Fundamental study on HLW glass corrosion and minera]ization

Inagaki, Yaohiro*

A large number of studies on aqueous corrosion of HLW glass have shown that the glass react with water to form more stable solid phases (alteration-phases or secondary phases). The process of alteration-phase formation is expected to play an important role in the radionuclide release from the glass, because it can affect both the glass dissolution rate and the retention of radio nuclides in the phases. Recent studies have indicated that analcime (zeolite) forms during aqueous corrosion of the glass in certain conditions, and the analcime formation can accelerate the glass corrosion by consuming orthosilicic acid (HSiO) from the solution. On the other hand, the alteration-phases such as zeolite and smectite are expected to have a retention capacity for some radio nuclides by sorption or incorporation. Therefore, a sound understanding of the alteration phase formation is expected to be essential for validation of the long-term performance. The purpose of this study is to understand, qualitatively and quantitatively, the alteration-phase formation and associated elemental release during aqueous corrosion of HLW glass. Static corrosion tests were performed with a simulated HLW glass, P0798 glass, in NaOH solutions at elevated temperatures, in order to accelerate the reaction, as a function of temperature, time and NaOH concentration. Crystalline alteration-phases formed in the corroded glass were analyzed by use of XRD, and the solution concentrations of dissolved elements were measured by use of ICP-MS. The results indicated that; (1)Analcime or Na-beidellite or both of them form during the corrosion depending on the conditions, (2)Si rich amorphous phases are contained in the alteration-phases, (3)In addition to solution pH, solution concentrations of Na and K sensitively affect formation of analcime and Na-beidellite, (4)Analcime formation accelerates the glass corrosion, (5)Most of Cs in the glass is retained in the alteration-phases by sorption ...