Tritium Breeding Materials Research Articles

Li vaporization behavior and mechanical properties of Li8ZrO6 under high temperature reducing atmosphere

Li8ZrO6 sintered compacts are one of the promising candidates for innovative tritium breeding materials from the viewpoint of lithium density, but there are concerns such as a decrease in lithium atomic density and mechanical strength due to Li2O vaporization. In this study, we fabricated a two-phase mixed sintered body of Li8ZrO6 with a high lithium atomic density, as the main component, and relatively a large amount of Li2O, and thermally annealed it in an environment simulating actual use conditions to vaporize lithium. It is shown that this material is stable at 320°C, which is the main temperature in the blanket space, Li2O vaporizes and part of Li8ZrO6 changes to Li6Zr2O7 at least above 700°C, and vaporization of Li2O occurs more rapidly to finally become to a single phase of Li2ZrO3 at 800−900°C. In addition, it is shown that this material has a higher lithium density than Li2TiO3, one of the Japanese candidate materials, in a wide temperature range below 770 °C during the expected period of practical use of three years. Finally, it is concluded that loading Li8ZrO6-based material and Li2TiO3 in the high and low temperature regions, respectively, achieves the highest lithium density.

Li4SiO4 slurry conditions and sintering temperature for fabricating Li4SiO4 pebbles as tritium breeders for nuclear-fusion reactors

A tritium breeder is a lithium-based material capable of producing tritium. Many researchers designing nuclear-fusion energy are studying tritium production using pebbles, which are solid-type breeders. The sphericity and size of the pebbles are critical in obtaining pebbles with good tritium-breeding efficiency. Furthermore, tritium-release efficiency can be increased by using pebbles with appropriate porosities. Promising raw materials for tritium-breeding materials include Li4SiO4 and Li2TiO3. Li4SiO4 has a higher lithium density than Li2TiO3 and exhibits excellent tritium-breeding efficiency. However, it has the disadvantage of being easily decomposed during the Li4SiO4-green-pebble sintering process because of its low structural stability at high temperatures and high lithium density. In this study, we attempted to determine the optimal conditions for manufacturing Li4SiO4 pebbles using the droplet–freeze-drying method. The optimal Li4SiO4 slurry conditions and sintering temperatures were determined. The optimal Li4SiO4 slurry-fabrication conditions were 3 wt% polyvinyl alcohol and 75 wt% Li4SiO4 based on the deionized-water weight content. The sintering temperature at which Li4SiO4 did not decompose and exhibited the optimum porosity of 10.8% was 900 °C.

Effects of atmospheric gases and compression load on effective thermal conductivity of Li2TiO3 pebble bed

Tritium breeder material in the solid-type of breeding blanket concepts is usually used in a pebble bed form because of the efficiency and convenience of tritium extraction. The pebble bed is continuously heated by the exothermal reaction between neutron and lithium-6 during the operation of a fusion reactor. Thus, a compression pressure is applied on the pebble bed by the thermal expansion of pebbles and container structure. Therefore, the accurate thermal properties of the pebble bed are one of the important design parameters to ensure a function and stability of the breeding blanket. This study aims at the investigation of the change on effective thermal conductivity of Li2TiO3 pebble beds under the operation conditions of breeding blanket.The measurement of effective thermal conductivities of Li2TiO3 pebble beds has been performed by laser flash technique in several atmosphere gases, such as helium, nitrogen, and air, under the statically compression load controlled by specially design pneumatic device incorporated to the laser flash apparatus. Also, in the case of helium atmosphere, the effects of hydrogen concentration from 0.1 wt.% to 1.0 wt.% on the effective thermal conductivity were also investigated. The effective thermal conductivity of the Li2TiO3 pebble bed was strongly dependent on a kind of atmosphere gases, especially its thermal conductivity, in the relatively low temperature. However, the concentration of hydrogen in the helium atmosphere did not significantly affect the effective thermal conductivity of the pebble bed. Applied axial compression load has influenced on the effective thermal conductivity of the Li2TiO3 pebble bed, especially at high temperature. However, the obvious change of effective thermal conductivity with the value of compression load was not observed.

