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Beryllium and beryllium intermetallic compound (beryllide) pebbles have been regarded as a neutron multiplier in an international thermonuclear experimental reactor (ITER), as well as a demonstration (DEMO) fusion reactor. A novel fabrication process of the beryllide pebbles has been successfully established by combining the plasma sintering and rotating electrode processes. However, owing to the brittleness of beryllides, their granulation yield is approximately 70%, which does not generally satisfy the requirement, whereas the fragments (designated to be not spherical) with 30% are generated as by-products. To improve the granulation yield and in considering a new recycling process, a novel step on fundamental experiments was adopted to confirm feasibility on the recycling process using the same plasma sintering and rotating electrode processes. Because the formation of oxidized surface and neutron-induced defects in these materials is anticipated, these defects should be eliminated during the recycling process. The plasma sintering process is known to remove impurities on powder surfaces by applying a pulse current, whereas the rotating electrode process (REP) is a granulation process that uses arc melting at a temperature higher than the melting point. Hence, a feasibility test on the recycling process was performed by applying this process with the fragments for the pebbles simulated as the used pebbles. In the case of mixture ratios of 1:1 and 2:1 for the mixed powders and fragments, respectively, and the powders pulverized by 100% fragments, the rods produced through plasma sintering were successfully fabricated even if several areas with low density are identified. Not all rods were broken during the REP, indicating granulation results with similar size distribution and yield. Regarding the oxygen contents of as-received pebbles, fragments, and rod and pebbles produced with 100% fragments, the plasma sintering effect on impurity cleaning is therefore not significant, whereas the REP evidently leads to remarkable reduction of oxygen as impurity. [ABSTRACT FROM AUTHOR]

• Prototypic pebbles of Be 13 Zr were successfully fabricated directly by the rotating electrode granulation method using the plasma-sintered beryllide electrode without homogenization treatment. • Be 13 Zr is one of intermetallic with the pest reaction that is disintegration caused by oxidation. • The dispersion of insoluble element in Be 13 Zr was tried for reduction of stress of oxidation reaction. • The Be 13 Zr pebbles without the pest reaction successfully fabricated by the addition of Si as insoluble element in Be. Pebbles with Be 13 Zr composition that do not exhibit a peritectic reaction during granulation were successfully fabricated directly by a rotating electrode granulation method without homogenization treatment. However, Be 13 Zr 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 Be 13 Zr pebbles without the pest reaction with the addition of Si. The pest reaction was supposedly prevented by the uniform dispersion of Si in Be 13 Zr pebbles. [ABSTRACT FROM AUTHOR]

Abstract Beryllium intermetallic compounds (beryllides) such as Be 12 Ti, Be 13 Zr and Be 12 V 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 Be 13 Zr 1-x Ti x 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 Be 12 Ti and Be 13 Zr 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. [ABSTRACT FROM AUTHOR]

Abstract: Advanced neutron multipliers with low swelling and high stability at high temperatures are desired for pebble bed blankets of demonstration fusion power (DEMO) reactors. Beryllium intermetallic compounds (beryllides) are the most promising advanced neutron multipliers. In order to fabricate the beryllide pebbles, beryllide with shapes of block and/or rod is necessary when a melting granulation process is applied such as a rotating electrode method. A plasma sintering method has been proposed as new technique which uses a non conventional consolidation process. It was clarified that the beryllide could be simultaneously synthesized and jointed by the plasma sintering method in the insert material region between two beryllide blocks. Beryllide rod of Be12Ti with 10mm in diameter and 60mm in length has been successfully fabricated by the plasma sintering method. Using this plasma-sintered beryllide rod, fabrication of prototype beryllide pebble was performed by a rotating electrode method as one of the melting methods. The prototype pebbles of Be12Ti with 1mm in average diameter were successfully fabricated. [Copyright &y& Elsevier]

Abstract: Fusion reactors require advanced neutron multipliers with higher stability at high temperatures. Beryllium intermetallic compounds (beryllides) such as Be12Ti are the most promising advanced neutron multipliers. In order to fabricate the beryllide pebbles, a new granulation process has been established that combines a plasma sintering method for beryllide synthesis and a rotating electrode method for granulation. The results of synthesis show that beryllide rod has been successfully fabricated by the plasma sintering method. From this plasma-sintered beryllide rod, prototypic beryllide pebbles of 1mm average diameter were also successfully fabricated, by the rotating electrode method. Unfortunately, remelting changed the compositional structure of the beryllide pebbles. To homogenize the Be12Ti phase, annealing treatments were examined. The pebble phase was successfully homogenized to a single phase of Be12Ti by annealing either at 1473K for more than 8h or at 1673K for 1h. [Copyright &y& Elsevier]

