Tritium Breeding Materials Research Articles

A preliminary study on the preparation of nanostructured Ti-doped Li4SiO4 pebbles by two-step sintering process

Li4SiO4 has been widely studied as attractive tritium breeding materials due to its innate merits. Considering the potential advantages of nanostructure in tritium breeding materials, a distinctive process was developed to obtain nanostructured Li4SiO4 pebbles. In brief, ultrafine precursor powders were synthesized by solvothermal method without using surfactants, and then indirect wet method was adopted to generate the green spheres with homogeneous microstructure. After that, the suitable sintering conditions were defined by studying the effects of sintering parameters on the grain size evolution, and nanostructured Ti-doped Li4SiO4 pebbles were first obtained by two-step sintering method. This study will be expected to provide references for fabricating other Li-based tritium breeding materials.

Influence of ion irradiations on the microstructure in the tritium breeder material Li2TiO3

Tritium breeder materials are significant for the blanket design of a fusion reactor. Because of its good chemical stability and available tritium release behavior, Li2TiO3 has been selected as one of leading candidates for ceramic breeder materials. During a blanket operation, defects are introduced into tritium breeder materials by high energy neutrons and energetic particles from nuclear reactions, resulting in performance degration of the materials. He and O ion irradiation were applied to introduce irradiation damage into Li2TiO3 in this study. X-ray Diffraction (XRD) and Raman spectra experiments were performed to identify the evolution of the Li2TiO3 microstructure. The experimental results show that the atomic arrangement in Li2TiO3 is strongly disordered by the ion irradiation. The destruction of long-range order is confirmed by the reduction in XRD intensities. The destruction of short-range order is validated by the reduction in the Raman intensities and disappearance of Raman bands with increasing irradiation dose. The disorder in Li2TiO3 structure is considered to be associated with the species and energy of the ions. In order to further clarify the defects induced by ion irradiation, Electron Spin Resonance (ESR) was employed. E-centers which are oxygen vacancies occupied by one electron have been formed by ion irradiation. Compared with He ion irradiation, O ion irradiation produces relatively less E-centers, but more Ti3+ defects. These different defects induced by irradiation are discussed in relation to the disorder of microstructure.

Li vaporization property of Li8ZrO6 and Li5AlO4 as tritium breeders

New tritium breeding materials that maintain large tritium breeding ratio for thermonuclear fusion reactors should be developed. In this study, we investigate the lithium-vaporization behavior from the sintered bodies of Li8ZrO6 and Li5AlO4 having high lithium atom densities. From the viewpoint of lithium density, we investigate the possibility of using the sintered compacts of Li8ZrO6 and Li5AlO4 as a tritium breeder. Lithium vaporization rates from the sintered bodies of Li8ZrO6 and Li5AlO4 are high. However, for both materials, the lithium vaporization rate gradually decreases with the annealing time by “self-stabilization” in which the surfaces of each sintered body are covered by the stable layer of the second phase. Considering the temperature dependency of equivalent vapor pressure and the volume fraction of tritium breeding material loaded at high-temperature region, it is suggested that the sintered compacts of Li8ZrO6 and Li5AlO4 have high potentials for the tritium breeder.

Physicochemical stability under inert and reductive atmospheres of Li2TiO3 produced from Li2CO3 obtained from Argentinean brines

Lithium metatitanate (Li2TiO3) is one of the most promising candidates as tritium breeder material in a fusion reactor due to its physical and chemical properties. In this paper, the syntheses of Li2TiO3 by combustion in solution (SCS) and solid-solid (SSS) were developed using as raw material Li2CO3 produced from Argentinean brines and TiO2. In SCS, aqueous solution of Li2CO3 and TiO2 as metal precursors, citric/tartaric acids as complexing agent/fuel and HNO3 as oxidant was formed, heated to dryness and then self-combusted. The solid obtained was calcined at 550 °C for 12 h to obtain nanometric Li2TiO3 (monoclinic phase, 90%), with particle sizes <0.5 μm and meso/macropores. In SSS, Li2CO3-TiO2 mixture was ball milled in air at room temperature and subsequently annealed. The effect of milling time and calcined temperature in the formation of Li2TiO3 was studied. High yields of Li2TiO3 (>90% and 99%) were obtained even at low heating temperatures (400 and 600 °C for 24 h, respectively). The synthesized powders show mean grain sizes in the nanometric range, particle sizes <0.7 μm and macropores. Changes that occur during heat treatment in inert and slightly reductive atmospheres (5% H2/Ar) were identified.The SSS and SCS methods developed using easy to handle and low-priced precursors constitute cost-attractive processes for large scale production of Li2TiO3 nanopowders.

