Blanket Materials Research Articles

Fusion energy: technological challenges

This paper presents an overview of the main technological challenges of magnetic confinement fusion. Many of the challenges are being addressed in the context of the ITER construction and exploitation. Specifically, the demonstration of high-fusion gain regimes of operation will also provide a test of the technological solutions presently foreseen for the management of high heat and particle loads and the integration of the main technologies of a fusion power plant. In preparation of DEMO, reliable solutions for the breeding blanket and neutron resistant materials have to be developed.

Study of Phase Formation Processes in Li2ZrO3 Ceramics Obtained by Mechanochemical Synthesis

The article is dedicated to the study of the phase formation processes in Li2ZrO3 ceramics obtained by the method of solid phase synthesis. Interest in these types of ceramics is due to their great potential for use as blanket materials in thermonuclear reactors, as well as being one of the candidates for tritium breeder materials. Analysis of the morphological features of the synthesized ceramics depending on the annealing temperature showed that the average grain size is 90–110 nm; meanwhile the degree of homogeneity is more than 90% according to electronic image data processing results. The temperature dependences of changes in the structural and conducting characteristics, as well as the phase transformation dynamics, have been established. It has been determined that a change in the phase composition by displacing the impurity LiO and ZrO2 phases results in the compaction of ceramics, as well as a decrease in their porosity. These structural changes are due to the displacement of LiO and ZrO2 impurity phases from the ceramic structure and their transformation into the Li2ZrO3 phase. During research, the following phase transformations that directly depend on the annealing temperature were established: LiO/ZrO2/Li2ZrO3 → LiO/Li2ZrO3 → Li2ZrO3. During analysis of the obtained current-voltage characteristics, depending on the annealing temperature, it was discovered that the formation of the Li2ZrO3 ordered phase in the structure results in a rise in resistance by three orders of magnitude, which indicates the dielectric nature of the ceramics.

Corrosion behavior and mechanism of CLAM and 316L steels in flowing Pb–17Li alloy under magnetic field

The liquid lead-lithium (Pb–17Li) blanket has many applications in fusion reactors due to its good tritium breeding performance, high heat transfer efficiency and safety. The compatibility of liquid Pb–17Li alloy with the structural material of blanket under magnetic field is one of the concerns. In this study, corrosion experiments China low activation martensitic (CLAM) steel and 316L steel were carried out in a forced convection Pb–17Li loop under 1.0 T magnetic field at 480 °C for 1000 h. The corrosion results on 316L steel showed the characteristic with a superficial porous layer resulted from selective leaching of high-soluble alloy elements and subsequent phase transformation from austenitic matrix to ferritic phase. Then the porous layers were eroded by high-velocity jet fluid. The main corrosion mechanism of CLAM steel was selective dissolution-base corrosion attack on the microstructure boundary regions and exclusively on high residual stress areas. CLAM steel performed a better corrosion resistance than that of 316L steel. The high Ni dissolution rate and the erosion of corroded layers are the main causes for the severe corrosion of 316L steel.

Comparative of blanket reactor design in assuring of tritium self-sufficiency

The comparison of four blanket modules in DEMO made up the optimization material having a reasonable requirement as blanket material in this study. Either neutron flux distribution in blanket material or material endurance under neutron irradiation, from four modules, the WCLL has a high tolerance neutron distribution and the best neutron irradiation endurance. Furthermore, many suggestions closed to the statement to use the benefits of water coolant and lithium lead (compose Li-6) as a material component in the blanket.

The dislocation-based fatigue deformation mechanism of a RAFM steel under multi-axial loadings

Reduced Activation Ferritic/Martensitic (RAFM) steel is a candidate blanket material for a fusion reactor, which should have outstanding performance under extreme environments containing complex thermal and stress damage during operation. To date, the properties under a single-axial loading type of tensile, creep and fatigue have been extensively reported, while the multi-axial loadings were rarely studied. Here, the multi-axial fatigue behaviors of a RAFM steel were investigated in an axial-torsional cyclic tester with controlled strain and different loading paths. The results show that the fatigue behavior of the RAFM is strongly determined by the shear-stress condition, where the lifetime under the pure torsional loading is only 16% of the uniaxial cyclic loading one. The fatigue life of the specimens under multi-axial loadings with a phase angle of 0° or 180° are comparable to that of uniaxial tension-compression one. However, it was decreased by ∼28% as the loading angle changed to 90° with a circular path. Besides, we found the fatigue softening under the proportional multi-axial loading while additional hardening in the non-proportionally multi-axial cyclic loading related to the dislocation activities during loadings. Under the proportional-multiaxial loading and uniaxial tension-compression loading and torsion loading, the high density of dislocation was rearranged and annihilated by the cyclic shear stress, while the tempered martensite lath structure was mainly retained. However, under the non-proportional multi-axial loading, dislocations transform the lath structure into a finer cell structure, improving the resistance upon fatigue deformation.

