The Effect of Increased Waste Loading on the Durability of High Level Waste Glass

Abstract

This paper describes the results from static leach tests using the ASTM International standard Materials Characterisation Centre (MCC-1) and Product Consistency Test (PCT) protocols for inactive High Level Waste (HLW) glasses fabricated at full scale on the Sellafield Vitrification Test Rig. The samples comprised monoliths and powders of a 75:25 Oxide:Magnox Blend glass with 31 wt% waste incorporation and a Magnox-only glass with 35 wt% waste incorporation. The tests were carried out in de-ionized water at 90 °C for durations up to 42 days and normalized mass losses calculated.The results of MCC-1 and PCT tests on both 31 wt% Blend and 35 wt% Magnox glasses, showing measurable differences to the corresponding standard 25 wt% waste incorporation glasses, are presented. A series of Scanning Electron Microscopy (SEM) investigations were also undertaken. The variation in composition and thickness of the alteration layer with sample type and duration is reported.

The Effect of Composition on Short- and Long-term Durability of UK HLW Glass

“…Under these conditions, when the waste loading is ~25 wt%, Magnox and 75o:25m Blend glasses give very similar elemental releases up to 112 days. However, when the waste loading is increased to 38 wt%, the test responses are different, with the Magnox glass apparently having a significantly higher residual rate than the 75o:25m Blend, see Brookes et al (2010). In addition, at high Magnox waste loadings, the Mo release under PCT test conditions is again significantly lower than that of B in contrast to the 75o:25m Blend glass.…”

“…Comparison of 112 day PCT durability tests (powder in DIW at 90 °C with S/V = 2,000 m -1 ) for 25 and 38 wt% Magnox and 75o:25m Blend glasses[Brookes (2010)]. …”

Melting behaviour of simulated radioactive waste as functions of different redox iron-bearing raw materials

“…Ironbearing spinel crystals are chemically durable and are therefore less of a concern for the quality of the final vitrified product, when present at levels of up to ∼2 wt% [53] . However, these spinels can agglomerate and, due to their higher densities, settle to the bottom of the melter, which is intolerable in the JHCM melters as they are susceptible to clogging [54] , as opposed to induction melters, such as those used in the UK, where a modest level of solid settling is considered acceptable [55] . The glass product discharged from the DM100 melter test contained only trace amounts of crystal precipitation upon melting and cooling, and 0.65 vol% spinel crystals con- taining Fe, Cr, Ni and Mn oxides were measured after heat treatment at 950 °C for 72 h [47] which is broadly consistent with being within the acceptable range of product quality ( < 1 vol% of crystalline phases at 950 °C) [ 56 , 57 ].…”