First-principles calculation of the structural, electronic, dynamical, and thermodynamic properties of Li4TiO4

The compound Li4TiO4 (Tetralithium Titanium) has attracted widespread scholarly interest for its sharp nose about carbon dioxide and high lithium density in the atmosphere and tritium breeder materials. At present, the structural, electronic, dynamical and thermodynamic properties of Li4TiO4 are studied by means of density functional theory (DFT) and phonon lattice dynamics. The calculated structural parameters and available experimental measurements are corresponding to each other, with the deviation being less than 1.5%. The obtained electronic band structure and density of states manifest that Li4TiO4 is an insulator with the indirect gap of 4.23 eV. Furthermore, the vibrational properties of Li4TiO4 are investigated usi ng the linear-response method from ab initio calculation. The calculation of phonon spectrum cures, the Born effective charges, the longitudinal optical (LO)-transverse optical (TO) splitting and optical-modes (IR- and Raman-active) are achieved in the first place. Additionally, the thermodynamic properties (F, S, Cv and E) are firstly evaluated ground on the phonon dynamics contribution. The formation of this paper will benefit the characterization of Li4TiO4, which may be subservient to further experimental researches in some degree.

Impact of Blanket Configuration on the Design of a Fusion-Driven Transmutation Reactor

A configuration of a fusion-driven transmutation reactor with a low aspect ratio tokamak-type neutron source was determined in a self-consistent manner by using coupled analysis of tokamak systems and neutron transport. We investigated the impact of blanket configuration on the characteristics of a fusion-driven transmutation reactor. It was shown that by merging the TRU burning blanket and tritium breeding blanket, which uses PbLi as the tritium breeding material and as coolant, effective transmutation is possible. The TRU transmutation capability can be improved with a reduced blanket thickness, and fast fluence at the first wall can be reduced. Article History: Received: July 10th 2017; Received: Dec 17th 2017; Accepted: February 2nd 2018; Available onlineHow to Cite This Article: Hong, B.G. (2018) Impact of Blanket Configuration on the Design of a Fusion-Driven Transmutation Reactor. International Journal of Renewable Energy Development, 7(1), 65-70.https://doi.org/10.14710/ijred.7.1.65-70

Sol-gel synthesis of lithium metatitanate as tritium breeding material under different sintering conditions

Lithium metatitanate (Li2TiO3) is a promising tritium breeding material candidate for solid blanket of D-T fusion reactors, due to its high mechanical strength, chemical stability, and tritium release rate. In this paper, Li2TiO3 powder with homogeneous crystal structure is synthesized by sol-gel method. The chemical reactions in gel thermal cracking and sintering process are studied by thermo gravimetric/differential scanning calorimetry (TG-DSC). The relationship between the sintering condition and the particle/grain size is characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that below 673 K the gel precursor is completely decomposed and Li2TiO3 phase initially forms. The LiTiO2 by-product formed under the reductive atmosphere in muffle furnace, could be oxidized continually to Li2TiO3 at higher sintering temperature (≥1273 K) for longer sintering time (≥10 h). Both grain and particle sizes rely on a linear growth with the increase of sintering time at 1273 K. Over 1473 K, significant agglomerations exist among particles. The optimal sintering condition is selected as 1273 K for 10 h, for the purer Li2TiO3 phase (>99%), smaller grain and particle size.

A promising tritium breeding material: Nanostructured 2Li2TiO3-Li4SiO4 biphasic ceramic pebbles

As an advanced tritium breeder material for the fusion reactor blanket of the International Thermonuclear Experimental Reactor (ITER), Li2TiO3-Li4SiO4 biphasic ceramic has attracted widely attention due to its merits. In this paper, the uniform precursor powders were prepared by hydrothermal method, and nanostructured 2Li2TiO3-Li4SiO4 biphasic ceramic pebbles were fabricated by an indirect wet method at the first time. In addition, the composition dependence (x/y) of their microstructure characteristics and mechanical properties were investigated. The results indicated that the crush load of biphasic ceramic pebbles was better than that of single phase ceramic pebbles under identical conditions. The 2Li2TiO3-Li4SiO4 ceramic pebbles have good morphology, small grain size (90 nm), satisfactory crush load (37.8 N) and relative density (81.8 %T.D.), which could be a promising breeding material in the future fusion reactor.

