Long-term product consistency test of simulated 90-19/Nd HLW glass

摘要

Chemical durability of 90-19/Nd glass, a simulated high-level waste (HLW) glass in contact with the groundwater was investigated with a long-term product consistency test (PCT). Generally, it is difficult to observe the long term property of HLW glass due to the slow corrosion rate in a mild condition. In order to overcome this problem, increased contacting surface (S/V = 6000 m ~(-1)) and elevated temperature (150 °C) were employed to accelerate the glass corrosion evolution. The micro-morphological characteristics of the glass surface and the secondary minerals formed after the glass alteration were analyzed by SEM-EDS and XRD, and concentrations of elements in the leaching solution were determined by ICP-AES. In our experiments, two types of minerals, which have great impact on glass dissolution, were found to form on 90-19/Nd HLW glass surface when it was subjected to a long-term leaching in the groundwater. One is Mg-Fe-rich phyllosilicates with honeycomb structure; the other is aluminosilicates (zeolites). Mg and Fe in the leaching solution participated in the formation of phyllosilicates. The main components of phyllosilicates in alteration products of 90-19/Nd HLW glass are nontronite (Na _(0.3)Fe_2Si_4O_(10)(OH)_2· 4H_2O) and montmorillonite (Ca_(0.2)(Al,Mg)_2Si_ 4O_(10)(OH)_2·4H_2O), and those of aluminosilicates are mordenite ((Na_2,K_2,Ca)Al_ 2Si_(10)O_(24)·7H_2O)) and clinoptilolite ((Na,K,Ca)_5Al_6Si_(30)O _(72)·18H_2O). Minerals like Ca(Mg)SO_4 and CaCO_3 with low solubility limits are prone to form precipitant on the glass surface. Appearance of the phyllosilicates and aluminosilicates result in the dissolution rate of 90-19/Nd HLW glass resumed, which is increased by several times over the stable rate. As further dissolution of the glass, both B and Na in the glass were found to leach out in borax form.