article posted 30 March 2016
Shengheng Tan is a postdoctoral research associate in the University of Sheffield, UK, where he currently carries out his research on
vitrification of intermediate level nuclear waste. He completed his MSc and PhD degrees in Nuclear Environmental Science and Technology in the University of Sheffield
in 2011 and 2015, respectively. Before that he obtained his Bachelor’s degree in Materials Science and Engineering in Zhejiang University, China, in 2009.
Vitrification of intermediate level Magnox sludge nuclear waste containing metals
Shengheng Tan* & Russell J. Hand
Immobilisation Science Laboratory, Department of Materials Science & Engineering, University of Sheffield, United Kingdom.
Vitrification can be a competent choice to immobilise intermediate level nuclear waste. This paper presents the results of vitrifying an intermediate level Magnox
sludge waste using various glass compositions. The waste contains significant amount of Mg and U (partially present as metals), coupled with notable amount of Cl and S
which are not very soluble in traditionally used borosilicate glasses.
The presence of metals in glass melt can cause redox issues in which other glass components may be reduced by the metals, giving rise to changes in glass structure thereby
affecting its loading capacities. In this study, it has been found that, at high MgO additions, a small amount of additional Mg metals to glass could lead to prominent
phase separation in glass. It is also observed that addition of Mg metals made the melt more aggressive to the mullite crucibles, in some cases the melt penetrated crucible
walls whereas the melt without Mg addition did not under the same conditions.
The glass compositions were analysed by XRF and EDX. XRD, DTA, Raman and Mössbauer spectroscopies were used to characterise the formed glasses and to assess the changes of
glass structure and properties caused by Mg addition. The morphology of separated phases within glass matrices due to excess loadings was observed with SEM and TEM.
Finally those candidate compositions with promising properties will be qualified for further investigations.
Fig.1 XRD patterns of melt residuals of HM08 glass with 1.16 wt% Mg addition (separated phases are precipitated on the bottom of crucible).