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[en] In the temperature range from room temperature to 973 K and the mechanical loading range from 0.1 to 3 MPa, a Li2TiO3 pebble bed was successively loaded and the packing behaviour of the bed was observed. Deformation caused by the mechanical loading is partly relaxed when the bed is heated without the load. After a large numbers of thermal and mechanical loading cycles, the packing factor of the bed increased from the initial packing factor of 66.9% to finally about 68.5%. This progressive increase in packing leads to production of a cavity region at the top of the pebble bed, therefore it is important to obtain a high initial packing factor.
[en] A tritium release model has been developed by the present authors. The tritium release curves estimated by this tritium model give good agreement with experimental curves for Li 4SiO4, Li2TiO3, Li2ZrO3 or LiAlO2 under various purge gas conditions in our out-of-pile bred tritium release. The characteristics of tritium release behavior from various solid breeder materials carried out by us and in EXOTIC experiments at Petten are discussed in this study. (authors)
[en] In the previous blanket neutronics experiments conducted at the FNS facility of Japan Atomic Energy Agency, the following disagreements between experiments and analyses have been pointed out: (1) in the experiment with a 6Li-enriched Li2TiO3 layer and a beryllium layer, the calculation was found to overestimate the tritium production rate (TPR) by approximately 10% when a neutron source reflector composed of SS316 was attached. (2) In the experiment with natural Li2O pebbles sandwiched by beryllium layers, TPR near the rear beryllium layer was overestimated by up to 10%. In order to identify the cause of the above problems clearly, a new blanket neutronics experiment with DT neutrons using natural Li2TiO3 layer and beryllium layers was conducted at FNS. TPR distributions inside the natural Li2TiO3 layer in assemblies with and without the source reflector were measured with Li2CO3 pellets. The measured TPR agreed well with the calculations within 6% in both assemblies. The influence of the reflector and beryllium on TPR prediction accuracy was not seen in the present experiment.
[en] Nano-indentation testing is used to evaluate the mechanical properties of materials with limited size and of thin coatings. The indentation depth is the prime parameter which is measured to evaluate the hardness and modulus. The materials generally used for this technique are dense and pore free. Of late, attempts are being made to extend the nanoindentation technique to evaluate the properties of porous materials. In this work, nanoindentation technique is employed to investigate the bulk mechanical properties of LiTiO3 with low pore fraction. Here, the number of pores in the indentation volume is made to vary by varying the indentation load and the relevant mechanical properties are estimated by conventional analysis
[en] The irradiation experiment EXOTIC 9/1 is the latest in a series of EXOTICs that has been irradiated in the high flux reactor in Petten and studies tritium release and inventory in ceramic pebbles containing lithium, which are key properties for the fusion fuel cycle. New production routes of pebbles are developed, leading to different thermomechanical and tritium release properties. The pebbles, produced by an extrusion-spheroidisation-sintering process at CEA in 2004, differ in porosity and density from the Li2TiO3 ceramics tested in the previous EXOTIC 8 programme. The pebbles have a diameter in the range from 0.6 to 0.8 mm, a high density (93% TD) and an open porosity of 1.7%. The pebbles mainly differ in enrichment (7.5% and 30% 6Li-enrichment). During irradiation of 300 Full Power Days in the HFR in Petten, the temperature in EXOTIC 9/1 was varied between 340 and 580 deg. C. The final irradiation (EOL) temperature is 480 deg. C and the average total 6Li burn-up is 3%. The total measured activity from tritium during irradiation is 220.42 Ci. After the completion of the irradiation, the out of pile release behaviour was studied by temperature programmed desorption (TPD). More specifically, the remaining tritium inventory in the pebbles and the activation energy of different release mechanisms were studied. The TPD was carried out for Li2TiO3 samples with 7.5% (natural) and 30% (enriched) 6Li-abundance and revealed very different curves, indicating that the materials have different release mechanisms. Dissolving the irradiated samples in hydrogen peroxide indicates that no tritium is left in the pebbles after TPD. Results from optical microscopy show it is likely that more intense bubble formation has taken place in the enriched samples, compared to the natural samples.
