Advanced Neutron Multipliers Research Articles

Blistering Behavior of Beryllium and Beryllium Alloy under High-Dose Helium Ion Irradiation.

Beryllium (Be) has been selected as the solid neutron multiplier material for a tritium breeding blanket module in ITER, which is also the primary option of the Chinese TBM program. But the irradiation swelling of beryllium is severe under high temperature, high irradiation damage and high doses of transmutation-induced helium. Advanced neutron multipliers with high stability at high temperature are desired for the demonstration power plant (DEMO) reactors and the China Fusion Engineering Test Reactor (CFETR). Beryllium alloys mainly composed of Be12M (M is W or Ti) phase were fabricated by HIP, which has a high melting point and high beryllium content. Beryllium and beryllide (Be12Ti and Be12W) samples were irradiated by helium ion with 30 keV and 1 × 1018 cm-2 at RT. The microstructures of Be, Be12Ti and Be12W samples were analyzed by SEM and TEM before and after ion irradiation. The average size of the first blistering on the surface of Be-W alloy is about 0.8 μm, and that of secondary blistering is about 79 nm. The surface blistering rates of the beryllium and beryllide samples were also compared. These results may provide a preliminary experimental basis for evaluating the irradiation swelling resistance of beryllium alloy.

Compression properties of beryllide pebbles at high temperatures

DEMO (demonstration) fusion reactors require advanced neutron multipliers with low swelling and high stability at high temperatures. Research on beryllium intermetallic compounds (beryllides (Be12V)) has been conducted, and the authors have successfully fabricated Be12V and Be12Ti0.3V0.7 ternary pebbles, which are considerably stable at high temperatures. In this study, to evaluate the mechanical properties of these pebbles, compression tests for a single pebble were performed at room temperature and high temperatures of 600 and 800 K. Be12Ti0.3V0.7 pebbles exhibited a higher crush load than Be12V pebbles; Be12Ti0.3V0.7 pebbles comprised remarkably fine grains due to dual phases. Scanning electron microscopy images of the fractured area demonstrated that the Be12V pebbles had a relatively large fracture with sharp edges, whereas the Be12Ti0.3V0.7 pebbles included considerably small grains. There was no noticeable temperature dependence of the crush load. The fracture and tensile strengths of Be12V and Be12Ti0.3 V0.7 pebbles were evaluated.

Deuterium desorption and retention of Beryllium intermetallic compounds for fusion applications

Beryllium intermetallic compounds (beryllides) such as Be12Ti and Be12V are the most promising advanced neutron multipliers in demonstration (DEMO) power reactors because of their low swelling and high stability at high temperatures. In this work, beryllides pebbles with binary and ternary compositions were successfully fabricated by combining plasma sintering and rotating electrode methods. After 3 keV D2+ ions were implanted to the beryllides pebbles, the deuterium desorption and retention properties were investigated by thermal desorption spectroscopy to investigate hydrogen desorption and retention of these materials for fusion application.The desorption properties and retention of hydrogen isotopes (deuterium) using the newly developed beryllide pebbles indicated that the beryllide pebbles exhibited better deuterium desorption properties, such as lower starting-up temperature, total retention, and activation energy for deuterium desorption than beryllium.

A recycling process on vanadium beryllium intermetallic compounds as advanced neutron multipliers for DEMO fusion applications

Abstract Beryllium intermetallic compounds (beryllides) are known as promising materials for advanced neutron multipliers for fusion applications owing to their high stability and low swelling. Because a large amount of beryllium is used for each solid breeding blanket in fusion reactors, the development of effective and efficient recycling processes is essential. In this study, a proper recycling process of Be12V pebbles was proposed, which combines a plasma sintering and a rotating electrode method for the fabrication of beryllide pebbles. As a result of experiments, it is determined that the rotating electrode method is available to reduce oxygen impurities, whereas the plasma sintering process can eliminate Li impurities and hydrogen isotope depending on sintering temperature. Regarding the recycling process, the beryllide pebbles used can be recycled into rods by plasma sintering, in which Li impurity and tritium can be eliminated. Then, recycled rods can be granulated by the rotating electrode method. During this process, it is anticipated that oxygen impurities and irradiation defects can be eliminated because the rotating electrode method includes the melting process. Thus, the current process was determined to be appropriate as a recycling process for beryllide pebbles.

