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Lithium titanate ( Li 2 TiO 3 ) was synthesized; without and with excess lithium (Li) in quantity of its stoichiometric requirement, with 5, 10, 15 and 20% excess and pebbles were fabricated by Solid State Reaction Process (SSRP). The green pebbles were sintered at 900 °C for 6 h . XRD analysis of the synthesized powders, confirmed the formation of single phase Li 2 TiO 3 , when 0–10% excess of lithium; compared to the stoichiometric requirement; were used and the presence of multiple phases when more than 10% excess lithium were used. Morphological modifications of mesoscopic structure in Li 2 TiO 3 pebbles with different quantities of excess lithium were investigated using Ultra-Small Angle Neutron Scattering (USANS) and Scanning Electron Microscopy (SEM). USANS measurements reveal the presence of sub-micrometric pores of size about 750 nm. From the experiments it was observed that addition of 10% of excess Li in Li 2 TiO 3 is the optimum for the Li 2 TiO 3 pebbles, in which all the desired properties remain within desired limit, without any compromise of properties of Li 2 TiO 3 pebbles. [ABSTRACT FROM AUTHOR]

Lithium titanate (Li2TiO3) and lithium orthosilicate (Li4SiO4) are the promising solid breeder materials for the fusion reactors. Packed bed of Li2TiO3or Li4SiO4pebbles is considered in the fusion reactor blanket for in situ production of tritium and for this a good effective thermal conductivity of the pebble bed is necessary. In recent past, Mandalet al.[26] studied the hydrodynamics and heat transfer properties of bed of lithium titanate pebbles at different operating conditions viz., gas flow rates, pebble sizes, bed wall temperatures, etc. In the present study laminar,k – εand low Reynoldsk – εmodel have been used to simulate the hydrodynamics and heat transfer data of Li2TiO3pebble bed. The computational fluid dynamics (CFD)-simulated hydrodynamics results have been compared with hydrodynamics and heat transfer results of bed of Li2TiO3pebbles reported by Mandal et al. [26] and others. It was found thatk – εand low Reynolds numberk – εmodel shows better agreement with experimental results. The CFD study were carried out using low Reynoldsk – εmodel for pebble bed of different materials viz. Li2TiO3, Li4SiO4and alumina (Al2O3). The effect of flow rate, pebble size, wall temperature, solid properties viz. thermal conductivity and specific heat on effective thermal conductivity and overall heat transfer coefficient has been discussed in this paper. [ABSTRACT FROM AUTHOR]

Abstract: Packed fluidization is a novel technique, in which small particles are allowed to fluidize in the interstices of relatively large and stationary packing to enhance heat transfer rates of a unary packed bed of same size pebbles. In the present study, heat transfer in unary packed bed and binary packed fluidized bed were investigated and compared in terms of the effective thermal conductivity. In the experimental works, large pebbles (size: 3–10mm) of two different materials viz. lithium titanate and alumina and small particles (size: 231–780μm), also of two different materials viz., lithium titanate and silica were used. It was found that the heat transfer in unary packed bed is enhanced due to the packed fluidization and in terms of the effective thermal conductivity; the enhancement was up to 260%. It was found that the volume fraction of small particles, operating gas velocity, particle to pebble size ratio and the type of materials have a significant effect in enhancing the effective thermal conductivity and heat transfer rates. It was also found that 60% (v/v) of small particles in the interstitial voids of packing pebbles can give much improved effective thermal conductivity keeping all other operating parameters same. Possible mechanism for heat transfer enhancement due to packed fluidization has been proposed. Based on the results for different particle and pebble sizes, materials and process variables viz. particles to pebble size ratios, operating gas velocity ratios, volume fraction of small particles in the interstices and bed wall temperatures, we could arrive at optimum conditions for determining effective thermal conductivity and a correlation to estimate the same. [Copyright &y& Elsevier]