An update on the latest and most relevant improvements achieved in the European helium-cooled ceramic breeder TBM design

The European TBM (Test Blanket Module) program under development will test two alternative concepts for tritium generation and extraction in ITER: a helium cooled / ceramic pebble breeder concept and a water cooled / lithium lead breeder concept.The former implements Advanced Ceramic Breeder pebbles that act as tritium breeding material, and Beryllium pebbles as neutron multiplier. A Reduced Activation Ferritic Martensitic steel, the EUROFER-97 (X10CrWVTa9-1), is used as structural material and pressurized Helium technology is implemented for efficient heat extraction (300-500°C, 8 MPa).The design of the TBM box involves challenges that must be tackled with a holistic approach to simultaneously consider a variety of aspects. Some of these challenges include: the thermal performance and the structural integrity of the TBM under ITER normal operations and accidental conditions, the implementation of pressurized equipment regulation(s), the convergence with manufacturing activities being developed in parallel and the high congestion in the reduced TBM volume –especially when considering instrumentation integration– without affecting too much the tritium breeding capability. It is also key to develop advanced methodologies based on design by analysis to virtually test alternative design solutions in an agile manner. These should be linked to the applicable nuclear design code (RCC-MRx) to consolidate design choices. In this way, a traceable evolution of the TBM design process can be built where alternatives are tested, compared and either discarded or selected in a consistent and comprehensive framework.This paper presents an overview of the very significant progress achieved in the design of the helium cooled concept TBM over the last two years, a period that corresponds to the first steps of the preliminary design phase towards the Preliminary Design Review (PDR) gate. This includes a significant change in the design of the back manifold area and the connection with the rest of the TBM-Set that solves long-standing historical problems inherited from pre-conceptual design stage. An update on the latest and most relevant methodological developments achieved is also provided in this paper, since these have been key to progress with the design evolutions in a sound and traceable manner. To end, the paper also presents some examples of the instrumentation definition and its complex integration within and outside the TBM box.

Long‐term thermal stability of Li4TiO4–Li2TiO3 core–shell breeding pebbles under continuous heating in H2/Ar atmosphere

AbstractThe long‐term thermal stability of tritium breeding materials during service is a key factor to ensure efficient tritium release. In this study, the long‐term thermal stability of advanced Li4TiO4–Li2TiO3 core–shell breeding pebbles under continuous heating in 1%H2/Ar at 900°C was investigated for the first time. The results show that this core–shell material loses 3.4% Li mass after heating for 30 days, resulting in a reduction in Li density to .415 g/cm3, which is still significantly higher than other breeding materials. The moisture in the sample bed will determine the form of Li volatilization and thus affect the rate of Li mass loss. The core–shell pebbles maintain favorable phase stability during long‐term heating, and the grain sizes of the Li2TO3 shell and Li4TiO4 core after 30 days of heating are 6.5 ± 1.5 and 6.9 ± 2.5 μm, respectively. Moreover, the samples did not crack or collapse during long‐term heating and still had a satisfactory crushing strength of 37.61 ± 7.13 N after 30 days of heating. Overall, the high Li density and good thermal stability during long‐term heating demonstrate that the Li4TiO4–Li2TiO3 core–shell breeding pebbles are a very reliable tritium breeding material for long‐term service under harsh operating conditions.

Study on the chemical compatibility between Li2TiO3 ceramic pebbles and diverse advanced structural materials

AbstractThe tritium breeder and structural materials are necessary components in the blanket to realize tritium (T) self‐sustainment of nuclear fusion. The long‐term exposure between tritium breeders and structural materials will cause surface corrosion in irradiation environments and then further affect the tritium release behavior. In this study, chemical compatibility between Li2TiO3 ceramic pebbles and advanced structural materials was studied systematically at 700 °C for 300 h under He+0.1 % H2 environment, respectively. The color of the Li2TiO3 ceramic pebbles changes from white to dark grey and black. Moreover, the grain size of Li2TiO3 ceramic pebbles increases to more than 5 μm, and the crushing load decreased slightly. For the structural materials, the Al‐rich oxide layer with about 188.7 nm of 14Cr‐5Al oxide dispersion strengthened (ODS) steel and Cr‐Fe rich oxide layer with about 1.04 μm of 14Cr‐ODS steel were observed on the cross‐section. The effective diffusion coefficient of O element in Li2TiO3 ceramic moved into ODS steel at 700 °C was calculated to be 3.3 × 10−16cm2/s and 1.02 × 10−14 cm2/s. Unfortunately, when SiC ceramics were contacted with the pebbles, the crystal phase transformed into SiO2, which severely limits its application. Therefore, these results will provide guidance for the selection of structural materials in the future.