Tunable Reverse Offset Printing with a Stretchable Blanket for Fabricating Flexible Printed Electronics

The cover page shows the illustration of controlled pattern shrinkage in reverse offset printing. Young Tae Cho and co-workers demonstrate in their article, number 2001537, that the pattern size reduction by a flexible blanket material with simple mechanical stretching and releasing shed light on the low-cost, scalable, and high-resolution printing for printed electronics.

Study of Corrosion Resistance and Degradation Mechanisms in LiTiO2-Li2TiO3 Ceramic

The interest in lithium-containing ceramics is due to their huge potential as blanket materials for thermonuclear reactors for the accumulation of tritium. However, an important factor in their use is the preservation of the stability of their strength and structural properties when under the influence of external factors that determine the time frame of their operation. This paper presents the results of a study that investigated the influence of the LiTiO2 phase on the increasing resistance to degradation and corrosion of Li2TiO3 ceramic when exposed to aggressive acidic media. Using the X-ray diffraction method, it was found that an increase in the concentration of LiClO4·3H2O during synthesis leads to the formation of a cubic LiTiO2 phase in the structure as a result of thermal sintering of the samples. During corrosion tests, it was found that the presence of the LiTiO2 phase leads to a decrease in the degradation rate in acidic media by 20–70%, depending on the concentration of the phase. At the same time, and in contrast to the samples of Li2TiO3 ceramics, for which the mechanisms of degradation during a long stay in aggressive media are accompanied by large mass losses, for the samples containing the LiTiO2 phase, the main degradation mechanism is pitting corrosion with the formation of pitting inclusions.

Study of the corrosion characteristics of 304 and 316L stainless steel in the static liquid lithium

• Corrosion behavior of 316L SS and 304 SS exposed to liquid Li at 600 K for 1320 h under Argon (Ar) atmosphere were investigated. • The corrosion characteristics of 316L SS and 304 SS was compared. • 316L SS was found to be more corrosion resistant in high-temperature liquid lithium than 304 SS. Liquid lithium (Li) is considered as the tritium breeder as well as a potential blanket coolant and/or plasma-facing material (PFM) in fusion devices, while steels are widely used as an important structural material in the fusion reactors. Investigation of corrosion behaviors of steels exposed to liquid Li is one of the keys to simultaneous apply Li and steels as potential PFM or blanket materials in the fusion devices. Hence, in this study, the corrosion behavior of 304 stainless steel (304 SS) and 316L stainless steel (316L SS) in static liquid Li, at 600 K, for 1320 h, under Argon (Ar) atmosphere is analyzed. After exposed to liquid Li, the mass loss of 304 SS is about 3.6 times more than that of 316L SS. And the corrosion depth rate of 316L SS and 304 SS is 0.71 μ m / a and 2.6 μ m / a , respectively. Both the materials have shown a non-uniform corrosion behavior. The Signs of grain boundary attack, pitting corrosion, and corrosion products formation, due to the selective dissolution of elements and chemical reactions are also observed. The percentage of corrosion product formation (i.e., carbides) on the surface of 304 SS, is higher than 316L SS. The hardness of two SS materials has a slightly increased after liquid Li exposure.

Numerical study of 3D MHD flow of Pb-Li liquid metal in a rectangular U-bend

The eutectic Pb-Li alloy has been chosen as a candidate material for the liquid breeder blanket, as it offers a unique combination of tritium breeding neutron absorbing and neutron multiplying capabilities. In fusion blanket, molten Pb-Li moves under plasma confining toroidal magnetic field, producing an induced electric current inside the liquid metal due to the interaction of the moving fluid with the magnetic field. The coupling of induced electric current and magnetic field generates a Lorentz force opposite to the flow direction, and this in turn, modifies the flow profile. The experimental and numerical flow studies of liquid Pb-Li under transverse magnetic field are of great importance, as it directly impacts the blanket performance. A liquid Lead Lithium MHD loop is being developed at Institute for Plasma Research (IPR), Gujarat, India for isothermal and thermo-fluid MHD studies in blanket relevant flow geometries such as sudden expansion/contraction, coupled channels and multiple bends. A test mockup with rectangular flow cross-section and having bends perpendicular to the magnetic field has been fabricated. A 3D MHD flow analysis has been performed numerically for the test mock up at a magnetic field of 1.4T (Hartmann number of order of 1500). The fabrication details of test mockup and the results of the Pb-Li flow analysis are presented and discussed. The flow field and pressure distribution in the presence and absence of the magnetic field are also compared. The existence of recirculation zones and their redistribution in the presence of magnetic field are discussed.