Development and characterization of advanced neutron multiplier materials

Neutron multiplier materials are essential for self-sufficient tritium production and are closing the fuel cycle of fusion reactors. Until now, a concept of pebble bed consisting of interchanging layers of beryllium and lithium ceramic pebbles was considered for the Helium-Cooled Pebble Bed (HCPB) tritium-breeding module of the first experimental fusion reactor ITER as well as for the next demonstration fusion reactor DEMO. However, this concept depends on the availability of large amounts of pure beryllium pebbles and is also limited by its material properties like for example the tritium accumulation under irradiation.The results of tritium retention and analytical microstructural studies of beryllium pebbles obtained within the framework of the HIDOBE irradiation campaign suggest that a significant fraction of generated tritium (up to 100% below 500°C) is trapped within helium bubbles. Being negligible in the ITER tritium-breeding module (TBM), the total accumulated tritium inventory imposes severe safety issues and exceeds acceptable limits for the DEMO blanket. Therefore, advanced neutron multiplier materials such as beryllides have to be well characterized for their applicability in the HCPB blanket of DEMO and beyond. The usage of an advanced material with lower volumetric swelling, lower tritium retention, increased irradiation and chemical resistance as well as with higher melting temperature allows to switch from the pebble bed concept to a solid hexagonal block-based one. For the fabrication of titanium beryllide samples both the semi-industrial fabrication route utilizing the hot extrusion of rods and the industrial approach using vacuum hot pressing of a Be-Ti powder mixture were explored. In this contribution, we discuss reasons for the transition from pure beryllium to beryllides, respective changes of the HCPB blanket design and a successful demonstration of the feasibility of a beryllide block fabrication by an industrial method.

Tritium release and retention in beryllium and titanium beryllide after neutron irradiation up to damage doses of 23-38 dpa

• For the first time, beryllium and titanium beryllide as massive pellets were irradiated in a nuclear reactor at temperatures of 710−1040 K up to production of 430–653 appm tritium and 4144–5992 appm helium, respectively. • The tritium retention in irradiated Be-7at.%Ti pellets is much lower than that in Be pellets, for example, 1 and 0.5 % to 48 and 34 % at 940 and 1040 K, respectively. • Open channels along grain and sub-grain boundaries are formed under neutron irradiation in beryllium, essentially contributing to the enhanced tritium release. Titanium beryllide is considered as an advanced neutron multiplier in the Helium Cooled Pebble Bed (HCPB) blanket of DEMO. Neutron irradiation of titanium beryllide together with beryllium as a reference material in material testing nuclear reactors can give essential data for the DEMO blanket design. Be-7at.%Ti (Be-7Ti) as well as Be were irradiated in the HFR, Petten, the Netherlands, at four temperatures of 710, 800, 940, 1040 K up to 23, 31, 36, 38 dpa, respectively. The post-irradiation examination (PIE) included thermal-programmed desorption (TPD) and Vickers hardness tests as well as microstructure study by optical metallography. Be and Be-7Ti pellets maintained their integrity after irradiation. Microstructure of Be-7Ti contains two phases, mainly, TiBe 12 , and also small amount of Be. Under irradiation, gas bubbles were formed in Be samples as well as in Be-phase in Be-7Ti samples. These bubbles contain helium and tritium produced in Be under irradiation. TPD tests showed a much lower tritium retention in Be-7Ti than in Be for all four irradiation temperatures. Vickers hardness of TiBe 12 phase is much higher than that of Be-phase. According to the obtained data, Be-7Ti could be considered more preferred than Be as a neutron multiplier material in future fusion reactors due to the enhanced radiation damage resistance.

Compatibility of advanced tritium breeders and neutron multipliers

Abstract A new blanket concept of demonstration (DEMO) fusion reactors has been suggested using a mixture of tritium breeders and neutron multipliers. This concept requires long-term stability between tritium breeders and neutron multipliers. To verify the feasibility of the mixing pebble packing concept, compatibility tests of Li-access Li2+xTiO3+y with 20 % Li2ZrO3 (hereinafter referred to as LTZO) and Be12V as an advanced tritium breeder and neutron multiplier, respectively were performed at 973 K, 1073 K, and 1173 K for 100 h, 300 h, and 1000 h, respectively. Cross-sectional scanning electron microscopic observations and X-ray diffraction (XRD) analysis revealed that Be oxides (Li with small intensity) were formed on the surface of Be, however, no reaction layer or a very thin layer was identified. Clarity was received that as the time at each temperature increased, the thickness tended to increase. The thickness of the reaction layer could be described by a parabolic rate law. The conclusion was reached that Be12V in contact with LTZO had a reaction layer whose growth rate was considerably lower by one order of magnitude than that of Be in contact with LTZO.