Mass fabrication of Li2TiO3–Li4SiO4 ceramic pebbles with high strength by facile centrifugal granulation method

AbstractThe bi‐phase Li2TiO3–Li4SiO4 ceramic pebbles have been considered a promising breeder to realize the tritium self‐sustainment in the blanket. However, up to now, the reported ceramic pebbles have the disadvantages of low yield, poor crushing load, and loose internal structure, which cannot meet the practical application requirements. In this work, the Li2TiO3–Li4SiO4 ceramic pebbles with excellent mechanical properties were fabricated successfully via the centrifugal granulation method with the assistance of introducing a spray‐drying process, simulating particle trajectory by discrete element software and improving bonding interface between core and shell with ethylene glycol. The composition, microstructure, and inner structure of the Li2TiO3–Li4SiO4 ceramic pebbles were investigated, respectively, through X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and X‐ray computed tomography (CT). It can be found that the employment of the ethylene glycol solution on the surface of Li2TiO3 can make the core and the shell combine well. Moreover, the effect of the rolling speed of the Li2TiO3–Li4SiO4 ceramic pebbles was investigated via discrete element method (EDEM) simulation and experiments. The experimental results displayed that the Li2TiO3–Li4SiO4 ceramic pebbles sintered at 1100°C for 2 h have a uniform diameter of 1 mm, a good sphericity of 0.97, and an excellent crushing load of 82.4 N, which are superior to those pebbles that obtained by using the traditional wet methods. Moreover, the CT results showed that the appropriate porosity of the core was 3.21% and of the shell was 10.73%. Therefore, the simple centrifugal granulation method can be applied to prepare the Li2TiO3–Li4SiO4 ceramic pebbles in a large scale and shed a light to investigate the relevant advanced biphasic tritium breeder materials in the future.

Lithium fire protection design approach in IFMIF-DONES facility

Several experimental facilities, mainly focused on nuclear fusion applications, propose lithium as main coolant and/or tritium breeder material, limiter or divertor for its advantageous properties. Lithium fire hazard represents a critical risk for the production of an important population of reactive, corrosive and toxic aerosols, and for the potential mobilization, transport and release of radioactive species, initially retained in the molten metal, as in experimental facilities like the IFMIF-DONES accelerator neutron source. Consequently, a specific methodology should be developed for managing possible lithium fire scenarios that could occur during the lifetime of these unique facilities. Applying the Defense-in-Depth principle to minimize the fire risk in the particular case of the IFMIF-DONES plant, this work describes a set of passive and active measures for lithium fire prevention, detection and mitigation in compliance with main international and national standards on fire protection. According to the present safety analyses, active measures, including the use of fixed extinguishing systems employing chemical agents, do not seem to be entirely reliable in case of large lithium fires, for which more preferable passive fire protection measures are also being considered to be implemented in the final design of IFMIF-DONES, such as room inertization, catch pans and drain systems, constituting together a main line of defense to safely manage potential lithium fire scenarios.

Ion irradiation study of lithium silicates for fusion blanket applications

This study reports on the ion-irradiation induced microstructural and compositional evolutions, behavior of deuterium release, and lithium loss from lithium silicates. Pellets of biphasic Li4SiO4 and Li2SiO3 were fabricated using hot pressing of milled powders. Sequential irradiation with Si+, He+ and D+ ions was performed up to 773 K to emulate one-year 6Li burnup in 6Li4SiO4 inside the SlimCS DEMO. Crystalline Li4SiO4 phase was not observed in the irradiated depth region in this study. In spite of full amorphization in the near-surface region, Li2SiO3 irradiated to a high dose at 773 K remained crystalline in the damage peak region, suggesting that Li2SiO3 is more irradiation resistant to amorphization than Li4SiO4. Radiolysis may be primarily responsible for the silicate decomposition and amorphization. Data from this study also show that D release from the pellet is very efficient during ion irradiation at 773 K, which is accompanied with a significant Li loss. Thermal annealing for 10 min at 773 K for the room-temperature irradiated pellet leads to a nearly complete D release without an observable Li loss. A concept of Ni coating on tritium breeder materials is discussed with supporting data to minimize Li loss without a significant impact on tritium diffusion and release.