Tritium release behavior from neutron-irradiated FLiNaBe mixed with titanium powder

FLiNaBe is a promising liquid blanket material for a fusion reactor. Since hydrogen solubility for FLiNaBe is low, one concern is the permeation of bred tritium. In order to increase effective solubility of hydrogen, the addition of Ti powder was proposed. In this study, the influence of Ti addition on the behavior of tritium generated inside FLiNaBe by neutron irradiation was investigated. The samples of FLiNaBe and FLiNaBe mixed with Ti of 5 wt% and 0.5 wt% were prepared and the solid-state samples were irradiated by thermal neutrons at Kyoto University Research Reactor. The neutron-irradiated samples were heated to 700 °C in an Ar gas flow. The released tritium was collected by a water bubbler and the temporal variation of TF and HT release was observed. Initially, the most of tritium was released as HT from both FLiNaBe with and without Ti but eventually, the most of released tritium was HT after long time heating from FLiNaBe with Ti. This result suggests that the addition of Ti can decrease the release of TF very much. The amount of tritium released from FLiNaBe with Ti was lower than that from FLiNaBe without Ti. This result suggests that the addition of Ti can suppress the release rate of tritium from FLiNaBe.

Study of a stainless steel porous membrane for recovering tritium from Pb-Li alloys: Assessment of mass transfer coefficient

The eutectic Pb-Li alloy is used as liquid breeding blanket material in the concept design of future fusion nuclear reactors where the effective extraction of generated tritium is an important unit operation of the fusion fuel cycle. In this context, the adoption of porous stainless steel tubes working as Membrane Gas-Liquid Contactors (MGLCs) has been proposed for recovering hydrogen isotopes from liquid Pb-Li alloys. Taking into account the results achieved in a previous experimental campaign carried out at 370 °C, the hydrogen mass transfer coefficient has been evaluated and compared with data available in literature.The present study reveals that hydrogen extraction consists of diverse steps, although it is mainly controlled by recombination of hydrogen atoms and their desorption from the gas-liquid interface. The overall permeation exhibits mass transfer resistance values in the range 10−7 – 10-6 m2 s Pa mol-1, while hydrogen transport through the MGLC pores takes place with mass transfer resistances significantly smaller (around 10-4 m2 s Pa mol-1). These results make the use of MGLCs very promising for an effective extraction of tritium from liquid breeders in fusion reactors.

Study of morphological features of lithium-containing ceramics obtained by solid-phase synthesis

This work is devoted to the study of various morphological features of LixTi1-xO3 ceramics obtained by solid-phase synthesis and subsequent thermal annealing. Interest in these ceramics is due to the great potential for their use as materials for breeders or blankets for tritium reproduction. The choice of synthesis technology is due to the wide possibilities of changing morphological features and elemental composition, due to mixing of various components in different stoichiometric ratios. During the research, it was found that for lithium-containing ceramics, thermal annealing at a temperature of 800°C leads to the following changes: for ceramics with a lithium content of X=0.1-0.2, a change in shape is observed from rhomboid and cubic to diamond-like and hexahedral, with a sharp increase in grain sizes, which is associated with sintering processes. An increase in lithium concentration in the ceramic structure of X=0.3 leads to the formation of large grains, the size of which varies from 300 nm to 500 nm. Keywords: lithium-containing ceramics, solid-phase synthesis, titanium dioxide, agglomerates, thermal annealing

Different Oxygen Desorption Durabilities of Lithium Titanium Oxides as Confirmed by Transmission Electron Energy-Loss Spectroscopy Analysis of Li4Ti5O12 and β-Li2TiO3 Biphase Specimens

