycles. Then, the density and the crush load of the GPs were improved by high-speed rolling. Finally, the ceramic pebbles were produced by sintering. The phase, the microstructure, and the crush load of the ceramic pebbles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and with a universal tester, respectively.
Tritium localisation and release from the ceramic pebbles of breeder
Journal of Nuclear Materials, 2004
Magnetic field (MF) effects on the radiolysis and tritium release from Li 4 SiO 4 (FZK) and Li 2 TiO 3 (CEA) ceramic pebbles were investigated. The tritium chemical forms in Li 4 SiO 4 were estimated by means of lyomethods. In the case of the neutron fluence F n 6 10 18 n m À2 , the tritium is mostly in the T þ form, but in the case of F n % 10 25 n m À2 , the T þ form accounts for 86-95% of the tritium. A high subsurface concentration of tritium is characteristic of a separate pebble and correlates with the distribution of radiation-induced defects. The MF increases the radiolysis of Li 4 SiO 4 by 20-25%. Irradiation with electrons to 1000 MGy at 1200 K increases the grain size by 5-10%, decreasing the parameters of tritium release. The increased grain size was observed for the Li 4 SiO 4 pebbles irradiated in EXOTIC-8. A considerable tritium detention (up to 40%) was observed after annealing to 1120 K in the MF of 2.4 T.