No abstract

The behaviour of the platinum metals in nuclear waste glass produced in a lab scale liquid fed ceramic melter was investigated. The platinum metals form two kinds of metallic conductive particles in the glass melt: RuO2 (preferentially needle shaped) and a Pd—Rh—Te alloy (tear—shaped). These phases decrease the electrical resistivity of the glass melt. Resistivities were measured at 950º and 1150 ºC. Powdered glass was used as starting material. For the same temperatures resistivities were calculated applying an equation derived for an embedment structure of highly conductive particles in a matrix of low conductivity. To match calculated and measuredresistivities one must assume needle—shaped particles. This gives evidence that mainly RuO2 contributes to the observed decrease in resistivity. If the measurements are started with glass blocks instead of glass powder, remarkably lower resistivities are measured in the melt. A comparison of both results indicates a partial destruction of particles or particle contacts by grinding. Thus, resistivities measured with ground samples are not representative of those effective in a melter.The investigation of solid glass samples yielded the following results: Within a few hours, Pd—Rh—Te and RuO2 particles form fine sediments in the melter. The development of stable coarse sediments needs some 1000 h of melter operation. The Pd—Rh—Te alloy particles reach a mean diameter of 5 μm in the fine sediment and of 20 μm in the coarse one. With time, the alloy dissolves more Rhand Te. Finally, the alloy separates into two phases. RuO2 dissolves Cr and Rh.

No abstract

No abstract

No abstract