Low-temperature sintering of Li4SiO4 spheres with high crushing load using mesoporous silica as Si sources

Li4SiO4 has been widely studied as tritium breeder and high temperature CO2 capture material. Tritium breeding rate and CO2 adsorption capacity are closely related to lithium content and microstructure. Since high sintering temperatures result in grain coarsening and lithium sublimation, it is a great challenge to prepare Li4SiO4 ceramics with a satisfactory mechanical strength at low sintering temperature. In this work, mesoporous silica was used as Si source to prepare Li4SiO4 spheres. The mesoporous structure might provide more reaction sites for lithium ions, thereby facilitating the reaction between LiOH and mesoporous silica. The sintering temperature of Li4SiO4 spheres was greatly reduced by using mesoporous silica as Si source. The Li4SiO4 spheres with a homogenous fine-grained microstructure (the average grain size of 2.2 ?m) and high crushing load (41.65N) could be obtained at 675?C.

An Innovative Approach to Prepare Liquid-Solid Dual-Phase Flowable Tritium Breeder with Low MHD Effect

In present paper, a novel flowable tritium breeder is prepared by mixing the Li2TiO3 micro-powders and liquid GaInSn alloy, where GaInSn alloy is used to simulate the fluid behaviors of lithium-based liquid tritium breeder, forming a type of composite characterized by liquid-solid dual phase. In detail, the effects of the volume fraction of ceramic micro-powders on viscosity and conductivity of the composite in magnetic field are the focus. The XRD results prove that the obtained Li2TiO3 micro-powders contained Li2TiO3 phase without impurities. The results shows that once the magnetic field intensity exceeds the critical value, the viscosity of liquid GaInSn metal becomes significantly greater than that of liquid-solid dual-phase composites. Furthermore, the addition of Li2TiO3 micro-powders could effectively reduce the magneto hydro dynamic (MHD) fluid effect, and the dual-phase composites exhibit comparatively lower flow resistance under the strong magnetic field. Moreover, the conductivity of the tritium breeder composites decreases rapidly with the addition of Li2TiO3 micro-powders. The MHD pressure-drop-increasing rate decreases with the increase of viscosity, which indicates that the addition of Li2TiO3 micro-powders effectively reduces the MHD effect. The conductivity of the composites increased slightly and then remained stable after static placing for several tens of minutes. The present investigation provides a novel insight into the fabrication strategy of tritium breeder materials with low MHD effect.

Pressure-induced phase transition toward high symmetry in zero-strain Li2TiO3.

As a typical layered oxide material, Li2TiO3 has attracted considerable attention in the energy revolution and military industries, owing to its lithium-rich and "zero-strain" characteristics. However, its phase-transition behavior under high pressure remains unclear. Herein, we report a second-order phase transition from the monoclinic phase to a higher-symmetry phase in nano-polycrystalline Li2TiO3 at 43 GPa by in situ high-pressure Raman experiments and first-principles calculations at 300 K. As validated by the experiments and calculations, the distortion of layered oxide-TiO6 in Li2TiO3 is crucial in the phase transition. By modulating the gap between octahedral-TiO6 layers, we propose a potential Li2TiO3 structural model for improving the electrochemical performance of lithium-ion batteries. Our findings suggest that, based on its high-pressure phase, Li2TiO3 is a promising candidate for layered cathode materials and solid tritium breeding materials for lithium-ion batteries.

Modified Freeze-granulation method for fabricating Li2TiO3 ceramic tritium breeding pebbles

Lithium metatitanate (Li2TiO3) ceramic is an important candidate for tritium breeding material in fusion reactor blanket. Nevertheless, mass production has become an important factor restricting the application of Li2TiO3 pebbles. In this paper, freeze-granulation method is innovatively modified by drying frozen pebbles in acetone. The principle of modified freeze-granulation method is explained in detail. Influence of PVA content, sintering temperature and sintering time on mechanical performance of frozen pebbles dried in acetone are carefully discussed. The modified process could shorten the drying time in 30 min under the premise of good crushing load and thus conducive to improve the efficiency of mass production of tritium breeding ceramic pebbles potentially in the future. Finally, the Li2TiO3 pebbles present good sphericity, high average crushing load (38 N), abundant and uniform pores which are beneficial to tritium release.

Effects of water adsorption on tritium release behavior of Li4TiO4 and Li4TiO4-Li2TiO3 core-shell structure breeding ceramics

Li4TiO4 and Li4TiO4-Li2TiO3 core-shell breeding ceramics were considered as promising tritium breeding materials in fusion reactor blanket, and the effect of adsorbed water on the tritium release behavior of these two types of materials was investigated and compared in this study. All samples were first irradiated by thermal neutrons at Kyoto University, followed by out-of-pile tritium release experiments at Kyushu University. It was found that both Li4TiO4 and Li4TiO4-Li2TiO3 core-shell breeding ceramics have two tritium trapping sites, mainly due to the overlapping of the tritium release temperature of Li2TiO3 with the second tritium release site of Li4TiO4. Besides, it was observed that the adsorbed water can slightly reduce the tritium release temperature of the two types of tritium breeding materials. More importantly, the effect of adsorbed water on tritium release form (HT/HTO ratio) was quantitatively studied. The results demonstrate that water adsorption has a significant effect on the tritium release form of the breeding ceramics, and the core-shell structure can inhibit the hygroscopicity of Li4TiO4 to increase the fraction of tritium release in the HT form.

