Blanket Materials Research Articles

Atom Probe Tomography investigation of lithium uptake from liquid Pb-17Li by nanocrystalline/amorphous Al2O3 coatings

Atom probe tomography has been applied to study lithium-induced corrosion of Pulsed-Laser Deposition grown Al2O3, which is a candidate coating material for breeder blankets for nuclear fusion reactors. Coated Eurofer97 specimens were immersed in static Pb-17Li for 7000 h with samples extracted from the regions near the ceramic-substrate interface to determine the extent of Li penetration. Li-enriched regions, which are non-stoichiometric with respect to any known equilibrium phases predicted by the Li-Al-O phase diagram at 823 K, are reported for the first time in Al2O3. The nature and composition of the Li-enriched features were characterized with nanometre resolution. It was found that the Li content inside these features may increase to a maximum of 35 at%, with the adjacent Al2O3 matrix containing approximately 5–10 at% Li. Based on these results, the corrosion mechanism of amorphous Al2O3 is proposed to be Li substitution of Al atoms.

Crustal origin for olivine in the lunar Shioli crater ejecta boulders: Insights from the geological setting of Theophilus crater and Nectaris basin

On the Moon, impact craters and basins expose a wide range of crustal and mantle rocks that provide excellent opportunity for sampling them, understanding their origins and reconstructing spatial and temporal evolution of lunar interior. The previous studies detected olivine-bearing mantle rocks in and around large impact craters and basins. The Japanese SLIM mission landed on the ejecta of a ∼ 280-m-diameter Shioli crater that was emplaced on the ejecta blanket of ∼ 103-km-diameter Theophilus crater, for characterizing potential mantle-derived olivine in the Shioli crater ejecta boulders. To test this hypothesis, we studied the geological setting of Shioli crater, host Theophilus crater and Nectaris multi-ring basin using the orbiter data from Chandrayaan-1 and 2, Lunar Reconnaissance Orbiter, and Kaguya missions and the earth-based Arecibo radar observation. The asymmetrically distributed secondary craters and impact melt ponds around Theophilus crater suggests that a northeast-directed oblique impact produced this crater. Composition of Theophilus crater and surrounding region indicates that the crater excavated a heterogeneous target composed of a thin layer of high-Al olivine basalt (Mare Nectaris) underlain by anorthositic highland rocks possibly intruded by Mg-suite plutons; layers of Cyrillus crater ejecta blanket and Nectaris basin materials (both ejecta and impact melt sheets) were also present beneath the mare basalt flows. Hence, the Theophilus ejecta blanket is a mixture of all these materials. Our dating of Theophilus crater suggests that it is a ∼ 2 Ga Eratosthenian crater. Shioli is a fresh simple crater that was formed at ∼ 1 Ma on the uprange ejecta blanket of Theophilus, where the Arecibo radar data indicated the presence of abundant buried Theophilus ejecta boulders. An ESE-directed hypervelocity oblique impact event produced the elongated Shioli crater and its asymmetrically distributed bright ejecta. Shioli is a primary impact crater indicating the role of impact spallation processes associated with this hyper-velocity impact in producing thousands of ejecta (or spall) boulders around Shioli crater, displaying their asymmetric dispersal pattern and spatial variation of boulder sizes and shapes. The larger and elongated boulders are concentrated near the crater rim, while their size and axial ratio gradually decreases outward from the crater rim. The SLIM mission landed on a thin downrange ejecta of Shioli crater, where fewer large-size boulders are present. Our compositional study suggests that the Shioli ejecta boulders are composed of olivine basalt (Mare Nectaris) mixed with highland anorthositic fragments, including the reworked Cyrillus ejecta and Nectaris basin materials. The Shioli ejecta boulders were produced by complex impact fragmentation of already existing, buried Theophilus ejecta boulders. The regional crustal structure of Nectaris basin and its petrological composition suggest that both Nectaris basin and Theophilus crater did not excavate the lunar mantle. Therefore, the Shioli ejecta boulders are of crustal origin, including the olivine minerals present in them. Our results have important implications for the origin of olivine in the Shioli crater boulders being investigated by the SLIM mission.

