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Packed pebble bed of ceramic solid breeder materials viz. lithium titanate or meta-titanate ( Li 2 TiO 3 ), lithium orthosilicate ( Li 4 SiO 4 ) etc. is being considered for fusion blankets. During the breeding of tritium, helium will be produced and also it is proposed to flow helium from outside through the bed to extract tritium, as well as to remove thermal energy from the bed. Experimental determination of thermal property data of the pebble bed under helium gas flow is important for the blanket design. Such study of determination of effective thermal conductivity with flowing helium condition was not performed previously. Though, it is known that with an increase in gas flow rate, the effective thermal conductivity of pebble bed increases, it is necessary to conduct experiments to know the exact values and the degree of variation. Model and experimental setup used in our previous study was used to for this present work. Effects of process parameters viz., helium gas flow rate, bed temperature, pebble size etc. on the effective thermal conductivity of the bed have been studied. Correlations have been developed from these experimental data to estimate effective thermal conductivity at different particle Reynold’s number and bed temperature. It was found that with the use of helium, the effective thermal conductivity of bed increases by many folds. Experimental details and results are discussed in this paper. [ABSTRACT FROM AUTHOR]

Lithium orthosilicate (Li 4 SiO 4 ) was synthesized; without and with excess lithium (Li) in quantity of its stoichiometric requirement, with 5, 10, 15 and 20% excess lithium, and pebbles were fabricated by Solid State Reaction Process (SSRP), similar to that of lithium titanate. The green pebbles were sintered at 900 °C for 6 h. XRD analysis of the synthesized powders, confirmed the formation of single phase Li 4 SiO 4 when stoichiometric ratio of lithium carbonate and silica were used and the presence of multiple phases when excess lithium was used. Morphological modifications of mesoscopic structure in Li 4 SiO 4 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. It also indicates density fluctuations, even at nanometer length scale. Slight variation in pore size distribution with the amount of excess lithium was observed. Average size of the pores shows a decreasing trend initially with increase in Li amount but shows an opposite trend at around 15% of excess Li. [ABSTRACT FROM AUTHOR]

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]

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: Lithium titanate is a promising solid breeder material for the fusion reactor blanket. Packed lithium titanate pebble bed is considered for the blanket. The thermal energy; that will be produced in the bed during breeding and the radiated heat from the reactor core absorbed must be removed. So, the experimental thermal property data are important for the blanket design. In past, a significant amount of works were conducted to determine the effective thermal conductivity of packed solid breeder pebble bed, in helium atmosphere, but no flow of gas was considered. With increase in gas flow rate, effective thermal conductivity of pebble bed increases. Particle size and void fraction also affect the thermal properties of the bed significantly. An experimental facility with external heat source was designed and installed. Experiments were carried out with lithium-titanate pebbles of different sizes at variable gas flow rates and at different bed wall temperature. It was observed that effective thermal conductivity of pebble bed is a function of particle Reynolds number and temperature. From the experimental data two correlations have been developed to estimate the effective thermal conductivity of packed lithium-titanate pebble bed for different particle Reynolds number and at different temperatures. The experimental details and results are discussed in this paper. [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]

The following figure shows the effect of induction heating temperature on the effective thermal conductivity of packed bed filled with 10 mm lithium titanate pebbles. • Numerical investigation to study effect of process and operating parameters on effective thermal conductivity of pebble bed with non-uniform internal heat generation using experimental inputs was done. • In house fabricated Li 2 TiO 3 pebbles of size: 1-10 mm were used. • Empirical equations were developed and to study spatial variation of power generated by Induction Heating Furnace and were optimized using experimental inputs. • Finite Difference Method based mathematical model was developed to estimate k e f f with average accuracy of around 79 %. • Empirical correlation was proposed to predict k e f f with average accuracy of 75–83 %. Test Blanket Module (TBM) of the fusion reactor has the vital role of removing heat generated from the fusion reactor along with the heat generated internally due to tritium breeding reaction. In the initial startup phase of fusion reactor, neutron flux has a climbing ramp nature and heat gets generated in discrete locations of TBM due to non-uniform nature of neutron irradiation. Thus, there is need to establish mathematical method to estimate Effective Thermal Conductivity (ETC) of packed bed with randomly scattered internal heat sources. Novel Induction Heating technique was used to simulate above mentioned conditions in packed bed of Li 2 TiO 3 pebbles. An input-output FDM (Finite Difference Method) based model has been developed to estimate ETC of packed beds with non-uniform and discrete Internal Heat Generation (IHG). The inputs to the FDM based model are experimental results along with various operating and process parameters of the packed bed system under consideration. Also, an empirical correlation has been proposed to yield ETC of above mentioned packed bed systems valid for bed voidage of 0.44-0.47. The experimental and analytical methods used for this study are detailed in this paper. [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]