Some Reactions Between Thorium Oxide And Inhibited Heavy Liquid Metals

As part of a study of liquid metal slurries as blanket materials for liquid metal fuelled reactors, thoria prepared by calcination of the oxalate has been mixed vigorously with inhibited lead, lead-bismuth eutectic and bismuth at temperatures in the range 500-600°C to form slurries containing up to 18 per cent (by volume) solids. Solidified samples have been examined for reactions between the corrosion inhibitors (zirconium and magnesium) and thoria, immediately after preparation and after circulation in thermal convection loops and in a pumped loop.

Magnesium at eutectic concentration in lead and bismuth reacted with thoria to produce intermetallic compounds which plugged thermal convection loops. Magnesium at normal inhibitor levels did not reduce thoria to give a thorium concentration in excess of the solubility limit in bismuth at 400°C.

Thoria concentrations of up to 7 per cent in bismuth were not found to effect the rheological properties of the liquids in these experiments, nor to alter corrosion inhibition effects by the ZrN film technique. The rheology of lead slurries was influenced principally by thoria settling upwards. Apart from settling effects the slurries were physically stable.