Tensile and creep properties of small specimens of reduced-activation ferritic steel F82H, and the correlation to standard specimen data

Background A reduced-activation ferritic/martensitic (RAFM) steel, F82H steel, is the primary candidate structural material for fusion reactor blanket. Small specimen test technique is essential to develop the blanket materials using limited irradiation volume in high flux neutron field. An international collaboration activity “Towards the Standardization of Small Specimen Test Techniques for Fusion Applications” has been initiated under the framework of the International Atomic Energy Agency Coordinated Research Project for Phase I from 2017 to 2021, and Phase II from 2022 to 2026. The present paper reports the preliminary results on tensile and creep tests as a summary of the above Phase I activity. Methods Tensile and creep tests were conducted at 550 and 650°C, using flat-plate SSJ type small specimens with various gauge thickness ranged from 0.14 to 1.2 mm, while gauge length and width are 5 and 1.2 mm, respectively. In addition, round bar type standard specimens with a gauge geometry of 6 mm in diameter and 30 mm in length was also tested for comparison. Results Tensile yield stress, ultimate tensile strength and uniform elongation were independent of the gauge thickness of SSJ specimens, and agreed with the data from the standard size specimens. On the other hand, total elongation was decreased with decreasing the thickness. In creep tests, rupture time was decreased with decreasing the gauge thickness of SSJ specimens. Standard size specimens exhibited shorter rupture time than the SSJ specimens. Conclusions The SSJ type specimens provided similar tensile parameters to those from the standard specimen, except total elongation. Creep rupture time of the SSJ specimens were different from the standard specimen, and decreased with decreasing the gauge thickness.

Selection signatures of wool color in Gangba sheep revealed by genome-wide SNP discovery

BackgroundGangba sheep as a famous breed of Tibetan sheep, its wool color is mainly white and black. Gangba wool is economically important as a high-quality raw material for Tibetan blankets and Tibetan serge. However, relatively few studies have been conducted on the wool color of Tibetan sheep.ResultsTo fill this research gap, this study conducted an in-depth analysis of two populations of Gangba sheep (black and white wool color) using whole genome resequencing to identify genetic variation associated with wool color. Utilizing PCA, Genetic Admixture, and N-J Tree analyses, the present study revealed a consistent genetic relationship and structure between black and white wool colored Gangba sheep populations, which is consistent with their breed history. Analysis of selection signatures using multiple methods (FST, π ratio, Tajima's D), 370 candidate genes were screened in the black wool group (GBB vs GBW); among them, MC1R, MLPH, SPIRE2, RAB17, SMARCA4, IRF4, CAV1, USP7, TP53, MYO6, MITF, MC2R, TET2, NF1, JAK1, GABRR1 genes are mainly associated with melanin synthesis, melanin delivery, and distribution. The enrichment results of the candidate genes identified 35 GO entries and 19 KEGG pathways associated with the formation of the black phenotype. 311 candidate genes were screened in the white wool group (GBW vs GBB); among them, REST, POU2F1, ADCY10, CCNB1, EP300, BRD4, GLI3, and SDHA genes were mainly associated with interfering with the differentiation of neural crest cells into melanocytes, affecting the proliferation of melanocytes, and inhibiting melanin synthesis. 31 GO entries and 22 KEGG pathways were associated with the formation of the white phenotype.ConclusionsThis study provides important information for understanding the genetic mechanism of wool color in Gangba, and provides genetic knowledge for improving and optimizing the wool color of Tibetan sheep. Genetic improvement and selective breeding to produce wool of specific colors can meet the demand for a diversity of wool products in the Tibetan wool textile market.