Inelastic scattering and first principles study of tritium breeder materials Li2TiO3 and Li2ZrO3

First ever Compton spectroscopy of Li2TiO3 (LTO) and Li2ZrO3 (LZO) have been performed using 100 mCi 241Am Compton spectrometer. The experimental electron momentum densities (EMDs) of these compounds are compared with the theoretical EMDs computed using various generalized gradient approximations (GGA) under linear combination of atomic orbitals (LCAO) method namely Becke-Lee-Yang-Parr (BLYP), Perdew-Burke-Ernzerhof (PBE), revised Perdew-Burke-Ernzerhof for solids (PBEsol) and Perdew-Wang GGA (PWGGA). The BLYP based theoretical Compton profiles show best agreement with the experimental data for both the Li-ceramics. The electronic structure calculations predicted indirect band gap nature of both compounds with major contributions of Ti-3d, Zr-4d and O-2p states with some minor part due to Li-2sp states around Fermi energy. Further, experimental EVED profiles anticipated more covalent or less ionic character of LTO as compared to LZO. The elastic properties calculations verified mechanical stability of both compounds at ambient temperature and pressure. In addition, the optical properties of LTO and LZO are derived using full potential linearized augmented plane wave (FP-LAPW) method, which revealed high absorbent feature and photoconductive behavior of both compounds in UV region. Moreover, large values of electrical and thermal conductivities at high temperature make them suitable candidates for electrode materials in Li-ion batteries.

Analysis of effective thermal conductivity of pebble bed by artificial neural network and its computational and experimental verification

While dealing with a solid-type ceramic breeding blanket for a fusion reactor, it is critical to determine the basic and thermal properties of the functional material in the form of a pebble bed. In the form of pebbles, lithium ceramics serve as the tritium breeder material in the fusion blanket. Effective thermal conductivity (keff) is one of the important thermal properties for the design and useful parameter to determine the performance of the blanket component. Artificial Neural Networks (ANN) are a popular machine learning technique for tuning between input and output parameters. These networks can learn from examples (data set) and apply them when a homogeneous event arises, making them able to work through genuine-time events. Hence, it can save a lot of time and money for doing repetitive experiments and high-end simulations. This will aid in the creation of a huge database on the pebble bed's keff, which will be useful in the design and development of fusion blankets. The findings of simulations and experiments are compared to those predicted by the ANN model for the pebble bed's thermal conductivity.At IPR, a test setup for experiments has been developed using the steady-state and axial heat flow approach. keff of Li2TiO3 has been measured for the pebbles of diameter of 0.8–1.2 mm having packing fraction of ∼62% and using helium environment at different temperatures ranging from 100 °C to 600 °C at constant atmospheric pressure. keff has been compared with pebble bed of stainless steel pebbles of different diameters (1, 2, 3, 1&3, & 2&3 mm) as well. DDPM-DEM model has been used to generate the pebble bed and ANSYS-CFD simulations using FLUENT have been performed to validate the results. The projected values using ANN are within 5% of the results obtained from simulations and experiments. The details of the DDPM-DEM and ANN models, FLUENT simulations, and experimental results will be discussed in this paper.

Solubility of Bi in Li–Pb Eutectic Alloy Between 508 and 623 K

Liquid lithium–lead (Li–Pb) eutectic alloy is one of the candidate liquid tritium breeding materials of fusion blanket and it contains bismuth (Bi) as an initial impurity or transmutation product from lead. The saturated solubility of Bi, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> (wt.ppm), in Li–Pb was measured in the temperature range from 508 to 623 K. The measured results were plotted on the graph with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> (wt.ppm) versus 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T$ </tex-math></inline-formula> . From these plots, a positive temperature dependence, where the solubility decreases as the temperature is lowered, is confirmed. The equation of the solubility of Bi in Li–Pb was obtained, too. In addition, the dissolution enthalpy of Bi in Li–Pb, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta H_{\mathrm {sol}}$ </tex-math></inline-formula> , was quantified from this equation. The precipitation morphology of Bi in Li–Pb was also investigated. X-ray diffraction was used to analyze the precipitates collected from the surface of the liquid phase. As a result, the peak pattern of Li3Bi was found from the precipitate. Moreover, the amount of polonium produced when the cold trap is introduced to a Li–Pb loop of a fusion reactor was predicted from the solubility obtained in this study.