[en] The description of algorithm to design in-pipe experimental ampoule devices (IPAD) is presented here, including description of IPAD design for irradiation tests of highly enriched lithium ceramics at WWR-K reactor. The description of the system for registration of tritium release from ceramics during irradiation is presented as well. Typical curve of tritium release from the IPAD during irradiation under various temperatures of the samples is shown here
[en] Li2Ti3−xVxO7 and Li4Ti5−xVxO12 (x = 0–0.1) are successfully fabricated using the conventional solid-state reaction technique. The battery performance of the cells showed that the highest capacity of Li2Ti3−xVxO7 was obtained for the sample of x = 0.025 which has 153 mAh/g and 123 mAh/g for 1 and 1000, respectively. In addition to this, the best capacity of the cell of Li4Ti4.5V0.5O12 was found as 202 mAh/g for the first cycle and it was decreased to 194 mAh/g for 1000 cycles. To understand the capacity fade mechanism, we performed ex situ structural experiments and it is found that the unit cell of the crystalline phase is directly affected to battery performance. We concluded that in this study the V-substituted samples have a potential for next-generation battery fabrication since it may cause the increase of the stability of the cells.
[en] Medium sized spherical particles of Li2TiO3 (with diameters below 100 μm) can be prepared from peroxy lithium titanate solution (stabilized with citric acid) by a modified INCT (Institute of Nuclear Chemistry and Technology) variant of the sol-gel process. The process consists of the following main steps: (I) formation of aqueous phase emulsion in 2-ethylhexanol-1; (II) gelation of emulsion drops by extraction of water with partially dehydrated EH; (III) filtration and washing with carbon tetrachloride or acetone; (IV) non-destructive thermal treatment. The medium size particles can be used for increasing pebble bed density by infiltration them into bed larger spheres (1 mm diameter). The tritium release from sol-gel process preparation of Li2TiO3 microspheres was found very close to that observed for other traditional material however, the new process is more efficient than other processes because of the morphology of the sintered specimens.
[en] Lithium titanate (Li2TiO3) is one of the most promising candidates among tritium breeding materials because of its good tritium release characteristics. However, the mass of Li2TiO3 decreased with time by Li evaporation in a hydrogen atmosphere and by Li burn-up. In order to prevent the mass decrease at high temperatures, Li2TiO3 with added Li (Li2+xTiO3+y) have been developed as one of advanced tritium breeders. Li2TiO3 with added Li was synthesized from proportionally mixed LiOH.H2O and H2TiO3 with a Li/Ti ratio of 2.2, and then the sol-gel method were selected as the candidate for the pebble fabrication technique of advanced tritium breeders. In this study, trial fabrication of pebbles was performed by the sol-gel method. The diameter of the pebbles is 1.18 mm, and the sphericity is 1.04. The density of the pebbles is about 89%T.D analyzed by mercury intrusion technique. Molar ratio (Li/Ti) of the sintered pebbles evaluated by inductively coupled plasma atomic emission spectrometry (ICP-AES) is 2.12. These results show that the pebble fabrication using the sol-gel method is a promising production technique for mass production of the advanced tritium breeder pebbles.
[en] Highlights: • Silica excess in the lithium orthosilicate favors the formation of vitreous corrosion layers that adhere to the Eurofer and passive it. • Lithium titanate produces corrosion layers of oxidic-like that do not protect the Eurofer. • The addition of a small proportion of water to the purge gas produces a slight increase in corrosion. - Abstract: Advanced lithium-rich ceramic materials are under consideration for the helium cooled pebble-bed breeder unit prototype in ITER. Although chemical compatibility issues with reduced activation steels have in general been associated with liquid breeders, corrosion has also been observed to be produced by some solid compositions under specific conditions. In this work, the mechanisms including the corrosion process considering different lithium ceramics (lithium orthosilicate and lithium metatitanate) are examined, together with the influence of temperature and exposure time. The effect of the composition of the purge gas, intended for tritium extraction, is also evaluated. Corrosion in Eurofer was found to severely occur for metatitanate composition, where temperature plays a major role. Corrosion in Eurofer is produced all over the sample (out of contact areas), as a consequence of the gas swept.