Proof-of-principle of parametric stellarator neutronics modeling using Serpent2

This contribution presents neutron transport studies for the 5-period helical-axis advanced stellarator stellarator using the Serpent2 code. These studies utilize a parametric geometry model, enabling scans in neutronics modeling by varying the thickness of the reactor layers. For example, the tritium breeding ratio (TBR) can be determined by exploring various blanket material options and thicknesses to identify the threshold configuration that meets the TBR design criterion of 1.15. We found out that with the helium-cooled pebble ped candidate option, the TBR criterion is met with a breeding zone thickness of 26 cm, while with the dual-coolant lithium lead the threshold is exceeded at a thickness of 46 cm. Furthermore, the geometry includes non-planar field coils, allowing to study the fast neutron flux in these superconducting coils with a technological limit of 1×1091/cm2s . It is shown that the neutron fast flux is not constant at the coils, necessitating a neutron transport simulation to determine the distribution of the fast-flux at the coils. We show that the peak fast flux can be more than a factor of 2 higher than the average flux, and that the peak flux location rotates helically.

Preliminary experimental studies into the storage capacity of cryogenic hydrogen in aerogel blanket materials

The abundance and diversity of hydrogen applications necessitates continued and accelerated research into advanced storage technologies. Traditionally, hydrogen has been stored as either a high-pressure, warm gas; or a low-pressure, cryogenic liquid. Methods such as cryo-supercritical and cryo-adsorbed have been explored, but are not yet mainstream. Cryo-adsorbed is attractive because higher storage densities at higher temperatures than liquid may be achieved. Recently NASA, in partnership with Eta Space, Southwest Research Institute, the University of Central Florida, and Air Liquide, have been exploring the use of inexpensive, commercially available silica aerogel blanket materials for cryo-adsorbed hydrogen storage. Unlike most adsorbents, aerogel blanket is not a powder, but a robust, composite material that can be formed into complex shapes to aid in more efficient storage system designs, and has already been proven to uptake large quantities of fluids such as nitrogen and oxygen. Recent experimental efforts into the uptake of low-pressure hydrogen gas at 77 K, and liquid hydrogen at normal boiling point (NBP) will be discussed. Although preliminary in nature, the test results are promising, showing up to a 49% increase in storage density at 77 K over the gas alone, and greater than a one-to-one volume equivalency with NBP LH2.

Hydrogen isotope permeation and retention behavior in the RAFM steel manufactured by laser powder bed fusion

Laser powder bed fusion (LPBF) has emerged as a promising additive manufacturing technique for producing complex components across various industries. This method is particularly instrumental in fabricating reduced activation ferritic/martensitic (RAFM) steel, a candidate structural material for the tritium breeding blanket. Hydrogen transport behaviors in the conventional RAFM steel have been largely investigated; however, they are not well understood in the LPBF-RAFM steel. In this work, we studied the hydrogen isotope permeation and retention behavior in the RAFM steel fabricated by LPBF, utilizing the deuterium gas driven permeation and thermal desorption spectroscopy experiments. The results show that the hydrogen isotope permeability of the LPBF-RAFM steel is close to the conventionally fabricated RAFM steel, but the diffusion coefficient is greatly lower and the retention is markedly higher in the LPBF-RAFM steel compared to the conventional RAFM steel. The large number density of microvoids and TiC precipitates in the LPBF-RAFM steel could be the predominant factors that result in the decrease in hydrogen isotope diffusion coefficient and the increase in the total amount of deuterium retention.

The effect of Li2TiO3 pebbles on the mechanical properties of ARAA under breeding blanket conditions

The breeding blanket serves as a critical element for achieving a self-sustaining tritium cycle and generating sufficient energy in fusion reactors. This study focuses on candidate materials of the helium-cooled solid breeder blanket designed for a demonstration fusion reactor breeding blanket in Korea. We conducted compatibility tests between advanced reduced-activation alloy (ARAA) and Li2TiO3 pebbles at 550 °C for 28 days in He-0.1 vol% H2 purge gas conditions. Surface oxidation on ARAA was observed regardless of pebble presence. Double oxide films comprised of Fe-rich and Cr-rich layers formed on the surface of ARAA with pebbles. Lithium deposition was verified in both contact and non-contact areas of ARAA. Despite surface oxidation, the impact on tensile strength and elongation was found to be negligible.