Mechanical compression behaviors of single phase Be and binary Be12Ti pebbles

Beryllium pebbles are planned to be used as a neutron multiplier in the Helium-cooled ceramic breeder (HCCB) tritium breeding blanket module (TBM) of ITER, which is also the primary option of the Chinese TBM program. Advanced neutron multipliers such as Be12Ti beryllide with high stability at elevated temperature are desired for demonstration power plant (DEMO) reactors. Prototypic pebbles 1 mm in diameter of single phase Be and 0.7 mm in diameter of binary Be12Ti beryllide were successfully fabricated by a combination method involving hot isostatic pressing and rotating electrode process. Surface microstructure of Be and Be12Ti pebbles were analyzed by using AFM and SEM. Compression properties of Be and Be12Ti pebbles were evaluated by mechanical compression. Beryllium pebbles displayed high ductility (50% deformation without fracture), which is better than that of beryllide pebbles. One method based on contact mechanics was introduced to evaluate the range of effective modulus and stiffness of Be and Be12Ti from compression load curves in the elastic regime.

Characterization of modified Be13Zr beryllide pebbles as advanced neutron multipliers

Pebbles with Be13Zr composition that do not exhibit a peritectic reaction during granulation were successfully fabricated directly by a rotating electrode granulation method without homogenization treatment. However, Be13Zr pebbles found out to exhibit the pest phenomenon at low temperatures and the disintegration to powdery caused by catastrophic oxidation. Results obtained from trial granulation experiments with modifications revealed the successful development of Be13Zr pebbles without the pest reaction with the addition of Si. The pest reaction was supposedly prevented by the uniform dispersion of Si in Be13Zr pebbles.

Anomalous oxidation behavior in a zirconium beryllium intermetallic compound

Beryllium intermetallic compounds (beryllides) are well-known refractory and functional materials for fission and fusion applications, specifically as reflectors and multipliers. For advanced neutron multipliers, our research group has investigated many kinds of beryllides. Due to its nuclear properties, single phase Be13Zr beryllide was selected and successfully fabricated via plasma sintering of the homogenized Be13Zr powder. Its reactivity against 15% H2O was evaluated, and unexpected catastrophic oxidation (pest reaction) occurred at a low temperature range, from 973 to 1123 K, leading to the disintegration into a powder. This is caused by the intergranular degradation on the boundaries between the oxide layer and the matrix, as well as the continuous oxidation through cracks that arise from stress generation on the oxides. However, this pest reaction was suppressed by Si doping. Si likely relieves the stress near the grain boundary and in the oxide layer. The Si-doped Be13Zr had the lowest hydrogen generation rate among the evaluated samples at 1273 and 1473 K, which is also much lower by approximately two or three orders of magnitude than that of Be at 1273 K.

Valence Electron and Chemical State Analysis of Be12M (M = Ti, V) Beryllides by Soft X-ray Emission Spectroscopy

Be-rich intermetallics (beryllides) have gathered wide attentions to be adopted for high temperature environments, such as an advanced neutron multiplier in fusion reactors. This study reveals the ...

Fabrication and characterization of Be12V pebbles with different diameters

Neutron multipliers with lower swelling and higher stability at elevated temperatures are desired for the pebble bed blankets of designed DEMO rector. Among beryllium-based intermetallic alloys, vanadium beryllide Be12V is considered to be an attractive material from the point of view of its potential use as an advanced neutron multiplier of the breeding blanket.Rotating electrode method (REM) was applied in this study for fabrication of sphere-shaped Be12V pebbles using a plasma-sintered Be-V electrode. Be-V electrode as raw material played a role of the target which was melted and centrifugally ejected in the form of spherical droplets in the helium-filled atmosphere of REM apparatus. Since the angular rotation speed of Be-V rod is one of the important technological parameters which significantly influences the sizes of produced pebbles, the wide operating range (2000–10000 rpm) was selected by granulation process and produced batches of pebbles were analyzed. The yield properties, sizes and some characteristics of microstructure of fabricated vanadium beryllide pebbles are summarized and discussed in this work. Besides this, the first results on investigation of the packing density of single- and binary-sized pebble beds consisting of Be12V pebbles showed that the maximal achieved packing factor values are, accordingly, about 64–65 and 80%.

