Glass - Back to the Future!

Presenting Author:
Michael Ojovan

article posted 06 April 2016

Michael Ojovan has been Nuclear Engineer at International Atomic Energy Agency, Assistant Professor (Reader) in the Department of Materials Science and Engineering of the University of Sheffield and Visiting Professor in the Department of Materials of Imperial College London. He has been awarded the degrees of Doctor of Science in Physical Chemistry and PhD in Solid State Physics. Michael is Editorial Board member of following journals: International Journal of Corrosion, Science and Technology of Nuclear Installations, Innovations in Corrosion and Materials Science, and Journal of Nuclear Materials.

Michael has published over 300 peer-reviewed scientific papers and co-authored 12 monographs on nuclear materials including the second edition of “An Introduction to Nuclear Waste Immobilisation” by Elsevier. He has been known for the two-exponential universal viscosity equation, the connectivity-percolation theory of glass transition, condensed excited state of matter (Rydberg matter), glass-composite materials for nuclear waste, and metal matrix immobilisation technology.

Fundamentals of the glass transition and vitreous materials for nuclear waste immobilisation

Michael I. Ojovan* & Russell J. Hand
Department of Nuclear Energy, International Atomic Energy Agency, Vienna, Austria ISL, Department of Materials Science and Engineering, The University of Sheffield, UK.

Nuclear power is a reliable solution to a shrinking conventional energy supply and the problem of global warming. However, nuclear waste management and long-term disposition of current and legacy nuclear wastes remain an open issue in the movement to a true renaissance of nuclear power generation. The physical and chemical durability of many glasses combined with their high tolerance to compositional changes make glasses irreplaceable materials for the immobilisation of highly toxic substances, such as nuclear waste, to ensure safe long-term storage, transportation and disposal. Nuclear waste vitrification is attractive because of technological and compositional flexibility, the large number of elements which can be safely immobilised, high corrosion resistance, mechanical and radiation durability, as well as the reduced volume of the resulting wasteform. Borosilicate and to a lesser extent phosphate glasses are the overwhelming world-wide choice for the immobilization of high level radioactive wastes resulting from nuclear fuel reprocessing and low- and intermediate level radioactive wastes such as those from operation of nuclear power plants and legacy waste. Vitrification is a mature technology which has been used on an industrial scale for more than 50 years. Continued advances in glassy wasteforms and nuclear waste vitrification technologies will be keys in enabling widespread deployment of nuclear energy.

Understanding whether glassy or crystalline wasteforms are produced requires an understanding the glass transition. Glasses transform into liquids upon heating through the glass transition, structurally however a glass is very similar to a liquid despite the completely different type of behaviour of glasses as compared to melts (e.g. silicate glasses at room temperature are essentially archetypal brittle solids). This has led to a lack of consensus as to whether the glass transition is a true or quasi-second order phase transformation, or is just a gradual change due to the increase of viscosity. Although difficult to observe, rearrangements at the glass transition (i.e. vitrification) are responsible for drastic changes of material properties and characteristic sudden changes of derivative thermodynamic parameters. Interpretation of the glass transition in terms of a transition from Deborah numbers < 1 to > 1 does not describe the experimental results which clearly show kinks and discontinuities in the glass transition region. Models of the glass transition are thus important to successfully reveal the rearrangements behind changes in the behaviour of amorphous materials on vitrification.

The purpose of this paper is to review advances in understanding the fundamentals of vitrification and utilisation of vitreous materials for immobilisation of nuclear wastes. It focuses on practical results revealing the long-term stability and durability of glassy materials to ensure safe storage and disposal conditions of vitrified radioactive waste.