Beryllides as advanced materials for neutron multiplication

The neutron multiplier is an essential component of the blanket of future thermonuclear reactors, which should provide the tritium breeder with a sufficient amount of neutrons of a certain energy. Among all chemical elements, only beryllium and lead have an advantageous ratio of high neutron multiplication reaction at low neutron absorption rates. However, pure metals – beryllium and lead – for various reasons cannot be used in the harsh operating conditions of a fusion reactor blanket. Intermetallic compounds of beryllium – beryllides have a number of advantages over pure beryllium and are currently considered to be the reference neutron multiplication material for the Helium Cooled Pebble Bed (HCPB) breeding blanket concept of EU DEMO fusion reactor. Recently, a batch of full-size beryllide blocks has been manufactured on an industrial scale in cooperation with the Ulba Metallurgical Plant. The present work is devoted to the characterization and analysis of these beryllide blocks so that the material could be used for the manufacture of a blanket. Titanium beryllide (TiBe12) blocks are hexagonal prisms with an internal hole, while chromium beryllide (CrBe12) blocks are solid prisms of complex shape. The resulting blocks have a single-phase structure of the corresponding beryllide with a small impurity in the form of beryllium oxide. One of the titanium beryllide blocks also has about 7% residual beryllium phase. Grains of titanium beryllide have an average size of about 7–8 μm, while grains of chromium beryllide are much larger and reach 40–50 μm. Mechanical compression and bending tests of beryllides showed their very high strength, which is maintained up to 1000°C. In terms of specific compressive strength, the single-phase TiBe12 surpasses all materials, except diamond, in the 700–1000°C temperature range. Chromium beryllide and titanium beryllide with 7% of the beryllium phase have lower strength, but higher ductility. Corrosion tests were carried out in air and in He + 2% water vapor at 800–1200°C. Beryllides have high corrosion resistance similar to Ni-base superalloys and high temperature ceramics. Long-term thermal cycling tests with rapid heating and cooling, simulating operation in a fusion reactor, showed high resistance of beryllides to thermal shocks. The results obtainedare also discussed from the point of view of the application of beryllides in other areas

Tritium and helium release from beryllium pebbles neutron-irradiated up to 230appm tritium and 3000appm helium

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

Effect of heat treatment of titanium beryllide on tritium/hydrogen release

In the present paper, a homogenization heat treatment at 1473 K for 8 h was carried out with the aim to obtain the single-phase Be12Ti structure in the pebbles of three Be-Ti compositions: Be-7.0Ti, Be-7.3Ti, Be-7.7Ti at.%. After the heat treatment the average porosity in the pebbles increased from 5 to 8% to 36–47%, which resulted in lower amount of tritium/hydrogen retention during the loading. Temperature-programmed desorption tests showed that the performed heat treatment facilitates tritium/hydrogen release from Be-Ti pebbles. Assessment of the effective activation energies of tritium desorption reveals that the tritium release from titanium beryllide occurs much more easier than from pure beryllium