Dissolution Behavior of Lead Borate Glass under Simulated Geological Disposal Conditions
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.284
Dissolution Behavior of Lead Borate Glass under Simulated Geological Disposal Conditions Atsushi MUKUNOKI1, Takahiro KIKUCHI1, Tamotsu CHIBA1, Tomofumi SAKURAGI2, Toshihiro KOGURE3, Tsutomu SATO4 1 JGC
Corporation, Minato-Mirai 2-3-1, Nishi-ku, Yokohama, Japan Waste Management Funding and Research Center, Akashicho 6-4, Chuo-ku, Tokyo, Japan 3 The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, Japan 4 Hokkaido University, Kita13, Nishi8, Kita-ku, Sapporo, Hokkaido, Japan 2 Radioactive
ABSTRACT Development of an iodine immobilization technique that can fix radioactive iodine in waste form for a long period and constrain its leaching into pore water is necessary in order to secure the long-term safety of geological disposal of transuranic (TRU) waste. Lead borate glass vitrified at a low temperature is regarded as one of the promising immobilization materials of Iodine-129 which will be removed from spent AgI filters generated from reprocessing plants and may have a significant effect on long term safety of geological disposal. Leaching experiments in bentonite-equilibrium water have been conducted to understand the lead borate glass dissolution behaviors in possible geological disposal conditions. Boron dissolved with the highest rate in all types of the solutions and was regarded as an index element to represent the glass dissolution rate. On the other hand, lead dissolved with a far slower rate. The chemical species and possible precipitating minerals of lead were examined by a geochemical calculation code for typical underground water. Altered glass surfaces were investigated by SEM, TEM and XRD. XRD analysis showed that the main constituent phase of the altered layer was hydrocerussite, Pb3(CO3)2(OH)2, that was predicted by the geochemical simulation as well.
INTRODUCTION A recent review [1] states that Iodine-129 is a key radionuclide in the safety assessment for the geological disposal of TRU waste. One immobilization candidate is low temperature vitrification with BiPbO2I (BPI) [2-4]. Initially, H2 is used as a reductant to release iodine from a spent iodine filter. Then, the iodide ion is fixed in the BPI through a reaction with an inorganic anion exchanger, BiPbO2NO3 (BPN) [5-6], by the following ion exchange reaction: (1) BiPbO2NO3 + I- → BiPbO2I + NO3In the vitrification process, a low melting temperature of 540 °C is used to avoid iodine volatilization during the vitrification process. The glass frit is composed of PbO: B2O3: ZnO at ratios of 65:30:5 [mol%] and the target composition of the BiPbO2I (BPI) vitrified waste form is shown in Table I.
Elements mol%
Table I. Composition of BPI vitrified waste form I B Pb Zn Bi 1.0 19.8 22.1 1.6 1.0
O 54.5
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EXPERIMENTS Table II shows t
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