High pressure stability of lithium metatitanate and metazirconate: Insight from experiments & ab-initio calculations

Lithium metatitanate (LTO) and lithium metazirconate (LZO) are lithium rich ceramics which can be used as tritium breeder materials for thermonuclear reactors. In-situ x-ray diffraction and ab-initio studies at high pressure show that LTO has a higher bulk modulus than that of LZO. In fact these studies indicate that they are the least compressible of the known lithium rich ceramics like Li2O or Li4SiO4, which are potential candidates for blanket materials. These studies show that the TiO6 octahedra are responsible for the higher bulk modulus of LTO when compared to that of LZO. It has also been shown that the compressibility and distortion of the softer LiO6 octahedra can be controlled by altering the stacking sequence of the more rigid covalently bonded octahedra. This knowledge can be used by chemists to design new lithium based ceramics with higher bulk modulus. It was observed that LTO was stable upto 34 GPa. Ab initio DFT calculations helped to understand the anisotropy in compressibility of both LZO and LTO. This study also shows, that even though the empirical potentials developed by Vijaykumar et al. successfully determine the ambient pressure structure of lithium metatitanate, they cannot be used at non ambient conditions like high pressure [1].

Structural, electronic, elastic and thermodynamic properties of Li2ZrO3: A comprehensive study using DFT formalism

Lithium zirconate is considered to be potential tritium breeder material for fusion reactors. Here I report a comprehensive study on structural, electronic, elastic, and thermodynamic properties of Li2ZrO3 using plane wave based density functional theory. While the electron-ion interaction term has been described by projected-augmented wave method, the exchange-correlation energy was taken care of through generalized gradient approximation scheme. The optimized lattice and internal parameters of Li2ZrO3 unit cell agree well within ±1–2% from the experimental values. From the electronic structure analysis it is seen that the Fermi energy has significant contribution from the 2s, 2p and 4d orbitals of Li, O and Zr atoms, respectively. Elastic property calculation of Li2ZrO3 showed mechanical stability and anisotropy at ambient pressure. The formation energy (ΔfH) of Li2ZrO3 at 0 K, after zero point energy correction, has been estimated to be −1550 kJ/mol. The temperature dependent thermodynamic functions of Li2ZrO3 have also been calculated from the Debye-Grüneisen quasi-harmonic approximation and reported here.

Functional materials for breeding blankets—status and developments

The development of tritium breeder, neutron multiplier and flow channel insert materials for the breeding blanket of the DEMO reactor is reviewed. Present emphasis is on the ITER test blanket module (TBM); lithium metatitanate (Li2TiO3) and lithium orthosilicate (Li4SiO4) pebbles have been developed by leading TBM parties. Beryllium pebbles have been selected as the neutron multiplier. Good progress has been made in their fabrication; however, verification of the design by experiments is in the planning stage. Irradiation data are also limited, but the decrease in thermal conductivity of beryllium due to irradiation followed by swelling is a concern. Tests at ITER are regarded as a major milestone. For the DEMO reactor, improvement of the breeder has been attempted to obtain a higher lithium content, and Be12Ti and other beryllide intermetallic compounds that have superior chemical stability have been studied. LiPb eutectic has been considered as a DEMO blanket in the liquid breeder option and is used as a coolant to achieve a higher outlet temperature; a SiC flow channel insert is used to prevent magnetohydrodynamic pressure drop and corrosion. A significant technical gap between ITER TBM and DEMO is recognized, and the world fusion community is working on ITER TBM and DEMO blanket development in parallel.

The influences of deuterium irradiation defects on mechanical properties for ceramic breeder material Li2TiO3

Tritium breeder materials are significant for blanket design of fusion reactor. However, during blanket operation, the ceramic breeder materials will be subject to neutron irradiation, which could be detrimental to mechanical properties. Because of good chemical stability and available tritium release behavior, Li2TiO3 is becoming one of candidate ceramic breeder materials. In this study, Li2TiO3 samples are irradiated by 120keV deuterium ions. For sample characterization, the phase composition is investigated by X-ray diffraction (XRD) before and after irradiation. After deuterium irradiation, the Electron Spin Resonance (ESR) experiments are employed to investigate the irradiation defects. Micro-hardness measurement is applied to study the changes of mechanical properties. XRD results indicate that Li2TiO3 crystals are damaged by deuterium irradiation, but no new phases are produced. According to ESR experiment, the main defect type after deuterium irradiation is F-center which are vacancies trapping one electron. According to Vickers hardness measurement, size effect of micro-hardness is observed. The Meyer coefficient obtained in the experiment is 1.65, which is less than 2. Vickers hardness increases as applied loads decrease which are consistent with Meyer theory. And Vickers hardness of Li2TiO3 decreases as irradiation doses increase.

