Corrosion Behavior of a Powdered Simulated Nuclear Waste Glass Under Anoxic Condition
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CORROSION BEHAVIOR OF A POWDERED SIMULATED NUCLEAR WASTE GLASS UNDER ANOXIC CONDITION
YInagaki, H.Furuya, K.Idemitsu, T.Maeda and A.Sakai, Dept. of Nucl. Eng., Kyushu Univ., Fukuoka 812, JAPAN. T.Banba and S.Muraoka, Dept. of Environmental Safety Research, JAERI, Tokai-mura, Ibaraki
319-11, JAPAN. ABSTRACT
Static corrosion tests were carried out with a powdered simulated waste glass in deionized water at 90 'C under oxic and anoxic conditions, respectively. The corrosion tests under anoxic condition were performed in a globe box purged with mixed gas (N2+5%H2), where the pH and Eh of deionized water were maintained at 6.9 and -0.35 V vs.S.H.E. at 25 'C, respectively. It was observed that there is a little difference between NL values under oxic and anoxic conditions. For soluble elements (Li, B, Na, Mo) and Ca, NL values under anoxic condition were slightly smaller than those under oxic condition. For Fe and Al, NL values under anoxic condition were slightly larger than those under oxic condition. For Si, Ce, La and Nd, there was no difference between NL values under oxic and anoxic conditions. The experimental results were analyzed on the basis of a corrosion model (Diffusion-combined Model), in which the solution concentration of elements associated with solution pH and Eh can be derived thermodynamically by use of PHREEQE. The analysis suggests that precipitating minerals controlling the solution concentrations of Fe and Ca under anoxic condition are different from those under oxic condition. INTRODUCTION Most of hazardous elements in nuclear waste glasses are redox active elements, and their
equilibrium solubilities, dissolution/precipitation reactions and release rates from the waste glass are greatly influenced by oxidation potential (Eh) of the solution. Therefore, corrosion behavior of the waste glass under low Eh conditions (predicted in repository environments) must be revealed for making the accurate long-term prediction of the repository performance. In recent years, some corrosion tests of the waste glass under anoxic conditions have been performed, and dissolution behavior of some elements has been investigated[l,2,3]. However, most of the previous tests have been performed under the conditions of low S/V ratios and short-term periods, and the results are insufficient for understanding the corrosion behavior of the waste glass in the repository condition. The purpose of this study is to understand the effects of solution Eh on the corrosion behavior of the waste glass. Static corrosion tests were performed with a powdered simulated waste glass in deionized water at 90 'C with S/V ratio of 1200 m 1 under oxic and anoxic conditions, respectively. The corrosion tests under oxic condition were performed in air. While, the corrosion tests under anoxic condition were performed in a globe box purged with mixed gas(N2+5%H2, purity 99.99%), in which the pH and Eh of deionized water were maintained at 6.9 and approximately -0.35 V vs. S.H.E. at 25'C, respectively. Under both oxic and anoxic conditions, norm
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