Insurgent envelopment: The emergency blanket and scenes of exposure at border zones

AbstractCritical engagement with spaces of exposure is an important research agenda in the contemporary social sciences and humanities. Developing and extending this agenda, this paper offers an account of how scenes of exposure at border zones are mediated materially, aesthetically, and politically by forms of envelopment. Specifically, it discusses the geographies of exposure and envelopment that unfold through the use and re‐use of the emergency blanket at these zones. Fabricated from metallised polymer films, emergency blankets are used commonly to provide thermal protection for bodies at risk of exposure in a range of situations. More than functional, however, these objects also have a distinctive aesthetic allure. By attending to the material and aesthetic qualities of the emergency blanket, this paper explores its visibility and significance in scenes of exposure at border zones. Highlighting how the blanket is deployed as a device of minimal comfort, the paper then considers artistic works that repurpose this object as part of a creative critique of conditions at these zones. Drawing on the work of Stacy Alaimo and Ronak Kapadia, among others, the paper develops the concept of insurgent envelopment to understand how artists use the emergency blanket in works that simultaneously foreground, disrupt, and reimagine relations between exposure and envelopment.

Corrosion resistance of 9–12Cr ODS steels in pressurized water for fusion application

The blanket design of Chinese fusion engineering test reactor (CFETR) may utilize pressurized water as coolant. The fusion structural materials will endure high temperature, high pressure and result in corrosion in the pressurized water. It is necessary to verify corrosion resistance of the materials. In the present study, three kinds of advanced fusion structural materials with excellent mechanical properties and neutron irradiation resistance, i.e., 9Cr-ODS steel, 9CrODS-Al steel, and 12CrODS-Al steel were immersed in pressurized water at 325 °C under the pressure of 15.5 MPa up to 859 h. Room-temperature tensile properties were investigated for the materials before and after corrosion. The oxidation layers of the steels were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ODS steels have good corrosion resistance in the pressurized water, especially the 9CrODS-Al and 12CrODS-Al steels. The outer oxide layer is identified as Fe2O3 for all the steels. The inner layer is mainly FeCr2O4 for the 9CrODS steel, and Fe(Al,Cr)2O4 for the ODS steels with Al element which better protect the steels from further corrosion. The relevant properties data can provide reference for the blanket materials choice of CFETR and the future fusion reactors.

Study of hydrogen sorption and desorption processes of zirconium beryllide ZrBe2

One of the promising intermetallic compounds for use in nuclear and fusion reactors, as well as in hydrogen energy technology, are intermetallic compounds of beryllium with metals such as Ti, V, Zr and Nb. Beryllium-based intermetallics are not only a promising material for blankets of future fusion reactors, but can also be utilized in other areas of the nuclear industry, including fission reactor reflectors, rocket and space technology. The interest in studies of the interaction of hydrogen isotopes with beryllides is related to the accumulation of tritium and helium in the material, formed as a result of nuclear reactions under neutron irradiation, and is caused by the need for understanding the processes arising from such interaction.In this work, hydrogen sorption and desorption processes of zirconium beryllide ZrBe2 produced by industrial technologies at JSC “Ulba Metallurgical Plant” (JSC UMP) were investigated. The experiments were performed by the Sievert’s and thermal desorption spectrometry (TDS) methods. In TDS experiments deuterium was chosen for samples saturation to reduce the possible error in determining fluxes associated with the release of hydrogen from the elements of the vacuum chamber.An equation for hydrogen solubility in zirconium beryllide ZrBe2 was obtained by processing the experimental data obtained by the Sievert’s method:S=0.46±0.1molm3∙Pa12∙exp-13.3±0.5kJmolRTThe temperature intervals of formation and decomposition of two different hydride phases (deuterides) of zirconium beryllide ZrBe2 at ∼ 600 K and ∼ 900 K have been established in TDS experiments.

Evaluation of the strength of FeCrAl alloy/surface Oxide film interface by micro double-notch shear test

The shear strength of the film formed by pre-oxidation treatment of FeCrAl(-ODS) alloys, likely to be used as pipework material for liquid LiPb breeder blankets, was evaluated by micro double-notch shear testing. Fracture generally occurred at the interface between the oxide film and the alloy substrate, but the pop- in the stress-strain curves was difficult to interpret, so all the test results in this study were compared to the full rupture strength. The rupture strength appears to be a function of the nature of the interface between the film and the alloy rather than the thickness of the film; for APMT and FeCrAl-ODS, the rupture strength was greater for FeCrAl-ODS.

