• Energy Research

The paper presents the results of a molecular dynamics simulation of cascade damage production in beryllium caused by self-ion recoils in the energy range of 0.5–3 keV. It is demonstrated that point de- fects are produced in Be preferentially in well-separated subcascades generated by secondary and higher order recoils. A linear dependence of the point defect number on the primary recoil energy is obtained with the slope that corresponds to formal atom displacement energy of ~21 eV. Most of the damage is created as single defects and the relatively high part of created point defects ( ∼50%) survives the corre- lated recombination following the ballistic cascade stage and becomes freely-migrating.

Study of tritium and helium release from beryllium pebbles with diameters of 0.5 and 1 mm after high- dose neutron irradiation at temperatures of 6 86–96 8 K was performed. The release rate always has a single peak, and the peak temperatures at heating rates of 0.017 K/s and 0.117 K/s lie in the range of 1100–1350 K for both tritium and helium release. The total tritium release from 1 mm pebbles decreases considerably by increasing the irradiation temperature. The total tritium release from 0.5 mm pebbles is less than that from 1 mm pebbles and remains constant regardless of the irradiation temperature. At high irradiation temperatures, open channels are formed which contribute to the enhanced tritium release.

Beryllium is proposed to be a neutron multiplier and plasma facing material in future fusion devices. Therefore, it is crucial to acquire an understanding of the microscopic mechanisms of tritium accumu- lation and release as a result of transmutation processes that Be undergoes under neutron irradiation. A multiscale simulation of ad- and desorption of hydrogen isotopes on the beryllium (0 0 01) surface is developed. It consists of ab initio calculations of certain H adsorption configurations, a suitable clus- ter expansion approximating the energies of arbitrary configurations, and a kinetic Monte Carlo method for dynamic simulations of adsorption and desorption. The processes implemented in the kinetic Monte Carlo simulation are deduced from further ab initio calculations comprising both, static relaxation as well as molecular dynamics runs. The simulation is used to reproduce experimental data and the results are compared and discussed. Based on the observed results, proposals for a refined model are made.

This purpose of study is to establish the material database of neutron multiplier for the JA DEMO design. In the previous study, we reported the effects of sintering conditions as temperature and pressure on hardness and sintered density mainly in the sintering temperature from 1050 °C to 1200 °C. In this study, the microstructure observation and compressive tests were carried out. As results of microstructure observations, the pores were almost disappeared, and the grain size increased with increase in sintering temperature. Compression tests were carried out from room temperature (R.T.) to 1000 °C with the samples sintered at 1200 °C. The compressive strength at R.T. was approximately 1.69 GPa. With the increase in testing temperature, there was a tendency for the strength to decrease from 800 °C to 1000 °C. In addition, the load-compressibility indicated that the yield point appears at 850 °C.

Hot isostatic pressing (HIP) has been proposed for manufacturing large hexagonal TiBe12 blocks for neutron multiplication in the new reference design of the DEMO blanket. This paper investigates the effect of HIP at 800 and 900 °C on the microstructure and the properties of extruded Be-Ti composites with the main aim of optimizing HIP parameters. Be-Ti composites produced by powder extrusion at 650 °C consist exclusively of Be and Ti phases. During HIP, they interact forming titanium beryllides with a volume fraction of 70–79%. These beryllides have a very high microhardness of 1130–1680 HV.X-ray diffraction showed that the main beryllide phase is TiBe12. After HIP at 900 °C, it has a very fine-grained microstructure with a mean grain size of 190 nm. Auger electron spectroscopy revealed that the TiBe2 beryllide forms a thin layer surrounding the remaining Ti phase. Ti2Be17 can be found at the prior titanium phase locations in the form of small particles. The titanium and beryllium phase do not dissolve completely during the used HIP process. In addition, the beryllium phase exhibited a higher porosity after HIP. This results in densities as low as 94.4% and 95.9% of the theoretical density of TiBe12 after heat treatment at 800 °C and 900 °C, respectively.Differential scanning calorimetry showed that beryllides are mainly synthesized in the temperature range of 670–740 °C, which can be monitored by the observation of a heat release. To accomplish diffusion processes in the Be-Ti composite, HIP should be carried out at temperatures exceeding 900 °C. Heating rates should be less than 10 K/min to avoid excessive overheating.

Superpermeation allows for hydrogen fluxes through metal foil membranes at rates orders of magnitude higher than pressure driven permeation. This process occurs only for hydrogen isotopes, meaning it is hydrogen-selective, and it can work against a pressure gradient, implying pumping capabilities. These characteristics allow for using superpermeation as the base process for a very efficient, selective separation of hydrogen from other gases. However, the efficacy of superpermeation needs further research both experimentally and theoretically. Its efficiency relies on a surface energetic barrier that hinders both adsorption of molecular hydrogen on the downstream side and desorption on the upstream side, while leaving atomic hydrogen absorption unaffected. Such a barrier can be created by a monolayer of non-metallic impurities (usually oxygen) that naturally develops at group 5 metal surfaces. The physics explaining why such a monolayer drastically affects atomic hydrogen reactions are being explored in this work via density functional theory (DFT) calculations for the implementation of which we use the Vienna ab-initio Simulations Package (VASP). By performing structural relaxations and saddle point-searching calculations deploying a dimer method using VASP, energy diagrams for atomic hydrogen absorption are obtained for two representative materials, namely niobium and vanadium. The differences in these diagrams are analyzed and compared in order to determine which material is optimal for superpermeation. To that end, slabs with (1 0 0) surface orientation are compared for the case with and without an O monolayer coverage. The characteristic energies involved according to the diagrams and the types of absorption sites will be key parameters to understand and, eventually, optimize for the emerging phenomena. It was found that the presence of an oxygen monolayer is necessary of superpermeation to occur, and that for the 100 orientation, the vanadium system provides better characteristics.

Solid titanium beryllide blocks will be used for neutron multiplication in the helium-cooled pebble bed (HCPB) blanket concept of EU DEMO. A combination of hot extrusion of Be-Ti powders and subsequent hot isostatic pressing (HIP) of the obtained Be-Ti composites has been proposed for manufacturing such blocks. This work is devoted to the study of the effect of HIP at 1000–1200 °C on the structure and properties of Be-Ti composites in order to optimize the HIP parameters. The HIP at 1000–1200 °C resulted in an almost single-phase titanium beryllide (TiBe$_{12}$) with small amounts of Be and other phases, which gradually dissolve with an increase in the HIP temperature. Such a treatment at 1000 and 1100 °C provides a very fine-grained microstructure of TiBe$_{12}$ with an average grain size of 0.3 and 0.6 μm, respectively. The resulting titanium beryllide is characterized by high microhardness of 1350–1480 HV$_{0.1}$ depending on the HIP temperature. According to the nanoindentation tests of the Be-Ti composite after HIP at 1100 °C, the indentation modulus of TiBe$_{12}$ can be estimated as 295 GPa. The fracture toughness of the TiBe$_{12}$ was determined as 1.5–1.7 MPa·m$^{1/2}$. The temperature of 1100 °C was chosen as optimal for the HIP of Be-Ti composites after hot extrusion. The titanium beryllide obtained in this way was used to manufacture a reduced size mockup of Ø20 mm × 18 mm. The mockup has no visible surface defects and can be used for further experiments.