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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: 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]

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]