Microstructure refinement and enhanced mechanical properties of wire arc additively manufactured RAFM steel via post heat treatments

Reduced activation ferritic/martensitic (RAFM) steel with high strength and neutron radiation damage resistance is deemed one of the promising structural materials for fusion blankets. In this study, RAFM steel tube was prepared through wire arc additive manufacturing, and the evolution of phase composition, microstructural features and mechanical properties during the as-built and heat treatment processes were investigated. The results show that the as-built state is predominantly composed of α-Fe, and the microstructure's morphology from bottom to top consists of alternating columnar grain regions, equiaxed coarse grain regions, and fine grain regions. Normalizing and tempering treatment eliminates the heterogeneous microstructure, resulting in the presence of M23C6 carbides enriched with Cr and W, as well as MX phases enriched with Ta and V. Partitioning heat treatment results in the formation of ultrafine martensitic, quenched martensite and bainitic microstructures. The mechanical properties of wire arc additively manufactured RAFM steel are influenced by variations in microstructure. The coarse-grained region formed in the as-built state represent weak links. Normalizing and tempering treatment reduces the strength while improving ductility. Partitioning heat-treated RAFM steel exhibited a high strength of 1.1 GPa and an elongation of approximately 10.9%. This study provides a method of combining additive manufacturing with heat treatment to enhance the strength and ductility of RAFM steel simultaneously.

Development of thermo-physical property database and code of fusion materials for CFETR blankets

The conceptual design of China Fusion Engineering Test Reactor (CFETR) has been completed and is currently in the engineering design phase. In this paper, focusing on three categories of candidate blanket designs and divertor designs, the selection schemes for materials of plasma-facing components, solid structure, tritium breeding materials, neutron multiplier, coolant, and divertor were extracted. Thermo-physical property data was compiled to form a material thermo-physical property database, named Thermo-physical Property Database (ThePD), which is the first advanced thermo-physical database for materials of CFETR blankets. Besides, the callable code was generated, which can be directly applied in the system code for the blanket. Based on internationally available database from National Institute of Standards and Technology (NIST) and similar software AP1700, the correctness of the data and the transitional analysis of regions designed by International Association for the Properties of Water and Steam (IAPWS) were verified. Using the thermal-hydraulic system analysis code, integrated validation was performed for the validated thermo-physical property data and code, demonstrating the applicability and accuracy of the data. ThePD is conducive to addressing the issue of incomplete thermo-physical property data faced by blanket design and safety analysis software for CFETR, and it can fill this gap.

The Influence of High-Temperature Tests on the Resistance to Degradation and Reduction in Strength Properties of Lithium-Containing Ceramics Used as Blanket Materials for Tritium Breeding

Conducting high-temperature tests on ceramics-containing lithium, which are employed as tritium breeding materials, plays a crucial role in comprehending their ability to withstand degradation and maintain their strength properties throughout operation. From the standpoint of fusion research, it is imperative to grasp these phenomena in order to guarantee the safety and effectiveness of reactors. Additionally, these factors could impact the choice of particular materials and designs for blanket materials. The primary objective of this research is to evaluate alterations in the strength characteristics of ceramics-containing lithium when subjected to high-temperature thermal stability tests, while also preserving the hardness stability and resistance to cracking in ceramics subjected to cyclic tests. Lithium-containing ceramics based on lithium titanate (Li2TiO3), lithium orthosilicate (Li4SiO4), and lithium methacyrconate (Li2ZrO3), having a high structural ordering degree and good strength properties, were chosen as objects for assessing resistance to high-temperature degradation. During the studies, it was discovered that the presence of interphase boundaries in the composition of ceramics linked to the development of impurity phases results in crack resistance growth during long-term high-temperature tests simulating the stress effect on the material. At the same time, an assessment of high-temperature aging as a result of modeling destruction processes showed that ceramics based on lithium metazirconate are the most resistant to degradation of strength properties. By simulating high-temperature aging processes, it became feasible to establish connections between structural alterations resulting from the thermal expansion of the crystal lattice and oxygen migration phenomena occurring at elevated temperatures. These factors collectively contribute to a detrimental reduction in the strength properties of ceramics-containing lithium.

