Aqueous dissolution tests were performed for a Japanese type of simulated high-level waste (HLW) glass P0798 by using a newly developed test method of micro-channel flow-through (MCFT) method, and the initial dissolution rate of glass matrix, r 0 , was measured as a function of solution pH (3-11) and temperature (25-908C) precisely and consistently for systematic evaluation of the dissolution kinetics. The MCFT method using a micro-channel reactor with a coupon shaped glass specimen has the following features to provide precise and consistent data on the glass dissolution rate: (1) any controlled constant solution condition can be provided over the test duration; (2) the glass surface area actually reacting with solution can be determined accurately; and (3) direct and totally quantitative analyses of the reacted glass surface can be performed for confirming consistency of the test results. The present test results indicated that the r 0 shows a ''V-shaped'' pH dependence with a minimum at around pH 6 at 258C, but it changes to a ''U-shaped'' one with a flat bottom at neutral pH at elevated temperatures of up to 908C. The present results also indicated that the r 0 increases with temperature according to an Arrhenius law at any pH, and the apparent activation energy evaluated from Arrhenius relation increases with pH from 54 kJ/mol at pH 3 to 76 kJ/mol at pH 10, which suggests that the dissolution mechanism changes depending on pH.

A new type of flow-through test method using micro-reactor was developed and applied to measurement of the dissolution/alteration kinetics for a Japanese type of simulated HLW glass, P0798. In this test method, a face of coupon shaped glass specimen (30mm × 10mm × 4mm size) is in contact with a micro-channel (20mm length, 2mm width, 0.16mm depth) constructed on a PTFE (Teflon®) plate, and a solution is injected into the inlet of micro-channel at a constant rate. The injected solution, which flows through the micro-channel reacting with the glass to the outlet, is retrieved at certain intervals to be analyzed for determination of the glass dissolution/alteration rate. After the test, the glass specimen removed from the micro-reactor is subjected to surface analyses. This test method has major features as follows, 1) any controlled solution condition can be provided over the test duration, 2) a relatively high S/V ratio can be provided by use of micro-reactor in spite of using coupon shaped glass specimen, which results in precise and consistent analyses of both the solution and the reacted glass surface, 3) the test apparatus is simple with compact size and easy operation, which allows a flexible setup of test conditions. By use of this test method the dissolution/alteration rate for P0798 glass was measured as a function of pH, temperature, and time, and the results indicated that this test method is applicable and suitable for evaluation of the dissolution/alteration kinetics.

We applied a new type of flow-through test method using micro-reactor consisting of a simple test apparatus with compact size to measurement of the dissolution rate of a Japanese type of simulated waste glass (P0798 glass). In this test method, a solution flows through a micro-channel (20 mm length, 2 mm width, 0.16 mm depth) in contact with a face of coupon shaped glass specimen, and the output solution is retrieved at certain intervals to be analyzed for determination of the glass dissolution rate. By using this test method the initial dissolution rate of glass matrix or forward dissolution rate was measured as a function of pH (3 to 11) and temperature (25°C to 90°C). The present test results indicated that the initial dissolution rate has ‘V-shaped’ pH dependence, and the effect of pH on the dissolution rate decreases with increase in temperature similar to the results measured by using the Single-pass flow-through (SPFT) method. The present test results also indicated that the dissolution of B is controlled by diffusion process and that of Si is controlled by surface reaction process.