Helium cooling systems for Indian LLCB TBM testing in ITER

One of the key missions of ITER is to test and validate the various design concepts of tritium breeding blankets relevant to a power-producing reactor like DEMO. India is developing lead-lithium cooled ceramic breeder (LLCB) test blanket module (TBM) along with associated systems for testing in ITER. In LLCB TBM, Pb-Li eutectic alloy is used as multiplier, breeder, and coolant for the ceramic breeder (CB) zones, and lithium meta-titanate (Li2TiO3) the ceramic breeder is used as a tritium breeding material. The outer box structure is India-specific reduced activation ferritic martensitic steel (IN-RAFMS) and is cooled by high pressure, high temperature (8MPa, 300–500°C) helium gas named as first wall helium cooling system (FWHCS). The molten Pb-Li eutectic, flows separately around the lithium ceramic breeder pebble bed compartments to extract heat from the CBs. The Pb-Li system is cooled by separate helium system named as lead-lithium helium cooling system (LLHCS). This paper discusses the details of the process design, and process flow diagrams of the both the helium cooling systems, their operational states with reference to the ITER machine operational states, and performance & behavior of the helium systems during normal operation and accidental conditions.

Measurements of the effective thermal conductivity of a non-compressed Li4SiO4 pebble bed

Li4SiO4 is a tritium breeder material for helium cooled solid breeder blanket concept. The thermal properties of ceramic pebble beds provide important support for designing the solid breeder test blanket module (TBM). A new apparatus was developed to measure the effective thermal conductivity of a packed ceramic pebble bed by steady state method. Accordingly, the effective thermal conductivity of a non-compressed Li4SiO4 pebble bed at temperatures ranging from 300°C to 640°C was measured as well in this study. The packing factor was about 59.7% for the single size pebble bed and helium at atmospheric pressure was used as a filling gas. The experimental results show that the effective thermal conductivity increased with increasing the average bed temperature.

Li2TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material

The tritium breeding materials require small particle size to reduce the diffusion distance of generated tritium in the intercrystalline. In addition, the essential resource, especially enriched Li-6, has to be recovered from the used tritium breeding material. For the hands-on operation during the recovery process, the activation level of the used breeder is strictly limited in order to reduce the impurities of long-lived radioactive nuclides in the tritium breeding material. In this study, lithium oxide (Li2O) and titanium dioxide (TiO2) were used as starting materials in the synthesis of Li2TiO3 powder. The starting materials were mixed by wet ball-milling process. The mixed powders were synthesized by heat treatment. The average particle size of synthesized Li2TiO3 powder was approximately 150nm. And, the long-lived radioactive nuclides, such as aluminum (Al) and cobalt (Co), were not accumulated in the synthesized Li2TiO3 powder during the synthesis process. The Li2TiO3 pebbles were fabricated by slurry droplet wetting method using the synthesized Li2TiO3 nano-powder. The particle size, crush load, and porosity of fabricated Li2TiO3 pebbles using the synthesized nano-powder were investigated.

Influence of gas pressure on the effective thermal conductivity of ceramic breeder pebble beds

Lithium ceramics have been considered as tritium breeder materials in many proposed designs of fusion breeding blankets. Heat generated in breeder pebble beds due to nuclear breeding reaction must be removed by means of actively cooled plates while generated tritiums is recovered by purge gas slowly flowing through beds. Therefore, the effective thermal conductivity of pebble beds that is one of the governing parameters determining heat transport phenomenon needs to be addressed with respect to mechanical status of beds and purge gas pressure. In this study, a numerical framework combining finite element simulation and a semi-empirical correlation of gas gap conduction is proposed to predict the effective thermal conductivity. The purge gas pressure is found to vary the effective thermal conductivity, in particular with the presence of various sized gaps in pebble beds. Random packing of pebble beds is taken into account by an approximated correlation considering the packing factor and coordination number of pebble beds. The model prediction is compared with experimental observation from different sources showing a quantitative agreement with the measurement.