Improving thermal conductivity of reduced-activation ferritic/martensitic steel using three-dimensional woven copper fiber

Reduced-activation ferritic/martensitic (RAFM) steel is a primary candidate for blanket modules in nuclear-fusion reactors. Blanket modules transfer thermal energy generated by nuclear-fusion reactions to the coolant; therefore, blanket materials must have high thermal conductivity. RAFM steel is suitable for fusion reactors owing to its high strength, toughness, and resistance to neutron irradiation; however, its thermal conductivity is lower than that of other metals. This study fabricates RAFM steel–copper composites using three-dimensional (3D) woven copper fibers with different volume fractions as a preform to improve the thermal conductivity of RAFM steel around the coolant pipes. The microstructural, mechanical, and thermal properties of the developed composites and the correlations between them are experimentally investigated. Finite element simulations were also conducted on the composites comprising 3D woven copper fibers to evaluate the effective thermal conductivity. The factors that improve the effective thermal conductivity of RAFM steel–copper composites are discussed through a comparison with copper-powder composites with comparable volumes. This study demonstrates the manufacturing of composites with excellent thermal and mechanical properties using various 3D woven structures as preforms.

Reactor experiments on irradiation of two-phase lithium ceramics Li2TiO3/Li4SiO4 of various ratios

The design of future fusion reactors involves the production of tritium inside the breeder blanket. The most promising material for solid breeder blankets is a two-phase lithium ceramic containing orthosilicate Li4SiO4 (LOS) and metatitanate Li2TiO3 (LMT) of lithium in various proportions. Tritium is formed in lithium under neutron irradiation by the reaction 6Li(n,α)T. Further, this tritium is extracted from the blanket with a purge gas and returned to the fusion zone, realizing the concept of a closed fusion cycle.Irradiation under fission reactor conditions is still one of the few available methods for estimating the parameters of tritium generation and release from lithium-containing materials in the "in-situ" mode. This paper presents the results of experiments on neutron irradiation of two-phase lithium ceramics of various ratios (LOS + 35 mol. % LMT (pebble size 250–1250 μm), LOS + 35 mol. % LMT (pebble size 500–710 μm) and LOS + 25 mol. % LMT (pebble size 500–710 μm) at the WWR-K research reactor.Irradiation of each batch of samples lasted from 5 to 22 days. The experiments were carried out by the vacuum extraction method. This paper describes the main methodological aspects of the studies, namely the technical features of four irradiation campaigns, the sequence and scope of the studies. A comparison is also made of the initial sections of reactor experiments for all campaigns, where the reactor was sequentially brought to power, according to which the parameters of the Arrhenius dependence of the effective tritium diffusion coefficients were estimated.

Calculation of Temperature Fields in a Lithium Ceramic Pebble Bed during Reactor Irradiation in a Vacuum.

Two-phase lithium ceramic Li2TiO3-Li4SiO4 is considered as a tritium multiplier for use in the solid blanket of fusion reactors. To date, the most accurate understanding of the processes of tritium and helium production and release occurring in the breeder blanket materials under neutron irradiation can only be obtained from experiments in fission research reactors. At that, irradiations in vacuum give the possibility to register even very fast gas release processes (bursts) from the ceramics' voids and pores, although it reduces the thermal conductivity of the pebble bed. The purpose of this work was to simulate the heating of mono-sized pebble bed (1 mm in diameter) of two-phase lithium ceramic 25 mol%Li2TiO3+75 mol%Li4SiO4 in an ampoule device during neutron irradiation at the WWR-K research reactor under vacuum conditions, and to determine experimental parameters in order to prevent heating of the lithium ceramics up to the Li4SiO4-Li2SiO3 phase transition temperatures (>900 °C). For the first time, it was obtained that the effective thermal conductivity of a 1 mm mono-sized pebble bed of 25 mol%Li2TiO3+75 mol%Li4SiO4 significantly decreases (four times) when it is irradiated with neutrons in a vacuum (at a helium pressure of approximately 10 Pa), compared to a similar calculation at 100 kPa of helium (when the He sweep is used). It was concluded that it is difficult to evaluate the maximal temperature of the ceramics in the capsule by measuring the temperature of its outer metal wall (according to thermocouple readings) without using the results of thermophysical calculations for each type of ceramic, taking into account its quantity, specific heat release and pebble size(s). To control the temperature of the ceramics during an irradiation experiment in a vacuum, an in-capsule thermocouple should be used, placed in the center of the pebble bed. Measuring the temperature of the pebble bed based on the capsule wall temperature can lead to overheating of the ceramics and phase changes.