Abstract: In the first generation fusion reactors the fusion of deuterium (D) and tritium (T) is considered to produce energy to meet the future energy demand. Deuterium is available in nature whereas, tritium is not. Lithium-6 (Li6) isotope has the ability to produce tritium in the n, α nuclear reaction with neutrons. Thus lithium-based ceramics enriched by Li6 isotope are considered for the tritium generation for its use in future fusion reactors. Lithium titanate is one such Li-based ceramic material being considered for its some attractive properties viz., high thermal and chemical stability, high thermal conductivity, and low tritium solubility. It is reported in the literature, that the burn up of these pebbles in the fusion reactor will be limited to only 15–17 atomic percentage. At the end of life, the pebbles will contain more than 45% unused Li6 isotope. Due to the high cost of enriched Li6 and the waste disposal considerations, it is necessary to recover the unused Li from the spent lithium titanate pebbles. Till date, only the feasibilities of different processes are reported, but no process details are available. Experiments were carried out for the recovery of Li from simulated Li2TiO3 pebbles and to reuse of lithium in lithium titanate pebble fabrication. The details of the experiments and results are discussed in this paper. [Copyright &y& Elsevier]

Abstract: In many industrial processes, solid particles of different sizes are mixed in different volume or mass fractions for various applications, primarily to reduce void volume or to increase the density of the mixture. A few of these processes include; production of high density ceramics, mortar, concrete, graphite, bricks and carbon blocks. Experiments were carried out with alumina and lithium titanate pebbles (size≥1mm) and particles (size<1mm) of different sizes and volume fractions in cylindrical and rectangular vessels to study the variation of void fraction with volume fraction of component pebbles and with large pebble to small pebble or pebble to particle size ratio. It was observed that the variation of void fraction with volume fraction of smaller pebbles or particles is ‘V-shaped’. Thus there exists a minimum void fraction and two different volume fractions of smaller pebbles or particles which can give same void fraction. The effect of void fraction on the effective thermal conductivity of binary bed of lithium titanate and alumina pebbles and particles of different sizes and volume fractions was investigated. From the experimental results it was found that the binary particulate bed has higher effective thermal conductivity that that of a unary particulate bed. Effective thermal conductivity of binary particulate bed is the maximum when its void fraction is the minimum. The binary particulate bed with less volume fraction of small particles has higher conductivity than that of the binary bed of higher volume fraction of small particles and having same void fraction. This is due to the fact that with increase in volume fraction of small pebbles or particles, the number of small-to-small and large-to-small pebbles and or particles contact point increases resulting in higher resistance to heat transfers. The experimental details and results are discussed in this paper. [Copyright &y& Elsevier]

Abstract: Uniformly sized particulate solids often fluidize poorly with bubbling and slugging. Slugging is a phenomenon associated with the geometry of the vessel, gas flow rate and properties of gas solid particles. It is severe with Geldart Group B particles especially in bed with high aspect ratio and beyond the minimum bubbling velocity. Geldart B particles fluidize well, but bubbles appear as soon as the operating gas velocity exceeds the minimum fluidization velocity. Fluidization of small Geldart B particles in the interstitial void space of large and stationary particles, called packing, overcomes these drawbacks and changes the hydrodynamic characteristics of the bed. Experiments were carried out to investigate these characteristics as a function of the size of the small particles, fraction of voids of packing filled by the small particles and bed wall temperature. Small particles in the voids of packing start to fluidize at a lower superficial velocity (flow-rate divided by empty bed cross-sectional area) than small particles in unary beds. This velocity decreases with increase in wall temperature. A correlation is proposed to estimate the minimum fluidization velocity of the small particles in the voids as a function of measurable variables. [Copyright &y& Elsevier]

Abstract: For the development of TBM for fusion reactors, lithium containing ceramics as against the metal are preferred as tritium breeding material. Lithium titanate (Li2TiO3) is one such chosen ceramic tritium breeder. Li2TiO3 pebbles are conventionally prepared by sol–gel process and wet process. Solid state reaction of lithium carbonate with titanium dioxide is preferred route for the bulk production of Li2TiO3. Thermo-gravimetric and differential thermal analysis (TG–DTA) techniques have been used in the present study to understand the solid state reaction of intimate mixture of lithium carbonate and titanium dioxide. It was found out that single phase lithium titanate (Li2TiO3) is produced at 750°C and the reaction is completed in 6h. Fine powders of lithium titanate obtained after milling and classification were mixed with aqueous solution of PVA to prepare green pebbles of desired size and shape. The pebbles were subsequently sintered at 900°C and the effect of sintering time on the properties of sintered pebbles was studied. The reaction mechanisms and the product qualities obtained by the solid state reaction, extrusion and spherodization techniques are discussed in this paper. [Copyright &y& Elsevier]

