Beryllium pebbles

The magnesium-reduced beryllium pebbles generally assay 96% beryllium and are always associated with residual magnesium and slag. These pebbles are purified to about 99.5% by vacuum induction melting in beryllia crucibles at temperatures of about 1400 °C. The ingots are machined and machined scarf is milled to produce beryllium powder. The ground metal powder is pressed and sintered under vacuum. The product is called vacuum hot-pressed beryllium, and this is machined for component manufacture. 

Beryllium is extracted from the main source mineral, the alumino-silicate beryl, by conversion to the hydroxide and then through either the fluoride or the chloride to the final metal. If the fluoride is used, it is reduced to beryllium by magnesium by a Kroll-type reaction. The raw metal takes the form of pebble and contains much residual halides and magnesium. With the chloride on the other hand, the pure metal is extracted by electrolysis of a mixture of fused beryllium chloride and sodium chloride. The raw beryllium is now dendritic in character, but still contains residual chloride. 

One method of obtaining beryUium metal is by chemical reduction, whereby beryllium oxide is treated with ammonium fluoride and some other heavy metals to remove impurities while yielding berylhum fluoride. This beryllium fluoride is then reduced at high temperatures using magnesium as a catalyst, which results in deposits of pebbles of metallic beryllium. 

Unlike other fuel forms, the ratio of fuel and moderator to liquid coolant is fixed in a pebble-bed reactor. This places major constraints on the choice of coolant (it most likely will require the use of a salt with enriched lithium-7 and beryllium) and other core design parameters. While this salt is more expensive, it has very low parasitic neutron capture, which combined with the very small excess reactivity and large cylindrical core, would provide high fuel utilization. Initial studies on a liquid-salt-cooled pebble-bed reactor have been conducted at Delft University in the Netherlands. 

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