article posted 21 March 2016/em>
Nikos Galanakis is a research PhD student at the University of Sheffield, developing topological methods to characterize the radiation damage effects in amorphous materials, such as glasses, that are used to encapsulate High Level Radioactive Waste. Mr. Galanakis completed his undergraduate studies in Physics and his M.Sc. studies on Mathematical and Theoretical Physics, Astronomy and Astrophysics at the University of Patras. Prior to his PhD studies, he worked for 5 years as a teaching assistant in the Department of Physics at the University of Patras. His research interests include atomistic level computer simulations involving Classical, Statistical and Quantum Mechanics and Electrodynamics.
Using topological methods to characterize radiation damage effects in iron phosphate glasses
Nikos Galanakis* & Karl P. Travis
University of Sheffield, Department of Materials Science & Engineering, Sir Robert Hadfield Building, Sheffield, S1 3JD, UK
One of the most important aspects of the nuclear industry is the immobilization of spent nuclear waste. Many spent fuels, contain isotopes such as 99Tc and 129I that remain radioactive for thousands or million years, making almost impossible to verify the reliability and integrity of new wasteforms only by experimental methods. In order to perform a successful and detailed study of the radiation damage effects, it is extremely important to retrieve dynamic information regarding the structural changes in the waste form, both in the bulk and at the surface. The better option to obtain such results is to use computer Molecular Dynamics simulations.
The DREAM II project is a part of an EPSRC-India link. This consortium developed computer models of the radiation induced structural changes due to alpha particles and recoil nuclei damage on the structure, and speciation of redox active elements in the immobilization materials over long time scales. The main wasteforms that were investigated are the well-known borosilicate glasses and iron phosphate glasses.
Part of this project was to develop topological methods to characterize radiation damage effects in this wasteforms. In contrast with the crystalline materials, were the radiation damage can be characterized by simply comparing the positions of the particles in the damaged structure with the positions in the initial undamaged reference crystal, in glasses there is no reference system to make the comparison and a topological approach is necessary. In this work we show how three different topological concepts – Steinhardt order parameters, Hermite polynomial parameters and ring statistics – can give important information regarding the radiation damage effects in glasses used for nuclear waste encapsulation.