Immobilization of CsCl and SrF_2 in iron phosphate glass

摘要

A large part of the radioactive ~137Cs and ~90Sr stored at the Hanford site is present as CsCl and SrF_2. Attempts to incorporate halides in borosilicate glass often produces immiscibility which is undesirable for immobilizing nuclear materials. Conversely, iron phosphate glasses have been made with up to 26 and 31 mol/100 CsCI and SrF_2. respectively, and up to 34 mol/100 CsCl and SrF_2 combined. These compositions are melted at temperatures as low as 950℃ for 2 h and form fluid melts. The low melting tem- perature of the iron phosphate wasteforms reduces the probability that radiouctive ~137Cs will vaporize from the melt,which becomes increasingly likely at the higher temperature ( ≥ 1150℃) used to melt borosilicate glasses. Analysis of the glasses produced in this study show that very little, if any, Cs and Sr was volatilized from the batches, although the majority of the halide is released during melting. All of the iron phosphate glassy wasteforms in the current study had a total ion release in distilled water of approximately 10 mg/l which is about one tenth that measured for the approved reference material (ARM-l), a reference bor- osilicate glass. The dissolution rate of the iron phosphate wasteforms in distilled water decreased with increasing iron content.