Glass - Back to the Future!

Presenting Author:
Jack Clarke

article posted 18 March 2016

Jack Clarke I graduated with a first class honours (MChem) in Chemistry from the University of Manchester. Then I moved to the University of Sheffield and am currently in the second year of my PhD in the Department of Materials Science and Engineering. My thesis is funded through an EPSRC iCASE studentship with my industrial sponsor being the NDA and NNL. My thesis as a whole looks at using vitrification as a means of treating intermediate level waste (ILW) (i.e. materials that have been contaminated fission products, but are not sufficiently heat-generating) and then characterising the resulting waste forms.

Vitrification as a means of reworking problematic cemented nuclear waste forms

Jack Clarke*1, Dr. Martin Stennett1, Dr. Claire Corkhill1 and Professor Neil Hyatt1.
Immobilisation Science Laboratory, Department of Materials Science and Engineering, The University of Sheffield, UK

The UK’s preferred method for treatment of intermediate level waste (ILW) is cementation. One of the plants at Sellafield that cements waste is the Magnox Encapsulation Plant (MEP) that encapsulates Magnox fuel cladding in a blend of Ground Granulated Blast furnace Slag (GGBS) and Ordinary Portland Cement (OPC). When a sample of these drums were monitored, in interim storage, it was observed that several of them had expanded due to metal corrosion in the grout. Here we present findings on the possibility of reworking problematic cemented drums into a stable vitreous waste form. See Figure 1. We utilise the glass-formers present in the waste as well as the addition of readily-available glass-formers (sand, boron oxide and sodium carbonate), with a range of different waste loadings utilised. We aim for target temperatures of 1300 and 1200oC. Waste forms are characterised by different techniques including SEM/EDX, XRD, DTA, Mössbauer, density, X-ray, XAS and PCT durability studies

Mass balance reveals that the stainless steel content of the waste is oxidised to different extents depending on the glass composition. The more of the stainless steel oxidised the greater the degree of spinel crystallisation, with a composition of (Mg0.59Fe0.41)(Cr0.94Al0.06)2O4 found. Results show that vitrification is a feasible solution- oxidising reactive metals, evaporating the water content and showing the possibility of volume reduction. Higher waste loadings show crystallisation of mineral phases as well as evidence of porosity whereas at lower waste loadings a homogenous, vitreous waste form is produced