Reactivity and thermal stability of ternary Be-Zr-V beryllides

A water-cooled solid breeder blanket of a fusion reactor has been adopted in Japan, which focuses on safety concerns; safety is one of the most critical issues. In particular, as a multiplier, Be pebbles are well known to possibly generate hydrogen and react in an exothermic manner due to reaction with H2O during the loss of coolant accident. In contrast to these Be pebbles, beryllium intermetallic compounds (beryllides) demonstrate promise due to their more stable chemical reactivity at high temperatures. Currently, several studies have reported the development of advanced neutron multipliers in Japan, and the EU is part of the demonstration R&D activities at the International Fusion Energy Research Center project, which forms a part of the Broader Approach program. Fabrication methods for beryllide pebbles have been successfully developed by the combination of plasma sintering synthesis and a rotating electrode granulation method.By employing these methods, ternary beryllide pebbles with mixtures of Be13Zr and Be12V were first synthesized with ratios of 1.0:1.0, 1.0:0.8, 1.0:0.6, 1.0:0.4, 1.0:0.2, and 1.0:0.1. The small-sized Be13Zr phase as the precipitate and the Be12V phase were formed without the formation of the Be phase as these compositions did not exhibit the peritectic reaction. In addition, ternary beryllide pebbles exhibited a lower reactivity to water vapor as well as a higher thermal stability than Be pebble. In this study, not only the synthesis but also characterizations at high temperatures were discussed.

Granulation of Be12V pebbles using the rotating electrode method

Hydrogen generation via the oxidation of beryllium (Be) in the presence of water vapor at high temperatures needs to be minimized in fusion reactors because of safety concerns. Advanced neutron multipliers with increased stability at high temperatures are desirable in pebble bed blanket design with water coolant. Beryllium intermetallic compounds (e.g., vanadium beryllide Be12V) are a promising material that can be used as advance neutron multipliers. Granulation aims to produce beryllide pebbles that are a critical element in the development of advanced neutron multipliers.Based on previous trial granulations of beryllides, a rotating electrode method (REM) was selected [1–3]. Furthermore, its experimental dataset is broad, covering beryllium and metallic pebbles. Rod-shaped beryllide blocks are necessary to fabricate beryllide pebbles via the REM. Hot isostatic pressing and casting have been proposed to synthesize beryllides. However, pure beryllium-based intermetallic compounds have very limited plasticity at high rotational speeds. The use of Be–V rods containing pure beryllium phase was considered a reasonable solution to this problem. The microstructure of Be–V rods and pebbles confirmed that the REM produced single-phase Be12V pebbles from multiphase Be–V rods. Special emphasis has been placed on the yield properties, size distribution, and sphericity of vanadium beryllide pebbles fabricated under different granulation conditions. The effect of rotational speed and electric current on pebble fabrication with the REM is discussed in this study. Taking into account the high costs and restricted availability of beryllium products, the perspective of material re-use was also considered by the process development and appropriate granulation trials were performed.

Fabrication and characterization of Be-Zr-Ti ternary beryllide pebbles

Beryllium intermetallic compounds (beryllides) such as Be12Ti, Be13Zr and Be12V are the most promising advanced neutron multipliers for DEMO reactors (DEMOnstration fusion power plant). Plasma sintering and the rotating electrode methods for the fabrication of beryllide rods and pebbles have been established and a new chemical composition has been suggested as development of more advanced neutron multipliers. By using these methods, preliminary synthesis of the ternary Be-Zr-Ti pebbles has been conducted. In the Be13Zr1-xTix composition (x = 0.1, 0.3, 0.5, 0.7 and 0.9), some of the pebbles showed the existence of a Be phase on the surface, which results in mass gain and hydrogen generation. Ternary beryllide pebbles were successfully fabricated from mixtures of Be12Ti and Be13Zr with ratios of 1:1, 1:0.6, 1:0.4, 1:0.2 and 1:0.1. As a result of the SEM observations, it was clear that no Be phase was found on the surface of the pebbles despite of the fact that some fractions were identified inside the pebbles. For stability with 1% water vapor of as-received ternary pebbles at high temperatures, it was clear that those indicated much lower hydrogen generation, which corresponds to much higher stability than Be pebbles at high temperatures.