Estimation of Tritium Release from LLCB TBM and Its Ancillary Systems and Tritium Management in Different Locations of ITER

The Indian Lead Lithium Ceramic Breeder (LLCB) Test Blanket Module (TBM) is to be installed in one half of equatorial port #2 for testing in ITER machine. Liquid Pb-Li and solid Li2TiO3 are the tritium breeder materials in LLCB TBM. Tritium permeates through structural materials in particular at higher temperatures, which is a major operational and safety concern. Therefore, tritium flows in different locations of ITER Tokamak complex have been estimated.Tritium transport from LLCB TBM and its ancillary systems into process rooms has been studied and analyzed in this work. A steady state diffusion limited permeation model neglecting surface effects has been used for the analysis. Tritium permeation to the Vacuum Vessel, Pipe Forest Area, Port Cell, Pipe Chase Area, Tokamak Cooling Water System Vault Annex (TCWS-VA) and Tritium Process Room in L-2 level has been estimated.The requirement to be fulfilled in each equatorial port cell is that the tritium concentration in the port cell during maintenance operations should be below the admissible limit for human access (regulatory maximum allowable value < 1 DAC = 3.4 × 105 Bq/m3, Derived Air concentration). The presence of the Detritiation System (DS) in the Port cell has to be taken into account.This admissible limit for human access has to be reached in a sufficiently short time (target = 12 h) after plasma shutdown. Additional release during maintenance and radiological zoning with recommended <10 µSv/h need to be considered. Management of concentration of permeated tritium in different locations considering above requirement has also been discussed in this paper.

Neutronics study on HCCB blanket for CFETR

Chinese Fusion Engineering Testing Reactor (CFETR) is aimed to obtain the technologies to fill the gaps between ITER and DEMO. The helium cooled ceramic breeder (HCCB) blanket is one of the candidates for CFETR. Ceramics Li4SiO4, beryllium and helium of 8MPa were selected as tritium breeding material, neutron multiplier and coolant, respectively. CLF steel, one of reduced activation ferritic/martensitic (RAFM) steels, was applied as structural materials of blanket. Neutron and gamma transport was simulated with MCNP code and FENDL/MC-2.1 neutron cross section data. Activation calculation was performed with FISPACT-2007 code and EAF-2007 activation file. In this study, neutronics characteristic of HCCB blanket such as tritium breeding ratio (TBR) and shielding were assessed. The arrangement of Be, Li4SiO4 and cooling plate in blanket module was optimized to improve TBR. The sensitive study for First Wall on TBR was also performed. The radioactivity inventories of HCCB blanket were estimated. The dominant radionuclides in structural materials, Li4SiO4 and Beryllium were discussed, respectively. The damage of plasma facing components such as First Wall and divertor due to DT neutron irradiation was analyzed in terms of DPA value and gaseous product.

Fabrication of nanostructured Li2TiO3 ceramic pebbles as tritium breeders using powder particles synthesised via a CTAB-assisted method

Nanostructured Li2TiO3 ceramics which may have effective thermal conductivity, excellent tritium release behaviour and good irradiation resistance are regarded as a promising solid tritium breeding material for the fusion reactor blanket of the International Thermonuclear Experimental Reactor (ITER). However, due to the limitations of the preparation technology, reports concerning Li2TiO3 nanoceramics have been rare. In this paper, uniform nano-Li2TiO3 powder particles which were essential to obtain nanostructured Li2TiO3 ceramics pebbles were synthesised via a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal method, and then rare, homogeneous nanostructured Li2TiO3 ceramic pebbles were fabricated with the as-prepared powder particles. The mechanisms by which CTAB can reduce particle agglomeration and be of assistance in achieving a nanostructured Li2TiO3 ceramic were also investigated. In addition, systematic experiments on the relationship between the added amount of CTAB and the mechanical properties of the Li2TiO3 ceramic structure were also carried out. The results revealed that the desired Li2TiO3 nanoceramic could be fabricated when 3% CTAB was introduced, as the Li2TiO3 pebbles obtained had a small grain size (90nm), high relative density (89.71%T.D.) and crush load (99.93 N), which were expected to show favourable potential as a promising tritium breeder material in the fusion reactor blanket.

Fabrication methods for lithium based ceramic material development-A Review

The development of breeder fabrication technology has been exclusively devoted to manufacturing processes for pebbles, since most solid breeder blanket designs are based on pebble-beds and TheLithium based ceramics is one of the most important components of a fusion reactor because it directly involvesboth energy extraction and tritium production, both of which are critical to fusion power and have a long been recognized as promising tritium-breeding materials for Test Blanket Modules (TBM) of the International Thermonuclear Experimental Reactor (ITER) The world-wide efforts on ceramic breeder materials in the last two years concerned Li2O, Li4SiO4, Li2TiO3 and Li2ZrO3, and Li2TiO3. The lithium-basedceramics have shown good irradiation behavior and excellent tritium release characteristics. Individual materialsperformance will depend upon the actual application, namely, pebble bed versus pellet concept, higher versus lower cooling temperature, etc. There are different methods: extrusion/spheronization, melting/spraying, gelcasting, wet method.