Radiation Damage of Glasses for Nuclear Waste Storage: Optical and Microstructural Aspects

Abstract

615A possible way to achieve a stable nuclear waste form consists of incorporating the different radionuclides in borosilicate glasses. As a consequence of the long meanlife of some active species, e.g. actinides, radiation damage is produced in the storage matrix, which may potentially affect its long-ter~ stability.Glasses based on Si02 have a mixed ionic-covalent bonding, hence both ionization and atomic displacements are of relevance in determining the damage. Precursor atomic defects, present before irradiation, as well as added modifiers, including sodium, interact with the bombarding particles: y-rays, electrons, light and heavy ions. Under certain circumstances, individual defects tend to coalesce and defect clusters, usually in the form of gas bubbles, nucleate and grow.The overall damage thus consists of relatively strong modifications of the atomic bonding and of the local microstructure. Such modifications have been examined. Optical absorption spectra of pure Si02 provide the basis of interpretation for individual defects. Results of High Voltage Electron Microscopy, where irradiations and "in situ" observations take place simultaneously, allow to discuss the agglomeration effects.Both aspects of radiation damage are discussed in connection with the vitrification of nuclear waste, with special regard to possible implications upon the leaching of active species.