Abstract: Beryllium intermetallic compounds (beryllides) such as Be12Ti are very promising candidates for advanced neutron multiplier materials in a demonstration fusion power reactor (DEMO). However, beryllides are too brittle to be fabricated either into pebble-type or rod-type shapes via conventional methods (i.e. arc melting and hot isostatic pressing). We have proposed a plasma sintering technique as a new method for beryllide fabrication, and our studies on the properties of plasma sintered beryllides are ongoing. In the present work, the oxidation properties of plasma sintered beryllides were investigated at 1273K for 24h in a dry air atmosphere to evaluate the high temperature properties of this material. Thermal gravimetry measurements indicate that specimens with larger fractions of Be12Ti phase corresponding to samples that have been sintered for longer time periods, exhibit superior oxidation properties. Our evaluation of the oxidation behavior of each phase in our beryllide samples is as follows: Be12Ti and Be17Ti2 both have good oxidation resistance, owing to the formation of dense and protective scales, while the Be and Be2Ti phases are mainly responsible for thermal-gravimetry (TG) weight gains, which is indicative of severe oxidation. We attribute the degradation in oxidation resistance specifically to Be2Ti that transforms into TiO2, and also find this phase to be the cause of deterioration in the mechanical properties of samples, owing to cracks near Be2Ti phase conglomerates. [Copyright &y& Elsevier]

Abstract: Advanced neutron multipliers with low swelling and high stability at high temperature are desired for pebble bed blankets, which will impact on the DEMO design features, especially blanket operating temperature. Among candidates for multiplier, beryllium intermetallic compounds (beryllides) are one of the most promising advanced neutron multipliers. In order to fabricate the beryllide pebble, beryllide with the shape of rod are necessary if a melting granulation method is applied. A plasma sintering method and a high-frequency heating method have been proposed as a new technique, because these methods are simple process and easy to control. A plasma sintering method for beryllide synthesis has been proposed as a new technique which uses a non-conventional consolidation process. The present paper describes beryllide synthesis results using this method for development of fabrication technique for a beryllide rod. It was clarified that the beryllide could be both synthesized and jointed with no variation of phase and hardness by the plasma sintering method. Additionally, trial synthesis of beryllide by a melting process using high-frequency heating was carried out. Although there were some pores in a melted ingot, beryllides could be also synthesized by this method. [Copyright &y& Elsevier]

Abstract: Beryllium metal is considered as the neutron multiplier in the pebble bed blanket. On the other hand, advanced neutron multipliers with lower swelling and higher stability at high temperature are desired in pebble bed blankets for DEMO. Beryllium intermetallic compounds (beryllides) are the most promising advanced neutron multipliers. However, beryllides are too brittle to allow production of pebbles. Establishing fabrication techniques for beryllides is a key issue of advanced neutron multiplier development. In the previous study, it was clear that the intermetallic compound beryllides of Be–Ti can be directly synthesized by the plasma sintering method. In this study, it reports on the trial fabrication results of beryllides synthetic such as Be–V and Be–Nb using plasma sintering method for applicability evaluation of beryllide synthesis. The formation of Be–V and Be–Nb intermetallics was identified using a mixture of Be and V or Be and Nb particles for the plasma sintering method. [Copyright &y& Elsevier]

• Compatibility tests between advanced tritium breeders and neutron multipliers were performed at 973, 1073 and 1173 K. • A reaction layer with a thickness of less than a few μm at 1073 K or 1173 K for 100 h formed on the Be 12 V surface. • Be 12 V in contact with LTZO had a reaction layer whose growth rate was considerably lower than Be in contact with LTZO. 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 Li 2+x TiO 3+y with 20 % Li 2 ZrO 3 (hereinafter referred to as LTZO) and Be 12 V 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 Be 12 V 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. [ABSTRACT FROM AUTHOR]

Abstract 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 Be 12 V) 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 Be 12 V 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. [ABSTRACT FROM AUTHOR]

Abstract: Beryllides are advanced neutron multipliers, and many research studies on their fabrication have been carried out. In this study, the effect of sintering time on synthesis of beryllides fabricated by plasma sintering was investigated. Stoichiometric mixtures of fine Be and Ti powders were sintered to more than 98% of their theoretical density value. From X-ray diffraction and electron probe microscopic analysis measurements, the formation of beryllides such as Be12Ti, Be17Ti2, and Be2Ti intermetallics was identified at 1273K for sintering times from 5 to 90min under 50MPa pressure, starting from mixed powder particles of Be and Ti. Although there was a deviation of phase between the center and the edges in the disks, it was confirmed that with increasing time, the area fraction of Be12Ti, which is the compositional target for neutron multipliers, was increased about 96%. [Copyright &y& Elsevier]