Abstract: Experiments were conducted to investigate the hydrodynamic behaviour of lithium titanate (Li2TiO3) in gas-solid fluidized bed. The objective of the study was to study the fluidization properties of Li2TiO3 particles. These studies will be useful to find the applicability of fluidization to increase the effective thermal conductivity and wall to bed heat transfer coefficient of Li2TiO3 particulate bed in test blanket module of fusion reactor. Li2TiO3 was synthesized by solid state reaction process and different particle sizes were classified. Experiments were conducted in a cylindrical column of 90mm diameter and 650mm height in perspex material with metallic distributor plate. Dry compressed air was used as fluidizing medium. From the experiments it was observed that Li2TiO3 is fluidizable, but severe slugging and bubbling were observed in the fluidized bed. Minimum fluidization and bubbling velocity of Li2TiO3 particles were determined and compared to that of white sand of similar particle size and density. The experimental details and observations are discussed in this paper. [Copyright &y& Elsevier]

Abstract: 6Li produces tritium by (n, α) nuclear reaction, 6Li+ 1 n → 4He+ 3H. Lithium titanate (Li2TiO3) enriched with 6Li, is the most promising candidate for solid test blanket module (TBM) material for fusion reactors. Various processes are reported in literature for the fabrication of Li2TiO3 pebbles for its use as TBM material. A process has been developed based on the solid state reaction of lithium-carbonate and titanium-dioxide for the synthesis of lithium titanate and pebble fabrication by extrusion, spherodization and sintering. This paper discusses the sequence of steps followed in this process and the properties obtained. Analytical grade titanium-dioxide and lithium-carbonate were taken in stoichiometric ratio and were milled to ensure thorough intimate mixing and obtain fine particles less than 45μm before its calcination at 900°C. Following calcination, the agglomerated product was again milled to fine particles of size less than 45μm. Aqueous solution of ploy-vinyl-alcohol was added as binder prior to its feeding in the extruder. The extruded strips were spherodized and spherical pebbles were dried and sintered at 900°C for different duration. Pebbles of desired density and porosity were obtained by suitable combination of sintering temperature and duration of sintering. Properties of the prepared pebbles were also characterized for sphericity, pore size distribution, grain size, crushing load strength, etc. The values were found to be conforming to the desired properties for use as solid breeder. The attractive feature of this process is almost no waste generation. [ABSTRACT FROM AUTHOR]

Photograph of rotary reactor and automated granulation system for the synthesis and fabrication of pebbles of solid breeder materials viz. Li 2 TiO 3 installed at site. • A semi-automatic system for bulk production of Li 2 TiO 3 pebbles has been designed. • The process is based on the Solid-State Reaction Process. • The system has been fabricated, installed, tested, commissioned and demonstrated. • The synthesized Li 2 TiO 3 was single phase material. • Sintered Li 2 TiO 3 pebbles meets all the desired properties. • The system can be easily scaled up and made fully automated. Lithium titanate (L i 2 T i O 3) has been selected as ceramic solid tritium breeding materials for the ITER Test Blanket Module (TBM) and also for DEMO reactor. Looking towards its future demand in large quantities, it is necessary to develop a system for bulk production of the lithium titanate pebbles. A semi-automatic system for the bulk production of lithium titanate (Li 2 TiO 3) pebbles by Solid-State Reaction Process (SSRP) has been designed, developed and successfully demonstrated. Raw materials; viz. lithium carbonate (L i 2 C O 3) and titanium dioxide (T i O 2) were mixed in required stoichiometry and fed into the continuous rotary synthesizer. L i 2 T i O 3 powder was synthesized in a continuous rotary synthesizer at 10 kg/h production capacity. This synthesized powder was milled in air jet mill. Milled powder was fed into the extrusion-spheronization based automated granulation system and green, spherical L i 2 T i O 3 pebbles of were produced at the production rate of 25 kg/h. Green spherical pebbles were dried, classified and sintered It was found that the synthesized L i 2 T i O 3 was in monoclinic β- L i 2 T i O 3 phase according to JCPDS No. 33-0831 and the properties of the sintered Li 2 TiO 3 pebbles were well within the desired values. The process and various process parameters are discussed in details in this paper. [ABSTRACT FROM AUTHOR]

