Measurement of initial dissolution rate of P0798 simulated HLW glass by using micro-reactor flow-through test method
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Measurement of initial dissolution rate of P0798 simulated HLW glass by using microreactor flow-through test method H.Makigaki1, Y.Inagaki1, K.Idemitsu1, T.Arima1, S.Mitsui2, T.Banba3, K.Noshita4 1 Department of Applied Quantum Physics & Nuclear Engineering, Kyushu University, Japan 2 Geological Isolation Research and Development Directorate, Japan Atomic Energy Agency, Japan 3 Nuclear Safety Research Center, Japan Atomic Energy Agency, Japan 4 Energy & Environmental Systems R&D Laboratory, Hitachi, Ltd, Japan ABSTRACT 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 microchannel (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. INTRODUCTION In safety assessment of long-term geological disposal of high-leveled radioactive waste glass (HLW glass), a conservative value of glass dissolution rate has been usually adopted as a source term of radionuclide release. For realistic and reliable evaluation of the glass dissolution rate under disposal condition, it is necessary to understand the long-term glass dissolution mechanisms with respect to key environmental variables affecting glass dissolution rate such as solution composition, pH, temperature and time [1]. For glass dissolution modeling, it is also necessary to evaluate glass dissolution rates systematically as a function of environmental variables. For the last 30 years, several test methods have been developed and applied to the measurement of the glass dissolution rate, and they are categorized into two types, static test and flow-through test. For measurement of the dissolution rate as a function of environmental variables, the flow-through test is adequate since it can provide any controlled solution condition over the test duration. Single-pass flow-through (SPFT) method is one of major flow-through test methods of great use for measuring the glass dissolution/alteration rate as a function of environmental variables. However, the use of powdered glass specimen in usual SPFT method in order to provide a high S/V ratio leads to some difficulties in precise determination of the actually r
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