Oxidation state and local environment of iron in multicomponent aluminoborosilicate glasses

Abstract

For safe longterm storage, highlevel radioactive wastes (HLW), generated during the processing of spent nuclear fuel or execution of defense programs, are subjected to hightemperature processing (vitrifi� cation) to obtain aluminophosphatebased (in Russia) or borosilicatebased (abroad) glass (1). Some HLW batches remaining after such processing in Russia and the United States and currently stored in stainless steel tanks contain high concentrations of iron, as well as a number of other transition metals (chromium, man� ganese, nickel) and aluminum. Vitrification of such HLW faces problems since these components contrib� ute to glass crystallization with a change in the rheo� logical properties of glass and in the characteristics of the final products intended for longterm storage. Consequently, it is necessary to develop new glass compositions with a high content of irongroup ele� ments. In the United States, borosilicate glasses are suggested for this purpose (2). In Russia, the only HLW vitrification plant to produce aluminophos� phatebased glass operates at the "Mayak" production association (Chelyabinsk oblast). This glass is also sug� gested for highiron waste; however, the possibility of using borosilicateor aluminoborosilicatebased glass is considered as well (3). In this context, it is necessary to study the influence of iron and other transition met� als on the structure and properties of the glasses, in particular, it is necessary to determine the effect of the oxidation state and speciation of iron on its phase composition and interphase distribution in vit� rified HLW.