article posted 30 March 2016
Tracey Taylor Senior Research Technologist at the National Nuclear Laboratory for 6 years. Responsible for delivering research campaigns on the Vitrification Test Rig to support operations on the Waste Vitrification Plant on the Sellafield Site.
The vitrification of molybdenum rich waste streams in a Ca/Zn borosilicate glass
Tracey Taylor 1*, Carl Steele 2 and Michelle Cowley 2
1 National Nuclear Laboratory, Seascale, Cumbria, CA20 1PG
2 Sellafield Ltd, Seascale, Cumbria, CA20 1PG
The liquors generated during the post operational clean out of the highly active liquor storage tanks at Sellafield site are anticipated to be rich in solids containing of molybdenum. The solids are expected to be predominantly zirconium molybdate and caesium phosphomolybdate. The conventional alkali borosilicate glass used to vitrify the UKs high level waste has limited solubility for molybdenum. Beyond the solubility limit, molybdenum is known to combine with alkali, alkali earth and rare earth metals to form an undesirable secondary phase, known as yellow phase, within the glass product. Yellow phase is undesirable as it is partially soluble in water and therefore affects the product quality of the glass. A new glass formulation containing calcium, zinc and aluminium in alkali borosilicate glass (known as Ca/Zn glass) has been developed that enables the incorporation of higher molybdenum concentrations, without the formation of detrimental yellow phase.
The calcium reacts with molybdenum to form a stable secondary phase, calcium molybdate, which forms in preference to yellow phase, once the solubility of molybdenum into the glass had been reached.
This paper details the research undertaken in the development of the new glass formulation and initial results from full scale trials with simulated waste streams.