Physical and chemical characteristics of lead-iron phosphate nuclear waste glasses

Abstract

Experimental determinations of the properties of lead-iron phosphate glasses pertinent to their application to the problem of the permanent disposal of high-level nuclear wastes have been carried out. These investigations included studies of the composition and physical properties of nuclear waste glasses (NWG), as well as the effect of preparation conditions. Lead-iron phosphate nuclear waste glasses were prepared by dissolving simulated US defense wastes or simulated commercial power reactor wastes in molten lead-iron phosphate melts at temperatures between 900 and 1050°C. The measured physical and chemical properties of the nuclear waste glasses formed by cooling these melts and annealing included the following: (1) aqueous corrosion resistance as a function of the solution pH, solution temperature, and glass composition, (2) glass density, (3) thermal expansion coefficient, (4) glass transition temperature and softening point, (5) heat capacity, (6) critical rate (7) temperature for the maximum crystallization rate, (8) relative solubility of waste oxides in the glass melt, (9) reactions between the molten glass and the melting crucible (Pt, ZrO 2, Al 2O 3), and (10) studies of possible metal cannister materials. Experimental results for the lead-iron phosphate NWG are compared to available data for borosilicate NWG. Relative to borosilicate NWG, the lead-iron phosphate glasses have several distinct advantages which include a much lower aqueous corrosion rate, a lower preparation temperature, and the ability to immobilize many types of commercial and defense-related high-level radioactive wastes.