Influence of sintering atmosphere on phase, microstructure and mechanical properties of Li4Si0.7Ti0.3O4 tritium breeding ceramics

Li4Si1–xTixO4 ceramic solid solution was considered as a promising tritium breeding material for fusion reactor blanket. In this work, the effects of the sintering atmosphere on the phase composition, microstructure, and mechanical properties of Li4Si0.7Ti0.3O4 ceramic pebbles were investigated for the first time, aiming to explore the optimal sintering atmosphere for this solid solution. The results show that compared with air and argon atmosphere, the negative pressure of vacuum atmosphere was more favorable for Ti to enter the Li4SiO4 crystal structure as a substitute for Si atom to form a solid solution. More importantly, sintering in argon-vacuum atmosphere can ensure the formation of solid solution while fully exerting the liquid phase sintering effect. The crushing load of the Li4Si0.7Ti0.3O4 ceramic pebbles sintered at 800 °C in argon-vacuum atmosphere reaches 30.3 ± 3.2 N. In general, the appropriate sintering atmosphere was of great significance for obtaining Li4Si0.7Ti0.3O4 solid solution to meet the performance requirements of tritium breeding blanket.

Densification behavior and properties of Li4SiO4 ceramic breeder with the addition of SiC as a sintering aid

Lithium orthosilicate (Li4SiO4) is regarded as a vital tritium breeder candidate due to its favorable properties, such as high lithium contents, superior tritium release behavior, and irradiation stability. However, the poor crushing load and low thermal conductivity of the Li4SiO4 ceramic pebbles fabricated via existing methods will lead to the blocking of the tritium release channels, giving rise to thermal stress concentration. To overcome the above shortcomings, the SiC was employed as sintering aid to improve Li4SiO4 ceramic pebbles via simple wet method in this paper. The effects of SiC content on the shrinkage, internal structure evolution, and crushing load of the Li4SiO4 ceramic pebbles are comprehensively investigated, and the densification process is analyzed in detail. It was found that the addition of SiC improves the crushing load (54 N) significantly owing to decreasing the densification activation energy. Moreover, the Li4SiO4 ceramic pebbles with excess Li2CO3 further displays excellent properties at 800 °C, such as the relative density of 90.3%, the crushing load of 65.3 N, and the thermal conductivity of 1.97 W/(m·K) respectively, which is much higher than that of traditional methods (at least 1000 °C). The Li4SiO4 ceramic pebbles with homogeneous micro-pore distribution, the porosity of 7.3% were further measured by using the X-ray computer tomography technique. Therefore, this proposed tactic has great prospects for the service performance of tritium breeding materials in the blanket.

Alkaline hydrothermal treatment of P25 titanium dioxide for low temperature sintering of Li2TiO3 tritium breeding ceramics

• The structural properties of Ti sources affect the sintering activity of Li 2 TiO 3 . • P25-AHT is superior to anatase TiO 2 in reducing sintering temperatures of Li 2 TiO 3 . • The prepared Li 2 TiO 3 ceramics have high crushing load and thermal conductivity. For solid tritium breeding materials, a high sintering temperature is essential to achieve satisfactory density, high crushing load, favorable physical and chemical properties, while lithium volatilization and grain coarsening occur at higher sintering temperature, which are not conducive to tritium production and release. Therefore, low temperature sintering of lithium containing ceramics needs to be studied. In this work, P25 titanium dioxide was hydrothermally treated in alkaline solution, and then used as titanium source to prepare Li 2 TiO 3 ceramics. The prepared Li 2 TiO 3 ceramics exhibit uniform and dense microstructure and extremely high crushing load (a.v. 78.93 ∼ 83.98 N) at a relative low sintering temperature (750 ∼ 800 °C). The thermal conductivity of Li 2 TiO 3 ceramic sintered at 800 °C is calculated to be 3.48 W/m•K at room temperature, retaining 2.50 W/m•K at 773 K, which is comparable to the values in literatures. The results suggest the sintering activity of Li 2 TiO 3 is greatly enhanced when alkaline hydrothermally treated P25 is used as titanium source.