Leaching behavior of simulated high-level waste glass in flowing water

Simulated high-level waste glass was leached at 70 deg C for 28 days in various kinds of water by the MCC-4 flow leach test method and the MCC-1 static leach test method. One kind of water used was synthesized groundwater containing the cations of Ca2+, Mg2+ and Na+, and the anions of HCO3- and SO42-. The other kinds of water were those containing the only one or two of the ions cited above. A leach test in deionized water was also carried out as a reference. The flow rates in the MCC-4 method were 0.1, 0.01 and 0.001 ml/min which correspond to those expected in natural geological formations. The results obtained were summarized as follows: (1) The normalized elemental mass loss (NL) for elements studied tended to increase with increasing flow rate. (2) The values of NL by the MCC-1 method were larger in the case of deionized water than those obtained by the MCC-4 method at the slowest flow rate of 0.001 ml/min. (3) The values of NL for Na, Cs and B tended to be larger than those for Si, indicating the formation of Si-rich surface layers, except in the case of the fastest flow rate of 0.1 ml/min. (4) The values of NL obtained in synthesized groundwater were generally smaller than those of other leachants studied, and the surface of the specimen leached in synthesized groundwater was similar to that leached in natural groundwater when observed by a scanning electron microscope. (author)