Spinel-type Li4Ti5O12 and monoclinic β-Li2TiO3 phases are well known as typical functional materials in lithium titanium oxide. The former phase is practically applied as a negative electrode material for Li-ion battery systems, while the latter phase is used as a tritium breeder blanket material for thermonuclear reactors; thus, the material stability of these phases is essential for their functions. In this study, we investigate the oxygen desorption durability of oxide materials with different structures and chemical formulas by transmission electron microscopy-based electron energy-loss spectroscopy. To compare the different properties of these two phases, biphase specimens that consisted of Li4Ti5O12 and β-Li2TiO3 phases with a homogeneous thickness were successfully prepared by a two-step thermal process to perform suitable analysis by transmission electron microscopy. Irradiation with a scanning transmission electron microscopy probe, followed by electron energy-loss spectroscopy analysis, was performed in the Li4Ti5O12/β-Li2TiO3 interphase region of the biphase specimen, revealing that the oxygen desorption feature of β-Li2TiO3 was approximately one-third that of the Li4Ti5O12 phase. The stability of the cation–oxygen bond in each oxide crystal was also simulated by reaction enthalpy analysis based on density functional theory calculations, and the lattice stability of the Li4Ti5O12 phase was estimated to be three times higher than that of the β-Li2TiO3 phase. The oxygen vacancy formation energy of the β-Li2TiO3 lattice was approximately 0.8 eV higher than that of the Li4Ti5O12 phase. Thus, the reason for the different oxygen desorption durabilities of these oxide phases is not the stability of the cation–oxygen bond but the ease of reduction phase formation via oxygen desorption.

Conceptual design progress of advanced fusion neutron source

Based on the results of the IFMIF/EVEDA project in the broader approach (BA) activities, the conceptual design of the Advanced Fusion Neutron Source (A-FNS) to obtain irradiation data of DEMO blanket materials is under consideration in Japan.This paper describes the progress of the A-FNS conceptual design, which consists of a 40 MeV, 125 mA deuteron beam, a liquid lithium target system, and a test and post-irradiation test facilities. the main objectives of the A-FNS are the acquisition of RAFM irradiation data up to 2035 and the tritium recovery test on the blanket. In addition, it is expected to be used for various neutron researches.The technical design activities of the A-FNS are focused on improvement of the lithium target design, review of impurity criteria, remote handling, and irradiation application plan.

Impact of blanket material and configuration on the size of a tokamak fusion reactor

Abstract On the basis of the Korean fusion roadmap, conceptual design of the DEMO and RD the HCLL concept among liquid blanket concepts does as well, due to the good shielding capability of PbLi. The outcomes of this study provide useful guidelines for the feasibility assessment and selection for the blanket concept of the tokamak fusion reactor.

Microstructural evolution and strain hardening rule for V-5Cr-5Ti alloy

Abstract V-5Cr-5Ti alloy is a promising candidate structural material for fusion-power reactor blankets. However, its plastic deformation behavior, which is important to the safety and reliability of a fusion reactor, is not sufficiently understood. The present paper develops a physically based strain hardening model to characterize the plastic deformation of V-5Cr-5Ti alloy. Using miniaturized specimens of V-5Cr-5Ti alloy, uniaxial tensile tests and microstructural evolution analysis are performed at different strain levels. Microstructural evolution results show that the existence of Ti-enriched second phase and the dislocation interactions are critical to the plastic deformation of V-5Cr-5Ti alloy. On the above physical basis, the Ti-enriched second phase and the evolution equations of the dislocation density are developed, while the flow stress rule is formulated from the summation of athermal stress, thermally activation stress, and dispersed-phase stress. The finite element method based on the user-material subroutine UMAT (User-defined Material Mechanical Behavior) of commercial ABAQUS code (finite element analysis software) and the implicit stress update algorithm are adopted to realize the proposed physically based strain hardening model. Results suggest that this new strain hardening model is superior to conventional models for providing a more accurate and reasonable prediction of the plastic deformation behavior of V-5Cr-5Ti alloy.