It is often important to know minimum fluidization velocity of particles in gas-solid fluidized bed at different temperatures and with different fluidizing gases. Generally, carrying out such experiments are often time consuming as well as very expensive. Computational fluid dynamic (CFD) modeling is presently an important tool that can be extended to solve these problems. The present work demonstrates the use and advantages of CFD modeling to study the effect of temperature on fluidization velocity for lithium titanate (Li 2 TiO 3 ) particles which fall under Geldart B type and air as fluidizing media. 2D simulation of fluidized bed was performed using Eulerian-Eulerian approach. The inlet superficial air velocity was varied and pressure drop across the bed was predicted at different temperatures from 30 to 600 °C for spherical particles of diameter from 231 to 780 μm. Minimum fluidization velocity was also determined using experiments for validation for different temperatures and diameter of particles. CFD predicts the minimum fluidization velocity with 95% accuracy when compared to experimental observations. The minimum fluidization velocity decreases with increase in temperature which is confirmed with validated model. The data from simulations was also compared with correlations reported in literature. [ABSTRACT FROM AUTHOR]

A benchmark experiment was performed to obtain the neutron spectra in a breeding blanket assembly consisting of lithium titanate and Lead using multiple foil activation technique with unfolding code SAND-II-SNL. The purpose of the experiment was to validate the calculated neutron spectra and neutron induced reaction rates with MCNP-4A code and FENDL-2.1 & FENDL-3.0 transport libraries in the layered geometry of lithium titanate and Lead. Measured reaction rates in different activation foils were compared with MCNP-IRDFF-1.05 and FISPACT-EAF2007 calculated values. In general, FENDL-3.0 calculated reaction rates are closer to the measured reaction rates than FENDL-2.1 calculated rates. Calculated Lead multiplication is improved from FENDL-2.1 to FENDL-3.0 up to 2%. Unfolded neutron spectra in the multiplier zones are slightly underestimated by calculations in the secondary neutron emission range of Pb(n, x n) reactions indicating the need of improvement in the (n, 2n) cross-section of Lead isotopes. The observed underestimation in the Lead multiplication puts the tritium production calculations of breeding blankets using Lead as multiplier on conservative side. The inelastic scattering range of Lead isotopes is overestimated by calculations as large as 80% in one of the breeder zone. This observation requires improvement in the inelastic scattering cross-sections of Lead isotopes in FENDL evaluations. [ABSTRACT FROM AUTHOR]

Experiments were conducted with breeding blanket mock-up consisting of two layers of breeder material lithium titanate pebbles and three layers of pure lead as neutron multiplier. The radial dimensions of breeder, neutron multiplier and structural material layers are similar to the current design of the Indian Lead–Lithium cooled Ceramic Breeder (LLCB) blanket. The mock-up assembly was irradiated with 14 MeV neutrons from DT neutron generator. The local tritium production rates (TPR) from 6 Li and 7 Li in breeder layers were measured with the help of two different compositions of Li isotopes (60.69% 6 Li and 7.54% 6 Li) in Li 2 CO 3 . Tritium production in the multiplication layers were also measured with above mentioned two types of pellets to compare the experimental tritium production with calculations. TPR from 6 Li at one location in the breeder layer was also measured by direct online measurement of tritons from 6 Li(n, t) 4 He reaction using silicon surface barrier detector and 6 Li to triton converter. Additional verification of neutron spectra ( E n > 0.35 MeV) in the mock-up zones were obtained by measuring 115 In(n, n′) 115m In reaction rate and comparing it with calculated values in all five layers of mock-up. All the measured nuclear responses were compared with transport calculations using code MCNP with FENDL2.1 and FENDL3.0 cross-section libraries. The average C/E ratio for tritium production in enriched Li 2 CO 3 pellets was 1.11 in first breeder zone and 1.09 in second breeder zone with uncertainty 8.3% at 1 σ level. The experimental details and results are discussed in this paper. [ABSTRACT FROM AUTHOR]