Re(Ⅶ)在辐照膨润土中的扩散行为研究

Diffusion Behavior of Re(Ⅶ) in Compacted Irradiated Bentonite

高庙子(GMZ)膨润土在长期深地质处置过程中会受到高放废物的辐照,物理化学性质可能会发生改变。本文采用贯穿扩散实验法,研究了pH=3.0和10.0条件下,Re(Ⅶ)在1MGy辐照的蒙脱石和膨润土中的扩散行为,并与未辐照的蒙脱石和膨润土相比较,得到了有效扩散系数De和有效孔隙率εacc。结果表明:pH=3.0时,De=(1.00~1.49)×10^(-11) m^2/s,εacc=0.09~0.14;pH=10.0时,De=(1.50~2.10)×10^(-11) m^2/s,εacc=0.07~0.11。随着酸度的增加,有效扩散系数和孔隙率基本不变,说明pH值对Re(Ⅶ)的扩散过程无影响。在蒙脱石中,辐照后的有效扩散系数降低;而在膨润土中,辐照后的有效扩散系数升高,这可能是由于γ辐照改变了膨润土除蒙脱石以外黏土的微观结构,有效孔隙率的增加导致Re(Ⅶ)扩散通道的宽度增加。但由于有效扩散系数和有效孔隙率的改变不大,γ辐照对Re(Ⅶ)的表观扩散系数的影响不明显。此外,De与εacc的关系可通过Archie定律表述,胶结因子n=1.7~2.4。

The physical and chemical properties of GMZ bentonite will be changed by irradiation from high level nuclear waste after long time deep geological disposal. In this study, the diffusion behaviors of Re（Ⅶ） in 1 MGy irradiation montmorillonite and ben- tonite were investigated by a through-diffusion method at pH = 3.0 and 10.0. The results were also compared with the unirradiated montmorillonite and bentonite. The effective diffusion parameter Do and accessible porosity εacc were obtained. The results show that De and εacc are （1.00-1.49） ×10^-11 m^2/s and 0.09-0.14 at pH=3.0, while Drand εacc are （1.50-2.10）×10^-11 m^2/s and 0.07-0.11 at pH=10.0, respectively. De and εacc remained unchanged with the increase of pH, which indicates that pH has insignifi- cant effect on Re （Ⅶ） diffusion. In case of montmorillonite, Do of irradiated clay is lower than that of unirradiated one, whereas, it is higher than that of unirradiated ben- tonite. It is probably because of that the component of bentonite except montmorillonite may change by the y-irradiation. The increase of εacc indicates that the diffusion path of Re（Ⅶ） is broaden. However, y-irradiation has no obvious effect on Da because of the minor change of both De and e Moreover, the relationship of De and εacc can he described by Archie＇s law with exponent n=1.7-2.4 for ReO4-.