Thermal properties of beryllides as advanced neutron multipliers for DEMO fusion application

The hydrogen generation with steam is a major drawback of using beryllium (Be) as neutron multipliers in water-cooled blankets. Advanced neutron multipliers having considerable stability at high temperatures are desirable and beryllides depict a strong potential to be applied. Be12V pebbles were successfully fabricated directly using the rotating electrode method. Hydrogen generation ratio and heat of reaction due to the hydrogen generation reaction of Be12V was observed to be two orders of magnitude less than that of Be. Be12V exhibited good resistance to steam. By performing computer simulations at the loss of coolant accident (LOCA), thermal excursion was observed to be very sensitive to the initial temperature under Be pebble packed blanket conditions. However, better thermal stability was observed for the beryllide-steam reaction.

Characterization of vanadium beryllide pebble bed for the Japan DEMO blanket application

Beryllium intermetallic compounds (beryllides) are promising materials as advanced neutron multipliers for high-temperature applications. Methods of fabricating beryllides pebbles have been successfully developed by combining plasma sintering and rotating electrode granulation. To prevent an increase in the surface area and reactivity, as in the homogenized Be12Ti, we fabricated and characterized prototype pebbles of Be12 V, which do not undergo peritectic reactions during cooling. The Be12V pebbles were successfully fabricated without homogenization. The Be12V pebbles have good oxidation resistance with low hydrogen generation. The granulation yield of Be12 V pebbles was 70%. Packing fraction exhibited 60.5%. by vibration compaction with constrain. The effective thermal conductivity of a Be12V pebble bed with no-constraint was successfully measured.

Development of beryllide pebbles with low-hydrogen generation as advanced neutron multipliers

Hydrogen generation via an oxidation reaction of Be with water vapor at high temperatures should reduce the safety associated with fusion reactors. Advanced neutron multipliers with higher stability at high temperatures are desired as replacements for the existing Be neutron multipliers for the pebble bed blanket design using a water coolant. Beryllium intermetallic compounds (beryllides) are the most promising material for advanced neutron multipliers. In this study, prototypic beryllide pebbles, Be12Ti and Be12V, were successfully fabricated using the rotating electrode granulation method with a plasma-sintered beryllide electrode. The beryllides pebbles were much more resistant to water vapor than pure Be pebbles. The surface BeO layer on the beryllide pebbles was shown to act as a protective barrier against hydrogen generation reaction.

Deuterium retention and desorption properties of ternary beryllide pebbles as advanced neutron multipliers

Beryllium intermetallic compounds (beryllides) such as Be12Ti and Be12V are the most promising advanced neutron multipliers in demonstration (DEMO) power reactors because of their low swelling and high stability at high temperature. In this work, single-phase Be12Ti and Be12V pebbles produced by a novel process combining plasma sintering and rotating electrode methods were successfully fabricated. In parallel to the successful fabrication of binary beryllide pebbles, new research and development on ternary beryllides was begun to determine preferable pebble compositions in terms of mass production and improved properties. The desorption properties and retention of hydrogen isotopes (deuterium) using the newly developed ternary beryllide pebbles indicated that the ternary pebbles exhibited better deuterium desorption properties, such as lower starting-up temperature, total retention, and activation energy for deuterium desorption, than these for beryllium.

Thermal analyses of beryllide pebbles in water vapor atmosphere as advanced neutron multipliers

The safety of the water coolant solid breeder blanket of a fusion reactor has become one of the most critical issues. In particular, Be pebbles as a multiplier material have been well-known to generate hydrogen and exothermally react while reacting with water vapor at high temperature. Unlike these Be pebbles, beryllium intermetallic compounds (i.e., beryllides) are one of the most promising materials because of their significantly higher chemical stability.Beryllides pebbles have been successfully fabricated by a number of approaches developcombining plasma sintering synthesis and rotating electrode granulation methods Thus, as-received Be12Ti pebbles (consisting of Be, Be12Ti, and Be17Ti2 phases), homogenized Be12Ti pebbles, and as-received Be17Ti2 pebbles have been successfully fabricated. The oxidation, hydrogen generation, and thermal expansion properties of these pebbles were investigated and compared with those of the reference Be pebbles.Beryllides pebbles were significantly more resistant to oxidation by H2O while generating lower amounts of hydrogen as compared to Be pebbles. Among these beryllides pebbles, homogenized Be12Ti pebbles and as-received Be17Ti2 pebbles showed lower weight gain and hydrogen generation than as-received Be12Ti because the latter contained some fractions of Be phase inside the pebbles. With regard to thermal expansion, it was obvious that the beryllides exhibited lower coefficients of thermal expansion (CTE) than Be.