Leaching behaviour of and Cs disposition in a UMo powellite glass–ceramic

A UMo powellite glass–ceramic designed by French workers to immobilise Mo-rich intermediate-level waste was found to be quite leach resistant in water at 90°C with the dissolution of Cs, Mo, Na, B and Ca not exceeding 2g/L in normalised PCT tests. 133Cs solid state nuclear magnetic resonance and scanning electron microscopy (SEM) showed the Cs to inhabit the glass phase. The microstructures were not greatly affected by cooling rates between 1 and 5°C/min or by introducing 10times as much Cs and Sr. Protracted leach tests at 90°C showed surface alteration as evidenced by SEM and particularly transmission electron microscopy; the main alteration phase was a Zn aluminosilicate but several other alteration phases were evident. Voidage in the alteration layers was indicated from enhanced lifetimes in positron annihilation lifetime spectroscopy.