Study of Gas Swelling Processes under Irradiation with Protons and He2+ Ions in Li4SiO4–Li2TiO3 Ceramics

One of the important areas of research in the energy sector is the study of the prospects for using new types of nuclear fuel, including tritium, which is one of the most promising types of fuel for thermonuclear energy. At the same time, for the production of tritium in the required quantities, the one that is the most optimal is the use of blanket materials based on lithium-containing ceramics. This is where tritium is released from lithium under the influence of neutron irradiation. The paper presents the results of an investigation of the influence of two-phase ceramics based on Li4SiO4–Li2TiO3 compounds on the resistance to external influences (mechanical loads) during the accumulation of hydrogen and helium (He2+) in the near-surface layer. The interest in such studies is primarily related to the search for solutions in the field of creating high-strength materials for tritium generation for its further use as nuclear fuel for thermonuclear fusion, as well as to the study of the mechanisms of the influence of different phases on the changes in the strength properties of ceramics, which provides an opportunity to expand fundamental knowledge in this area. The proposed method of obtaining two-phase ceramics by mechanical-chemical mixing and subsequent sintering into spherical particles enables the production of well-structured, high-strength ceramics of specified geometric dimensions (limited only by the dimensions of the mold) with a controlled phase ratio. During the experiments, it was found that increasing the content of Li4SiO4 phase in ceramics leads to an increase in strength characteristics (hardness, resistance to cracking) by 15–20% compared to single-phase ceramics. The most optimal composition of two-phase ceramics with high resistance to destructive embrittlement is the ratio of phases 0.75Li4SiO4–0.25Li2TiO3. One of the factors explaining the increase in resistance to destructive embrittlement under high-dose irradiation for two-phase ceramics is the increased dislocation density and the presence of interphase or intergranular boundaries, the high concentration of which leads to the creation of additional obstacles to the agglomeration of hydrogen and helium in the near-surface layer.

He atoms diffusion and aggregation in Li2TiO3: A molecular dynamics study

Advanced reactor projects will consider the utilization of Li2TiO3 as a potential material for neutron moderation and certain radiation shielding applications in fission reactors, as well as for tritium breeder blanket material in fusion reactors. He is one of the particles produced by the reaction of Li with neutrons during the service of Li2TiO3. The diffusion and aggregation of He in Li2TiO3 can cause embrittlement failure of Li2TiO3. Understanding the diffusion and aggregation behavior of helium in Li2TiO3 is crucial for evaluating service life, as well as for the selection and design of advanced nuclear reactor components. In this paper, the diffusion of He in Li2TiO3 and the nucleation behavior of a He cluster were studied by molecular dynamics simulations. The following results were mainly obtained: (1) The long-range diffusion activation energy of He atoms in Li2TiO3 is about 0.5 eV, and it varies significantly with the change of Li vacancy content. (2) He atoms tend to be distributed in the Li layers after sufficient diffusion in Li2TiO3, so the best nucleation site for He clusters in Li2TiO3 may be located in the Li layers. (3) After a He cluster reaches a certain size, it can trigger defects by extruding an O-LiTi2-O layer in its immediate vicinity on one side and migrating with the extruded O-LiTi2-O layer. (4) A He cluster can promote their own growth by releasing pressure.