Physical and optical properties of the International Simple Glass

Abstract

Radioactive waste immobilization is a means to limit the release of radionuclides from various waste streams into the environment over a timescale of hundreds to many thousands of years. Incorporation of radionuclide-containing wastes into borosilicate glass during vitrification is one potential route to accomplish such immobilization. To facilitate comparisons and assessments of reproducibility across experiments and laboratories, a six-component borosilicate glass (Si, B, Na, Al, Ca, Zr) known as the International Simple Glass (ISG) was developed by international consensus as a compromise between simplicity and similarity to waste glasses. Focusing on a single glass composition with a multi-pronged approach utilizing state-of-the-art, multi-scale experimental and theoretical tools provides a common database that can be used to assess relative importance of mechanisms and models. Here we present physical property data (both published and previously unpublished) on a single batch of ISG, which was cast into individual ingots that were distributed to the collaborators. Properties from the atomic scale to the macroscale, including composition and elemental impurities, phase purity, density, thermal properties, mechanical properties, optical and vibrational properties, and the results of molecular dynamics simulations are presented. In addition, information on the surface composition and morphology after polishing is included. Although the existing literature on the alteration of ISG is not extensively reviewed here, the results of well-controlled static alteration experiments are presented here as a point of reference for other performance investigations.Nuclear Glass: A problem sharedIngots of a reference nuclear-waste glass created in a single batch were distributed among collaborators, tested, and the results compared. Borosilicate glasses are used to immobilize and store radioactive waste, with the aim of containing it for long periods of time. However, corrosion is an inevitable issue and data are needed to understand the glasses’ long-term behavior. To simplify and standardize the study of nuclear-waste glasses, a six-component glass, known as International Simple Glass (ISG), was developed, representing a compromise between simplicity and similarity to actual waste glasses. Now, an international collaboration of scientists from the UK and USA led by Joseph V. Ryan at Pacific Northwest National Laboratory has studied a single batch of ISG, distributing ingots among the collaborators and individually measuring their properties—with very good agreement observed between the laboratories.