Preparation of Hydrated Glass as a Model of Long-Term Leached Nuclear Waste Glass
- PDF / 426,070 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 79 Downloads / 201 Views
PREPARATION OF HYDRATED GLASS AS A MODEL OF LONG-TERM LEACHED NUCLEAR WASTE GLASS HIROSHI YAMANAKA, JUNJI NISHII, TOMOKO AKAI, MASARU YAMASHITA, AND HAJIMU WAKABAYASHI* Osaka National Research Institute, 1-8-31 Midorigaoka, Ikeda, Osaka 563, Japan *Yamamura Glass Co., Ltd., New Glass Research Center, 2-1-8 Naruohama, Nishinomiya, Hyogo 663, Japan. ABSTRACT Hydrated glass was prepared by the treatment in an autoclave. Specimen in a good state was obtained under unsaturated water vapor pressure conditions. The obtained glass has an silica-rich hydrated layer and proved to be more durable than the original glass. There are some kinds of hydroxyl species in the hydrated glass and there are some patterns in the depth profile of water, indicating that the rate-controlling process is not a simple diffusion and the hydration process is a complicated reaction depending on the conditions. Water in hydrated glass is tightly bonded and a disintegration of hydrated glass in this study occurs at more than 560'C. INTRODUCTION Natural glasses are used as "natural analogues" of nuclear waste glasses leached for a long period [1]. Among various types of natural glasses, basalt-type glass has similar silica content to nuclear waste glasses. There, however, are many differences in composition between them such as the contents of alkali oxides, boron oxide, and alumina. Both glasses are also different in the environmental conditions. These differences may cause the difference in leaching behavior. To evaluate the effects of composition, we had measured the leach rate of' each element in relation to glass structure and diffusion [2]. For long-term leaching, however, information on a hydrated glass is important, since glass leached for a long time has a surface layer altered by water. The thickness
of this layer is available to the demonstration of leaching time in the natural analogue study. As the leaching always occurs at the surface, leaching behavior over a long period should be analyzed on the hydrated glass. In order to investigate the general behavior of hydrated glass which will be a example of surface for long-term leached glass, we have prepared hydrated glass and measured some properties of hydrated layer. EXPERIMENTAL Bubbling method The glass compositions were selected as xNa 2 O.(25-x)CaO.1OAI 2 O3,101B2 O:3 55SiO 2, x=15 and 20 (molA), which are named as Na-15 and Na-20, respectively. These are the intermediate compositions between typical nuclear waste glass and basalt-type natural glass. This base glass system is suitable for not only the comparison of both glasses but the measurement of water content using spectroscopy because of having no transition metal oxides. In order to prepare a hydrated glass, first we tried to blow bubbles containing water vapor into the glass during melting. Air saturated of water vapor at 80'C was introduced into the glass melt at 1400'C using platinum pipe. Carrier gas rate was selected at 40cm 3/min in normal condition. It was the maximum rate which did not cause a spill of molten glass f
Data Loading...
