Stability of Cubic Zirconia in a Granitic System Under High Pressure & Temperature
- PDF / 3,248,118 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 26 Downloads / 139 Views
Stability of Cubic Zirconia in a Granitic System Under High Pressure & Temperature Fergus G.F. Gibb1, Boris E. Burakov2, Kathleen J. Taylor3 and Yana Domracheva2 1 Immobilisation Science Laboratory, Department of Engineering Materials, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK. 2 Laboratory of Applied Mineralogy and Radiogeochemistry, The V.G. Khlopin Radium Institute, 28, 2-nd Murinskiy Ave., St. Petersburg, 194021, Russia. 3 Department of Geography, University of Sheffield, Winter Street, Sheffield S10 2TN, UK. ABSTRACT Cubic zirconia is a well known, highly durable material with potential uses as an actinide host phase in ceramic waste forms and inert matrix fuels and in containers for very deep borehole disposal of some highly radioactive wastes. To investigate the behaviour of this material under the conditions of possible use, a cube of ~ 2.5 mm edge was made from a single crystal of yttriastabilized cubic zirconia doped with 0.3 wt.% CeO2. The cube was enclosed in powdered granite within a gold capsule and a small amount of H2O added before sealing. The sealed capsule was held for 4 months in a cold-seal pressure vessel at a temperature of 780°C and a pressure 150 MPa, simulating both the conditions of a deep borehole disposal involving partial melting of the host rock and the conditions under which the actinide waste form might be encapsulated in granite prior to disposal. At the end of the experiment the quenched, largely glassy, sample was cut into thin slices and studied by optical microscopy, EMPA, SEM and cathodoluminescence methods. The results show that no corrosion of the zirconia crystal or reaction with the granite melt occurred and that no detectable diffusion of elements, including Ce, in or out of the zirconia took place on the timescale of the experiment. Consequently, it appears that cubic zirconia could perform most satisfactorily as both an actinide host waste form for encapsulation in solid granite for very deep disposal and as a container material for deep borehole disposal of highly radioactive wastes (HLW), including spent fuel. INTRODUCTION Cubic zirconia based crystalline ceramics have considerable potential for the immobilisation and storage of actinides, for use in inert matrix fuels, as waste forms for geological disposal of actinides and for use in containers for the high-temperature very deep borehole disposal of HLW. Immobilisation and storage Because of their ability to accommodate actinide ions in the crystal structure and their durability under a wide range of physical and chemical conditions, cubic zirconia ceramics have been proposed as suitable host matrices for the immobilization and safe interim storage of Pu and other actinides [1-14]. Ceramics based on gadolinia-stabilized cubic zirconia or hafnia-zirconia solid solutions could also be used for the safe storage of significant amounts of excess weaponsgrade Pu [15] without the risk of criticallity. A study of cubic zirconia irradiated by Xe2+ and I+ ion implantation confirmed the high resistance of its
Data Loading...