Corrosion of 304 stainless steel in static liquid lithium under high vacuum

• Corrosion behaviors of 304SS exposed to liquid Li at 700 K for 1320 h under high vacuum were investigated. • Corrosion of 304 SS in liquid Li at 700 K was compared to at 600 K and 640 K. • Cu of sealing gasket was deposited on the wall of test vessel. To study the compatibility especially the corrosion characteristic of structural material stainless steel (SS) with liquid lithium (Li) is an important factor for the simultaneous application of liquid Li and SS as a blanket material or potential plasma facing material (PFM) in future fusion devices. The corrosion behaviors of 304SS exposed to liquid Li at 700 K for 1320 hr under high vacuum were investigated. After exposure to liquid Li, 304SS produces non-uniform corrosion which includes corrosion products and grain boundary corrosion. Compared with the corrosion behaviors at 600 K and 640 K, temperature plays an important role in the corrosion behaviors of 304SS in static liquid Li. The weight loss, corrosion depth and corrosion products of 304SS specimens increase with the corrosion temperature. In general, the compatibility between 304SS and static liquid Li is relatively good under the experimental conditions. And besides, it is unexpectedly found that the compatibility of copper with Li is not good.

Intrinsic defect migration in Be12Ti

Be12Ti is a leading candidate neutron-multiplier material for fusion breeder blankets; yet the evolution of the crystal defects under irradiation is poorly understood. Here, the migration of intrinsic defects in tetragonal Be12Ti was predicted using atomic scale computer simulation. Transport of titanium and beryllium through the interstitial, interstitialcy and vacancy-mediated models was considered, along with the migration of divacancy clusters, previously identified as important to the defect chemistry of Be12Ti. It was found that titanium defects exhibit much higher migration energies than beryllium for most migration pathways, leading to a dramatic difference in the self-diffusivity of the two species. Both beryllium vacancy and interstitial diffusion is close to isotropic with vacancy transport exhibiting the highest self-diffusion coefficient. Migration of beryllium di-vacancies is also isotropic with activation energy equal to that of isolated vacancies. The titanium interstitial exhibits significantly lower migration energy than its vacancy (1.00 eV and 6.75 eV respectively), with both mechanisms strongly anisotropic: the activation energy for [001] migration is at least 5 eV lower than other directions. Even the more exotic mixed titanium beryllium vacancy migration exhibits a much higher migration energy than [001] titanium interstitial transport. The framework used for predicting defect transport kinetics, including vacancy-mediated, interstitial and interstitialcy mechanisms, can be applied to any complex-structured intermetallic compound.

Conceptual design of DEMO blanket materials test modules for A-FNS

• A-FNS is a fusion-like neutron source for irradiation of fusion reactor materials. • We established conceptual designs of 3 test modules for DEMO blanket materials. • 1-BFMTM: Irradiation data for blanket functional materials are obtained. • 2-TRTM: In-situ tritium recovery properties for the materials are evaluated. • 3-ACPM: ACPs are evaluated under the fusion-like neutron irradiation. A conceptual design of A dvanced F usion N eutron S ource, A-FNS, has been conducted to achieve early realization of fusion-like neutron irradiation test for fusion reactor materials in Japan. A-FNS provides eight test modules to obtain irradiation data for fusion reactor materials. Conceptual design activities on Blanket Functional Materials Test Module (BFMTM), Tritium Release Test Module (TRTM) and Activated Corrosion Products Module (ACPM) were described among the A-FNS test modules. Also, basic concepts of the sub-system cells for the TRTM and the ACPM were also discussed.

Mechanical properties of several newly produced RAFM steels with Tungsten content in the range of 2 wt%

Abstract The contribution of ENEA together with Rina-CSM to the Eurofusion programme “WPMAT-Advanced Seels” deals with the development of innovative RAFM steels able to withstand the critical temperatures typical of the different operational environments foreseen for the blanket of the first DEMO reactor. The optimization of the chemical composition and the Thermo Mechanical Treatment for these materials should be done according to the blanket operating temperatures that are related to two possible working conditions: the WCLL-BB (Water Cooled Lead Lithium Breeding Blanket) or the H(D)CLL-BB (Helium (Dual) Cooled Lead Lithium Breeding Blanket). On the one hand the “water-cooling” option implies a minimum irradiation temperature for the blanket material in the range of 280–350 °C. On the other hand, the “helium-cooled” and the “dual-coolant” solutions imply an operating temperature for the blanket material in the range of 650 °C. Therefore in the first case the target is the improvement of the toughness of the martensitic alloys; whilst concerning the second scenario the target is the development of more creep resistant martensitic steels, suitable to tolerate such a high operating temperature. In both the cases the Tungsten content plays a key role, both in terms of solid solution hardening and influence on the DBTT. Two alloys aimed at fulfilling the specifications for the two DEMO operating conditions, both with increased Tungsten content respect to Eurofer, have been produced and characterized. The mechanical properties of these two alloys are hereby reported and discussed.