Beryllium intermetallic compounds (beryllides), are the most promising advanced neutron multipliers in demonstration (DEMO) fusion power reactors because of their low swelling and high stability at high temperatures. From the viewpoint of tritium production in beryllium/beryllides induced by several continuous reactions to neutrons, an application for use as a fuel as well as an appropriate management of tritium is of considerable importance. To simulate the high-temperature behavior of tritium, in this study, the desorption and retention properties of deuterium were investigated by evaluating deuterium ion implantation at high temperatures and desorption behaviors. As results of the desorption properties and retention of Be 12 V, deuterium implanted at high temperatures tends to easily desorb whereas Be 12 V has a considerably low retention of deuterium in the case of implantation at high temperatures. Moreover, the TEM observation proved that deuterium bubbles in Be 12 V implanted at R.T. and 573 K disappeared at annealing temperatures above 773 K, whereas deuterium bubbles in Be 12 V implanted at 773 K were not identified, indicating that the bubbles were generated but desorbed. [ABSTRACT FROM AUTHOR]

To investigate feasibility for application of Be 17 Ti 2 as a neutron multiplier as well as a refractory material, single-phase Be 17 Ti 2 intermetallic compounds were synthesized using an annealing heat treatment of the starting powder and a plasma sintering method. Scanning electron microscopic observations and X-ray diffraction measurements reveal that the single-phase Be 17 Ti 2 compounds were successfully synthesized. We examined the reactivity of Be 17 Ti 2 with 1% H 2 O and discovered that a larger stoichiometric amount of Ti resulted in the formation of TiO 2 on the surface at high temperatures. This oxidation may also contribute to an increase in both weight gain and generation of H 2 . This suggests that the formation of the Ti-depleted Be 17 Ti 2− x layer as a result of oxidation facilitates an increased reactivity with H 2 O. To evaluate the safety aspects of Be 17 Ti 2 , we also investigated the hydrogen positions and solution energies based on the first principle. The calculations reveal that there are 10 theoretical sites, where 9 of these sites have hydrogen solution energies with a positive value (endothermic) and 1 site located at the center of a tetrahedron comprising two Be and two Ti atoms gives a negative value (exothermic). [ABSTRACT FROM AUTHOR]

• The greatest degradation in the thermal conductivity of Be material occurs at highest irradiation temperatures of 940 and 1040 K. • Thermal conductivity of Be-5Ti and Be-7Ti materials decreases to a lesser extent but for all irradiation temperatures of 710, 800, 940, 1040 K. • The Be-7Ti material, containing a minimum volume fraction of Be-phase, has minimum values in the thermal conductivity before (43–50 W/(m·K)) and after (30–38 W/(m·K)) irradiation. The neutron irradiation of Be, Be-5Ti and Be-7Ti samples in the HFR, Petten, the Netherlands, at temperatures of 710, 800, 940, 1040 K up to damage doses of 23, 31, 36, 38 dpa, respectively, leads to a degradation in the thermal conductivity, depending on the Be-phase content and the radiation-induced porosity in these materials. The Be samples irradiated at the two highest irradiation temperatures of 940 and 1040 K have a maximum drop in the thermal conductivity because these samples have the highest porosity. A lesser decrease in the thermal conductivity of Be-5Ti and Be-7Ti materials occurs for all four irradiation temperatures of 710, 800, 940, 1040 K. The thermal conductivity of Be-5Ti and Be-7Ti depends on the Be-phase content in both initial and irradiated states. The Be-7Ti material contains a minimum volume fraction of the Be-phase, therefore, it has minimum values of the thermal conductivity for both unirradiated (43–50 W/(m·K)) and irradiated (30–38 W/(m·K)) states. [ABSTRACT FROM AUTHOR]

• Effective and efficient recycling processes are essential for solid breeding blanket in fusion reactors. • We evaluated the possibility of applying the currently used process for beryllide pebble fabrication for their recycling. • The current fabrication process found out to be effective to eliminate some impurities. • The plasma sintering can eliminate Li impurity and tritium while the REM can reduce oxygen impurity. 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 Be 12 V 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. [ABSTRACT FROM AUTHOR]